Electron microscopy of cerebral cortex in Arnold-Chiari type II malformation: report of two cases

Two samples of cerebral cortex of patients with clinical diagnosis of Arnold-Chiari type II malformation were studied with conventional transmission electron microscopy. Pyramidal and non-pyramidal nerve cells of layers II to V exhibited moderate and severe swelling of intraneuronal compartment. The cerebral cortex neuropile showed hydrocephalic edema featured by remarkable enlargement of the extracellular space, degenerated synaptic contacts and swollen dendrites. Interfascicular oligodendrocytes appeared extremely swollen with widened nuclear pores, apparent nucleo-cytoplasmic transfer of chromatinic substance and areas of focal necrosis. Swollen astrocytes displayed lamellar bodies, microfilaments and monogranular glycogen granules. The vacuolated astrocytes showed images suggestive of hydrocephalic edema resolution characterized by deep invaginations of the plasma membrane and formation of numerous cytoplasmic vacuoles. The cortical capillaries exhibited signs of increased cerebrovascular permeability, such as augmented endothelial vacuolar transport, open endothelial junctions and nodular thickening, thinnings and discontinuities of the basement membrane. A transparenchymal route for cerebrospinal fluid absorption through the cortical capillaries, as a means of hydrocephalic edema resolution, is proposed.