Lumps and Bumps

Soft tissue tumors of the foot and ankle are not uncommon. They may appear as innocuous soft tissue masses which can cause pain and discomfort. They are primarily neoplasms of connective tissue occurring anywhere in the body. The incidence of soft tissue tumors, in the lower extremities, is approximate 40%. They can develop in fibrous tissue, tendon, fat, muscle, and neurovascular tissue. Soft tissue tumors of the lower extremity are generally benign. They appear to be found on physical examination rather than routine x-rays. When these lesions are present, they are best evaluated with a magnetic resonance imaging (MRI). The MRI allows for exceptional soft tissue contrast and anatomic visualization.

Clinical presentation of a soft tissue mass is usually described as a localized lump or bump on the forefoot, rearfoot, or ankle area. The presentation by the patient may be rather innocuous without complaint of pain or symptomatic. The size of the soft tissue mass may vary from 2 cm to as much as 8 cm. The average soft tissue mass size is usually an inch and a half or 3-4 cm. Initial diagnosis and monitoring of the mass is recommended. MRI/extremity coil imaging is also recommended. (Weil foot and ankle Institute)

The most common soft tissue tumors, of the foot and ankle, appear to be cystic lesions, lipomas, fibromas, occasionally desmoid lesions, hemangioma, and rarely malignant lesions. MRI is useful in understanding the benign and malignant behavior and staging of musculoskeletal tumors. Accurate identification of the soft tissue mass and the extent of bone and/or soft tissue involvement can be established with a high degree of reliability. Significant understanding of the unique soft tissue characteristics is easily understood. The proverbial lump or bump can easily be recognized and benign or malignant behavior be understood.

The vast majority of soft tissue tumors of the foot and ankle are benign but may appeared to be inactive, active, or aggressive in behavior. Extremity coil MRI is very helpful in classifying these masses. The soft tissue appearance can indicate specific behavior characteristics. #1 Inctive benign tumors are usually encapsulated by mature fibrous tissue. They are very localized and rarely expand overlying tissues. They represent the most common type of soft tissue tumors in the foot and ankle. They may appear as a lump between the digits or toes, a lump on top of the foot, or a lump on the outer side of the ankle area. They also appear on the bottom of the foot. #2 Active benign tumor may appear to be more symptomatic and grow more rapidly, a painful expanding mass. The capsule around the mass may appear to be irregular and thin. #3 An aggressive benign tumor may have an indistinct capsule and show signs of expansion into other tissue. It is histologically benign but appears aggressive. The plantar fibroma/fibromatosis represents this type of mass. This mass may appear as several lumps on the bottom of the foot and may appear on the palms of the hands. The characteristics of these lesions can be easily appreciated with extremity coil MRI.

Malignant tumors of the foot and ankle are rare. These tumors appear as a metastatic lesion from a remote site to the feet or as primary site sarcomas. The malignant behaviors of these tumors vary with a low rate of metastasis, to a high rate of metastatic disease. Unfortunately, histologic behavior cannot be fully appreciated with an MRI alone. Morphologic features of soft tissue tumors can be appreciated with the MRI.

Cystic lesions, such as ganglia, are usually associated with tendons and joints. It is very common to see a ganglion cyst over a tendon or associated with a joint. The cyst is usually fluid-filled and is very characteristic.

Lipoma is a well circumscribed fatty tumor. Although uncommon in the distal extremities, they are observed to vary in size anatomically in the foot and ankle area. They are usually noted as a superficial solitary mass. This tumor also has distinct characteristics under MRI.

Fibromas may be a very localized lesions associated with fibrous tissue. They may appear to be nodular and small in size and in the foot and ankle area. Like cystic and lipomatous lesions, they are homogenous. The plantar fibromatosis is a unique benign tumor tends to be aggressive. Although homogenous and well marginated (MRI characteristics) it will show histologic signs of aggressive activity (nodular fibromatosis) although not metastatic.

Desmoid tumors of the foot and ankle are rare and are primarily observed as occurring in the digits or toes. They can be locally aggressive, but they do not metastasize. The unique tumor characteristics are observed on extremity coil MRI.

Hemangiomas will also have unique MRI characteristics. Arteriovenous malformations will also demonstrate neurovascular encasement and benign characteristics. This mass is more commonly found in the lower extremities and may involve the foot.

There are a variety of other soft tissue tumors that can be observed in the foot and ankle. They include smooth muscle tumors such as: leiomyoma and leiomyosarcoma, Neurilemmoma or schwannoma., Liposarcoma, Fibrosarcoma, Synovial sarcoma, Neurosarcoma and metastatic tumors.

Regardless of the concern, regarding potential malignancy with soft tissue tumors in the foot and ankle, an initial clinical examination is recommended. If the mass is painful or large (greater than 2 cm) extremity coil MRI is recommended. For the most part, 98% of the lesions are benign. These tumors can be easily classified and appreciated anatomically if they have to be removed surgically.

The lumps and bumps that we observe on the foot and ankle manifest a variety of tumors in the distal extremity from a simple ganglion cyst to a complex mass.

When concerned with a lump or bump on the foot and ankle, clinical assessment by our physicians is highly recommended. If required an extremity coil MRI can be very effective in establishing the characteristics of these lesions.

Robert G O’Keefe DPM FACFAS