A 26-year-old primigravida came to our Fetal Medicine Center for first trimester aneuploidy screening at 13 weeks. Ultrasound was done using Voluson E8 (GE Healthcare Ò , Milwaukee, WI, USA) with convex abdominal 4-8 MHz transducer and transvaginal 15-20 MHz transducer. On abdominal imaging, there was cardiomegaly with tricuspid regurgitation. On transvaginal scan, clear cardiac disproportion with a small left atrium and ventricle were seen (Fig. 1). On application of color Doppler, the flow across the mitral and aortic valves was negligible with hyperdynamic flow on the right side with tricuspid regurgitation (Figs. 2, 3). Foramen ovale was opening on the right side and the flow in the arch of aorta was reversed.

The authors report a case of mosaic trisomy 22 diagnosed antenatally by amniocentesis at 19 weeks. The ultrasound finding was an isolated posterior fossa fluid collection in the brain with features possibly suggestive of a Blake’s Pouch cyst with doubtful hypoplasia of cerebellar vermis. The karyotype of the amniocytes was mos47, + 22[6]/46[8] with two separate clones of cells. Trisomy 22 was seen in one clone (43%) while the other clone (57%) had a normal karyotype. On postnatal examination after termination, there were no dysmorphic features. A selective autopsy of the fetal brain was suggestive of normal posterior fossa anatomy with normal cerebellar vermis which retrospectively confirmed the diagnosis of a Blake’s pouch cyst.

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