Tumors of the Lower Extremity

HENRY DEGROOT

Soft tissue tumors of the foot and ankle are different from those of the rest of the musculoskeletal system in terms of type, risk of malignancy, age, treatment, and prognosis. Tumors of the foot and ankle may be degenerative, reactive, posttraumatic, or neoplastic in origin, or they may arise from an unknown cause. The treatment varies widely depending on the type of tumor. To select the appropriate treatment, the surgeon must begin with an accurate diagnosis. The ultimate goals of treatment are to eliminate the tumor and restore the patient’s long-term mobility and function.

According to the most recent World Health Organization definitions, soft tissue tumors should be described as benign, intermediate (locally aggressive), intermediate (rarely metastasizing), and malignant. These terms have been introduced to eliminate confusion arising from outdated descriptions such as “intermediate malignancy.” According to this terminology, benign tumors grow locally, do not infiltrate, do not recur, or recur in a nondestructive fashion. Schwannoma is an example of a benign tumor. Intermediate (locally aggressive) tumors may grow in an infiltrative fashion and may recur locally unless excised with a wide margin of normal tissue. Plantar fibroma is an example. Intermediate (rarely metastasizing) tumors are locally aggressive, grow in an infiltrative fashion, and are likely to recur locally, and also have a demonstrated ability to metastasize to distant sites. An example of this type of tumor is angiomatoid fibrous histiocytoma. Malignant tumors such as synovial sarcoma (SS) and clear cell sarcoma (CCS) grow in an aggressive, infiltrative, and locally destructive manner, and carry a high risk of regional and distant metastasis.

The most common benign soft tissue tumors in the foot and ankle include ganglion cyst, plantar fibroma, hemangioma, schwannoma, neurofibroma, pigmented villonodular synovitis (PVNS), and giant cell tumor of tendon sheath. Lipoma is rare in the foot and ankle. Tumor mimics are benign non-neoplastic soft tissue masses whose behavior is similar to that of true tumors. Examples include gouty tophi, synovial cysts, synovial masses from degenerative tendinopathy, rheumatoid nodules, and epidermal cysts.¹ More than 100 other types of benign and malignant soft tissue tumors may occur in the foot, but a comprehensive description of them is outside the scope of this chapter. Instead, a strategy for evaluation and management is presented that applies to any tumor.

A larger proportion of soft tissue tumors in the foot and ankle are malignant than elsewhere in the body. Each individual surgeon’s chance of encountering a malignant tumor will vary depending on practice profile and referral sources. In some published reports, as many as 20% to 62% of soft tissue tumors in the foot and ankle are malignant, although the true incidence is not known.¹,²,³ All foot and ankle surgeons should be vigilant. The risk of malignancy increases with age. Malignant melanoma is the most common soft tissue malignancy in the foot. Pleomorphic sarcoma (PS; previously named malignant fibrous histiocytoma [MFH]), SS, and CCS are the most common soft tissue sarcomas in the foot and ankle.

Surgery is the primary form of local control for foot and ankle sarcomas. The surgeon must achieve an appropriate margin around the tumor to minimize the risk of local recurrence. Surgical margins are defined by the terms intralesional, marginal, wide, and radical. The term en bloc, meaning the tumor is removed in one piece, has no oncologic significance and is not by itself an adequate description. Opening, entering, or spilling the tumor by design or by accident such as during a curettage of a bone cyst always creates an intralesional margin. A marginal margin is created when the surgeon dissects outside the tumor adjacent to the capsule or pseudocapsule, even if the tumor is never entered or exposed. A wide margin is created when the surgeon dissects completely outside the pseudocapsule and all reactive or abnormal appearing tissues. By definition, a wide margin includes a continuous unbroken cuff of normal tissue surrounding the entire surgical specimen. A radical margin is achieved when the entire compartment or compartments containing the tumor are resected, along with any and all bone, nerve, vessel, or tendon in the compartment. To achieve a radical margin in the foot and ankle at least a partial amputation is required.

For benign tumors, simple removal with an intralesional or wide margin is adequate. There is no adverse effect if the surgeon spills tumor cells into the nearby tissues, or leaves a
portion of the tumor behind. For intermediate tumors, the risk of local recurrence and the debility associated with multiple surgeries demands a more thorough surgical approach. A wide margin is the goal, but a marginal margin is the most likely outcome. The surgical resection must encompass the entire tumor, any pseudocapsule, and the thickest possible cuff of normal tissue around the mass. The surgeon can adjust the size of the margins according to the propensity of the tumor to recur. For example, plantar fibroma is a benign tumor, but it carries a very high risk of local recurrence, and a margin of 1 to 2 cm is optimal. A schwannoma can be resected with a marginal margin.

Local control of malignant tumors requires an uncompromised wide margin. Wide resections are more likely to compromise the skeletal stability, neurovascular status, and soft tissue integrity of the limb. Surgeons seek to balance and optimize the oncologic and functional outcomes, and may accept marginal margins in order to facilitate limb salvage.⁴ The goal of surgery is to resect the entire tumor en bloc, with an uncontaminated margin of 5 to 10 mm of normal tissue surrounding all aspects of the mass. A true wide margin requires that no part of the tumor, its capsule, or the reactive zone around the tumor is ever seen in the surgical field. All parts of the dissection take place through uninvolved, nonreactive normal tissues, and these normal tissues completely envelop all parts of the excised specimen. Spilling or exposure of any part of the actual tumor is unacceptable. Surgeons who are unprepared for the degree of collateral damage to the foot that is required to achieve a true wide margin around a sarcoma should not attempt these resections.

Adjuvant chemotherapy and radiation therapy are given routinely for osteosarcoma and Ewing sarcoma, and are used for other high-grade sarcomas on a case-by-case basis. There is strong evidence that conservative surgery combined with radiation therapy result in effective local control. Postoperative radiation can be administered by external beam in fractionated doses or by brachytherapy using surgically implanted radiation sources with a shorter duration of treatment. No strong evidence favors one method over the other. There is increasing interest in preoperative radiation therapy, which more precisely targets the tumor and damages less normal tissue. However, a definite survival benefit has not yet been demonstrated.⁵ Preoperative radiation results in higher rates of major wound complications, which may have devastating effects in the foot and ankle.

Evaluation of a Soft Tissue Mass

History and Physical

The initial evaluation should include a complete history, a comprehensive regional examination, and plain radiographs of the affected area. This information is then used by the clinician to determine the likelihood of malignancy, to decide on the best type of advanced imaging to employ, and to evaluate the need for a diagnostic biopsy. For soft tissue tumors, history and physical examination findings can be used to determine the potential for malignancy, based on the presence or absence of five specific “good” or “bad” clinical findings. This assessment is made based solely on the clinical features of the tumor; no advanced imaging is necessary. Factors included in the assessment include pain, growth, size, location, and examination findings (Table 11-1). Benign tumors are more likely to be painful, not progressively growing, small, superficial to the fascia, and difficult to palpate as a distinct mass. Malignant tumors tend to be painless, progressively growing, large, deep to the fascia, and well defined on exam. The risk of malignancy increases with the number of “bad” features the tumor has.

