A rare case of leiomyoma of the internal anal sphincter

Leiomyoma is a benign tumour which derives from the smooth muscle fibres and it may occurs in every site in which this type of muscle is present. Among all benign soft tissue tumours it represents almost 3.8% and its pathogenesis remains still unknown.

The present case is about a 62year old woman referred to our centre complaining anal and perineal pain which increase after defecation in association with the appearance of a nodule in the perianal region fixed to the anal sphincter. A 360° tridimensional transanal ultrasound was performed and it showed an anterior nodular thickening of the internal anal sphincter. After an inconclusive preoperative biopsy and a counselling with the patient, the surgeons decided to proceed with the surgical excision. The immunohistochemical examination confirmed the preoperative suspicion of leiomyoma. At 1year follow-up the patient had not tumour-related symptoms or fecal incontinence and any signs of local recurrence at ultrasound imaging were demonstrated.

Leiomyomas are relatively insensitive to chemotherapy whereby surgery is the treatment of choice and it should be adequate to the site and dimension of the lesion achieving a complete resection with free margins. A further close follow-up is needed too.

Nowadays there is not a gold standard technique to treat such kind of lesions and the decision of the best surgical approach should depend on the dimension and site. In fact, surgery aims to the oncological outcome trying also to minimize the possible post-operative functional complications.