Benign Peripheral Nerve Tumors

Diagnosis

If, based on clinical history or physical examination, there are signs and symptoms of a benign peripheral nerve tumor, the doctor may recommend diagnostic tests to determine if a tumor is present and identify the type of tumor. In some cases, an enlarged nerve may be caused by inflammation due to other conditions, or peripheral neuropathies (damage to the peripheral nervous system).

Because of Mayo's sophisticated diagnostic capabilities, Mayo doctors are often able to identify nerve conditions which either had been misidentified or not identified at all, and many of these conditions can be successfully treated.

Diagnostic Tools

Computed Tomography (CT) Scan

The CT scanner rapidly rotates around the body, recording a series of images that are reconstructed by a computer into slices of the body. New 64-slice CT scanners can produce incredibly detailed views to identify a peripheral nerve tumor and evaluate how it may be affecting that area of the body.

Magnetic Resonance Imaging (MRI) Scan

This noninvasive test uses a powerful magnet and radio waves to produce a detailed, three-dimensional view of the nerves and surrounding tissue. High-resolution images are obtained with powerful magnets, dedicated coils (current run through electrical wire to transmit signals used to generate images) and imaging plans tailored to each patient.

Electromyogram (EMG or Electromyography)

By placing small needles in key muscles, Mayo specialists can identify and quantify abnormalities in muscles supplied by specific nerves. Nerve tumors can cause weakened electrical signals. An instrument records the electrical activity in the muscle at rest and as the patient tries to move or contract the muscle.

Nerve Conduction Study

A nerve conduction study measures how quickly nerves are carrying electrical signals to the muscles. A small shock is passed along the course of a nerve to measure the electrical impulses. Typically, a nerve conduction study is performed at the same time as an EMG.

Tumor Biopsy

If imaging tests identify a nerve tumor, a biopsy (a small sample of cells) may be taken from the tumor. The cell samples are then examined and tested to determine the type of tumor and whether the cells are benign (noncancerous) or malignant (cancerous).

The biopsy may be performed by:

• Image-Guided Biopsy
  In this minimally-invasive procedure, the physician, guided by a CT scan or ultrasound, inserts a needle into the tumor and removes a small, cylindrical-shaped tissue sample for examination under a microscope. The procedure requires only a topical anesthetic to numb the skin. Mayo Clinic uses core needle technology with a special vacuum-assisted needle to draw out tissue. It leaves little or no scarring.
• Surgical Biopsy
  

  The patient may be put to sleep under general anesthesia or receive numbing medication (local anesthesia) in the area of the nerve tumor. A small surgical incision is made to remove a sample of cells in the affected area.

Nerve Biopsy

Nerve Composition

Nerve biopsy may be necessary for some patients with progressive peripheral neuropathies or enlarged nerves that may mimic nerve tumors. Mayo Clinic has significant expertise in obtaining precise samples of tissue from peripheral nerves that allow Mayo specialists to identify and treat unusual nerve diseases.

The technique of biopsying a peripheral nerve for analysis was developed at Mayo Clinic in 1966. Mayo has significantly expanded this capability, biopsying small skin nerves and large, more important nerves, depending on what site is affected and the severity of the neurologic problem.

Often, subtle MRI abnormalities are detected that can help determine the affected site and guide surgeons to the site for a biopsy of a small piece of a nerve.

Small nerves that are biopsied may include the sural nerve in the calf and ankle or the superficial radial nerve in the arm. Large nerves that may be biopsied include the sciatic nerve or those that form the brachial plexus. These large nerves are composed of bundles of smaller nerves (fascicles). Mayo specialists can analyze portions of nerves one-twentieth the size of major nerves. This technique has helped diagnose many unusual conditions and has been performed safely.

The ability to biopsy peripheral nerves is the result of a Mayo team effort. Development of this technology involved many Mayo specialists, including neurologists with special interest in focal peripheral nerve problems and radiologists with expertise in obtaining highly detailed nerve images. Surgeons willing to remove a tiny piece of nerve for analysis and a nerve laboratory with expertise in staining, preparing, processing and interpreting the nerve specimen also played an important role.