Solitary circumscribed neuromas, also known as palisaded encapsulated neuromas, are benign tumors primarily occurring in the cutaneous tissues of the face, often at the mucocutaneous border 1.
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Epidemiology
Although they can occur at any age, there is a predilection for later middle age (40-60 years) 1.
Clinical presentation
Typically solitary circumscribed neuromas present as small (<1 cm) cutaneous nodules, usually affecting the face (90%), often adjacent to the lips or on the nose or forehead. They are rounded firm and painless and almost always solitary 1.
Diagnosis
The diagnosis of solitary circumscribed neuromas is a pathological one 1. Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5thedition) 1:
circumscribed cutaneous Schwann cell-rich nerve fiber proliferation
diffuse S100 positivity and focal NFP staining
possible incomplete peripheral capsule with positive perineural markers (e.g. EMA, Glut-1)
Pathology
Solitary circumscribed neuromas are composed of Schwann cells and to a lesser degree axons.
Macroscopic appearance
These tumors are usually spherical or ovoid, and usually solitary although occasionally a cluster of nodules is present 2. The cut surface of these tumors is pale grey and firm in texture 1.
Microscopic appearance
Solitary circumscribed neuromas are composed of bland spindle-shaped cells organized in fascicles. The cells have wavy nuclei that sometimes arrange themselves in parallel lines, reminiscent of palisading (thus the earlier term palisaded encapsulated neuroma) and are embedded in a background of hyalinized collagen below an intact epidermis 1,2. Involvement of the superficial subcutis is sometimes encountered 1,2.
A thin fibrous capsule is sometimes present. No anaplasia or atypia 1.
Immunohistochemistry
S100: positive
NFP: positive in small nerve fibers within the tumor
EMA: positive in the capsule but not in the tumor
claudin-1: positive in the capsule
GLUT-1: positive in the capsule
Radiographic features
As these are small and purely cutaneous lesions, they rarely if ever require imaging.
Treatment and prognosis
Solitary circumscribed neuromas are benign with no potential for local invasion or metastasis. Treatment with excision is for cosmetic purposes.
History and etymology
Solitary circumscribed neuromas were first described in 1972 using the name palisaded, encapsulated neuroma 3.
Differential diagnosis
Other cutaneous nodules, including:
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