Table 11-1. Clinical Features That Help Distinguish Benign Soft Tissue Masses from Malignant Soft Tissue Tumors

	Good	Bad
Pain history	Pain was present from the beginning	No pain or pain developed later
Growth history	Grows and shrinks	Grows progressively
Size	Small (<2 cm)	Large (>3 cm)
Location	Superficial	Deep
Findings on exam	An indistinct mass	A definite mass
The likelihood of malignancy increases as the number of “bad features” increases.⁶

Certain physical examination findings might point toward a specific diagnosis. For example, hemangiomas have a characteristic blue-purple color that may be visible in the overlying skin. These lesions are typically painful to palpation. Ganglion cysts can be transilluminated with a penlight or a laser pointer and, when transillumination is demonstrated, aspirated to confirm the diagnosis.

Laboratory tests are not generally useful in the initial management of tumors of the foot and ankle, unless there is clinical evidence of infection, an inflammatory condition such as rheumatoid arthritis, or gout. Nonspecific laboratory screening tests are not recommended.

Imaging Evaluation of Soft Tissue Tumors

The history and physical examination may be adequate to confirm the diagnosis of many common soft tissue masses in the foot and ankle, such as ganglion cyst and plantar fibroma. In these cases, imaging of the lesion may not be clinically indicated. For soft tissue tumors that cannot be readily diagnosed, two orthogonal high-quality plain radiographs are recommended as the initial imaging study. The radiographic findings may point to a possible diagnosis. For example, intramuscular hemangiomas (IMHs) may contain
small rounded pebble-like calcifications called phleboliths, whereas 30% of SSs contain amorphous calcifications. Soft tissue sarcomas and metastatic cancers in the foot may invade a nearby bone, a worrisome sign associated with malignancy. Advanced imaging other than MRI, such as CT scans, positron emission tomography (PET) scans, and bone scans, is not commonly useful in the evaluation of soft tissue lesions.⁷

The malignant potential of some soft tissue tumors may be difficult to determine with confidence. The history and physical examination findings can be unhelpful or even misleading. A contrast-enhanced MRI examination with a dedicated extremity coil is recommended for lesions larger than 2 or 3 cm and for all soft tissue tumors with worrisome clinical features. The MRI signal characteristics may in some cases be adequate to identify the exact nature of the lesion, or for the differential to be narrowed, but in other cases the MRI findings are nonspecific. Nevertheless, MRI is very helpful in determining the size and extent of the tumor as well as its relationship to the neurovascular elements. MRI is an essential tool for clinical staging, biopsy placement, surgical planning, and evaluation of response to therapy.

Determinate versus Indeterminate Soft Tissue Tumors

A systematic approach to assessment of the potential for malignancy of soft tissue masses has been proposed whereby soft tissue tumors are divided into two groups: “determinate” and “indeterminate” based on the clinical and radiographic findings. The subsequent management plan follows directly from this assessment.⁸,⁹

Soft tissue tumors for which a specific diagnosis can be made based on a combination of history, the physical examination, and analysis of the MRI findings are called determinate lesions. Determinate lesions that may occur in the foot and ankle include lipoma, hemangioma, ganglion cyst, some plantar fibromas, and PVNS. Determinate lesions are treated with observation or by excisional biopsy, depending on the clinical situation.

Soft tissue tumors for which no specific diagnosis is confirmed by the exam, X-ray, and MRI findings are called indeterminate lesions. These lesions are typically isointense with muscle (dark) on T1-weighted imaging and hyperintense (bright) on T2-weighted imaging. In the foot and ankle, this group of tumors includes all soft tissue sarcomas such as SS, CCS, and liposarcoma, as well as a number of benign tumors, such as giant cell tumor of tendon sheath, peripheral nerve sheath tumors, and some plantar fibromas. Indeterminate lesions are treated with incisional or needle biopsy, along with appropriate referral to an orthopedic oncologist. If there is any doubt, it is best to defer the biopsy to the specialist team. Definitive surgical removal of indeterminate lesions is always performed as a separate procedure after the final pathologic diagnosis and staging are completed.

Biopsy Planning And Techniques

Some foot and ankle surgeons refer extremity tumors to a specialist for biopsy and definitive treatment, whereas others feel comfortable managing soft tissue lesions within their scope of practice. A systematic approach to the performance of the biopsy is recommended because improper timing, technique, or management of the biopsy process increases the risk of complications. The biopsy technique should be chosen with care so that an accurate diagnosis is made with minimal risk. Complications of improperly planned or executed biopsies include errors in diagnosis, inadequate or nondiagnostic biopsy material, surgical site infection, hematoma, and contamination of nearby tissues. Biopsy complications have been shown to increase the risk of an otherwise avoidable amputation. These problems may be avoided by early referral to an orthopedic oncologist or tumor specialist prior to the biopsy.

The surgeon is responsible for consulting with the pathologist prior to performing a biopsy in cases where malignancy is possible (for all indeterminate lesions). Direct communication by telephone is highly recommended as a means of insuring that the surgeon and pathologist collaborate in an optimal fashion to maximize the diagnostic yield of the biopsy and minimize potentially devastating errors. Because the biopsy will alter the imaging appearance of the tumor, all diagnostic scans should be completed prior to biopsy.

The most appropriate biopsy technique should been selected according to the clinical and anatomic situation. Options include needle aspiration, tru-cut or large-bore needle biopsy, incisional biopsy, and excisional biopsy.

Fine needle aspiration (FNA) and core needle techniques have the advantage of being well tolerated by the patient and causing few complications. FNA is an appropriate choice for patients with a known cancer diagnosis who are suspected to have a recurrence or a metastasis in the foot or ankle. FNA is also useful for other lesions where there is little doubt about the diagnosis and the biopsy is only needed to confirm what is already known. However, FNA is inadequate to evaluate the tissue cytoarchitecture, and the amount of material obtained may be inadequate for tissue banking and ancillary studies. FNA and core needle biopsy is the first-line biopsy technique for soft tissue tumors in some cancer centers. In those centers, a dedicated and experienced team manages all soft tissue tumors. This approach can minimize or eliminate the shortcomings of needle techniques.

In settings where an experienced biopsy team and an experienced solid tumor cytopathologist are not available, needle biopsy may be inadequate or inconclusive. Open (incisional) biopsy techniques are preferred in these cases. Open biopsy is a safe and effective technique when properly planned and executed. More tissue allows for better understanding of the cytoarchitecture of the lesion and reduces the risk of a nondiagnostic result. Essential material for ancillary studies and tissue banking can be obtained.

