Palisaded Encapsulated Neuroma

A benign neural neoplasm, the palisaded encapsulated neuroma (PEN, solitary circumscribed neuroma) was first reported as a distinct entity in 1972.  It is now recognized as one of the more common of the superficial nerve tumors of the head and neck region, although neural tumors in general are rather rare events in that anatomic site. The etiology of this lesion is unknown, but trauma is considered by some to induce or trigger its development. Nine of every ten examples of PEN have been reported as facial lesions, usually from the region of the nose and midface. Oral/pharyngeal lesions are not uncommon, but are often misdiagnosed as neurofibroma or neurilemoma. The lesion is not associated with multiple endocrine neoplasia (MEN) syndromes.

Oral examples of PEN are seen most frequently on the hard palate, although any oral/pharyngeal mucosal surface may be affected.  The diagnosis is typically made during the fifth through seventh decades of life, but many lesions have been present for years prior to biopsy and formal diagnosis. There is no gender predilection. The lesion usually presents as a sessile, smooth-surfaced nodule of less than 1 cm. diameter; it may have a rubbery feel on palpation.

The PEN consists of interlacing bundles or fascicles of spindle cells (Schwann cells) with thin, wavy, pointed nuclei and with no dysplasia or mitotic activity. The cellular fascicles are typically 4-6 cells thick and are arranged in parallel streams in some areas, and nuclear palisading is seldom pronounced, as it is in neurilemoma. Nuclear pleomorphism and mitotic activity are not seen. Silver stains for axons and luxol fast blue stain for myelin will confirm the presence of neural tissue within the tumor, and the fascicles are immunoreactive for neural filaments.

The neural tissue of this lesion is well circumscribed and usually encapsulated, but large areas of the periphery may lack a capsule, especially along the superficial aspects. Pseudoepitheliomatous hyperplasia of the overlying epithelium has been reported. Occasional lesions demonstrate areas reminiscent of the palisading Verocay bodies of Antoni A tissue in neurilemoma, but true Verocay bodies are not seen. This lesion should be differentiated from neurilemoma and neurofibroma, as described below.

The treatment for this self-limiting lesion is conservative excision, with few recurrences reported.  Unlike neurofibroma and neurilemoma, the PEN is not a feature of von Recklinghausen neurofibromatosis or of multiple mucosal neuroma syndrome (MEN IIB, MEN III).

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