A case of cerebellar hamartoma suggesting abnormal cell migration

Summary A rare case of hamartoma of the left cerebellar hemisphere was recognized in an 11-monthold male infant whose mother had a history of unspecified medication in the early gestational period and had a difficult delivery. A notably large head and marked developmental disorders, like hypotonic cerebral palsy, were observed soon after birth. A computed tomogram revealed an iso-minimally enhanced large mass in the left cerebellar hemisphere, which deformed the fourth ventricle and compressed the right cerebellum, as well as moderate cerebral atrophy. Histologically, the border between the cerebellar cortex and this tumor was not apparent. The main tumor, located in the cerebellar white matter, was composed of numerous scattered Purkinje cell-like neurons and glial cells surrounded by abundant GFAP-positive matrix. The small part of the tumor, located near the choroid plexus, was composed of intensely proliferated capillaries such as in capillary hemangioma, and numerous fibrocytes, which were intermingled with several large Purkinje cell-like neurons and some GFAP-positive glial cells. The cerebellar cortex showed a thin molecular layer with some residual external granular cells, a marked decrease of Purkinje cells and a moderate decrease in the internal granular layer, in which large Purkinje cell-like neurons were scattered. Purkinje cells and large Purkinje cell-like neurons scattered in the internal granular layer, cerebellar white matter and choroid plexus showed positive immunoreactivity for anti-Leu-4 monoclonal antibody, which is known to be a marker for Purkinje cells. These findings suggest that this case had the background of abnormal cell migration caused by some kind of disorder during pregnancy.