The patient went on to have surgery.
MICROSCOPIC DESCRIPTION: Sections show subcutaneous tissue containing a non-encapsulated ill defined spindle cell tumour composed of short fascicles. Tumour cells contain scant eosinophilic cytoplasm and wavy nuclei. Scattered mast cells are present. No epidermis is present. No atypia or mitoses are seen. There is no evidence of malignancy. Immunohistochemically tumour cells stain: S100+, CD34-, SMA- and Factor XIIIa-.
FINAL DIAGNOSIS: Benign nerve sheath tumour.