Soft Tissue Masses

Michael S. Downey

Christa M. Gredlein

Soft tissue tumors of the foot and ankle region present a diagnostic and therapeutic challenge that, in some instances, may prove to be the difference between life and death. Although rare, malignant soft tissue masses can occur in the foot or ankle and can easily be mistaken for more common benign lesions. For this reason, the importance of the evaluation, diagnosis, and management of any suspicious soft tissue mass cannot be understated.

Soft tissue by definition is nonepithelial, extraskeletal tissue not including the reticuloendothelial system, glia, and connective tissue of the parenchymal organs. Skeletal muscles, fibrous tissue, fat, peripheral nervous structures, and the blood vessels supplying each of these tissues constitute soft tissue. Embryologically, soft tissue is derived mainly from the mesoderm, and a small fraction originates from neuroectoderm.

Soft tissue tumors are usually divided into benign or malignant types. Benign lesions closely resemble the tissue from which they were derived. Autonomous growth and local invasion are rare with such tumors, and, generally, they have a low recurrence rate after therapy, with few exceptions. Conversely, malignant tumors, also known as sarcomas, are aggressive, are capable of rapid destructive growth, and have a high probability of recurrence or metastasis.

Although rare, malignant tumors can present in the foot or ankle and may prove to be life threatening. Malignant soft tissue tumors more commonly present as primary lesions, meaning they originated in the foot or ankle; however, they can also present as secondary lesions, meaning they are metastatic from another distant part of the body.

INCIDENCE

The true incidence of soft tissue tumors, especially benign tumors, is almost impossible to estimate. This is because many soft tissue lesions are asymptomatic and go undetected or are ignored by the patient. Benign tumors outnumber malignant ones by a ratio approaching 100:1 in those patients presenting in a hospital setting (1). Although most soft tissue masses in the foot and ankle are inflammatory or benign, malignant tumors do occur. Soft tissue sarcomas are uncommon and represent about 1% of all malignant neoplasms in the adult population. In addition, the total number of sarcomas diagnosed in the United States each year is about 500 (2). Worldwide, primary sarcomas presenting below the knee constitute about 8% of the approximately 5,000 sarcomas diagnosed each year (3).

Many types of soft tissue masses are found in the foot and ankle. According to the World Health Organization classification system, 82 different benign and malignant soft tissue tumors can occur in the distal leg and foot. Because of the large variety of tumors that can occur and the low frequency, the literature is lacking regarding incidence and characteristics of soft tissue lesions in the foot and ankle. Kirby et al (3) retrospectively analyzed 83 cases of soft tissue tumors in the foot or ankle, which had been examined by biopsy over a 5-year period. Eighty-seven percent of the lesions were benign, and the remaining thirteen percent were malignant tumors. The most common benign lesions were ganglion cysts and plantar fibromatoses, and the most common malignant tumor was synovial sarcoma. Regarding the specific location, 40% were found in the dorsal midfoot area, 23% were located in the ankle region, 17% occurred in the plantar aspect of the foot, and the remaining tumors were in either the toes or heel.

Collin et al (4) performed a retrospective review of 315 patients with localized soft tissue sarcomas of the lower extremity. Of this sample size, only 21 (0.7%) sarcomas were located in the foot or ankle. In a study by Shiu et al (5) regarding the surgical treatment of 297 soft tissue sarcomas of the lower extremity, the foot was by far the least common site for tumor occurrence when compared with the thigh or the leg.

Finally, soft tissue tumors of metastatic origin cannot be overlooked in patients presenting with soft tissue masses. Although extremely rare, metastasis from distant carcinomas can result in soft tissue lesions of the foot or ankle. Hattrup et al (6) reviewed the Mayo Clinic files from 1947 to 1984 and found only 17 metastatic tumors of the foot and ankle region. Only two of these cases had solely soft tissue involvement.

ETIOLOGY

The exact cause of soft tissue tumors is essentially unknown. Recognized causes of malignant lesions include various chemical and physical factors, exposure to ionizing radiation, and various genetic or inherited factors. Each factor is thought to be related to the activation of oncogenes that lead to tumor proliferation. Etiologic factors responsible for the development of benign masses are also poorly understood; however, trauma and a familial distribution have been implicated. Transformation of a benign soft tissue mass into a malignant soft tissue mass is rare, except for the occurrence of malignant schwannomas arising from benign neurofibromas.

