Case report: adult rhabdomyoma of the lip

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The patient was a 53-year-old male, on disability pension with a background of asthma and smoking, who presented with a 5 month history of a slowly enlarging right lower lip lesion. There were no other associated symptoms. On examination, there was a 5 mm submucosal nodule located on the buccal region of the right lower lip. Wedge resection of the lesion was performed, and tissue was sent for histopathological examination. Macroscopically, the specimen consisted of a wedge excision of lip, composed of tan mucosa with underlying soft tissue measuring 13 × 10 mm with a depth of 2 mm. There was no evidence of ulceration. On cut surface, there was a small submucosal nodule with a tan and lobulated appearance. Microscopically, the lesion was composed of solid sheets of ectopic skeletal muscle extending to the epidermis. The lesional cells had large, polygonal eosino-philic cells with granular cytoplasm and small peripheral nuclei. There was no significant nuclear atypia, mitotic activity, or necrosis seen. Immunohistologically, the lesional cells were strongly positive for myogenic markers such as desmin and actin. The le-sional cells were negative for S100. The differential diagnoses that need to be considered are granular cell tumour, hibernoma, and oncocytoma. Rhabdomyomas are uncommon tumours of skeletal muscle differentiation and are classified into cardiac or extracardiac in location. Extracardiac rhabdomyomas comprise 2% of all tumours of skeletal muscle differentiation and are subclassified into adult and fetal types. Adult type rhabdomyomas most commonly present in the oral cavity or superficial soft tissue of the head and neck region and 20% are multifocal. Although the tumour is benign, local recurrences have been reported.