Differential ventricular expansion in hydrocephalus

In the large canine model of acquired obstructive hydrocephalus that we have developed recently, computer-assisted 3-dimensional morphometry has been performed on T₁-weighted Spin Echo MRI images from adult dogs before and after the induction of hydrocephalus. To date, 7 hydrocephalic animals have been analyzed that survived 7-83 days (median = 54) after receiving injections of cyanoacrylate glue into the anterior fourth ventricle. Measurements were obtained from lateral, 3rd, and 4th ventricles. The volumes of the left and right lateral ventricles were symmetrical before and after induction. Mean lateral ventricle volume increased 424% from a baseline of 0.63 cc to a post-induction value of 3.30 cc (p <0.01 with unpaired t-test). In contrast, the 3rd ventricle expanded 187% from a mean of 0.15 cc to 0.43 cc (p <0.05). The combined volume of the lateral and 3rd ventricles increased 369% from a mean of 0.78 cc to 3.69 cc (p <0.01). Evans' ratios, which are used routinely in the clinical setting, were also obtained from linear measurements of the lateral ventricle width divided by brain width at the level of the foramen of Monro. These values exhibited only a 94% increase from mean baseline ratios of 0.17 to post-induction ratios of 0.33 (p <0.05). These findings indicate that in mechanically-induced obstructive hydrocephalus the relative expansion of the lateral ventricles is greater than that of the 3rd ventricle. In addition, volumetric measurements of the lateral and 3rd ventricles suggest that the extent of ventriculomegaly is 3- 4 times greater than estimated by Evans' ratios.