Foot and Ankle Tumors
J.C. Neilson, MD
Joseph Benevenia, MD
Valdis M. Lelkes, MD
Dr. Neilson or an immediate family member has received nonincome support (such as equipment or services), commercially derived honoraria, or other non-research-related funding (such as paid travel) from Musculoskeletal Transplant Foundation and serves as a board member, owner, officer, or committee member of Musculoskeletal Transplant Foundation. Dr. Benevenia or an immediate family member has received royalties from Rutgers University/CreOsso LLC; is a member of a speakers’ bureau or has made paid presentations on behalf of the Musculoskeletal Transplant Foundation; serves as a paid consultant to or is an employee of Merete and Onkos; serves as an unpaid consultant to Implant Cast and the New Jersey Orthopaedic Society; has stock or stock options held in CreOsso LLC; has received research or institutional support from CreOsso, Merete Medical, and the Musculoskeletal Transplant Foundation; has received nonincome support (such as equipment or services), commercially derived honoraria, or other non-research-related funding (such as paid travel) from Implantcast, Merete, and Onkos; and serves as a board member, owner, officer, or committee member of the American Academy of Orthopaedic Surgeons, the Musculoskeletal Transplant Foundation, and the Musculoskeletal Tumor Society. Neither Dr. Lelkes nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.
ABSTRACT
Musculoskeletal tumors of the foot or ankle are rare tumors with varying pathology. Thorough history and physical assessment of the patient can provide insight into differentiating benign and malignant conditions and are essential for guiding further diagnostic workup. Radiographic imaging can assist in delineating types of different lesions and lead to a diagnosis. Plain radiographs can evaluate the soft tissues as well as bone and may indicate aggressiveness of osseous lesions. Further evaluation with CT or MRI may be needed to confirm diagnosis or for surgical planning. In many cases, diagnosis can only be made with tissue sample from biopsy. Tumors of the foot or ankle can range from benign soft-tissue tumors to malignant soft-tissue sarcomas. Benign osseous tumors may be found in the foot or ankle as well as malignant osseous tumors including osteosarcoma, ewing sarcoma, and chondrosarcoma. Metastatic carcinomas have been known to metastasize to sites in the foot or ankle. Malignant lesions about the foot or ankle may be more often misdiagnosed as benign conditions which can delay appropriate treatment. Reconstructive treatments for the foot and ankle include amputation, custom endoprosthetic reconstruction, and osseous grafting techniques.
Introduction
The evaluation, diagnosis, treatment, and referral of patients with a tumor of the foot or ankle are important in clinical practice. Orthopaedic surgeons should be vigilant to detect these tumors. A foot or ankle tumor is classified as benign or, less often, malignant and may occur within the soft tissue or bone. A mass can develop in the foot as a result of a posttraumatic or neuropathic condition or because of bone or soft-tissue infection.
Incidence
Tumors of the foot or ankle are rare, and their incidence has not been well studied. In a retrospective review of 2,660 musculoskeletal tumors at any anatomic site that were surgically treated at a tertiary center over 20 years, 153 tumors were in the bone or soft tissue of the foot or ankle (5.75%; mean patient age, 33.2 years).1 Sixty of the foot and ankle tumors (39.2%) were considered to be malignant, and the remaining 93 were considered to be benign. Eighty patients (52.3%) had a soft-tissue tumor, of which giant cell tumor of the tendon sheath and pigmented villonodular synovitis were the most common. The remaining 73 patients (47.7%) had a bone tumor; giant cell tumor was the most common type.