Excision of the tumor immediately after open biopsy is possible for a small group of tumors where the frozen section features of the tumor are highly diagnostic. This group includes giant cell tumor of tendon sheath, plantar fibroma, schwannoma, and other tumors depending on the experience and confidence of the pathologist. The surgeon and pathologist should both be highly experienced in managing tumors. If sufficient doubt about the final diagnosis exists or the pathologist is not comfortable making a decision based on frozen section alone, the definitive surgery should be delayed until the final pathologic analysis has been completed. Most indeterminate tumors will require immunohistochemical stains and other specialized examinations for diagnosis. Definitive surgery can take place 7 to 14 days after the biopsy.

The success of an incisional biopsy depends on careful prebiopsy planning, proper biopsy execution, and adequate postbiopsy care of the patient (Table 11-2). All imaging studies must be completed prior to biopsy. The pathologist and the surgeon should discuss the case prior to the biopsy or they may do so in the operating room. A tourniquet is applied after elevation but without exsanguination. Tumor sampling is accomplished through adequate longitudinal incisions that approach the lesion most directly. The incision should be long enough to allow visualization of the procedure, confirmation of appropriate sampling, and hemostasis. Small “key hole” biopsy incisions are not recommended. Contamination of uninvolved structures and the neurovascular bundles especially near the medial malleolus should be carefully avoided. The tourniquet should be released after the tumor is sampled, and measures should be taken to insure that the wound is completely dry. Unintentional spread of the tumor may occur because of postbiopsy bleeding. A hematoma may track under subcutaneous tissues or through intramuscular spaces, causing a wide zone of contamination. During open biopsy, the pathologist should examine a frozen section of the biopsy material to verify that an adequate amount of viable tumor has been obtained. Cultures should be performed unless the potential for infection has been definitively ruled out. A moderately compressive dressing should be applied and the patient is made nonweight-bearing with the extremity elevated for 3 or 4 days. The surgeon who performs the biopsy should schedule a face-to-face encounter with the patient in 7 to 10 days to discuss the results of the procedure and the future treatment plan. It is best to avoid delivering biopsy results over the telephone or via an intermediary.

Table 11-2. Checklist of Tasks Required for a Successful Biopsy

Prebiopsy

▪ All imaging studies completed

▪ Appropriate biopsy technique selected

▪ Imaging reviewed to plan approach and tumor sampling strategy

▪ Pathologist consulted by telephone or directly in operating room

▪ Operating room aware of a frozen section planned

During the Biopsy

▪ Adequate longitudinal incisions

▪ Direct approach with minimal dissection, no flaps or undermining

▪ Do not expose the neurovascular bundle

▪ Do not biopsy the pseudocapsule

▪ Biopsy the most cellular area of the tumor—usually the outermost part

▪ Pathologist performs frozen section to verify biopsy is adequate

▪ Perform cultures if indicated or if no evidence of a neoplasm seen on frozen section

Postbiopsy

▪ Meticulous hemostasis with tourniquet released

▪ Avoid drains

▪ Mildly compressive bandage or splint applied

▪ Strict activity restriction and elevation written in orders

▪ Schedule a face-to-face follow-up visit to share biopsy result

Excisional biopsy is appropriate for the determination of soft tissue tumors in the foot or ankle as discussed earlier, and may be advisable for small and superficial indeterminate tumors. During excisional biopsy, care should be taken that the tumor is not exposed or entered. The entire tumor, the surrounding capsule, and a small amount of surrounding normal soft tissue are taken en bloc. Excisional biopsy is never appropriate for large or deep soft tissue tumors.

Management of a Patient with an Unplanned Excision of a Soft Tissue Sarcoma

Soft tissue sarcomas are rare and may have an indolent presentation. As a result, unplanned excision of soft tissue sarcoma in the foot and ankle is common.¹⁰ Unplanned surgery is defined as excisional biopsy or unplanned resection of a malignant sarcoma without an adequate margin. Outcomes after unplanned excision in all body sites are inferior to those after planned surgery.¹¹ The implications of unplanned treatment of sarcomas in the foot may be more serious than elsewhere in the body. The potential for contamination of uninvolved structures is higher, and unplanned surgeries make the subsequent wide excision surgery more difficult.¹²

Management following unplanned resection of a sarcoma typically requires complete excision of the entire tumor bed and any surgically contaminated tissues to achieve a wide margin. Unplanned surgery results in additional soft tissue reconstruction compared with planned surgery.¹³ If the initial surgery resulted in extensive contamination of surrounding structures, amputation may be necessary to achieve local control. Following repeat excision in cases without clinically palpable residual tumor, 50% of the cases were found to have microscopic residual tumor. Following repeat excision, 85% of the patients were alive and disease free at 5 years.

Benign Soft Tissue Tumors

Ganglion Cyst

Clinical Presentation

Ganglion cysts tend to present in young to middle age adults, more commonly women, and are very rare in children. The most common location is around the ankle joint or midfoot, especially on the dorsolateral surface. The lesions may arise in association with peripheral nerves, joints, fascia, and bone. In the author’s experience, simple, superficial ganglion cysts rarely affect the forefoot. In these cases, examination reveals a palpable, well-defined mass, usually 1 to 3 cm, with no pain or very mild pain. The lesion occurs near the joint or along a tendon sheath. The mass may grow and shrink according to the activity level. In some cases, loading or flexing the tendon or joint will make the mass feel noticeably more firm. The ganglion cysts are typically not associated with significant degenerative pathology of the nearby tendon or joint.

Ganglion cyst may present in a patient with nonlocalized pain, in whom an MRI scan of the foot reveals a small periarticular cystic mass, often adjacent to a joint in the hindfoot, sinus tarsi, or midtarsal joint. These cysts can be aspirated and injected with ultrasound guidance, or excised. In addition, lesions that have MRI features consistent with ganglion cyst are occasionally found in the plantar aspect of the forefoot adjacent to the metatarsal phalangeal joints. In the author’s experience, these lesions are caused by plantar plate degeneration associated with aging and overuse. Treatment of these lesions is analogous to the treatment of metatarsalgia and plantar plate-related pain.

Clinical Exam

A typical ganglion cyst is superficial, firm, somewhat compressible, and usually painless. The cyst will transilluminate with a penlight or a laser pointer. Transillumination is the extended transmission of light through the lesion due to the semitransparent material in the cyst. The room lights may need to be dimmed and the area should be shielded from external light sources to maximize the effect. The surgeon should illuminate a nearby area to observe the expected amount of light transmission through normal tissue.

