Glomus coccygeum: an unexpected finding in an abdomino-perineal resection

Abstract

Aim To discuss a little known anatomical structure, the glomus coccygeum, and its presence in an abdominoperineal resection (APR). Methods A 63-year-old male underwent APR for a low rectal carcinoma following neo-adjuvant chemo-radiation. No residual tumour was identified macroscopically or microscopically, however there was a 2.5 mm diameter well-circumscribed lesion at the posterior resection margin. Microscopy and immunohistochemis-try were utilised to diagnose the lesion. Results Microscopy revealed nests of cells with clear to eosino-philic cytoplasm and plump nuclei, in association with small vascular spaces and small nerves. Immunohistochemistry was performed to exclude residual rectal adenocarcinoma and other possible causes. The lesion was negative for Cam5.2, CK20, CEA, PSA, CD56, synaptophysin and chromogranin, and positive for vimentin and SMA. CD31 highlighted the vascular spaces. The lesion was diagnosed as a glomus coccygeum. Discussion The glomus coccygeum is a vestigial innervated arterio-venous anastomosis located adjacent to the coccyx. Although first described in 1859, glomus coccygeum is not well known, which may lead to diagnostic confusion. Previously they have been misdiagnosed as paragangliomas and glomus tumours. While glomus coccygeum has previously been found in coccy-geal resections and pilonidal sinus excisions, this is the first reported case of a glomus coccygeum in an abdominoperineal resection.