Patient Evaluation
History
A thorough patient history is key to the differential diagnosis of a mass or lesion of the foot or ankle. The most
common initial symptom of a bony lesion is pain, and identifying the onset, duration, location, and character of the pain can be useful in determining the etiology. Any aggravating or alleviating activities may be especially important. In general, an aggressive malignant bone lesion is painful. Many benign bone lesions are found incidentally. NSAIDs can provide significant pain relief in a patient with aggressive tumor or some specific types of tumors, such as osteoid osteoma. A soft-tissue mass, whether malignant or benign, usually is not painful, although discomfort may result from displacement or destruction of adjacent structures or a change in gait pattern. When a mass has been identified, the duration, onset, as well as changes in the size, location, and number of masses can be helpful in determining the best management. Most masses that have been present for years without increasing in size are benign, but some benign masses are at risk for malignant dedifferentiation. A stable tumor that begins to grow may represent malignant progression to a sarcoma and should be evaluated and treated by a musculoskeletal oncologist. Some tumors, such as vascular anomalies, have a distinct pattern of enlarging and shrinking, especially with activity. Some foot masses, such as Morton neuroma and plantar fibroma, have a distinct location.
common initial symptom of a bony lesion is pain, and identifying the onset, duration, location, and character of the pain can be useful in determining the etiology. Any aggravating or alleviating activities may be especially important. In general, an aggressive malignant bone lesion is painful. Many benign bone lesions are found incidentally. NSAIDs can provide significant pain relief in a patient with aggressive tumor or some specific types of tumors, such as osteoid osteoma. A soft-tissue mass, whether malignant or benign, usually is not painful, although discomfort may result from displacement or destruction of adjacent structures or a change in gait pattern. When a mass has been identified, the duration, onset, as well as changes in the size, location, and number of masses can be helpful in determining the best management. Most masses that have been present for years without increasing in size are benign, but some benign masses are at risk for malignant dedifferentiation. A stable tumor that begins to grow may represent malignant progression to a sarcoma and should be evaluated and treated by a musculoskeletal oncologist. Some tumors, such as vascular anomalies, have a distinct pattern of enlarging and shrinking, especially with activity. Some foot masses, such as Morton neuroma and plantar fibroma, have a distinct location.
In addition to the history of the tumor itself, the patient history should include a complete discussion of any earlier tumors, whether benign or malignant, as well as any risk factors such as tobacco smoking, chemical exposure, recent or past trauma or infection, or a family history of tumors.
Physical Examination
In addition to the involved foot and ankle, a complete examination should include the contralateral extremity, proximal draining lymph node beds, any masses discovered while taking the history, and any skin lesions. This evaluation may lead to identification of primary or metastatic tumor sites or a syndrome such as neurofibromatosis or plantar fascial fibromatosis (Ledderhose disease). The size and depth of the mass should be measured because these are the two factors most useful for determining the likelihood of malignancy. A large subfascial tumor is most likely to be malignant. Direct palpation of the mass may elicit pain. The mass may be firm or fluctuant, although a mass that usually is fluctuant, such as a ganglion, can appear to be firm because of the tension exerted by the many structures in the foot. The mobility of the mass can help in identifying both its depth and its origin; for example, a schwannoma usually is only mobile perpendicular to the plane of the nerve. Provocative testing with percussion for a Tinel sign can be useful in evaluating neural tumors. Transillumination can help characterize solid, rather than fluid-filled, masses. Auscultation and palpation for bruits can be useful in identifying arteriovascular malformations. Evaluation for other common generators of pain in the foot should be undertaken as suggested by the patient’s history.
Imaging
Radiographic analysis is important in the evaluation of both soft-tissue and bone tumors. Radiographs can indicate the aggressiveness of an osseocentric tumor. A permeative pattern suggests an aggressive, often malignant process. A geographic pattern often is characterized by a thin, eggshell-like margin of bone around the tumor and connotes a less aggressive process. This observed difference is explained by the response of the bone to the tumor. The bone is able to respond to and even contain a relatively slow-growing, unaggressive tumor. Some types of tumors are most likely to occur in a diaphyseal, metaphyseal, or epiphyseal area, but because the foot bones are small and irregular, the specific origin of a tumor can be difficult to identify. Periosteal elevation may be the result of a mass effect from tumor, and subperiosteum elevated off the bone usually indicates a relatively aggressive tumor. The pattern of periosteal elevation is described as a sunburst, onion skinning, or a Codman triangle.
