Callosal agenesis with cyst - A better understanding and new classification

Objective: To analyze imaging studies of 25 cases of agenesis of the corpus callosum with interhemispheric cyst to assess this malformation itself and associated anomalies. Methods: CT (6 patients) and MRI (19 patients) were retrospectively reviewed. The patients were categorized according to morpho logic and clinical characteristics. Results: Based on morphology, the patie nts were separated into two major types, each with subtypes. Type 1 cysts a ppear to be an extension or diverticulation of the third or lateral ventric les, whereas Type 2 are loculated and do not communicate with the ventricul ar system. Type la were associated with presumed communicating hydrocephalu s but no other cerebral malformations. Type Ib were associated with hydroce phalus secondary to diencephalic malformations prohibiting egress of CSF fr om the third ventricle into the aqueduct of Sylvius. Type Ic were associate d with small head size and apparent cerebral hemispheric dysplasia or hypop lasia. Type 2a (multiloculated cysts) were associated with no abnormalities other than callosal agenesis/hypogenesis. Type 2b were associated with def iciencies of the fair cerebri, subependymal heterotopia, and polymicrogyria land were almost all in patients diagnosed with Aicardi syndrome). Type 2c were associated with subcortical heterotopia. Type 2d consists of interhem ispheric arachnoid cysts. Other than those with Type 2b cysts, gender predo minance was overwhelmingly male. Conclusion: Agenesis of the corpus callosu m with interhemispheric cyst appears to consist of a heterogeneous group of disorders that have in common callosal agenesis and extraparenchymal cysts , both of which are among the commonest CNS malformations. This article pro poses a classification system, based primarily on morphology, by which this complex group of disorders might begin to be better understood.