Extraparenchymal, meningocerebral, parenchymal and ventricular lesions of the posterior fossa and craniocervical junction

Abstract

The characterization of primary or developmental cysts is discussed in section 3.1. All the main varieties with the exception of colloid cyst have been described in the posterior fossa, and it is worth recalling the histological and immunocytochemical similarities between that entity and the neurenteric cyst. Within the posterior fossa, arachnoid and neurenteric cysts are usually restricted to the subarachnoid space, the former most often within the dorsal cerebellomedullary and quadrigeminal plate cisterns (Figure 6.1), whilst the latter extends with multiple loculations, through the prepontine and cervical subarachnoid space. Intra-extraparenchymal and intraventricular locations are more in favour of neuroepithelial cyst (Figure 6.2). Epidermoidoma (see below), which is also the commonest of the congenital cysts, favours the prepontine-cerebellopontine cistern. Fluid which is Ti hyperintensive relative to CSF suggests protein secretion or keratin. In all these examples, spurious enhancement may be caused by compressed choroid and meninges, and all may be mimicked by cysticercus (Figure 6.8).