When looking at any new lesion on the body, the first thing to think about should be differentiating between benign and malignant lesions. New lumps and bumps on the body can be of great concern to a patient, as they may have the tendency to think of them as cancerous. While it’s true that a new lump or bump of the foot and ankle may be malignant, most soft tissue tumors of the foot and ankle tend to be benign.
Important things to consider when deciding whether a lesion looks malignant or not include it’s rate of growth, its resemblance to the surrounding tissue, any invasion into surrounding tissues, size, whether the lesion is fluid-filled, and whether or not the lesion is freely movable. A benign lesion will typically show a steady growth rate, will resemble the surrounding tissue that it is in, will be freely movable, will typically be small, will not invade surrounding tissues and/or bone, and will commonly be cystic or fluid-filled. This last piece can be evaluated with trans-illumination of the lesion.
Some of the most common benign tumors of the foot and ankle include ganglion cysts, plantar fibromas, lipomas, neurofibromas, and neurolemoma.
Ganglion Cyst – These are soft, well-circumscribed, cystic masses that are often seen on the dorsum, or top, of the foot. They result from a weakness in the tissues surrounding a tendon or a joint, and will cause an out-pocketing of the fluid within the tendon or joint. They can be very painful, particularly when they rub against a shoe or compress a close-be nerve. They can also be present in the wrist. Historically they have been referred to as “bible bumps” due to the primative treatment of popping them with a heavy book, such as a bible. Today, they are more appropriately treated by surgical excision.
Plantar Fibroma – These lesions represent a thickening of the plantar fascia, which is a thick band of soft tissue that runs along the bottom of the foot. Most commonly, plantar fibromas are found in the central or medial portion of the plantar fascia. Between 10-15% of people will have them on both feet, and they can cause a considerable amount of pain due to the pressure that they cause on the foot when walking or standing. These two can be treated with surgical excision, but have a high rate of recurrence.
Lipoma – This is the most common of the benign soft tissue tumors. It results from a localized overgrowth of the fat cells in a particular area of the body, commonly seen in the foot. They are a soft, freely movable mass that may compress neighboring nerves, or cause pain with walking or standing. They can be treated with surgical excision.
Neurofibroma – These are tumors of the spindle cells found within a nerve, causing expansion of the nerve. Neurofibromas may affect both superficial and/or deep nerve. The superificial neurofibromas are often romeved, while the deep ones are often left alone, as they can be difficult to remove and may result in complications. A disorder known as von Recklinghausens disease is associated with the formation of many neurofibromas, some of which may turn malignant.
Neurolemoma - This is a tumor of a peripheral nerve sheath, which covers all peripheral nerves. They result in small, tender nodules along the nerve, which can be exquisitely painful. They typically effect the major nerves of the foot and ankle, and may be removed by teasing them out of the nerve surgically.
Many other soft tissue masses may present in the foot and ankle – this list is only some of the more common findings to affect the region. A doctor should examine any new or painful lesion. Imaging tests such as x-ray or MRI can be used to further evaluate the lesion. For unknown lesions, biopsies may be taken either as diagnostic testing or as definitive treatment.
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