Diagnostic Procedure

The combination of transillumination and needle aspiration confirms the diagnosis of ganglion cyst. Once transillumination is confirmed, aspiration should follow. Lesions that do not transilluminate should not be aspirated. Aspiration of ganglion cysts is simple, safe, and well tolerated in an office setting. A single puncture into the center of the cystic mass with a 22-gauge or larger needle should be performed. The diagnosis is confirmed if slightly yellow/clear, nonturbid, viscous or jelly-like material is aspirated from the cyst. This material can be identified by its characteristic appearance and material properties, and thus laboratory analysis is not required. If unexpected material, crystals, pus, or blood is encountered, cultures and laboratory and/or pathologic analysis is recommended. If aspiration is negative, the needle should be withdrawn. Additional punctures and multiple passes should not be made. An MRI is recommended to characterize the lesion.

Transillumination and aspiration may lead to a conclusive diagnosis and further workup can thus be avoided. MRI is unnecessary and treatment is at the discretion of the surgeon. The aspiration may be curative. If the lesion recurs after aspiration, surgical removal can proceed without further workup.

Plantar Fascial Fibroma and Fibromatosis

Clinical Presentation

Plantar fibromatosis (also known as Ledderhose disease) is a nonencapsulated thickening and proliferation of the central and medial bands of the plantar fascia. The lesions may also occur in atypical locations, such as in the distal or proximal plantar fascia and in subcutaneous tissues. The cause is unknown. One-third to one-half of patients also present with bilateral nodules. Approximately one-third to two-thirds of patients will also have fibromas in the palmar fascia, the knuckle pads, or elsewhere. Patients with Dupuytren contracture have an increased risk for plantar fibromas. Most patients are asymptomatic, but some have activity-related pain or shoe irritation. When the lesions are large enough to press on the plantar nerves, there may also be numbness or dysesthesia in the distal portions of the foot.

Differential diagnosis for this tumor is SS.¹⁴

Diagnostic Procedure

Plain radiographs are recommended to rule out the presence of intralesional calcifications that are seen in SS but not in plantar fibroma. No laboratory exams are recommended. MRI is not necessary for small, stable, and typically located lesions. MRI is strongly recommended if the lesion is large or enlarging, or atypical in any way.

Initial management should consist of shoe modifications, custom or readymade orthotics, and pain medication. Numerous nonsurgical treatments have been recommended or published in low-quality clinical studies, including external beam radiation,¹⁵ extracorporeal shockwave therapy,¹⁶ injections of corticosteroids, collagenase clostridium histolyticum injections,¹⁷ and transdermal therapy with 15% verapamil gel. None of these treatments can be recommended due to the low quality or total absence of any supporting data.

Surgical removal is reserved for large lesions that are causing significant disability that have failed a well-documented course of nonoperative care. Surgeons treating this lesion should be prepared to undertake an aggressive and comprehensive resection of the lesion, because recurrences after surgical treatment are inversely proportional to the quality of the margin.¹⁴,¹⁸

Local fasciectomy has a 100% recurrence rate. The presence of multiple fascial nodules, bilateral nodules, and family history is associated with increased risk of recurrence.¹⁴,¹⁹ Aggressive resection with a wide margin (subtotal fasciectomy) is necessary and carries a recurrence rate of 25%. Radical fasciectomy is a misnomer because the resection does not achieve a radical margin. The surgeon should achieve a minimum of a 1 cm margin at the fascial boundaries and the widest possible margin at the skin surface that will still permit primary closure. A marginal margin must be accepted at the deep surface of the lesion to allow preservation of the medial and lateral neurovascular bundles. In cases of recurrence after local excision, a subtotal fasciectomy can be expected to be successful in 75% of cases. Skin grafts and tissue transfers may be required to facilitate coverage and closure in reoperated cases. Fibromas that recur after subtotal fasciectomy should be observed.

Pigmented Villonodular Synovitis

Clinical Presentation

PVNS is a locally aggressive synovial proliferation of unknown origin. The tumor cells consistently overexpress colony-stimulating factor-1 (CSF1) that has been implicated in tumor growth.²⁰ In addition, DNA aneuploidy, chromosomal translocations, and tumor expression of p63 and nm23 have been reported in a variable proportion of cases.

Various clinical presentations of this benign tumor exist, including giant cell tumor of tendon sheath/tenosynovial giant cell tumor, which are described later, and PVNS. Most patients are in their thirties and forties. This lesion is rare in children. Approximately 2% to 10% of cases occur in the foot and ankle.²¹ There are two forms of PVNS: diffuse and nodular. Nodular PVNS occurs most commonly in the forefoot.²² Diffuse PVNS is found more commonly in the hindfoot and presents with osteoarthritis. PVNS may also occur in the ankle and often presents as a mildly painful joint with swelling.

Diagnostic Procedure

X-ray imaging is often used in identifying PVNS. The radiologic appearance of PVNS depends on the location. A nodule in the forefoot may have soft tissue swelling and bone erosion on plain X-ray. The ankle usually only has a soft tissue mass, but bone erosion or cysts may be present. The joint space is usually preserved and there may be an effusion. MRI scan is able to identify the hemosiderin contained in the lesion and can demonstrate the extent of the synovial involvement as well as bone erosion and cysts. Hemosiderin appears as low or absent signal (signal dropout) on both T1- and T2-weighted images.

On gross examination, the diffuse form of PVNS is a tan mass of villi and folds of synovium. The lesion may be sessile or have several pedunculated nodules. Bony invasion through the joint capsule is possible. The local form of PVNS is a pedunculated firm nodule. Microscopically, PVNS is characterized by synovial cell hyperplasia both on the surface and below the synovium. Also present are scattered giant cells, hemosiderin, and foam cells. The location of the polyhedral cells below the synovial membrane suggests that perhaps the cell of origin is a fibrohistiocyte. The pathologic differential includes hemosiderotic synovitis, rheumatoid arthritis, and synovial chondromatosis.

Treatment of mild cases of diffuse PVNS is by nonoperative means with clinical and radiologic follow-up. Symptomatic relief can be obtained with a combination of moderate activity restriction, offloading the joint with a removable fracture boot, and daily administration of ibuprofen or naproxen. Complete resolution of symptoms may take 12 to 24 months. Patients are at risk for recurrence of symptoms if they return to high activity levels too soon.

