Fig. 3

Histopathological findings at the interface between the tumor and peripheral brain. a The margins of the metastatic tumor are clear, and no tumor cell invasion can be seen (case 16). b The tumor margin is quite unclear, and large clusters of the tumor cells invade deep into the peripheral brain (case 8). The depth of invasion is 3–4 mm. c Columnar cell invasion in the microvessels of the peripheral brain can be seen (case 10). The depth of intravascular tumor invasion was approximately 0.82 ± 0.07 mm. The true depth of invasion is unknown because the distal end of invasion was not included in the specimen. d The margin of the metastatic tumor is markedly unclear (case 13). Single-cell and small-cell clusters invade the peripheral brain to a depth of 1.6 mm