Table 1.

Proposed Nomenclature for the Spectrum of NF1-associated Nerve Sheath Tumors

Diagnosis	Proposed Definition
Neurofibroma (NF)	Benign Schwann cell neoplasm with thin, often wavy nuclei, wispy cell processes, and a myxoid to collagenous (‘shredded carrots’) matrix. IHC includes extensive but not diffuse S100 and SOX10 positivity and a lattice-like CD34+ fibroblastic network
Plexiform	NF diffusely enlarging and replacing a nerve, often involving multiple nerve fascicles, delineated by EMA+ perineurial cells
Neurofibroma with atypia (“Ancient neurofibroma”)	NF with atypia alone, most commonly manifesting as scattered bizarre nuclei
Cellular	NF with hypercellularity, but retained NF architecture and <1 mf/50 HPF
ANNUBP	Schwann cell neoplasm with at least 2 of 4 features: cytologic atypia, loss of neurofibroma architecture, hypercellularity, mitotic index >1/50 HPF and <3/10 HPF
MPNST, low-grade	Features of ANNUBP, but with mitotic index of 3–9/10 HPF and no necrosis
MPNST, high-grade	MPNST with at least 10 mf/10 HPF or 3–9 mf/10 HPF combined with necrosis

ANNUBP = atypical neurofibromatous neoplasm of unknown biologic potential; loss of NF architecture = fascicular growth pattern and/or lack of CD34+ fibroblastic network; hypercellularity = ‘blue’ appearance at low magnification and nuclear overlap at high magnification; HPF = high power fields