Aneurysmal benign fibrous histiocytoma of the anal canal: a rare differential diagnosis.

BACKGROUND: To our knowledge, we report the first case of an aneurysmal benign fibrous histiocytoma occurring in the anal canal. METHODS: Clinical, histological, radiological and surgical data pertaining to this patient were analysed. Additionally, a literature review on aneurysmal benign fibrous histiocytoma was conducted. RESULTS: We describe a 48-year-old Caucasian male presenting with a 2-week history of a painful anus, fresh rectal bleeding and tenesmus. Digital rectal examination identified a tender firm mass in the anal verge. Magnetic resonance imaging revealed high signal in the anal canal. Flexible sigmoidoscopy revealed an ulcerated 3-cm indurated lesion at the four o'clock position. Biopsies taken of the mass confirmed the diagnosis of an aneurysmal benign fibrous histiocytoma (BFH). Following a discussion in the colorectal multi-disciplinary team, the patient was counselled for an excision of the lesion. Diathermy dissection was performed to completely excise the tumour with a margin involving the fibres of the anal sphincter. The patient made a full recovery and had no residual symptoms. Histology of the excised specimen confirmed clear margins of the BFH. CONCLUSIONS: This paper aims to highlight a rare differential diagnosis for an anal mass. An aneurysmal BFH most often presents as a painless mass within the dermis and subcutaneous tissue. As such, this case presents a diagnostic challenge to both colorectal surgeon and histopathologist due to its low incidence and unusual location. We further present the clinical and radiographic evidence to confirm the diagnosis. Additionally, we discuss the literature pertaining to this condition and its optimal management.