Nodular PVNS is treated by simple excision with a marginal margin. Nodular lesions rarely recur after complete excision, but will almost always recur if macroscopic amounts of the lesion are left behind after surgery. Surgical treatment of diffuse PVNS is indicated for bulky or painful lesions and cases with bone or joint damage, in order to prevent progression. Treatment is by aggressive means, either open or arthroscopic, without adjuvant therapy. There is a 10% to 15% risk of recurrence.²³ Adjuvant treatments including radiation²¹ have been used in severe and recurrent cases. In the ankle, arthrodesis or total arthroplasty with a prosthetic implant may be necessary in cases with severe joint damage.²⁴

Giant Cell Tumor of Tendon Sheath

Clinical Presentation

Giant cell tumor of tendon sheath is a rare, solitary benign variant of PVNS that may arise in the tendon sheath tissues of the hand and wrist as well as the ankle and foot. Most cases occur in the hand, where local recurrence after excision has been reported in up to 40% of cases. The tumor cells show consistent overexpression of CSF1, the ligand of the tyrosine kinase receptor, as well as frequent chromosomal translocations at 1p13, the locus of the CSF1 gene.

Clinically, the patients report a slow-growing, painless, firm solitary mass adjacent to the dorsal or plantar tendons, the midfoot joints, or the ankle joint, which has been present for 1 to 2 years on average. There may be a history of trauma, and neurologic symptoms occur rarely. In one study, lesions in the forefoot occurred in the first, second, and fifth rays exclusively, indicating that there may be some relationship between weight-bearing and this tumor. The tumor may cause or accentuate an angular deformity such as hallux valgus.

Diagnostic Procedure

On plain radiographs, there may be a visible soft tissue swelling, sometimes completely encasing the bony elements of the involved digit, and the tumor may invade the adjacent bone and cause cystic lesions that are clearly visible on X-ray.
Approximately 10% involve the bone. The bone involvement and destruction leads to concern for primary bone malignancy, and inappropriately aggressive treatments can result. CT scan will show the extent of the tumor, and clearly delineate any bony involvement. Some of these tumors have small calcifications, a feature shared with SS. MRI scans are helpful to define the extent of the lesion, and can be helpful in the preoperative diagnosis. Hemosiderin in the lesion may result in very low signal intensities on some sequences, and the lesions enhance on T1 sequences after administration of gadopentetate contrast agent, and these features help identify the tumor. Treatment is by complete, meticulous excision of the entire lesion. A wide or radical margin is not necessary. Intralesional margins are acceptable, as long as complete excision is not compromised. Recurrence has been reported in up to 45% of cases, but with careful removal, recurrence can be reduced to 10% to 20%. In the lesser toes, where the lesion has extensively invaded the soft tissues and bone, amputation may be preferable to excision. In the great toe, efforts should be made to preserve the mechanical integrity of the first ray, including complete meticulous excision of the lesion, followed by bone grafts, skin grafts, and fusions as necessary.

A separate, staged biopsy is recommended. The lesion cannot always be characterized by preoperative studies, and aggressive or destructive features may be present that are also consistent with malignancy. Open surgical biopsy with frozen section analysis is preferred, performed through a well-planned longitudinal incision that avoids any involvement of nearby neurovascular structures. If the lesion can be characterized by MRI, and the level of confidence in the preoperative diagnosis is very high, then excisional biopsy is appropriate.

Schwannoma/Nerve Sheath Tumors

Clinical Presentation

Schwannomas/neurilemmomas and neurofibromas are part of a large group of tumors believed to arise from Schwann cells. Schwann cells produce myelin and may also produce collagen, thus the neoplasms that arise from them have a range of histologic features. These tumors may arise in bone as well as in soft tissues. Neurofibromas are more likely to occur in younger individuals, are associated with neurofibromatosis, and carry a significant risk of malignant degeneration. Schwannomas/neurilemmomas occur in middle-aged and older individuals, are rarely associated with neurofibromatosis, and carry an extremely small risk of malignant degeneration. Numerous subtypes of nerve sheath tumors have been described, but an exhaustive review is outside the scope of this chapter. Morton neuroma is not a part of this group of tumors. Morton neuroma is not a true tumor, but rather a fibrotic and degenerative thickening of the plantar digital nerve.

Benign schwannoma/benign neurilemmoma is a slow-growing solitary nerve sheath tumor that typically presents in adults between age 20 and 50. Schwannomatosis/multifocal neurilemmoma has been observed in the foot and ankle and knee.²⁵,²⁶ The typical solitary tumor presents as a slow-growing painless mass that may have been present for 1 to 2 years or more. Some of these tumors are exquisitely painful and may cause severe radiating neurogenic pain, but others are completely painless. Schwannomas have been reported as a cause of tarsal tunnel syndrome.²⁷

Because of prolonged growth of these tumors, there may be local bony impingement and bone remodeling due to pressure from the tumor. However, these benign tumors do not invade the bone. MRI scans show typical features for an indeterminate tumor, with low signal intensity on T1-weighted sequences and high signal intensity on T2-weighted sequences. The anatomical relationship of the tumor to the nerve of origin may be obvious or so subtle as to be impossible to determine.

Because of the indeterminate MRI appearance of this tumor, a complete evaluation and staged biopsy is recommended before definitive surgical removal is planned. A small number of tumors can be definitively identified based on clinical findings and MRI examination. In a patient who does not have neurofibromatosis, the combination of a tumor causing significant neurogenic pain and an MRI demonstrating a clear anatomical relationship between the tumor and a peripheral nerve is diagnostic for benign schwannoma/neurilemmoma.

Treatment is by excision with a marginal margin. Some of these tumors have no obvious relationship to a peripheral nerve. Others occur inside the epineurium of a large nerve such as the posterior tibial nerve.²⁸ Intraneural schwannomas can usually be separated from the surrounding normal nerve fibers without significant damage. Incomplete excision or intralesional excision is acceptable for tumors that cannot be separated from a major peripheral nerve and where complete excision would cause significant morbidity and permanent nerve damage. Recurrence following resection with a marginal margin is rare.

Intramuscular Hemangioma

Clinical Presentation

IMHs typically present in the lower extremities of children and young adults. These vascular lesions are divided into several types, according to their histologic features. Capillary hemangioma is the most common type, consisting of small capillaries that have normal size and diameter, but that are excessive in number. Cavernous hemangioma is made up of larger dilated blood vessels. Compound hemangiomas have features of both the capillary and cavernous types. Lobular capillary hemangiomas are small, red bumps often occurring on the hands, face, and arms, especially during pregnancy. Most IMHs in the extremities are the capillary type. IMH is a benign lesion with a very low risk of malignant degeneration.

IMH occurs in the leg more commonly than the foot. Patients present with activity-related pain, night pain, and localized tenderness over the lesion. The tumor can cause equinus, toe-walking, and unilateral pes planus.²⁹ Lesions in
the heel may mimic plantar fasciitis. IMHs near the skin or dermis have a visible blue color.

Diagnostic Procedure

The appropriate age, location, history, and examination findings should lead the clinician to suspect a hemangioma. Phleboliths, which are small, rounded calcified intravascular thrombi, are seen on plain films in 50% of hemangiomas.

