The fine structure of the desmoplastic medulloblastoma
and of the myomedulloblastoma
J. BALOYANNIS, P. SELVIARIDIS, A. VLACHAKI, V. COSTA and S. BALOYANNIS

The desmoplastic medulloblastoma and the myelomedulloblastoma are very rare neoplasms of the central nervous system, which are almost exclusively grown in the posterior cranial fossa derived from the cells of the Obersteiner΄s layer of the cerebellar cortex. Both of the tumors retain the expanding capacity of the medulloblastoma, metastasizing sometimes in distal areas along the subarachnoid space. The therapeutic strategy consists of radical surgical excision followed by irradiation along the axis of the central nervous system.

The diagnosis of those unusual neoplasms is mostly based on histological techniques, which may apply special staining, such as Haematoxylin Van Gieson, which reveals the participation of the connective tissue as well as of the muscle fibers. Nevertheless the precise diagnosis is based on electron microscopy, which is able to visualize the typical medulloblastoma cells, which are characterized by the presence of large multilobal nuclei, and the numerous bridges between the lobes, which demonstrate the typical triple membrane arrangement. In addition the electron microscope visualize clearly the collagen fibers between the neoplasic cells in the case of the desmoplastic medulloblastoma as well as the striated or smooth muscle fibers in the case of myomeduloblastoma, which are the pathognomonic hallmarks of this type of tumors. Rarely the electron microscope may reveal muscle fibers at the stage of myotubule or a mixture of muscle fibers at various stages of maturation. The use of the electron microscopy in the study of those rare and unusual tumors is of substantial importance, since it facilitates the diagnostic procedure, proves the conclusive diagnosis and in addition throw some light on the cellular interactions, which may occur in the neoplastic tissue.

Key words: Medulloblastoma, desmoplastic meduloblastoma, myomeduloblastoma, electron microscopy.