The matrix of any lesion can give important clues to its origin. Cartilage tumors often have a lucent appearance and over time become mineralized in a punctate pattern. Fibrous dysplasia typically has a ground glass radiographic appearance. In comparison with normal bone, other tumors are more or less lucent or have mixed lucency; this characteristic often is helpful in the differential diagnosis of primary and metastatic tumors of bone. Cortical destruction also can indicate a relatively aggressive tumor. Extraosseous mineralization may appear adjacent to a bone lesion or in some soft-tissue masses. The most commonly seen forms of extraskeletal bone are phleboliths in an arteriovascular malformation or synovial sarcoma, mineralization of the necrotic center of soft-tissue sarcoma, peripheral mineralization of myositis ossificans, or cloudlike mineralization of an extraskeletal osteosarcoma. Radiographs can differentiate soft-tissue masses within different tissue planes by the density of air, fat, water (muscle), and bone.
CT is helpful for evaluating the character of mineralized structures, which have many characteristics in common with those of bone, as seen on plain radiographs. CT of the chest, abdomen, and pelvis is an important part of the workup for a patient with suspected metastatic carcinoma to bone.2 Although CT angiography is an effective tool for a patient who cannot undergo MRI, usually MRI is superior for precise evaluation of tumors and important surrounding structures in the foot and ankle. Obtaining high-quality MRI results for small structures in areas
such as the forefoot requires the use of small coils and a high-Tesla machine. MRI with gadolinium contrast is recommended for all soft-tissue and most bone lesions because this technique shows the amount of blood flow to a mass. By enhancing the rim of a cystic structure such as a ganglion, as well as some arteriovascular malformations and bone cysts, MRI can differentiate between a fluid-filled and a solid mass. Diffusion-weighted MRI sequences are most commonly used to assess the tumor response to radiation, chemotherapy, or ablative treatment. Magnetic resonance angiography has supplanted traditional angiography for most tumor indications, and it is useful for evaluating the blood supply to the foot before resection or reconstruction. The soft-tissue detail provided by a high-quality MRI is critical to the surgical resection of soft-tissue and bone tumors of the foot and ankle.3
such as the forefoot requires the use of small coils and a high-Tesla machine. MRI with gadolinium contrast is recommended for all soft-tissue and most bone lesions because this technique shows the amount of blood flow to a mass. By enhancing the rim of a cystic structure such as a ganglion, as well as some arteriovascular malformations and bone cysts, MRI can differentiate between a fluid-filled and a solid mass. Diffusion-weighted MRI sequences are most commonly used to assess the tumor response to radiation, chemotherapy, or ablative treatment. Magnetic resonance angiography has supplanted traditional angiography for most tumor indications, and it is useful for evaluating the blood supply to the foot before resection or reconstruction. The soft-tissue detail provided by a high-quality MRI is critical to the surgical resection of soft-tissue and bone tumors of the foot and ankle.3
Technetium Tc-99 bone scanning is useful for evaluating a stress fracture or a stress reaction that can masquerade as an osseous lesion of the foot. Whole body scanning is commonly used to identify malignant metastasis to bone, but it must be interpreted with caution because some tumors, such as multiple myeloma, eosinophilic granulomas, and large renal cell cancers, may not show significant uptake.
The use of ultrasonography in the diagnosis and management of soft-tissue tumors is constantly evolving. Ultrasonography is used to differentiate solid and fluid-filled masses, and it is an excellent tool for measuring flow in vascular anomalies. The usefulness of ultrasonography increases with the surgeon’s experience with this modality. In the treatment of tumors, ultrasonography most commonly is used for guidance during soft-tissue biopsy or the treatment of a vascular anomaly.
