Prenatal diagnosis of a cystic type IV sacrococcygeal teratoma mimicking a cloacal anomaly: contribution of MR

Objective: To report a case of pelvic midline cystic mass in a female fetus without visibility of the rectum and which is not a cloacal anomaly.

Methods: Ultrasound (US) and magnetic resonance imaging (MRI) were performed respectively at 27 and 27.5 weeks' gestation and the findings of these examinations were compared with post-mortem examination after termination of pregnancy (TOP).

Results: US showed a pelvic midline cystic mass in a female fetus with mild enlargement of the left ureter and renal pelvis. MRI did not show the T1 hypersignal of meconium in the rectum. The analysis of MR findings were suggestive of the diagnosis of a sacrococcygeal teratoma. Pregnancy was terminated because of the possibility of severe sphincterial disorders and the fetopathological examination confirmed this diagnosis.

Conclusion: This observation illustrates the diagnostic problems generated by the detection of a pelvic midline cystic mass in a female fetus. The absence of visibility of the T1 hypersignal of the meconium in the rectum is traditionally supposed to be highly suggestive of a cloaca, but may also be explained by the emptiness of the rectum, compressed by the mass.