Long-term observation of arachnoid villi after subarachnoid hemorrhage: an electron microscopic study in dogs.

The sequential electron microscopic examinations were carried out on arachnoid villi of the dog after subarachnoid hemorrhage (SAH). A few days after SAH, red blood cells were accumulated and degenerated in the villi. 10 days after SAH, remarkable phagocytosis and micropinocytosis were observed in the arachnoid villi, which may suggest increased metabolic activity of the arachnoid cells. 30 days after SAH, increased cellularity in the arachnoid villi developed and intercellular spaces became very narrow. 90 days after SAH, the arachnoid villi demonstrated many cytoplasmic filaments and hemidesmosome-like structures in the arachnoid cells, as well as narrowed intercellular space and increased cellularity. Microfibrils increased and structures resembling basal laminae were observed in the stromas. These morphological alterations may have a relation to the disturbance of absorption of cerebrospinal fluid.