Trauma or previous injury has been implicated in the development of soft tissue masses. In rare instances, sarcomas have developed after surgical procedures, after burn accidents, in fracture sites, or in the location of metallic implants. Ganglion cysts often occur in sites of chronic biomechanical irritation (7). Keloids form secondary to reactions at previous injury sites. Epidermal inclusion cysts most often result from the traumatic introduction of epidermal cells subepidermally (8).

Exposure to environmental carcinogens is related to the development of soft tissue sarcomas. Certain herbicides used in forestry and agriculture have been linked to an increased risk of sarcoma formation (9).

Although uncommon, radiation therapy for the treatment of malignant lesions has been related to sarcoma development. Radiation therapy may be responsible for the development of any type of sarcoma, but the most common types reported are
fibrosarcoma, malignant fibrous histiocytoma, and extraskeletal osteosarcoma (10).

Figure 92.1 A: A patient with von Recklinghausen disease. Note the cutaneous and subcutaneous nodules and the numerous cafe au lait spots. B: The same patient presented with a neurofibroma in the tarsal tunnel.

Hereditary or genetic factors play a role in the occurrence of certain types of soft tissue tumors. Certainly, the best-known inherited disease that is associated with soft tissue tumor development is neurofibromatosis, or von Recklinghausen disease (Fig. 92.1). This disease is inherited as an autosomal dominant trait, which is characterized by multiple cafe au lait spots and neurofibromas. Various other soft tissue tumors have been shown to occur on an inherited basis including plantar fibromatoses, lipomas, leiomyomas, neuroblastomas, and glomus tumors (11).

Oncogenic viral particles have been found in various soft tissue tumors, although their exact role has yet to be defined (9). This has been proven by the significant number of patients with acquired immunodeficiency syndrome who later develop Kaposi sarcoma.

CLASSIFICATION

Many different classification schemes exist for naming and differentiating soft tissue tumors, but the one most commonly used is that proposed by the World Health Organization (12). It delineates 16 different histologic categories, each of which is subdivided into benign and malignant tumors. The name of each tumor is based on the histologic type of the predominant cell. Table 92.1 is a chart that has been modified from the World Health Organization classification scheme with only the categories of soft tissue types applicable to the foot and ankle included.

Because the histologic classification of soft tissue tumors cannot be relied on for an accurate prediction of clinical course, grading and staging systems have been developed to assist in the prognostic and therapeutic aspects of tumor management. Many different authors have proposed such systems, which can be found specifically in more extensive oncologic texts. This section only serves as a brief overview.

GRADING

Grading is a measure of the degree of malignancy. The grade of malignancy is most often determined by the degree of cellularity, cellular anaplasia, mitotic activity, the amount of necrosis, and expansive or invasive growth (13). Of these factors, the degree of mitotic figures and the extent of necrosis seem to be the most predictive (1). The number of grades varies among systems from distinguishing between only high and low grades to four-grade differentiations.

STAGING

Staging of soft tissue tumors is a determination of the extent of the disease at the time of the initial histologic diagnosis. The stage is based on the size of the tumor, metastasis to local or regional lymph nodes or distant organs, and the anatomic location (intracompartmental or extracompartmental).

Currently, three systems exist for the staging of soft tissue sarcomas. The American Joint Committee on Cancer has published a staging system, the TNMG system (Table 92.2) (14). It uses the size and extension of the tumor (T), the involvement of lymph nodes (N), metastasis (M), and the grade (G) of the sarcoma. The system includes four stages, with stages I, II, III based on histologic grade and stage IV based on local or distant invasion. Another system, proposed by Enneking (15), is used for both soft tissue and bone tumors (Table 92.3). The three stages are based on surgical grade (G), surgical site (T), and metastasis (M). This system differs from the other two in that the tumor size is not taken into consideration. The last system, proposed by Hajdu (16), has four stages based on the tumor size, the site (above or below the superficial fascia), and the histologic grade (Table 92.4).

Currently, the appropriate method by which soft tissue sarcomas should be staged is debated. However, investigators agree that the appropriate treatment of a soft tissue sarcoma should be based on the stage of that tumor. Staging of soft tissue sarcomas requires a combined effort of the clinician, the oncologist, and the pathologist to provide the patient the best therapeutic approach.

