Hydrocephalus and achondroplasia. A study of 25 observations.

Two series of achondroplastic patients were studied. The first series included 5 patients referred to our neurosurgical department for macrocranium and/or mental retardation. The second series was composed of 20 patients arbitrarily chosen from a medical group. Macrocranium was observed in 60% of the patients and was related to hydrocephalus in all but 2 cases. Radiological studies demonstrated that the posterior fossa was deformed and narrowed in its 3 planes, while its volume was conserved because of an abnormal ascension of the tentorium. The conflict between normal brain development and the craniostenosis at the base of the skull is responsible for an upward tilt of the petrous pyramids, a lowering of the mastoid process, and the illusion of a basilar invagination. Ventriculographies, pneumoencephalographies and isotopic transits demonstrated normal CSF circulation. The study suggests that hydrocephalus is related to the stenosis of the sigmoid sinus at the level of narrowed jugular foramina with a resulting raise in intracranial venous pressure. The majority of patients with macrocranium stabilizes spontaneously. Thus, a surgical indication should be extremely limited.