[ELECTRON MICROSCOPIC STUDIES ON THE HUMAN CEREBRAL CORTEX IN HYDROCEPHALUS]

Ultrastructural changes in the deep cortical pyramidal cells of infant rats with inherited hydrocephalus and the effect of shunt treatment

Pathological changes in the cortical gray matter in infantile hydrocephalus vary with the age at onset and may not be reversible with shunt treatment. We have used electron microscopy to investigate the sequence of pathological change and the effect of shunt treatment on layer VI pyramidal cells from infant H-Tx rats with inherited early-onset hydrocephalus. Tissue was prepared from the frontal and visual cortex of control and hydrocephalic rats at 4, 11, and 21 days after birth, together with 21-day rats previously treated with ventriculosubcutaneous shunts at 4-5 or 10-11 days after birth. Both cortical regions gave similar results but the effects were more severe in the visual cortex. In the early stages of hydrocephalus, the pyramidal cells were in clusters with fewer mature dendrites and less cytoplasmic organization than those in control rats, and some neuronal processes were vacuolated. In intermediate hydrocephalus the changes were more severe, with vacuolated cytoplasm, fewer cytoplasmic organelles, frequent swollen processes, and infrequent synapses. In advanced hydrocephalus at 21 days, many neurons showed degenerative changes, with edematous Golgi and dilated endoplasmic reticulum, distorted mitochondria, and single ribosomes. The neuropil contained many spongy areas with distended profiles. Shunt treatment prevented most of the changes if carried out at 4 days. Shunt treatment at 11 days also gave a dramatic recovery at the cellular level, but there were more immature pyramidal cells and edematous processes in the neuropil than in the 4-day-treated rats. The changes in hydrocephalus are consistent with progressive neuronal damage, which is largely prevented by early shunt treatment.

Neuropathological changes caused by hydrocephalus

The medical literature concerning neuropathological changes caused by hydrocephalus is reviewed. In both humans and experimental animals the ependyma suffers focal destruction, cerebral blood vessels are distorted and capillaries collapse, there is damage to axons and myelin in the periventricular white matter, and occasionally neurons suffer injury. The damage appears to result from mechanical distortion of the brain combined with impaired cerebral blood flow. If ventriculomegaly develops very early, foci of cortical dysgenesis may be the result. The character and distribution of pathological changes are dependent on the age at which hydrocephalus develops, the rate and magnitude of ventricular enlargement, and the duration of hydrocephalus. Diversionary shunting of cerebrospinal fluid can only incompletely reverse the damage and the potential for reversal diminishes as the duration of hydrocephalus increases.

[Cerebral cortex in normal pressure hydrocephalus: an electron microscopy study (author's transl)]

A cortical biopsy was taken at the time when ventricular pressure was measured, or a ventriculo-atrial shunt placed, in 11 patients with Normal Pressure Hydrocephalus (N.P.H.), and was studied with the electron microscope. In 9 cases, a rather typical electron microscopic picture with marked increase of extracellular space in an otherwise normal cortical neuropil was observed. 2 patients did not exhibit this pattern and, coincendentally, did not benefit from the placing of the shunt. As a control, about 600 cortical biopsies that had been taken for other reasons were reviewed. In the group, there were only 3 cortices that had a pattern of increased extracellular space similar to the described in N.P.H. On review of the clinico-pathologic data of these cases, it was felt that all 3 probably represented cases of normal pressure hydrocephalus. It is concluded that the ultrastructure of the cerebral cortex is of at least nosological interest in the study of N.P.H.