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EXTENSIVE DEVELOPMENTAL DEFECT OF THE CEREBELLUM ASSOCIATED WITH POSTERIOR FOSSA VENTRICULOCELE

1. A case is described in which an extensive cerebellar cortical defect with modification of collateral roof and brain stem nuclei, periventricular leukomalacia in the cerebral hemispheres, and an anomalous midline thalamic fusion were associated in a neonate with severe hydrocephalus and a massive rhombie roof ventriculocele. 2. The positional interrelationships of the principal types of neurons in the defective cerebellar cortex were normal, implying that the pathologic process intercepted normal development after the 5th fetal month. The cytoarchitectonic and topographic features of collaterally modified nuclear structures and the quality of histopathologic reaction were consistent with this inference. 3. The topographic distribution of the cortical defect is most plausibly explained by perfusion failure in the end fields of perfusion of the principal cerebellar arteries. It is suggested that this perfusion failure was due to compression or torsion of arteries by the massive ventriculocele. Hydrocephalic force with mural compression and ischemia probably accounted for the leukomalacia in the cerebral hemispheres. Hydrocephalus may have played a role in the abnormal thalamic fusion via diencephalic compression. 4. The hydrocephalus appeared to have resulted from obstruction to CSF circulation at the level of the roofing membrane of the 4th ventricle. The ventriculocele was a massive hydrocephalic expansion of this membrane. The cause of the hydrocephalus was obscure. The outflow foramina were not patent but not internal morphological evidence bears upon whether or not the hydrocephalus antedated the normal opening of the foramina.