Posterior fossa anomalies and hydrocephalus

Abstract

The posterior fossa anomalies implicated with hydrocephalus mainly fall into three groups: (1) Chiari malformation with both Chiari Type I and Chiari Type II, (2) basilar invagination of idiopathic origin as in cases of osteogenesis imperfecta and related osteochondrodysplasias, and (3) Dandy-Walker abnormalities related to Dandy-Walker syndrome. The Dandy-Walker syndrome is being dealt with in the next chapter by another author. There are rare conditions of abnormalities at the craniovertebral junctions where hydrocephalus is likely to be an associated pathology. These are listed below: Cervical diastematomyelia in cervico-oculo-acoustic (Wildervanck) syndrome. CNS anomalies in oculoauriculovertebral dysplasia (Goldenhar-Gorlin syndrome). In some cases of vermian dysgenesis (Joubert syndrome). Rarely, there are cases with dural fibrous ring or fibrous adhesions blocking the fourth ventricular outlets. In this chapter, our main aim is to define the Chiari I and Chiari II malformation along with a brief description of Chiari III and Chiari IV malformations in relation to the epidemiology, aetiology, pathophysiology, relevant abnormal anatomy, clinical presentation, and management. We will also, briefly, discuss the basilar invagination and the four rare craniovertebral abnormalities associated with hydrocephalus. Chiari I malformation is mostly of congenital nature but can happen in a small percentage of patients after trauma. Chiari II malformation is associated always with an open spina bifida abnormality. Approximately 10-20% of Chiari I malformation patients have associated hydrocephalus, whereas 90% of the Chiari II malformation patients have hydrocephalus.