Neurofibroma classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Mohsin, M.D.[2]

Overview

Neurofibroma may be classified into 5 subtypes: cutaneous/dermal/localized, subcutaneous, diffuse, intramuscular, and plexiform neurofibroma. Plexiform neurofibromas may be further sub-classified into diffuse and nodular plexiform.

Classification

Neurofibroma may be classified into following 5 subtypes:

Types of neurofibromas	Characteristics/Description
Cutaneous/Dermal/Localized/Sporadic neurofibroma (90%)	Most common type Circumscribed but not encapsulated Permeative growth in nerve quickly proceeds to diffuse infiltration of surrounding soft tissue Occurs as lumps or bumps on skin Painless Slowly growing Often in dermis and subcutis ≤2-5 cm in diameter Arise from small cutaneous nerves Overrun axons may be identified within May contain fat < 5cm diameter Starts in teenage years or young adults and rarely starts in childhood Increases in size and number over the years Clearly defined borders hence, can be removed if necessary Number of skin tumors in each patient varies tremendously Mostly solitary and sporadic, not associated with NF1 Malignant transformation very rare
Localized Intraneural neurofibroma	Second-most common type Segmental, fusiform nerve enlargement Residual axons traverse through lesion Neurofilament immunohistochemistry and Bielshowsky stain show axons within center of lesion Often contains coarse, refractile collagen Malignant change infrequent
Subcutaneous neurofibroma	Common Present underneath the skin Can be single tumors or chains They are often a form of plexiform neurofibromas
Diffuse neurofibroma (superficial)	Superficial Uncommon Feels soft and squishy Most common in head (scalp) and neck region or trunk (often protruding out, like a “love handle”) Ill defined margins, can't tell where tumor stops Runs through the full skin thickness (from the surface all the way down to the base of the skin (subcutaneous fascia/fat) Doesn't go deeper than fascia Nondestructive, envelops normal structures (e.g., fat cells and adnexal structures) Uniform matrix of fine, fibrillary collagen Shorter, rounder Schwann cells Clusters of pseudomeissnerian body-like structures may be seen Usually seen in early childhood and young adults Usually associated with diffuse hyperpigmentation, so looks like a very large squishy café au lait spot Solitary lesions and not related to any inherited condition (rarely associated with NF1) Rare malignant change
Intramuscular neurofibroma	Common Usually isolated tumors in the muscle Growths along very small nerves Causes pain sometimes Can be removed (leaves a scar behind) Sometimes can occur as plexiform neurofibromas in form of chains or networks
Plexiform neurofibroma (deep)	Deep Associated with NF1 Diffuse involvement along a large nerve and its branches Mostly internal/ intraneural Can also involve small nerves and superficial skin Have more connective tissue/extracellular matrix than cutaneous neurofibromas, that separates the nerve fibers Gross enlargement of the nerve with nodular tumor development results in the gross pathologic appearance referred to as “bag of worms” Generally believed to be present at birth (congenital) Disfiguring Affects function due to sheer size as well as neurovascular compromise Upto 5% risk of malignant transformation Plexiform neurofibroma exhibits following features on T2-weighted MRI: Target sign (low signal intensity centrally with a ring of high signal intensity peripherally) Fascicular sign May appear as a larger and more infiltrating mass with lobulated borders with inhomogeneous enhancement
Pigmented neurofibroma	Neurofibroma with melanin-bearing pigmented cells, usually only appreciated microscopically Not considered a true subtype No increased risk of malignant transformation

Plexiform neurofibromas can be further subclassified into following:

Types of neurofibromas	Characteristics/Description
Diffuse Plexiform neurofibroma	It extends through the skin into fascia and muscle Lacks clear margins Has “little fingers” that invade muscle or other tissue May not be easy to see in infants May have a large café au lait spot “above” it
Nodular Plexiform neurofibroma	Usually involves nerves coming off the spinal cord or off of larger nerves (such as sciatic nerve) Usually enlarges or thickens the nerve Looks like little clusters of tumors along the nerve

References

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