What type of malignancies are most common in intracranial cases?

The most common type of malignancy found in intracranial cases is metastatic cancer. This is largely because the brain serves as a common site for metastasis from other primary tumors found in the body, such as lung, breast, and melanoma cancers. The blood-brain barrier, while challenging for some treatments, allows circulating cancer cells from other areas of the body to enter the brain tissue. As a result, metastatic lesions are frequently identified in the brain, which contributes to their prominence in intracranial malignancies.

While glioblastoma multiforme and astrocytomas are significant as primary brain tumors, they are not as prevalent as metastatic cases overall. Pituitary adenomas are benign tumors and, although they occur in the brain, they are not classified as malignancies. Thus, the leading cause of malignancies in the intracranial setting is indeed metastasis, making this the correct identification in the context of the question.