Causes

The cause of benign peripheral nerve tumors usually isn't known. Some are inherited. The most common type is schwannoma. It typically starts in a single bundle inside the main nerve, displacing the rest of the nerve.

Another common type is neurofibroma. These tumors often form inside the nerve. Sometimes they arise from several nerve bundles.

Perineuriomas are rare and can grow from inside or outside the nerve. Tumors outside a nerve can cause problems when they press on the nerve. Other benign tumors that form outside nerves are soft lumps of slow-growing fat cells called lipomas and ganglion cysts.