Partial urorectal septum malformation sequence: a report of 25 cases.

We have identified 25 cases with what we are calling the partial urorectal septum malformation (URSM) sequence, which were seen in our institution over the past 27 years. The partial URSM sequence is defined as a single perineal/anal opening that drains a common cloaca in combination with an absent (imperforate) anus. In the 25 patients reported here, the partial URSM sequence was more common in females, with a female to male ratio of 18 to 7. Ambiguous genitalia were common in both sexes. Internal pelvic structures typically showed a cloaca with the bladder and rectum (and vagina in females) coalescing into a common canal that connected to the external surface in the perineal or anal area. Abnormalities of the internal genitalia were also common, with 12 females having a bifid or septate vagina and 11 having a bicornuate uterus. Renal anomalies were frequent in both sexes, with 10 of 25 patients having unilateral cystic renal dysplasia and 7 of 25 patients having unilateral renal agenesis. Twenty-one of 25 patients survived long term. By definition, the partial URSM sequence is a milder expression of the full URSM sequence, which is defined as having no perineal or anal openings and is typically associated with an internal cloaca. The URSM spectrum, which encompasses the partial and full URSM sequences, is believed to be caused by abnormalities of septation of the primitive cloaca. The URSM spectrum is distinct from the VATER association and conditions caused by sex hormone abnormalities, such as congenital adrenal hyperplasia.