An interhemispheric cyst refers to a cyst located in the interhemispheric fissure, with or without communication with the ventricular system. The are often diagnosed antenatally on ultrasound (see fetal intracranial cystic lesions) 1-4.
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Classification
A number of classification systems have been described, with the Barkovich classification 5 probably being the most often used when concurrent agenesis of the corpus callosum is present (a common association).
In brief, the classification divides these cysts into two types:
type 1: communicate with the lateral or third ventricles
type 2: loculated without communication with the ventricular system
See Barkovich classification of agenesis of the corpus callosum with interhemispheric cyst for a complete description.
Pathology
There is relatively little pathological consensus on whether all interhemispheric cysts are histologically the same or whether they represent various cystic lesions depending on etiology; arachnoid cysts, ependymal cysts or even neurenteric cysts 3,5.
Associations
agenesis of the corpus callosum: strong association
Differential diagnosis
Considerations include:
midline fetal arachnoid cyst: no associated agenesis of the corpus callosum
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cyst-like lesions related to physiologic median structures
enlargement of the cavum septi pellucidi 2
enlargement of the cavum vergae 2
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