Although the staging of benign lesions is not as important as that of malignant lesions, a staging system can still be helpful in the evaluation and management of a benign soft tissue mass. Enneking (15) devised a staging system for benign soft tissue masses (Table 92.5). Stage 1 (benign, latent) lesions have a benign histologic pattern, are intracapsular, and do not metastasize. They are freely movable, nontender, do not enlarge, and

sometimes regress over time. Stage 2 (benign, active) lesions are histologically benign, are intracapsular, and also do not metastasize. Although intracompartmental, these lesions may distort or compress natural barriers. They are often painful and actively enlarge. They are freely movable within the soft tissues. Stage 3 (benign, aggressive) lesions are histologically benign. They are sometimes extracapsular and can cross compartmental barriers. Usually, these masses are painful, rapidly growing, and fixed to the underlying tissues. Most important, these lesions may undergo malignant transformation.

TABLE 92.1 Histologic Classification of Soft Tissue Tumors

1.	Fibrous
	Benign
		Fibroma, nodular fasciitis, proliferative fasciitis, myositis, keloid, elastofibroma, fibroblastoma
		Fibromatosis (superficial and deep)
	Malignant
		Fibrosarcoma
2.	Fibrohistiocytoma
	Benign
		Dermatofibroma, fibrous histiocytoma
		Fibroxanthoma, xantogranuloma, xanthoma
	Intermediate
		Dermatofibrosarcoma protuberans
	Malignant
		Malignant fibrous histiocytoma
3.	Adipose
	Benign
		Lipoma, angiolipoma, lipoblastoma, angiomyolipoma, myelolipoma
	Malignant
		Liposarcoma
4.	Muscle
	Smooth muscle
		Benign
			Leiomyoma, angiomyoma
		Malignant
			Leiomyosarcoma
	Striated muscle
		Benign
			Rhabdomyoma
		Malignant
			Rhabdomyosarcoma
5.	Blood vessels
	Benign
		Hemangioma (capillary, cavernous, arteriovenous, venous)
		Hemangiomatosis, glomus tumor, hemangiopericytoma
	Intermediate
		Hemangioendothelioma
	Malignant
	Angiosarcoma, Kaposi sarcoma, malignant glomus tumor
6.	Synovial tissue
	Benign
		Giant cell tumor of tendon sheath (localized, diffuse)
	Malignant
		Synovial sarcoma, malignant giant cell tumor of tendon sheath
7.	Peripheral nerves
	Benign
		Neuroma, neuromuscular hamartoma, nerve sheath ganglion
		Neurilemoma
		Neurofibroma (localized, diffuse, pacinian, pigmented)
		Granular cell tumor
		Neurofibromatosis (von Recklinghausen disease)
	Malignant
		Malignant schwannomas, neuroepithelioma
8.	Tumors of cartilage and bone-forming tissue
	Benign
		Panniculitis ossificans, myositis ossificans
		Extraskeletal fibroma, extraskeletal osteochondroma
	Malignant
		Extraskeletal chondrosarcoma, extraskeletal osteosarcoma
9.	Uncertain histogenesis
	Benign
		Tumoral calcinosis, myxoma, angiomyoma, amyloid tumor
	Malignant
		Soft part sarcoma, epithelioid sarcoma, clear cell sarcoma
		Extraskeletal Ewing sarcoma
10.	Unclassified tumors
Modified from Enzinger FM, Weiss SW. Soft tissue tumors, 2nd ed. St. Louis, MO: CV Mosby, 1988:1-42.

TABLE 92.2 American Joint Commission Staging System for Soft Tissue Sarcomas

		Tumor Characteristics
Stage		G	T	N	M
IA		1	1	0	0
IB		1	2	0	0
IIA		2	1	0	0
IIB		2	2	0	0
IIIA		3	1	0	0
IIIB		3	2	0	0
IIIC		1-3	1-2	1	0
IVA		1-3	3	0-1	0
IVB		1-3	1-3	0-1	1
Characteristics
Histologic grade (G)
	G1: well differentiated
	G2: moderately well differentiated
	G3: poorly differentiated
Size (T)
	T1: tumor <5 cm
	T2: tumor >5 cm
	T3: destruction of cortical bone, with invasion; histopathologic confirmation of invasion of major artery or nerve
Regional lymph node metastasis (N)
	N0: no detectable lymph node involvement
	N1: histologic lymph node involvement
Distant metastasis (M)
	M0: no clinically or radiographically detectable metastasis
	M1: distant metastasis
From Russell WO, Cohen J, Enzinger F, et al. A clinical and pathological staging system for soft tissue sarcomas. Cancer 1977;40:1562-1570.

