The brain of 17 asymptomatic normal adult beagles was evaluated with magnetic resonance imaging. Lateral ventricular size was quantified using computer algorithms. In beagles with large ventricles, contrast medium was introduced into the cerebellomedullary cistern to determine whether obstructive hydrocephalus was present. Total lateral ventricular volume ranged from 77 mm3 to 11,726 mm3. Based on Gd-DTPA diffusion, the CSF flow pattern was considered normal and normal neural morphology was seen using electron microscopy. Results suggest a high incidence of clinically asymptomatic ventriculomegaly in normal adult beagles.

Human spinal arachnoid villi and granulations were studied after distension by a subarachnoid perfusion of Berlin blue and trypan blue. These proliferations were distributed on almost every nerve root in the thoracic and lumbar region. Human spinal arachnoid villi and granulations were divided into those located entirely internal to the dura, those that extended into the dura, and those that penetrated the dura completely. Venous sinuses were closely related to most arachnoid proliferations.

The morphology of the choroid plexuses of the lateral, third, and fourth ventricles in dogs was studied by histological and ultrastructural techniques after in situ fixation. Most portions of the plexus in the lateral ventricle showed a parallel arrangement of capillaries, producing a fine corrugation of the overlying layer of epithelial cells. Relatively large amounts of connective tissue separated the capillaries from the epithelium. The fourth ventricle choroid plexus showed short capillary loops projecting into the ventricle and more intimately covered by epithelium. Smaller amounts of connective tissue separated the capillaries from the epithelium. The choroid plexus of the third ventricle showed characteristics seen in the plexuses of both the lateral and fourth ventricles. The total surface of the choroid plexuses in the dog averaged 10.7 cm2, of which 55% was fourth ventricle choroid plexus.