A novel concept of glomeruloid body formation in experimental cerebral metastases.

Glomeruloid bodies (GBs), tumor-associated vascular structures with a superficial resemblance to renal glomeruli, are important histopathological features of glioblastoma multiforme, but have also been described in other types of tumors and in cerebral metastases. The purpose of this study was to elucidate the pathogenesis of these lesions in an appropriate murine model of experimental brain metastases. To do so, we injected cells from 5 different tumor lines into the internal carotid artery of mice and investigated the development, composition, and fate of GBs growing within tumor nodules. Immunohistochemical analyses and 3-dimensional reconstruction of the cerebral vasculature showed clearly that the proliferating and migrating tumor cells pull the capillaries (and the adjacent capillary branching points) into the tumor cell nest. Initially, this process lead to the appearance of simple coiled vascular structures, which later developed into chaotic and tortuous vascular aggregates with multiple narrowed afferent and efferent microvessels. Despite the absence of sprouting angiogenesis, the very low level of endothelial cell proliferation index and the ruptures of the stretched and narrowed capillary segments observed frequently between the metastatic tumor nodules, necrosis was scarce in these lesions, implying that the blood supply from the multiple afferent microvessels and from the preexistent vascular bed sufficed to provide the tumor cells with oxygen and nutrients.