TABLE 92.3 Enneking System for Staging Soft Tissue Sarcomas

		Tumor Characteristics
Stage		Grade	Site	Metastasis
IA		G1	T1	M0
IB		G1	T2	M0
IIA		G2	T1	M0
IIB		G2	T2	M0
III		G1-G2	T1-T2	M1
Characteristics
Surgical grade (G)
	G1: low
	G2: high
Site (T)
	T1: intracompartmental
	T2: extracompartmental
Metastasis (M)
	M0: no regional or distant metastasis
	M1: regional or distant metastasis
From Enneking WF. Musculoskeletal tumor surgery, vols 1 and 2. New York, NY: Churchill Livingstone, 1983:1-38, 4647-4713.

TABLE 92.4 Hajdu System for Staging Soft Tissue Sarcomas

		Tumor Characteristics
Stage		*Size (cm)*	*Site*	*Grade*
0		<5	S	L
IA		<5	S	H
IB		<5	D	L
IC		>5	S	L
IIA		<5	D	H
IIB		>5	S	H
IIC		>5	D	L
III		>5	D	H
Characteristics
Site (S)
	S: superficial to fascia (subcutaneous)
	D: deep to fascia
Histologic grade (G)
	L: low
	H: high
From Hajdu SI. Pathology of soft-tissue tumors. Philadelphia, PA: Lea & Febiger, 1979:44.

EVALUATION AND DIAGNOSIS

Soft tissue tumors and tumor-like lesions are common in the foot and ankle. However, their presentation may be different from that in another anatomic location of the body. They often present earlier in their course compared with other locations. Soft tissue tumors are more easily palpated in the foot because of the relatively thin layer of subcutaneous tissue. The weight-bearing function of the foot often alters the clinical presentation or symptoms related to the soft tissue mass. Small lesions can easily cause local nerve entrapment because of the compartmental nature of the foot. Therefore, as a result of the earlier production of pain or discomfort in a mass that
otherwise may have gone unrecognized if not in the foot, the lesion may be more readily diagnosed, leading to better treatment options.

TABLE 92.5 Enneking System for Staging Benign Soft Tissue Masses

Stage	Definition	Behavior
1	Latent	Static condition or spontaneous regression
2	Active	Progressive growth, limited by natural barriers
3	Locally aggressive	Progressive growth, not limited by natural barriers
Adapted from Enneking WF. Musculoskeletal tumor surgery, vols 1 and 2. New York: Churchill Livingstone, 1983:1-38, 4647-4713.

All soft tissue masses in the foot and ankle should be approached as if they could be primary soft tissue sarcomas or secondary soft tissue carcinomas. A patient with a soft tissue mass usually presents to a physician for one of two reasons: pain or concern about the presence of a lump. Regardless of the reason for presentation, a thorough initial evaluation must ensue. The initial evaluation of any soft tissue mass should include a thorough patient history and physical examination, followed by the appropriate accessory studies. After the initial evaluation is complete, biopsy and execution of a definitive treatment plan are performed as needed.

PATIENT HISTORY

The initial step in the evaluation of a soft tissue mass is to obtain a concise and thorough patient history. A thorough history and review of systems are imperative in the initial evaluation of a patient presenting with a soft tissue tumor. The presentation of soft tissue masses is extremely variable. The tumor may be brought to the attention of the patient because of its size, rate of growth, amount of discomfort, or symptoms brought about by involvement of the peripheral nervous system. Questioning may reveal a sudden appearance of the mass or simply a gradually increasing fullness experienced while wearing shoe gear. The patient may have skin discoloration or hyperpigmentation in the area overlying the lesion.

