A nerve sheath tumor is a type of

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

of the

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

( nervous system neoplasm) which is made up primarily of the

myelin Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...

surrounding

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

s. Nerve sheath tumors can be

benign Malignancy () is the tendency of a medical condition to become progressively worse; the term is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous benign tumor, ''benign'' tumor in that a malig ...

malignant Malignancy () is the tendency of a medical condition to become progressively worse; the term is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous benign tumor, ''benign'' tumor in that a malig ...

, and may affect both the

peripheral A peripheral device, or simply peripheral, is an auxiliary hardware device that a computer uses to transfer information externally. A peripheral is a hardware component that is accessible to and controlled by a computer but is not a core compo ...

and central nervous systems. There are three main types of nerve sheath tumors:

schwannomas A schwannoma (or neurilemmoma) is a usually benign nerve sheath tumor composed of Schwann cells, which normally produce the insulating myelin sheath covering peripheral nerves. Schwannomas are homogeneous tumors, consisting only of Schwann cells ...

, neurofibromas, and malignant peripheral nerve sheath tumors.

Classification of nerve sheath tumors

Spinal nerve sheath tumors

Spinal nerve sheath tumors are typically intradural, meaning that they arise inside the dura mater surrounding the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

(

thecal sac The thecal sac or dural sac is the membranous sheath (theca) or tube of dura mater that surrounds the spinal cord and the cauda equina. The thecal sac contains the cerebrospinal fluid which provides nutrients and buoyancy to the spinal cord. F ...

), but may also be found in other areas of the spine. Spinal nerve sheath tumors generally arise as single

lesions A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...

. Presence of multiple lesions is associated with genetic conditions including

neurofibromatosis type 1 Neurofibromatosis (NF) refers to a group of three distinct genetic conditions in which tumors grow in the nervous system. The tumors are non-cancerous (benign) and often involve the skin or surrounding bone. Although symptoms are often mild, e ...

neurofibromatosis type 2 Neurofibromatosis type II (also known as MISME syndrome – multiple inherited schwannomas, meningiomas, and ependymomas) is a genetic condition that may be inherited or may arise spontaneously, and causes benign tumors of the brain, spinal cord, ...

, and

Schwannomatosis Schwannomatosis is an extremely rare genetic disorder closely related to the more-common disorder neurofibromatosis (NF). Originally described in Japanese patients, it consists of multiple cutaneous schwannomas, central nervous system tumors, ...

. Most spinal schwannomas are intradural-extramedullary, growing inside the thecal sac, but outside the spinal cord itself. Intradural-intramedullary schwannomas also develop, but tend to be rare.

Peripheral nerve sheath tumors

A peripheral nerve sheath tumor is a nerve sheath tumor in the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of Bilateria, bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside t ...

Benign Malignancy () is the tendency of a medical condition to become progressively worse; the term is most familiar as a characterization of cancer. A ''malignant'' tumor contrasts with a non-cancerous benign tumor, ''benign'' tumor in that a malig ...

peripheral nerve sheath tumors include schwannomas and neurofibromas. A malignant peripheral nerve sheath tumor is a cancerous peripheral nerve sheath tumor, which is frequently resistant to conventional treatments.

Symptoms

Spinal and peripheral nerve sheath tumors may lead to a variety of symptoms depending on tumor type, location, and severity, though they do share some symptoms. Some common findings for all nerve sheath tumors include: * Pain * Numbness * Tingling * Burning sensation * Weakness * Visible or palpable mass Many individuals are also asymptomatic.

Mechanism

The primary Schwann cell differentiation and neoplastic proliferations are characteristics of peripheral nerve sheath tumors. For instance, the Schwann cell, which is the major neoplastic cell component of neurofibroma, is cytologically distinguished by the expression of S-100 protein and wavy nuclear outlines. A variety of peripheral nerve cells, including axons, perineurial cells, fibroblasts, and varying inflammatory components such as mast cells and lymphocytes, are also present in neurofibromas. A population of CD34-positive cells with an unknown histogenesis is also found.

Diagnosis

Spinal nerve sheath tumors

Magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and ...

(MRI) is typically used in spinal nerve sheath tumor diagnosis. Each nerve sheath tumor type has a few different associated features on MRI imaging. Neurofibromas and malignant peripheral nerve sheath tumors can be difficult to distinguish from each other and may require additional testing, including

PET scans Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, re ...

(¹⁸FDG-PET). Image-guided needle biopsies may be performed if there is concern for malignancy.

Peripheral nerve sheath tumors

MRI, tissue, and nerve biopsies are also frequently used in diagnosis of peripheral nerve sheath tumors.

Computerized tomography A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

(CT) scans,

electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...

, and

nerve conduction studies A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called ...

are other options.

Management

Benign spinal nerve sheath tumors

Treatment of spinal nerve sheath tumors typically depends on presence and severity of symptoms. For asymptomatic or incidental schwannomas or neurofibromas, only continued imaging is typically indicated to assess whether tumor growth is occurring. Surgical resection may be an option for tumors causing extensive

radicular pain Radicular pain, or radiculitis (from the ), is pain "radiated" along the dermatome (sensory distribution) of a nerve due to inflammation or other irritation of the nerve root (radiculopathy) at its connection to the spinal column. A common form ...

or other symptoms, and for tumors exhibiting aggressive behavior. Plexiform neurofibromas (associated with neurofibromatosis type 1) have a higher risk of transforming into malignant tumors and require individual treatment plans. Surgical resection is the treatment of choice for symptomatic plexiform neurofibromas, though a new drug, selumetinib was approved in 2020, as a systemic therapeutic for inoperable cases in pediatric patients. Stereotactic body radiotherapy (SBRT) is a promising treatment option for benign spinal nerve sheath tumors, though more research is currently needed to determine effectiveness across different tumor types and to establish adequate clinical guidelines.

Malignant spinal nerve sheath tumors

Complete surgical resection is the current treatment of choice for malignant spinal nerve sheath tumors. Post-surgical radiotherapy has shown some promise in improving recurrence-free survival in intermediate and high grade tumors.

Chemotherapy Chemotherapy (often abbreviated chemo, sometimes CTX and CTx) is the type of cancer treatment that uses one or more anti-cancer drugs (list of chemotherapeutic agents, chemotherapeutic agents or alkylating agents) in a standard chemotherapy re ...

for malignant spinal nerve sheath tumors has shown mixed results and is typically only used in patients in which surgery is not an option, or with aggressive or metastatic disease.

Benign peripheral nerve sheath tumors

As with spinal nerve sheath tumors, continuous monitoring for asymptomatic, incidental, or slow growing tumors is generally the standard of care for peripheral nerve sheath tumors. Management of symptomatic tumors is also similar to spinal nerve sheath tumors. A complete surgical resection of peripheral tumors is typically done whenever indicated, and if possible. Gamma knife radiosurgery, a subset of SBRT, is an option for peripheral nerve sheath tumors growing near the brain.

References

External links

{{Nervous tissue tumors Nervous system neoplasia