Positron emission tomography (PET) is useful in the evaluation of many but not all types of malignancies. Inclusion of the lower extremities is not standard during PET staging of many cancerous conditions, and whole body PET should be specified if PET evaluation is appropriate for the patient’s lesion. PET is rarely ordered by a physician other than an oncologist. PET can be useful for evaluation of the lymphatic spread of hidradenocarcinoma, melanoma, or epithelioid sarcoma, usually in conjunction with lymphoscintigraphy and sentinel node resection.4 Although PET-MRI is a promising tool for identifying tumor metastasis at diagnosis and during subsequent staging, its use has not yet been completely validated.5
Laboratory Evaluation
Laboratory testing is not necessary for most tumors of the foot and ankle. However, inflammatory markers, white blood cell analysis, and cultures are appropriate if an infectious origin is suspected. Complete blood cell counts are useful for identifying leukemia or lymphoma and may reveal anemia in a patient with multiple myeloma or a widely metastatic cancer. Protein electrophoresis and light chain evaluations can be diagnostic for multiple myeloma. Some other primary cancers have blood markers, such as prostate-specific antigen. Metabolic analysis can reveal kidney or liver damage, malnutrition, or electrolyte abnormalities.2 Calcium levels should be checked in all patients with metastatic disease to the bone because increased bone turnover can lead to increased serum calcium or to cardiac conditions including fatal arrhythmias.
Biopsy
Pathologic analysis should be performed for all masses. An excision, incision, or needle technique can be used, depending on the size, location, and imaging characteristics of the lesion as well as the experience of the surgeon. Excisional biopsy is appropriate if a cuff of normal tissue can be obtained around the lesion to ensure negative margins. This saves the patient from a wider re-excision if the lesion is determined to be malignant by pathology. Incisional biopsy should be considered for a relatively large mass, which should be presumed to be malignant until histologic analysis proves otherwise. In general, biopsies should be performed or guided by a surgeon trained in treating primary malignant tumors of the extremity. Frozen section should be obtained during an open biopsy to determine whether lesional tissue is obtained and thereby increase the likelihood of a correct diagnosis. A needle biopsy can be done with or without imaging guidance. Ultrasonography or CT can be used to increase the likelihood of obtaining tissue from the lesion by targeting solid, nonnecrotic areas and correlating these findings with those of contrast-enhanced MRI. A thoughtful approach to needle biopsy is essential because bleeding from deep or subcutaneous vessels could allow tumor tissue to spread along uninvolved tissue planes and thereby increase the resection area.6 Fine-needle aspiration biopsy can be used in many masses, but this technique is operator dependent. Core biopsy allows more tissue to be obtained, but its use is limited to tumors large enough to accommodate the throw of the needle.
The small amount of subcutaneous tissue in the foot and ankle often allows relatively early identification of a mass. Usually, a mass smaller than 3 cm is benign. A mass larger than 3 cm is more likely to be malignant. However, a recent study found that malignant bone tumors in the foot are 5 to 30 times smaller than those in other skeletal areas.7 All biopsies should be done with great care; an inexpert biopsy can increase the likelihood that a secondary surgical procedure, tissue transfer, or amputation will be required.8
Benign Soft-tissue
Tumors
Synovial Tumors
Ganglion A synovial ganglion is the most common mass of the foot and ankle. An MRI study found that 5.6% and 0.4% of patients had a ganglion around the ankle or the foot, respectively.9 Synovial ganglia result from a weakness in the wall of a synovial structure. On MRI, a ganglion most commonly is seen in the tarsal canal and on the dorsum of the foot.10 Most common site of origin involves the lateral column of the Lisfranc joint. These structures often are painless but can create pain when they compress adjacent structures, and they can become irritating with shoe wear. Ganglia can be diagnosed clinically if they increase and decrease in size, are over a joint and superficial tendon, are subcutaneous, or can be transilluminated (if sufficiently large). In addition, fluid can be aspirated using a large-bore needle. If all of these factors are present, resection without advanced imaging may be appropriate. However, if these factors are not present, high-quality gadolinium-enhanced MRI is needed to consolidate the diagnosis. The mass should be characterized by a homogeneous low signal with T1 weighting, a high signal with T2 weighting, and rim enhancement with gadolinium3 (Figure 1). The use of hand/foot MRI coils decreases the field of view and improves the quality of the image for a small mass. The treatments include observation, corticosteroid injection, and surgical resection. Marginal resection can be undertaken with an attempt to remove the stalk and entire cyst capsule. Arthroscopic internal drainage or resection has been described with recurrence rate of 12%.11
Pigmented Villonodular Synovitis
Pigmented villonodular synovitis is an intra-articular process characterized by hemorrhage, hemosiderin deposition, giant cells, histiocytes, and fibrous stroma. The incidence is two per one million people.9 Although the knee is the most commonly affected joint, pigmented villonodular synovitis sometimes occurs in the ankle. In the earlier stages, patients may have a painful or painless effusion. Patients with long-standing disease may have large masses, poor joint motion, and arthritis. MRI classically shows a low signal with T1 and T2 weighting, with peripheral contrast enhancement. A blooming pattern can be seen in larger masses. In the foot or ankle, the tumor may involve more than one adjacent joint as a result of direct extension.
