A neuroma is the enlargement of the tissues surrounding sensory nerve(s) (nerve(s) that feel touch and pain), a result of a compression or trauma and or surgery to or near the nerve. They are often described as nerve tumors. However, they are almost never malignant. They are a swelling, a wrapping of layers of scar tissue around the nerve because of many months or years of irritation, which presses back on the nerve inside, "strangulating the nerve", causing pain. Neuromas can also be caused by surgery, where scar tissues that normally forms after surgery, will hold on to and trap a nerve: The most common type of such neuromas are "sural neuromas", the nerve that can become trapped after ankle joint surgery on the outside of the ankle joint.
The most common site for a neuroma in the foot - a Morton's Neuroma - is on the ball of the foot, and forms between the heads of the 3rd and 4th metatarsal bones. The most common cause of this neuroma is tight and high heeled shoes that press the metatarsal bones together exposing the nerve that travels between them to excessive irritation during walking. What results is burning, tingling, and numbness along the inside bottom of toes 3 and 4. Sometimes this pain can become so severe that it brings tears to a patient's eyes. Removing the shoe and rubbing the ball of the foot helps to ease the pain. As the nerve swelling gets larger, it can be felt as a popping sensation when walking and upon examination by the doctor. Pain is intermittent and is aggravated by anything that results in further pinching of the nerve. 90% of the time it is the nerve between the 3rd and 4th metatarsal heads that becomes a Morton's Neuroma. Less commonly it can also occur between the 2nd and 3rd metatarsal heads.
Sometimes nerves can even become entrapped in the heel, in the posterior "Tarsal Tunnel" (the area behind the inside ankle bone) or "Anterior Tarsal Tunnel" (the area in the front of the ankle joint). In the case of heel neuromas and tarsal tunnels, the treatment is first injection with local anesthetic and cortisone, and then release of the nerve if all else fails. The treatment of Morton's Neuroma is different, as will be explained.
The diagnosis of Neuromas are made by a physical exam and a thorough history of the patient's complaint. Weight bearing X-rays are always taken to rule out a possible stress fracture or arthritis. An MRI is often used, as are nerve conduction studies and or consultation with a Neurologist.
Conditions that mimic the pain associated with Neuromas are stress fractures, inflammation of adjacent tendons or joint tissues, arthritis, prominent bones or soft tissues, or even nerve compression or nerve damage further up in the leg or back.
Posterior Tarsal Tunnel Syndrome. Special mention should be made of posterior tarsal tunnel syndrome. This is a condition not unlike Carpal Tunnel in the hand. The main nerve group that senses the entire bottom of the foot and controls the muscles inside of the foot can sometimes become trapped/strangled. This will cause pain, burning, tingling, in the bottom of the foot or in the toes. This can be a difficult diagnosis to make in certain circumstances. We often refer to such a diagnosis as a "diagnosis of exclusion" - that is we do everything to find out if the cause is something else first. Most often if this diagnosis is suspected, a highly specialized physician called a Neurologist is employed to examine the patient and conduct specialized testing as she/he sees fit.
Treatment for all neuromas consists first and foremost removing the source of irritation such as improper shoes as in the case of Morton's Neuroma, and in most all cases at least one injection of local anesthetic mixed with cortisone, injected in the area of suspicion. The cortisone is used to break-up and thin the entrapping scar tissue envelope around the nerve and to also reduce inflammation in the area of the neuroma.
When all else fails, surgery can be an option. Morton's Neuromas and entrapment neuromas can be surgically removed. But 15% of the time they can either re-grow or become entrapped in surgical scar tissue. Posterior and Dorsal Tarsal Tunnel surgery involves freeing-up the nerve from surrounding tissues and sometimes even in combination with carefully cutting the outer envelope that contains the major nerve grouping.