Morphogenesis of Michaelis-Gutmann bodies in cerebral malacoplakia. An ultrastructural study.

Malacoplakia was found in the brain biopsy specimen from the wall of a cystic lesion in a 4-month-old girl. Ultrastructural study of the Michaelis-Gutmann bodies revealed that the initial stage of calcification appeared to be the deposit of needle-shaped apatite crystals within intracytoplasmic membrane-bound vesicles of histiocytes. Accumulation of apatite crystals and coalescense of calcified vesicles resulted in the formation of large laminated calcospherules. Extracellular Michaelis-Gutmann bodies and apatite crystal-containing matrix vesicles were also noted. Calcified vesicles and the Michaelis-Gutmann bodies were not observed in the phagolysosomes. Bacteria and viral particles were not identified. These findings suggest that matrix and intracytoplasmic membrane-bound vesicles play an important role in the initial stage of the formation of Michaelis-Gutmann bodies and that a mechanism other than bacterial or viral infection may be involved in cerebral malacoplakia.