Pigmented villonodular synovitis is categorized as localized or diffuse. The localized form more likely occurs in the forefoot11 and is treated with open or arthroscopic resection of the nodule, and recurrence rates are low. The diffuse form often occurs in the hindfoot11 and is treated with open and/or arthroscopic surgery but is associated with high recurrence rates up to 40%12 because of the difficulty of obtaining a complete resection. Some patients with degenerative disease can benefit from fusion or arthroplasty.13
Giant Cell Tumor of Tendon Sheath
Giant cell tumor of tendon sheath is histologically identical to pigmented villonodular synovitis but is extraarticular and associated with synovial structures such as tendon sheaths. The mass itself is painless, but it may impinge upon or irritate adjacent structures. The MRI signal characteristics are similar to those of pigmented villonodular synovitis. Marginal resection is the appropriate treatment. Needle or incisional biopsy should be considered for a relatively large and fast-growing tumor because it is possible for such a tumor to degenerate into a malignant giant cell tumor of tendon sheath that, like a sarcoma, should undergo wide resection.
 FIGURE 1 MRI studies showing the characteristics typical of a synovial ganglion on the dorsum of the ankle. A, A homogeneous low signal with T1 weighting. B, A high signal with T2 weighting. C, Rim enhancement with gadolinium-enhanced T1 weighting. |
Synovial Chondromatosis
Synovial chondromatosis is much less common than pigmented villonodular synovitis, but it can be no less debilitating. This abnormality is believed to be a cartilaginous metaplasia of the synovium that breaks off to form loose bodies. This tumor has been associated with an abnormality in chromosome 6. Open or arthroscopic treatment is appropriate. Synovial chondromatosis of the foot or ankle recurred locally in as many as 38.5% of patients in a small study, and two-thirds of the recurrent tumors degenerated into low-grade chondrosarcoma.14 Degeneration to chondrosarcoma is difficult to diagnose correctly, and a questionable diagnosis should be reviewed by an experienced musculoskeletal pathologist.
Lipoma Arborescens
Lipoma arborescens is an extremely rare synovial disorder that most likely represents a reactive process made up of intra-articular lipomalike masses of hypertrophic synovial villi distended by fat. Open or arthroscopic treatment usually is curative.15
Other Synovial Proliferations
Significant synovial proliferations similar to those of pigmented villonodular synovitis can be caused by medical conditions including acute or chronic infection, gout, calcium pyrophosphate disease, amyloidosis, rheumatologic disease, and foreign material in the joint.
Vascular Anomalies
Vascular anomalies are a broad group of tumors that stem from an abnormality in the arteries, veins, capillaries, or lymph tissues. These tumors can occur in any tissue in the body. A superficial vascular anomaly often is seen as a change in skin color and character. Deeper intramuscular growths often change in size with activity. Often the growth infiltrates areas between the muscle fibers, and as a result complete resection is difficult. A deep tumor can become painful or cause cramping as it grows. Well-circumscribed soft-tissue calcifications often are seen on radiographs. Ultrasonography and some MRI sequences can differentiate between high-flow and low-flow lesions. The appearance of the lesion on MRI often is serpiginous and has been described as an axial slice through a bowl of worms. Although surgical resection is an option, many vascular anomalies can be effectively treated with serial percutaneous sclerosing therapy, usually under ultrasonography guidance. Very few vascular anomalies of the foot require systemic treatment.16,17
Nodular Fasciitis
Nodular fasciitis is a rapidly growing, very cellular tumor with a high mitotic rate. It is sometimes misdiagnosed as a sarcoma, and only an experienced pathologist may be able to arrive at the correct diagnosis. Patients of age 20 to 40 years are most often affected. Unclear borders can be seen on MRI as the tumor infiltrates the surrounding soft tissue; T1- and T2-weighted signal intensities are mixed, and there is a mixed pattern with gadolinium enhancement. Pain can come from local irritation as the tumor grows to a significant size within weeks. The tumor is self-limiting and often regresses with biopsy.
