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.
Keywords
Posterior fossa fluid collection - Mosaic trisomy 22 - Blake’s pouch cyst