MRI scans are usually adequate to confirm the diagnosis. On MRI, IMH is a well-defined lobular heterogeneous intramuscular mass, isointense on T1 and hyperintense on T2, with fat and serpentine blood vessels, containing signal voids associated with the phleboliths. The MRI appearance has been described as a “bag of worms.” These lesions are usually definite as previously described, and may be treated without biopsy when the diagnosis is certain. It is not unusual for IMH to infiltrate both muscle and nearby structures, including skin, bone, and neurovascular bundles.

In most cases, nonoperative treatment should be attempted. Activity restriction, compression garments, nonsteroidal medications or acetaminophen are usually adequate to control the symptoms. Ultrasound-guided or fluoroscopically guided sclerotherapy using absolute alcohol or ethanolamine oleate has been successfully employed to treat IMH in the foot and ankle.³⁰ Complications of sclerotherapy include tendon contracture, skin breakdown, reversible nerve injury, and deep venous thrombosis.³¹

Localized, painful IMH that does not infiltrate critical structures can be treated with surgery. Excision with an intralesional or marginal margin is effective for symptomatic control.³² In pediatric patients, IMH has a high risk of recurrence. More ample margins should be used to lower the rate of recurrence and reoperations.³³ IMH may extend into nearby tissues such as bone, skin, and vascular structures. Resection of the accessible portions of the lesion combined with sclerotherapy, compressive garments, and medications is more suitable for complex lesions.

Tumor Mimics

Tumor mimics are non-neoplastic lesions (not true tumors) that may look and act like tumors. Gouty tophi, enlarged degenerated tendons, and focal collections of subcutaneous fat can sometimes be mistaken for tumors.

Gouty Tophi

Gout is an inflammatory arthropathy that occurs as a result of hyperuricemia. Gouty tophi represent the accumulation of calcium urate crystals within soft tissue and bone. Tophi may occur within the subcutaneous tissues, synovium, subchondral bone, and tendons, resulting in soft tissue masses, osseous erosion, tendon rupture, and tarsal tunnel syndrome. Tophi typically occur adjacent to the metatarsal phalangeal joints and along the lateral border of the foot. The patient may not carry an established diagnosis of gout. In severe cases, there is usually a history of skin breakdown and white pasty material draining from the mass. Treatment for gout is largely medical. Colchicine inhibits the phagocytosis of urate crystals by polymorphonuclear cells and blocks the release of chemotactic factors. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin can give patients relief from pain in 2 to 4 hours. Intra-articular steroid injections can also give relief of acute gout symptoms. Extremely bulky gouty tophi can be debulked, but the extensive infiltration of calcium urate crystals within the soft tissues makes it impossible to resect all the abnormal material.

Runner’s Bump

Older runners who average more than 30 miles per week may develop a mass on the tibialis anterior tendon sheath that may be mistaken for a tumor. This lesion is because of degeneration of the tibialis anterior tendon and a focal tenosynovial mass at the location of the damage. On examination, a soft, mobile lesion surrounds the tibialis anterior tendon at the level where the top of the shoelace rubs on the tendon. The tendon itself may retain normal caliber and function, depending on the severity. In some cases, the lesion can be partially eliminated by compressive massage, but recurs promptly. MRI shows a mild to moderate degree of tendon disease along with an intimately associated synovial mass. Treatment involves recognition of the origin of the problem, education of the runner, and padding, changing, or repositioning the laces and the tongue of the shoe to minimize the forces on the area. Surgical debulking of the excess synovium and tendon repair should be reserved for severe cases.

Localized Sinus Tarsi Fat Collection

In some overweight or obese individuals, a localized, well-defined subcutaneous collection of fat may occur anterior to the distal fibula in the area of the sinus tarsi. The patient is asymptomatic, but may be displeased with the appearance of the fatty collection. The mass typically measures 3 or 4 cm in proximal distal dimension and 2 or 3 cm in medial lateral dimension, and consists of soft compressible nontender subcutaneous fat. If there are atypical features or clinical suspicion, an MRI is recommended. The lesion consists entirely of fatty tissue that has identical signal characteristics to that of nearby normal subcutaneous fat. This collection of subcutaneous fat is not a lipoma, and surgical removal is not recommended.

Soft Tissue Sarcoma in the Foot and Ankle

Introduction

Soft tissue sarcomas are a heterogeneous group of malignancies that arise from mesenchymal tissues. These rare tumors comprise less than 1% of all malignancies. Most sarcomas are caused by molecular anomalies in the cellular DNA, such as chromosomal translocations and mutations that activate, inhibit, or amplify the expression of the genetic
material. Environmental factors, familial cancer syndromes, herbicides such as dioxin, radiation, and immune deficiency are rare causes of sarcomas.³⁴

Approximately 8,700 soft tissue sarcomas are diagnosed per year in the United States, with an estimated 10% of these occurring in the distal lower extremity.³⁵ Soft tissue sarcomas are more common in older individuals. Approximately one-third of these tumors are superficial, and three-quarters are histologically of high grade. When these tumors recur, it is more often a distal metastasis than a local recurrence.³⁶ At least one-third of patients with soft tissue sarcomas will die of their disease.

The American Joint Committee on Cancer (AJCC) staging system for soft tissue tumors has been shown to have a significant relationship to the prognosis. The staging system incorporates tumor size, depth, the presence or absence of nodal or distant metastasis, and histologic grade (Table 11-3). Staging is based on data from the CT or MRI of the tumor as well as a CT of the chest. This information is combined with the histologic grade, size, and the intracompartmental or extracompartmental extent of the tumor. Prognosis is strongly related to grade, size, and histologic subtype of sarcoma.

Treatment of soft tissue sarcomas is determined by the histologic diagnosis and stage of the tumor. With rare exceptions, surgical resection with a wide margin is the most effective method of primary tumor control. Wide margins reduce the chance of local recurrence, which has a strong negative impact on survival. Limb-sparing surgery is preferable to amputation when a durable, functional, and pain-free extremity can be achieved. Because of the anatomical constraints of the foot and ankle, it may be difficult to achieve a wide margin without resorting to at least a partial amputation. Approximately 15% to 20% of patients with distal lower extremity sarcomas require some kind of amputation.

