Cystic lesions accompanying extra-axial tumours

We examined the mechanism of cyst formation in extra-axial tumours in the c entral nervous system (CNS). Cyst fluid, cerebrospinal fluid (CSF) and bloo d plasma were analysed in eight patients with nine peritumoral cysts: four with meningiomas, two with intracranial and two spinal intradural schwannom as. Measuring concentrations of various proteins [albumin, immunoglobulin G (IgG), IgA, alpha(2)-macroglobulin and IgM] in cyst fluid, CSF and blood p lasma provides insight into the state of the semipermeability of the blood- brain barrier (BBB) and blood-cerebrospinal fluid barrier. Peritumoral cyst s accompanying intra-axial brain tumours are the end result of disruption o f the BBB and oedema formation. Unlike intra-axial tumours which lie embedd ed within nervous tissue, extra-axial tumours tend to be separated from ner vous tissue by arachnoid and pia mater. High concentrations of proteins wer e measured in the cyst fluid, approaching blood plasma levels, suggesting a local barrier disruption, and passage across the arachnoid, pia mater and cortical/medullary layer into the CNS parenchyma, leaving the protein conce ntrations of CSF practically unchanged. We confirmed that very high concent rations of protein are to be found in tumour cysts, plasma proteins forming almost 90 % of the total protein in the cyst. We review current hypotheses on the pathogenesis of cysts accompanying neoplasms, particularly meningio mas and schwannomas, and conclude that the majority of proteins in cyst flu id in extra-axial, intradural meningiomas and schwannomas are plasma protei ns. This provides a strong argument for pathogenesis of extra-axial intradu ral tumour cysts in favour of leakage of plasma proteins out of the tumour vessels into the nervous tissue.