CYSTIC LESIONS OF THE BRAIN - A CLASSIFICATION BASED ON PATHOGENESIS,WITH CONSIDERATION OF HISTOLOGICAL AND RADIOLOGICAL FEATURES

A classification of the existing multitude of cystic lesions of the br ain is proposed, which allows an understanding of their genesis and co nsequent therapeutic implications, as well as their diagnostic charact eristics. Essentially, cerebral cystic lesions may be classified into the following categories: Cysts containing CSF-like fluid, which inclu de ex vacuo type cysts, such as leptomeningeal cysts, and cysts follow ing surgical resection; cysts with fluid secreting walls and CSF-like content, such as arachnoid cysts; cysts associated with dysgenesis, fo r example Dandy-Walker cysts. The ex vacuo cysts increase craniospinal compliance, whereas the other cysts with CSF-like content do not; the y are not per se expansive, however, although their occasional locatio n along CSF pathways may cause obstruction and hydrocephalus. Another category includes cysts with a lining of non-neural epithelium like co lloid cysts, epidermoid cysts, or craniopharyngiomas. They may increas e in size and cause symptoms by compression, although not at the rate of tumour-associated cysts. The cysts associated with gliomas and othe r tumours have a pathogenesis bearing upon blood-brain barrier impairm ent and formation of vasogenic oedema. Finally, one may distinguish a category of cysts with infectious origin, such as brain abscesses and hydatid cysts. The cysts with CSF-like contents may be recognised by t heir magnetic resonance characteristics resembling those of CSF, where as cysts containing proteinaceous fluid are associated with blood-brai n barrier impairment and consequent contrast enhancement. The cysts wi th a lining of non-neural epithelium exhibit diverse properties of att enuation on comput tomography (CT) and magnetic resonance imaging (MRI ), depending on the nature of their cyst contents.