large monoventricle communicating posteriorly with dorsal cyst, exerting compression upon both cerebellar hemispheres, with subsequent tonsillar herniation below the foramen magnum
absent midline structures, including the corpus callosum, septum pellucidum, and falx cerebri
fused thalami
the remaining part of the cerebral cortex is compressed anteriorly and laterally by the large monoventricle