So-called membranocystic lesion (MCL)--a new variant of ceroid type lipopigment.

Structures very close morphologically to the so-called membranocystic formations of the Nasu-Hakola's disease and identical in histochemical properties with them were found in several other metabolically unrelated conditions such as cerebrotendinous xanthomatosis (perivascularly in the brain) and in human atheromatous plaques. This with some other literary data points to unspecific nature of the membranocystic lesion (MCL) which also has been resisting satisfactory classification in terms of pathobiochemistry. Evidence is presented suggesting the MCL is lipopigment in nature. This is based on its lipid histochemical properties dominated by prominent autofluorescence and marked sudanophilia resistant to lipid extraction procedures. Ultrastructural pattern of the MCL was membranous, being dominated by mostly individual trilaminar membranes about 15 nm thick which could be also occasionally identified in various intralysosomal ceroid type lipopigments. It is supposed that the MCL lipopigment is formed mainly extracellularly from the lipid rich debris.