The hugely dilated right lateral ventricle is protruding into the posterior fossa through a deficiency in its medial wall resulting in a posterior fossa pseudocyst:
- indenting the superior vermis, tectum and cerebellum
- measuring 5 x 3.5 x 2.7 cm in maximum dimensions
- communicating with the atrium of the right lateral ventricle through a wide-pore opening (9 mm in anteroposterior dimension)
- no patent communication to the subarachnoid spaces
Downwards cerebellar tonsillar descend about 18 mm below the opisthion-basion line indenting the cervicomedullay junction, consistent with Chiari I malformation.
Moderate to marked supratentorial hydrocephalic changes with reduced mamillopontine distance (1 mm) and effaced cortical sulci. No subependymal periventricular permeation.
Obstructed inferior aspect of the cerebral aqueduct of Sylvius, ectatic third ventricle with markedly stretched depressed third ventricular floor and cisterns indenting the posterosuperior clivus and sella, associated with deficient posterior clinoid processes reflecting long standing third ventricular outflow tract obstruction.
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CSF flow dynamic study with ultra-thin 3D sagittal T2 weighted images and phase contrast sequence revealed:
- patency of the aqueduct with absent flow through its lumen
- CSF flow noted between the medial aspect right lateral ventricle and the posterior fossa pseudocyst
- aliasing noted at foramen magnum, sequel to Chiari I malformation