Typically, the soft tissue mass itself is not specifically painful; however, impingement on adjacent structures can cause pain or discomfort. Numbness or paresthesias may result from pressure exerted on a peripheral nerve or nerves. Sensory abnormalities can be expected to predominate over motor abnormalities and are usually well localized over the distribution of the compressed nerve (17).

Rarely, systemic symptoms may be present that could suggest metastasis. Although infrequent, primary carcinomas located elsewhere in the body can metastasize to the foot or ankle, and this possibility should not be dismissed.

Occupational exposures and personal habits may also lead to the development of soft tissue tumors. Exposure to certain occupational carcinogens, either past or present, as well as exposure to ultraviolet or irradiation can cause tumor formation. Smoking cigarettes is a proven cause of tumor formation in major organs, which could possibly metastasize to the foot or ankle region. Certain medications, especially anticancer chemotherapeutic agents, may also cause the formation of soft tissue tumors (7).

Finally, questions regarding the patient’s past medical history and family history are important. Many medical conditions or syndromes are associated with the development of soft tissue masses including neurofibromatosis (von Recklinghausen disease), xeroderma pigmentosum, Gorlin syndrome, Muir-Torre syndrome, Cowden syndrome, and Gardner syndrome (7).

PHYSICAL EXAMINATION

Physical examination is the next necessary component in the evaluation of a patient with a soft tissue tumor, in an effort to determine the type of lesion present. This begins with a visual inspection of the mass. The presence or absence of edema and calor, the turgor and texture of the overlying skin, and the color of the lesion and surrounding tissues should be noted. The exact location of the mass in relation to adjacent structures should also be noted. Important physical characteristics of any soft tissue tumor are its size, consistency, mobility, tenderness, and the reaction of the surrounding tissues (15).

Figure 92.2 Measurement of size of a tumor on the plantar aspect of the foot.

The location of the mass should be noted, and its size should be measured (Fig. 92.2). Preferably, the mass should be either photographed or drawn in the patient’s chart to serve as a basis for subsequent observation and assessment of progression or regression of the lesion. Rapidly growing, larger lesions are more likely to be malignant than slowly growing, smaller lesions.

The consistency of the tumor should be determined by palpation of the lesion. In the foot, it may be difficult to differentiate a discrete mass from an area of localized edema or swelling. A mass typically has a distinct edge or border that sets it apart from the surrounding tissues. An area of localized swelling or edema has no discrete edge because it disappears into the normal surrounding soft tissues. What is important to recognize, however, is that an area of edema can overlie a deep mass. For the most part, tumors feel different from normal tissue. Benign lesions do not usually feel as firm as malignant lesions. Cystic or fluid-filled masses are most often benign. A cystic mass will often transilluminate if a small penlight is held adjacent to the lesion (Fig. 92.3). Usually, but certainly not always, large, firm, or solid lesions are more likely to be malignant (15,18).

Further, the mobility of a mass can provide clues about the possible depth of the mass. A movable mass is more likely to be subcutaneous, whereas a fixed, immovable mass is more likely to be deep to the deep fascia (Fig. 92.4).

Finally, pain or tenderness of the lesion is an important factor in the evaluation of a soft tissue tumor. Soft tissue tumors can cause two different types of pain. Pain elicited from direct palpation of the mass is usually the result of an inflammatory response within or around the mass. Only occasionally is the mass itself tender. The tumor may also be painful because of compression or impingement on peripheral nerves. When sensory
involvement is present, the patient may be able to map out an area of parasthesias distal to the lesion or surrounding the lesion that is indicative of the particular nerve involved (Fig. 92.5).

Figure 92.3 A penlight held against a cystic mass, such as a ganglion, transilluminates (i.e., causes light to pass through the walls of the mass). Conversely, a solid mass does not transilluminate.

In addition to examining the lesion in the foot or ankle region, the physician should also examine the rest of the patient’s body. Similar masses may be present elsewhere, as well as dermatologic manifestations of certain disease states that may offer clues to the type of lesion occurring in the foot. Although rare, lymph node involvement may be associated with a soft tissue tumor in the foot. Therefore, the examination should also include palpation of the popliteal and inguinal lymph nodes. Enlarged lymph nodes, which feel firm and fixed in place, suggest the possibility of a metastatic sarcoma (2).

