Location: (a): Superficial lesion in subcutis or dermis. (b): All sites and all organs.
Clinical: (a) Painless nodule, few symptoms. (b) Café au lait spots, typically in the axilla. More than six spots >1.5 cm are diagnostic; symptoms depend on location of neurofibromas: pigmented hamartomas of the iris (90 %), skeletal abnormalities (40 %), disorders of growth, sexual maturation, and abnormalities of the lung.
Imaging: On MRI: nerve trapped within or obliterated by the mass. Rarely encapsulated. Much more homogeneous, isointense to muscle with frequent areas of high signal on T1, more inhomogeneous, typical target appearance, higher than fat intensity on T2, centrally higher enhancement never with necrosis on contrast T1.
Histopathology: Spindle mass within the nerve, firm, grayish with pink areas. Interlacing bundles of elongated cells with dark wavy nuclei intimately associated with thick collagen fibers and mucoid material among bundles. Rare mitotic figures and necrotic areas. Scattered mast cells, lymphocytes, xanthoma cells. In type (b), there may be plexiform N. In large nerves, cordonal masses of convoluted aspect, a mixture of nerve trunks of different shapes and sizes, crossing each other along different planes or proliferation of Schwann cells producing collagen. Diffused N. in the subcutis of head and neck, a whitish plaque-like thickening of skin, diffusing along connective septa and among adipose tissue cells. Less evident fibrillary collagen matrix, more ovoid, round monomorphous cells, in a finely fibrillary homogeneous matrix or with organoid organization which looks like Meissner’s bodies.
Course and Staging: Malignant transformation is rare in type (a) but more frequent (5–30 %) in type (b). Usually, stage 1 or 2.
Treatment: Marginal excision in (a). In (b), only large, painful, and located in areas where continued growth would compromise organ function are treated by surgery.