Arachnoid diverticula of the 4th ventricle
Arachnoid diverticula are developmental malformations due to the splitting of the arachnoid membrane by CSF. In dogs, they have been reported in the brain at the level of the 4th ventricle and quadrigeminal cistern. Obstructive hydrocephalus and syringohydromyelia occurs by blockage of the CSF from the 4th ventricle.
1) Schmidt MJ, Klulpp S, Amort K, Jawinski S, Kramer M. MRI characteristics of fourth ventricle arachnoid diverticula in five dogs. Vet Radiol Ultrasound 2015, 56; 196-203.