On the pathogenesis of brain tumour cysts: a volumetric study of tumour, oedema and cyst

Chemical analysis of brain tumour cyst contents has invalidated the concept of cyst formation being the result of tumour necrosis, and a common mechan ism of vasogenic brain oedema and cyst formation, namely blood-brain barrie r (BBB) disruption, has been suggested. To analyse a possible relationship between the occurrence of vasogenic oedema and the presence, of cysts, we p erformed a volumetric analysis on the MRI and CT studies of 60 patients wit h primary or metastatic brain tumours. We compared four groups of tumours: 30 gliomas, of which 15 were cystic and 15 not and 30 metastatic brain tumo urs of which 15 were cystic and 15 not. Although the mean volume of oedema was similar for cystic and noncystic tumours, the ratio of oedema to tumour volume was approximately four times as high in cystic supratentorial tumou rs. This would support the view that cyst formation may be related to relat ively greater production of oedema, possibly due to fusion of microcysts co ntaining oedema fluid. The ratio of oedema to tumour volume is not greater in cystic cerebellar and intraventricular tumours. This may be due to the d ifferent anatomical organization of the cerebellar white matter, and the fa ct that the intraventricular tumours are bordered by subcortical grey matte r. In these cases, spread of oedema is impeded. Formation of a large amount of brain oedema is therefore not an essential prerequisite for cyst format ion.