Diagnostic Significance of Cellular Neuroglial Tissue in Ovarian Immature Teratoma

BACKGROUND Immature teratoma (IT) is a tumor containing immature neuroectodermal tissue, primarily in the form of neuroepithelial tubules. However, the diagnosis of tumors containing only cellular neuroglial tissue (CNT) without distinct neuroepithelial tubules is often difficult, since the histological characteristics of immature neuroectodermal tissues remain unclear. Here, we examined the significance of CNT and tried to define immature neuroectodermal tissues by comparing the histological features of neuroglial tissues between mature teratoma (MT) and IT. METHODS The histological features of neuroglial tissue, including the cellularity, border between the neuroglial and adjacent tissues, cellular composition, mitotic index, Ki-67 proliferation rate, presence or absence of tissue necrosis, vascularity, and endothelial hyperplasia, were compared between 91 MT and 35 IT cases. RESULTS CNTs with a cellularity grade of ≥ 2 were observed in 96% of IT cases and 4% of MT cases (p < .001); however, CNT with a cellularity grade of 3 in MT cases was confined to the histologically distinct granular layer of mature cerebellar tissue. Moreover, CNT in IT exhibited significantly higher rates of Ki-67 proliferation, mitoses, and necrosis than those in MT (p < .001). Furthermore, an infiltrative border of neuroglial tissue and glomeruloid endothelial hyperplasia were significantly more frequent in IT cases than in MT cases (p < .001). CONCLUSIONS Our results suggest that if CNT with a cellularity grade of ≥ 2 is not a component of cerebellar tissue, such cases should be diagnosed as IT containing immature neuroectodermal tissue, particularly if they exhibit an infiltrative border, mitoses, necrosis, and increased Ki-67 proliferation.