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, localized intraneural, subcutaneous, diffuse, intramuscular, plexiform and pigmented neurofibroma. Plexiform neurofibromas may be further sub-classified into diffuse and nodular plexiform.

Classification

Neurofibroma may be classified into following subtypes:[1][2][3][4]

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 subcutaneous
  • ≤2-5 cm in diameter
  • Arise from small cutaneous nerves
  • Overrun axons may be identified within
  • May contain fat
  • 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
  • Often contains coarse, refractile collagen
  • Malignant change infrequent
Subcutaneous neurofibroma
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 adenexal structures)
  • Uniform matrix of fine, fibrillary collagen
  • Shorter, rounder Schwann cells
  • Clusters of pseudo-meissnerian 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:[5]

Types of neurofibromas Characteristics/Description
Diffuse Plexiform neurofibroma
Nodular Plexiform neurofibroma

References


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