ADJUNCTIVE STUDIES

When a thorough history and physical examination have been completed, additional tests can be performed for further investigation of the suspicious soft tissue mass. Diagnostic tests such as radiographs, other imaging techniques, and laboratory studies may be beneficial.

Figure 92.4 A mass on the dorsum of the foot that is freely movable. This strongly suggests that the mass is subcutaneous and is not underneath the deep fascia.

Figure 92.5 A patient can be given a marker and asked to outline the area of pain or sensory distortion. In the case of a nearby soft tissue mass, this can provide the clinician with clues about potentially compressed nerves. In this figure, a mass is present in the arch, and the patient has roughly outlined the distribution of the medial plantar nerve, thus strongly intimating that this nerve is compressed by the mass.

Radiographs

Although of limited value, conventional radiographs are an important initial component of the evaluation of a soft tissue mass. Radiographs should always be performed to rule out any osseous involvement, especially in the case of a deep soft tissue mass. More often than not, however, plain films give no indication of the presence of a soft tissue mass. In other cases, nonspecific signs of a space-occupying lesion may be seen, including poorly visualized soft tissue opacity, extraosseous calcification (e.g., dystrophic or vascular), and subtle bony changes (e.g., pressure erosion or periosteal changes) (19). Specific tumors occasionally demonstrate unique characteristics on plain radiographs. Deep lipomas can sometimes be identified by their relatively low density. Calcifications within hemangiomas are usually small and smooth. Myositis ossificans displays peripheral ossification, and synovial sarcomas often have central calcification that is irregular (Fig. 92.6). Although chronic benign lesions can cause pressure changes in adjacent bone, these osseous changes more often result from malignant or aggressive lesions (Fig. 92.7) (20).

Ultrasonography

Ultrasonographic evaluation may provide some insight into the evaluation of a soft tissue mass. However, the use of this technique in the lower extremity requires a skilled technician and an experienced radiologist. Ultrasound may be used to determine the size and depth of a soft tissue mass and whether it is solid or cystic (19). The histologic type of the tumor cannot be determined by ultrasound, but there are means by which malignant tumors may be differentiated from benign tumors. Benign soft tissue tumors usually produce homogeneous echoes, regular margins, displacement of muscle fibers, and no involvement of adjacent tendons or muscles (21). In contrast, malignant tumors have inhomogeneous echoes, irregular margins, rupture of muscle fibers, and infiltration of surrounding tendons or muscles. Soft tissue tumors with a vascular component may show internal blood flow best seen with color Doppler
ultrasound enhanced by duplex ultrasonography (19). Since the advent of computed tomography (CT) and magnetic resonance imaging (MRI), ultrasound has become a less frequently used diagnostic tool for the evaluation of soft tissue masses.

Figure 92.6 Soft tissue mass in the tarsal tunnel. Radiographs of the ankle demonstrated significant intralesional calcification of the mass. This mass was examined by biopsy and was found to be a malignant schwannoma.

Computed Tomography and Magnetic Resonance Imaging

Computed tomography and magnetic resonance imaging are useful in the evaluation of soft tissue masses. Although still only two-dimensional, like plain radiographs, both techniques provide cross-sectional imaging of the structure in question. Three-dimensional CT scans are also now available in many areas, and three-dimensional MRI is an emerging technology.

Figure 92.7 Soft tissue mass of the forefoot. Radiographically, one can see pressure changes from the mass on the second metatarsal and the increased soft tissue density in the area. This mass was ultimately determined to be a benign fibrolipoma.

CT scans are best used for the evaluation of lesions within or arising from cortical bone, but the scan can be useful for the evaluation of soft tissue tumors. CT scans can be useful for the detection and determination of the size of a soft tissue mass. They are also useful in assessing the extent of the mass and its relationship with adjacent structures.

CT scans usually display a soft tissue tumor as an isodense, heterogeneous mass resembling muscle (Fig. 92.8). On CT images, muscles, tendons, nerves, and blood vessels all have similar appearances. Therefore, often a CT scan is not diagnostic.

The one advantage of CT scans as compared with MRI is in the evaluation of any lesion with an osseous component. The CT scan is better for evaluation of calcification within a lesion or for the demonstration of osseous changes or cortical erosions secondary to impingement by the soft tissue mass on adjacent bone (22).

Only gold members can continue reading. Log In or Register to continue