An ultrastructural study of the morphogenesis of membranocystic lesions in bone marrow.

A biopsy case of a man aged 30 years, who was admitted to the hospital for the fracture of his right talus, was reported. The X-ray analysis of his extremities revealed multifocal cystic lesions in bilateral tali, and carpal bones. Pathological examination of the cystic lesions of the bilateral tali showed the membranocystic lesion (MCL), which morphologically resembled that of "membranous lipodystrophy" reported by NASU et al. Minute tubulovesicular structure of the MCL observed in this case was proved to arise at the lipid-cytoplasmic-interface of degenerated fat cells and enter into the interstitium to form MCL, concurrently with collapse of the fat cells. Thus, at least one process responsible for the morphogenesis of MCL could be determined by our electron microscopic examination.