Palisaded encapsulated neuromas: a clinicopathological study

Abstract

Palisaded encapsulated neuromas (PFN) are uncommon benign neural neoplasms of the skin, first described by Reed, Fine and Meltzer (1972). Sixty consecutive cases of PEN were reviewed. Clinically these asymptomatic lesions appeared as shiny, dome-shaped, flesh- coloured, firm, 2–6 mm papules that were present for a few months to several years. Only twice was the correct diagnosis made, the usual clinical impression being basal cell carcinoma or melanocytic naevus. All lesions were solitary, most occurring on the central face, nose or lips, of middle-aged individuals of both sexes. Less than 10% occurred outside the facial area. By light microscopy, well-demarcated single or multiple nodules composed of fascicles of spindle cells were seen in the dermis. No mast cells were present and there were no areas resembling Antoni type B tissue. By electron microscopy (EM) the tumour consists of interlacing bundles of Schwann cells admixed with many non-myelinated C fibres. Only a few axons are myelinated. PEN should be included in the differential diagnosis of fiesh-coloured papules on the face. These are true neuromas that are distinctive pathologically and can be easily differentiated from neurilemmomas and neurofibromas. They most closely resemble traumatic neuromas but lack fibrosis surrounding the nerve bundles. They also are similar to neuromas in the multiple mucosal neuromata syndrome (Williams & Pollock, 1966; Reed et al., 1972). We speculate that minor injury to facial skin damages small peripheral nerve fascicles leading to proliferation of axons in a fashion similar to traumatic neuroma formation. As the lesion matures many of the small bundles of nerve regress, leaving either single or multiple lobules of axonal and Schwannian proliferation to produce the true neuroma seen on EM.