Microvascular Proliferation of Brain Metastases Mimics Glioblastomas in Squash Cytology

ObjectiveAlthough microvascular proliferation is a key feature in the diagnosis of high‐grade glioma, the characteristics of metastatic tumour vessels in smear preparations have not been documented. In this study, the vascular changes in metastatic brain tumours, using squash cytology to examine the vascular patterns in brain metastases, were reviewed.MethodsOne hundred and forty‐three squash smears of brain tissue, including 25 normal or reactive tissue, 23 malignant lymphomas, 8 grade I glioma (pilocytic astrocytoma), 23 grade II glioma (diffuse astrocytoma and oligodendroglioma), 42 grade IV glioma (glioblastoma), and 22 metastasis, were assessed. Two vascular patterns were assessed: thick and branching, and glomeruloid. The vessel density, nuclear layer and the number of vessel branches were compared. Furthermore, tumour vessels of brain metastases were analysed by histology and for immunohistochemical expression of CD34, α‐smooth muscle actin (SMA) and high‐molecular‐weight caldesmon (h‐CD).ResultsAmong 22 metastatic tumours, thick and branching vessels were found in 17 (77%) and glomeruloid vessels in 13 (59%). These incidences of microvascular proliferation patterns were similar to those of glioblastomas or pilocytic astrocytomas. Vessel density, nuclear layer and vessel wall branches were significantly higher in metastatic tumours than malignant lymphomas, grade II gliomas or normal brain tissues. Glomeruloid vessels consisted of CD34‐positive cells and α‐SMA‐positive cells, and α‐SMA‐positive cells had a low h‐CD expression. These immunohistochemical patterns were similar to those of high‐grade gliomas.ConclusionsThe vascular features of metastatic brain tumours are similar to those of glioblastomas, suggesting that these microvascular proliferations contribute to the progression of metastatic tumours.