Male, 2 days old, with unilateral hydrocephalus. Assess for evidence of pressure on brain or vascular issues. A large, multilocular cystic lesion is evident situated between the cerebral hemispheres, the larger part of which resides to the left of midline. The loculations are formed by thin septations which enhance minimally if at all. No solid nodular enhancement is seen. Most of the locules are variably T1 hyperintense relative to CSF, though one or two are fairly close in signal to CSF. No evidence of susceptibility effect is seen within or adjacent to the cysts to suggest hemorrhage.The presence of the cystic lesion causes significant deformity of the brain parenchyma. The thalami are formed but inferiorly and laterally displaced, particularly on the left. The interhemispheric fissure is present and seems to be fully formed. Both cerebral hemispheres are somewhat compressed and there may be a component of edema versus transependymal CSF flow in the temporal lobes, left more than right.No definite corpus callosum or cavum septum pellucidum is visualized. In addition, the morphology of the frontal horns and apparent colpocephaly of the right lateral ventricle are suggestive of agenesis of the corpus callosum. Both temporal horns are dilated, left side more than right, suggesting entrapment.The pituitary region is within normal limits. The brainstem appears to be normally formed and intact. The cerebellum is likewise normally formed but it does experience mass effect from deformity of the supratentorial structures.
A large multiloculated cystic lesion is evident situated between the cerebral hemispheres with the majority of the lesion residing to the left of midline. No solid enhancing components are seen to suggest that this lesion is neoplastic in nature. Rather, the location and features of the lesion, along with additional findings suggesting agenesis of the corpus callosum, suggest an underlying diagnosis of type II callosal agenesis with interhemispheric cyst. Based on their variable signal characteristics, it is unlikely that the individual cystic locules communicate with each other or with the ventricular system. Findings suggestive of ventricular entrapment are seen, particularly affecting the temporal horns.