Path Case 63: Case history and images:

Solitary, circumscribed neuroma is a distinctive benign cutaneous tumour that was first described under the name "palisaded encapsulated neuroma" in 1972 by Reed and colleagues. (Arch Dermatol. 1972 Dec;106(6):865-70 ).

These are slow growing lesions and are usually present on the face or close to a mucocutaneous junction in middle-aged adults. It is rarely found in other locations, such as the glans penis, oral mucosa, neck, shoulders, upper part of the arms.

Clinically, they are often diagnosed as basal cell carcinoma, melanocytic naevus, epidermal cyst  or skin appendage tumours.

Macroscopically these are usually firm sessile  well circumscribed intradermal nodules measuring between 2 mm to 6 mm in diameter.

Histologically solitary circumscribed neuromas are well-circumscribed dermal tumours composed of a partially encapsulated mass of bland Schwann cells and innumerable tiny axons arranged in interlacing fascicles. A fibrous capsule composed of flattened, elongated perineural cells is present around the nodule.  No pleomorphism is seen and mitotic figures are rarely present. Occasional small blood vessels are seen in the stroma but haemorrhage and necrosis have not been reported.

Variants: Nodular: Most common. Other rare variants: epithelioid ; plexiform ; multinodular ; increased vasculature ; fungating growth pattern.

Image Link1 ; Image Link2 ; Image Link3 ; Image Link4 ; Image Link5 ; Image Link6 ; Image Link7 .

Immunohistochemistry :   Interlacing fascicles of Schwann cells are S -100 protein and vimentin positive. Numerous tiny axons are neurofilament positive. The capsule is composed of perineural cells that show epithelial membrane antigen positivity.  

Differential diagnosis: 

1. Neurofibroma: click here : ( Neurofibroma lacks capsule and contains fewer axons with myelin sheaths. Mucopolysaccharide ground substance is present. May be associated with von-Recklinghausen's disease).

 2.Schwannoma: click here (Schwannoma lacks axons, contains Antoni A and Antonic B areas and Verocay bodies. Usually present in a subcutaneous location.

 3.Traumatic neuroma: click here: (Scarring and inflammatory cells are present together with Schwann cells and axons).   

4. Leiomyoma: click here: (Spindle cell lesion composed of muscle cells).

Solitary circumscribed neuroma is a benign lesion probably caused by primary hyperplasia of the nerve fibres.  Even after incomplete excision the lesion does not recur.  An association with neurofibromatosis or MEN syndrome type IIb has never been found.