Myelin is an electrically insulating material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system.
A nerve sheath tumor is a type of tumor arising from the nervous system (nervous system neoplasm) which is primarily made up of the myelin surrounding nerves. On the other hand, peripheral neural sheath tumors are those originating from the peripheral nervous system (it extends outside the central nervous system consisting of the brain and spinal cord).
Schwannoma tumours are slow-growing tumours that originate in myelin sheath. Schwann are specialized cells that surround the peripheral nerves and provide mechanical and physical support for nerves as well as insulate the nerves that transmit the nervous system's electrical signals.
The peripheral nervous system (the nervous system outside the brain and spinal cord)
Unlike other neural tumours that arise from the nerve sheath, schwannomas form from Schwann cells of the individual nerve fibres.
Peripheral nerve sheath tumor is the term that has been proposed to include schwannomas, neurofibromas (nerve fiber tumors), neurofibrosarcomas (malignant nerve fiber tumors), and hemangiopericytoma (tumor of blood vessels and soft tissue), since they are all believed to arise from the same cell type.
Common signs and symptoms associated with nerve sheath tumor include
Chronic, progressive forelimb lameness and muscle atrophy
Lameness in the hind limbs
Peripheral nerve disorder (from self-mutilation)
Palpable mass (mass can be felt by touch examination)
Horner's syndrome, a disease of the sympathetic nervous system: automatic nerve reaction, affects parts of the body not under direct control
If the Schwannoma is in the neck, only one side of the face will be affected:
Droopy eyelid
One sided facial paralysis
Decreased pupil size
Slight elevation of the lower eyelid