In adults with foot and ankle sarcoma, limb-sparing surgery has not been proven to be better than amputation in terms of functional, psychosocial, or quality of life outcomes.³⁷ Limb salvage is functionally superior to amputation in pediatric sarcoma patients. The soft tissue coverage of the foot and ankle is scant and subjected to high loads and repetitive shear stresses. The bony and articular elements must provide durable support and flexibility while withstanding the stresses of weight-bearing. Limb-sparing surgery must be carefully weighed against other options for tumors of the foot and ankle.³⁸ Ten percent of patients treated with limb-sparing surgery are ultimately amputated for reasons other than cancer.³⁹ Limb salvage for sarcomas in the forefoot using free vascularized osteomyocutaneous fibular and scapular grafts has been reported to be successful. All patients required multiple procedures due to complications.⁴⁰ In some series, less than half the patients treated with limb salvage regain normal functional status.³⁸

Table 11-3. The American Joint Committee on Cancer Staging System

Stage	Size	Depth	Node	Metastasis	Grade
I	Any	Any	None	None	G1-G2 (low)
II	<5 cm	Any	None	None	G2-G3/G3-G4 (high)
II	>5 cm	Superficial	None	None	G2-G3/G3-G4 (high)
III	Any	Deep	None	None	G2-G3/G3-G4 (high)
IV	Any	Any	Present	None	Any (high or low)
IV	Any	Any	None	Present	Any
AJCC, The American Joint Committee on Cancer; Superficial, above the fascia; Deep, deep to fascia; G1, well differentiated; G2, moderately well differentiated; G3, poorly differentiated; G4, undifferentiated. (Adapted from Green FL, Page DL, Fleming ID, et al. AJCC Cancer Staging Handbook. 6th ed. New York, NY: Springer-Verlag; 2002:221-225.)

Pleomorphic Sarcoma (Previously Identified as Malignant Fibrous Histiocytoma)

Introduction and Definition

PS is a term that recently replaced MFH. MFH was introduced as a diagnosis in 1963, and prior to that time, tumors of this type were classified as rhabdomyosarcoma or fibrosarcoma. The classification continues to evolve, and this fact makes it difficult to interpret the epidemiologic, clinical, and outcomes data from the past. This tumor is a pleomorphic high-grade tumor of unknown origin composed of fibroblasts, myofibroblasts, and histiocytes. PS/MFH is the most frequent soft tissue tumor in adults in some series. PS/MFH is found in the extremities 70% to 75% of the time, and 50% of all cases are in the lower extremity. Other less common sites include the retroperitoneum, and the head and neck. The highest incidence is during the fifth decade of life, and there is a male to female ratio of 1.5:1.

Incidence and Demographics

PS/MFH is secondary to another process such as radiation, surgery, fracture, osteonecrosis, Paget disease, nonossifying fibroma, or fibrous dysplasia 20% of the time. PS/MFH arising from a previous abnormality is usually more aggressive and has a poorer prognosis than primary PS/MFH.

Symptoms and Presentation

Clinically, PS/MFH presents with local pain and swelling. There is often a history of a rapidly enlarging mass. It usually presents with a soft tissue mass with or without nearby bone erosion.

X-ray Appearance and Advanced Imaging Findings

Calcifications may be seen at the periphery of the mass on plain X-ray. CT scan is helpful in determining any intraosseus extension. MRI findings in PS/MFH are intermediate signal intensity on T1-weighted images and high-intensity signal on T2-weighted images. MRI helps define the soft tissue mass, marrow involvement, neurovascular structures, and joint invasion. PS/MFH has increased uptake on bone scan, which helps demonstrate any metastases.

Differential Diagnosis

The radiologic differential includes metastatic cancer, plasmacytoma, lymphoma, and fibrosarcoma.

Histopathology Findings

On gross examination, MFH is a lobulated, fleshy, gray-white mass. There may be yellow areas of lipid or darker areas of hemorrhage. The mass may be all soft tissue or have intraosseus extension. The margins of the tumor are normally ill-defined and destructive. Under the microscope, there are plump spindle cells in a storiform pattern in fascicles. A pinwheel pattern is found especially around vessels. The tumor stains positive for histiocytic markers CD68 and lysozyme. Like other sarcomas, PS/MFH is graded from 1 to 4, with a higher grade having a worse prognosis. The classification and identification of PS continues to evolve. Some pathologists believe that many of the tumors now classified as PS/MFH should be reclassified with a more specific diagnosis such as synovial cell sarcoma or leiomyosarcoma, based on careful study of cellular markers.

Treatment Options for This Tumor

Treatment of PS/MFH depends on grade, stage, and site. Local tumor control is almost always accomplished with surgical resection with a wide margin. Radiation may be given preoperatively or postoperatively. Preoperative chemotherapy can sometimes reduce the tumor bulk and may increase the chances of a limb-sparing procedure. Selective transcatheter intra-arterial chemotherapy has been employed to reduce systemic toxicity. Local recurrences are common.

Outcomes of Treatment and Prognosis

The prognosis of PS/MFH becomes worse as the lesion is larger and deeper in the soft tissue. PS/MFH metastasizes to the lungs, lymph nodes, liver, and bone.

Synovial Sarcoma

Introduction and Definition

SS is the most common malignant soft tissue sarcoma in the foot, accounting for 18% to 22% of all such tumors. In some series, it is the single most common sarcoma of any type in the distal lower extremity. This tumor deserves the full attention of every foot and ankle specialist for several reasons. Among these is the slow, painless growth pattern that mimics a benign process, its peak incidence in young patients, and the serious consequences of delay in diagnosis.

SS was named in 1934 by Sabrazes based on what appeared to be synovial tissue on light microscopy. However, the name is misleading and bears no relation to the origin of the tumor. The inaccurate name continues to lead to mistaken assumptions about the location and behavior of the tumor. Recent complementary DNA microarray-based studies found that the gene expression profile of SS is closely related to neural crest-derived malignant peripheral nerve sheath tumor. SS displays two distinct types of chromosomal translocations t(X;18;p11;q11), named fusion type SYT-SSX1 and SYT-SSX2.

Incidence and Demographics

Most patients with SS are in their second through fifth decades, with the average age of incidence around 28 years, but SS can occur at any age. SS may occur anywhere in the leg, ankle, or foot.

Symptoms and Presentation

This tumor can exhibit slow, painless growth, and there are serious consequences due to the delay in diagnosis. The most common location is the leg, ankle, or foot. The presentation of SS is variable and may mimic a benign process such as ganglion cyst. The lesion is usually deeply seated, firm, and painless, but small subcentimeter lesions are also seen. The tumor is firm to examination and does not transilluminate. Metastasis may occur to regional lymph nodes and these should be included in the physical examination. The patient may have a mass that has been present for months, years, or even decades, with slow growth and little or no symptoms. There may have been recent rapid growth of a lesion that has been present for years without apparent change. Conversely, some SS may be very painful from the outset. The average duration of symptoms before diagnosis is 21 months.

