Surgical management of a retroperitoneal pelvic desmoid tumour involving the sacrifice of external iliac vein and internal iliac vessels

•Retroperitoneal pelvic desmoid tumours are rare with limited publications.•A rare case of a retroperitoneal pelvic desmoid tumour is discussed.•Excision was challenging requiring the sacrifice of some of the iliac vessels.•No other case reports document a surgical excision requiring this.•To date our patient suffers minimal morbidity and has had no recurrences.