Hydrocephalus in the laboratory rat.

The state of hydrocephalus is applied to all conditions in which the intracranial volume of cerebrospinal fluid is abnormally large in relation to the volume of the brain. Increase in volume of cerebrospinal fluid raises the pressure and results in brain tissue atrophy and enlargement of the cranial vault. The condition can be hereditary or acquired and commonly arises from congenital malformations, inflammatory processes or expanding lesions such as tumours. The laboratory rat has an incidence of hydrocephalus of about 0.3% but no satisfactory indication of hereditary linkage. A small breeding unit of laboratory rats consisting of 2 males and 3 females produced 32 offspring of which 13 exhibited varying degrees of hydrocephalus. Examination indicated that the hydrocephalus was congenital in type, that 11 of the 13 hydrocephalic rats were proven males, that the remaining 2 were likely to be male, that female young were unaffected and that the incidence of the condition was 40.62%. Craniofacial examination showed that the cranial vault enlarged due to intracranial pressure and that the facial and basal components were mainly unaffected. The olfactory aspect of the frontal bone bulged slightly outwards, medial walls of orbits were laterally displaced, parietal and interparietal showed distention and their related sagittal and coronal sutures unfused and open to 1 mm in places. The basioccipital width showed a significant increase to the normal state. It is postulated that this particular congenital hydrocephalus in the rat is a normal autosome mutation, sex limited to males and one in which both males and females could transmit the trait to male progeny.