X-ray Appearance and Advanced Imaging Findings

Imaging studies are not adequate to distinguish this tumor from benign soft tissue masses. Plain radiographs are still useful and may show the invasiveness and the stippled calcification some SSs have. MRI findings are “indeterminate” as defined previously, with intermediate or low signal intensity on T1 sequences and high signal intensity on T2 sequences. Axial imaging may reveal this lesion’s potential to invade and destroy adjacent bones or soft tissues, but the tumor may appear well circumscribed. Most lesions present in stage II, which indicates it has spread beyond the compartment of origin. Imaging of regional lymph nodes should be included in the MRI examination.

Differential Diagnosis

Plantar fibroma can be surprisingly large and aggressive, and its appearance and location overlap with SS. Biopsy is recommended for all soft tissue tumors greater than 2 or 3 cm in the foot unless the diagnosis is otherwise established with certainty.

Histopathology Findings

High-grade, monophasic, poorly differentiated SS may appear to be a “small round blue cell tumor,” a group of tumors that includes Ewing/primitive neuroectodermal tumor (PNET), rhabdomyosarcoma, lymphoma, and others. Final diagnosis requires immunohistochemical staining analysis. However, immunohistochemical markers such as epithelial membrane antigen (EMA) and cytokeratin that are considered to be the most specific for SS may be absent. Vimentin is typically positive in SS. EMA and cytokeratin are usually positive in SS. S-100 may be positive or negative in SS. On light microscopy, SS may be monophasic fibrous and biphasic. The monophasic type may appear to be a mass of small round blue cells, or more fibrous with spindle-shaped cells. The biphasic type is of fibrous areas with clefts or spaces or areas with epithelial cells.

Treatment Options for This Tumor

Surgical resection with a wide margin remains the cornerstone of treatment. Both chemotherapy and radiotherapy have been shown to have a positive effect on survival. In one series, 10 of 12 patients who had surgical treatment for SS in the foot required either a below-knee or a Chopart amputation.

Outcomes of Treatment and Prognosis

Overall prognosis of SS is only fair. Approximately 50% to 60% of patients will be free of disease at 5 years. There is an inverse correlation between prognosis and age at presentation. Distal lower extremity location may be a positive prognostic factor. Negative prognostic factors include large tumor size, high histologic grade, and metastasis at presentation.

Special and Unusual Features

Recent data have shown that SS displays two distinct types of chromosomal translocations t(X;18;p11;q11), named fusion type SYT-SSX1 and SYT-SSX2. Fusion type seems to have a significant impact on disease course and survival. In one study, median and 5-year overall survival for the SYT-SSX1 and SYT-SSX2 groups were 6.1 years and 53%, and 13.7 years and 73%, respectively.

Diagnostic Procedure

Imaging studies are not adequate to distinguish this tumor from benign soft tissue masses. Plain radiographs are recommended and may show the invasiveness of the lesion or the stippled calcification 30% of SSs have. MRI findings are indeterminate as defined previously, with intermediate or low signal intensity on T1 sequences and high signal intensity on T2 sequences. Axial imaging may reveal this lesion’s potential to invade and destroy adjacent bones or soft tissues, but the tumor may appear well circumscribed.

Clear Cell Sarcoma

CCS, also known as malignant melanoma of soft parts, is an aggressive malignant sarcoma arising from melanoblasts that occur in tendons, aponeuroses, and subcutaneous tissues of the foot and ankle. This tumor is one of a group of rare malignancies associated with the gene fusion product EWSR1/ATF1 or EWSR1/CREB1, which includes CCS of the salivary gland, CCS of the gastrointestinal tract, and others. More than 90% of CCS have a reciprocal translocation t(12;22) (q13;q12). This rare tumor differs from malignant melanoma in both histology and natural history.

Although CCS accounts for only 1% of soft tissue sarcomas, surgeons who treat the foot and ankle should be familiar with its presentation and treatment due to the predilection of CCS for the lower extremity. More than 90% of cases in some series involve the lower extremity.⁴¹ Unlike most sarcomas, CCS has a tendency to metastasize to lymph nodes. Late metastasis to locoregional nodes or lung may occur months or years after treatment. Long-term follow-up and surveillance for metastasis is warranted.

CCS may occur at any age including childhood, but is most likely to occur in adults 20 to 40 years of age. The tumor does not contain melanin pigment. Typical presentation of this tumor is of a benign, indolent appearing slow-growing soft tissue mass that is superficial or adjacent to a tendon or an aponeurosis in the ankle, the heel, or the plantar fascia. Average tumor size is 4 cm.⁴²

Treatment depends on early recognition, comprehensive staging, and aggressive surgical extirpation of the tumor. The workup should include CT scan of the chest and MRI of the entire limb and locoregional lymph nodes. The mainstay of treatment is resection with a wide margin. Multiagent chemotherapy has not been shown to have any impact on survival.⁴³ Overall disease-free survival at 5 years is approximately 68%.⁴⁴ Tumor size appears to be a prognostic factor. Prognosis was dismal in cases where metastasis was present.⁴⁵

Other Malignant Soft Tissue Tumors with Benign Clinical Appearance

Two other uncommon malignant soft tissue tumors also have a predilection for the foot. Acral myxoinflammatory fibroblastic sarcoma⁴⁶ and aggressive digital capillary adenocarcinoma⁴⁷ are indolent, often painless tumors that may mimic a benign process. Because these lesions may be mistaken for a skin condition such as a sebaceous cyst or a wart, it is recommended that all mass lesions removed from the foot be submitted for pathologic analysis to avoid a missed diagnosis in these potentially deadly tumors. Both these malignant tumors require aggressive surgical removal with wide margins, which usually requires at least a partial amputation.⁴⁶,⁴⁸

The term “tumor” originates from the Latin tumere “to swell” and denotes any type of mass or swelling of bone or soft tissue. Bone tumors can arise from several causes, including hamartomas (an overgrowth of normal tissues), reactive or posttraumatic processes, and inflammatory lesions, or they may be benign or malignant neoplasms. The foot is comprised of numerous tightly confined and well-vascularized anatomic compartments that predispose to local and distant spread of disease. The clinician examining the patient presenting with a tumor of the foot or ankle must approach the problem in an informed and systematic fashion.

Tumors of the foot and ankle represent a unique subset of all bone and soft tissue tumors, showing variance in type, location, age, prognosis, and treatment from tumors in the rest of the musculoskeletal system. In large series of tumors of the entire skeleton, approximately 3% to 4% of all bone tumors are located in the bones of the foot. Bone tumors in this location are more common in males by a small margin. Most are cartilaginous or cystic, with a minority of tumors being osteoblastic.

Certain tumors are overrepresented in the bones of the foot, likely because of the unique structure and functional demands placed on the bones. For example, aneurysmal bone cyst (ABC), a tumor that may develop following injury or trauma, is more common than expected in the foot.⁴⁹ Chondromyxoid fibroma (CMF) and chondroblastoma are generally rare tumors, but for unknown reasons these lesions are relatively common in the foot.

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