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Introduction

Blake’s pouch is normal, transient embryological structure that initially does not communicate with surrounding sub-arachnoid spaces. Subsequent spontaneous perforation of the pouch forms the foramen of Lushka.Blake’s pouch cyst (BPC) consists of marked caudal protrusion of the 4th ventricle resulting from fingerlike expansion of the posterior membranous area that does not perforate.Sonographically, BPC is characterized by a normal but displaced vermis and cerebro-spinal fluid collection in the posterior fossa. The imperforated BPC widely communicates with the 4th ventricle. The tentorium and torcular are usually in normal position.

Images 1, 2: Normal posterior fossa, the cerebellum, inferior vermis, cisterna magna and the 4th ventricle appears normal.

Images 3, 4: Normal intra-cranial anatomy; both lateral ventricles and corpus callosum are seen.

Images 5, 6: Image 5 shows cerebellum with normal vermis; Image 6 shows Blake's pouch cyst - the 4th ventricle communicates with cisterna magna giving appearance of absent inferior vermis.

Image 7: Mid-sagittal section of fetal brain is of fundamental importance for characterization of vermian anatomy.

 

Images 8, 9: Normal but displaced vermis in a case of Blake's pouch cyst can be seen using 3D VCI technique.

Images 10, 11: Mid-sagittal plane showing elevated vermis but otherwise normal superior and inferior portions of cerebellar vermis; the 4th ventricle communicates with the Blake's pouch cyst.

Dandy Walker Variant

Images 12, 13, 14: Defect in the inferior vermis can be seen; 4th ventricle communicates with cisterna magna.

Images 15, 16: Image 15 shows Dandy Walker Variant - anticlockwise rotation of vermis, normal insertion of tentorium, and underdeveloped postero-inferior part of vermis can be seen. For comparison the image 16 shows a case of the Blake's pouch cyst.