MRI of a twin pregnancy in a uterus bicornis unicollis.

February 2011, Vol. 101, No. 2 SAMJ A 30-year-old woman was seen at 24 weeks for a discrepancy between the symphysis-fundal height and the gestation by dates. Ultrasound examination revealed a twin pregnancy and showed the placentas to be implanted ‘back-to-back’ over what appeared to be a septum that extended from the uterine fundus to the cervix (Fig. 1). A bicornuate unicollis uterus was confirmed on MRI and revealed two divergent uterine horns separated by a deep fundal cleft, surrounded by myometrial tissue, containing a fetus within each horn (Fig. 2). A single cervix and vagina was visualised (Fig. 3), in keeping with a Class IVA Müllerian duct abnormality.1 At 33 weeks, an emergency caesarean section delivery was performed via two separate classic incisions into each corpus. A spectrum of congenital uterine malformations is attributed to the abnormal fusion of the pair of Müllerian ducts or failure of the absorption of the uterine septum;2,3 bicornuate uterus is the most common.3 Spontaneous twin gestation in a case of bicornuate uterus is rare. MRI is a valuable adjunct to sonar, which can be diagnostically limited in the third trimester. MRI assists in delineating external uterine contour, characterising septal composition, endometrial/myometrial ratio and defining the subtype of Müllerian duct anomalies.3 Deep uterine bifurcation causes myometrial distortion denying each corpus the full complement of musculature,