A<unk>  (or neurilemmoma) is a usually benign nerve sheath tumor composed of Schwann cells, which normally produce the insulating myelin sheath covering peripheral nerves.<unk> s are homogeneous tumors, consisting only of Schwann cells. The tumor cells always stay on the outside of the nerve, but the tumor itself may either push the nerve aside and/or up against a bony structure (thereby possibly causing damage).<unk> s are relatively slow-growing. For reasons not yet understood,<unk> s are mostly benign and less than 1% become malignant, degenerating into a form of cancer known as neurofibrosarcoma. These masses are generally contained within a capsule, so surgical removal is often successful.<unk> s can be associated with neurofibromatosis type II, which may be due to a loss-of-function mutation in the protein merlin. They are universally S-100 positive, which is a marker for cells of neural crest cell origin.<unk> s of the head and neck are a fairly common occurrence and can be found incidentally in 3–4% of patients at autopsy. Most common of these is a vestibular<unk> , a tumor of the vestibulocochlear nerve that may lead to tinnitus and hearing loss on the affected side. Outside the cranial nerves,<unk> s may present on the flexor surfaces of the limbs. Rare occurrences of these tumors in the penis have been documented in the literature. Verocay bodies are seen histologically in<unk> s.
Schwannoma
Meningioma
Ganglioglioma
Neurothekeoma
Pilocytic astrocytoma
Neuroma
Subependymoma
Pinealoma