Congenital Hydrocephalus vs. Arachnoid Cyst

Left picture: The diagnosis is most likely a hydrocephalus following congenital toxoplasmosis, in which the brain parenchyma may be involved to a different degree by the infectious disease, and/or an asymmetry and a segmentation of the ventricles can be observed. Right picture: This newborn has an arachnoid cyst of the left hemisphere which displaces the left ventricle. In macrocephaly, an additional differential diagnosis of hydrocephalus is a congenital intracranial cyst. It is possible that a hemimacrocephaly is visible and palpable in a similar case of arachnoid cyst as seen radiologically in the case report, or an occipital bossing in case of a Dandy walker cyst or other infratentorial cyst.

CT in two neonates with macrocephaly. In both cases the lateral ventricles are asymmetrically dilated. Left picture: The asymmetry of the vetricles is considerable. Subependymal calcifications are visible on both sides close to the ventricles. Right picture: The dilatation of the lateral ventricles is unequal, which means more on the left than on the right side. Right picture: Looking closely reveals that the left ventricle which is somewhat shifted to the right side is separated by a small tissue margin from a much larger CSF-containing cavity.