It may be analogous to the dermal dendritic fibroblast. The cytoplasm contains microfibrils, lysosomes, mitochondria. Antoni A areas. Long-spacing collagen in seen in the stroma of benign peripheral nerve sheath tumors and occasionally in malignant ones, but is not specific. In cellular schwannoma, the ultrastructure is that of well differentiated schwann cells but with less interdigitation than in regular schwannoma.
External lamina can be absent when processes are closely apposed.
EM is occasionally useful in the differential with smooth muscle tumor. EM shows numerous autophagosomes with various lipoid and membranous inclusions. Neurofibromas have focal S100 positivity in schwann cells but less strongly and in fewer cells than in schwannoma . Ultrastructurally there is a mixture of Schwann cells, with or without nerves, perineurial-like cells and fibroblasts, with intermediate forms between the cell types. In the plexiform type, the early stage is increased endoneurial matrix, separating nerve fibres, which are later replaced by Schwann cells with thick wavy collagen bundles, and scattered small axons.