Fibroma
Benign fibromas primarily occur in the subcutaneous tissues and can be found in any area of the body. Histologically dense, mature fibrocytes are present. T1- and T2-weighted MRI shows low signal intensity, and there is no enhancement with gadolinium. Marginal resection usually is curative, and recurrence is rare.
Plantar Fibroma/Fibromatosis
Plantar fibroma appears as one or more lesions, usually along the medial border of the plantar fascia, most often in adolescents or young adults. The tissue is histologically similar to that of Dupuytren or Peyronie contracture, which is found in older adults. The lesions rarely grow larger than 2 cm and remain static in size. Bilateral masses occur in as many as half of patients. On MRI, there is low T1 signal and low to intermediate T2 signal, with variable enhancement.
Most patients are asymptomatic. A patient with pain should be evaluated for the presence of another pain generator and should undergo extensive nonsurgical treatment including physical therapy and the use of night splints, shoe modification, and over-the-counter pain medications. Resection is rarely recommended. The recurrence rate is 100% after an isolated surgical resection and 25% after complete plantar stripping.18 Resection may leave a hypersensitive area on the plantar aspect of the foot. Novel treatments such as extracorporeal shock wave therapy have been used to treat symptomatic patients, with a resulting decrease in pain scores and subjective softening of masses.19
Extra-abdominal Fibromatosis
Extra-abdominal fibromatosis (also known as desmoid tumor) is a locally aggressive, monoclonal proliferative disease that occurs anywhere in the musculoskeletal system. The tumor grows at a variable rate and in some patients is latent for long periods of time. The peak incidence is in patients approximately 30 years old. These tumors are firm and may adhere to underlying structures. MRI classically shows low T1 and T2 signal, but some tumors have a mixed T2 signal; enhancement with gadolinium is low or mixed. Unlike a sarcoma, fibromatosis often
infiltrates the surrounding tissues, and planning a wide resection is difficult. As many as 28% of these tumors are associated with previous trauma, including a surgical scar. The treatment is evolving. Medical therapies have included the use of NSAIDs, antiestrogen therapies, and other chemotherapies. Radiation has been used alone and in conjunction with surgical resection for tumor control. Local control rates after surgical resection range from 50% to 80%.20,21
infiltrates the surrounding tissues, and planning a wide resection is difficult. As many as 28% of these tumors are associated with previous trauma, including a surgical scar. The treatment is evolving. Medical therapies have included the use of NSAIDs, antiestrogen therapies, and other chemotherapies. Radiation has been used alone and in conjunction with surgical resection for tumor control. Local control rates after surgical resection range from 50% to 80%.20,21
Epidermoid Inclusion Cyst
An epidermoid inclusion cyst usually is subungual and occurs as the result of traumatic disruption of the nail matrix beneath the skin, with subsequent collection of keratin in a cystlike structure that can erode into the distal phalanx. The treatment is with biopsy and intralesional excision and grafting, if necessary. Secondary infection can complicate the treatment.
Glomus Tumor
The vascular glomus tumor appears as a small, painful red to blue discoloration beneath the nail bed. Patients have a triad of symptoms involving paroxysmal pain, point tenderness, and cold hypersensitivity.22 Other subungual tumors, especially malignant melanoma, should be considered in the differential diagnosis. A glomus tumor usually is smaller than 1 cm. Imaging is difficult, but MRI signal is low with T1 weighting and high with T2 weighting; a low-intensity central nidus is seen with gadolinium enhancement. Tumor pressure on the bone can cause erosion of the phalanx. This tumor usually occurs in early adulthood and is treated with marginal excision with low rates of recurrence, except in cases of incomplete excision.23
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