Final answer:
Metastases are the most common cause of intracranial neoplasms, where cancerous cells spread to the brain from other parts of the body, making tumors like astrocytoma, meningioma, and pituitary adenoma less common in comparison.
Step-by-step explanation:
The most common cause of an intracranial neoplasm is metastases. A neoplasm, or tumor, can grow in the brain as a result of cancerous cells spreading from another part of the body; these are referred to as secondary tumors or metastases. Other intracranial neoplasms include astrocytoma, meningioma, and pituitary adenoma. Astrocytomas originate from star-shaped brain cells called astrocytes, meningiomas arise from the meninges (the membranes that cover the brain and spinal cord), and pituitary adenomas develop in the pituitary gland. However, metastatic tumors are more common than these primary brain tumors, as they can originate from various cancers such as breast cancer, non-Hodgkin's lymphoma, and multiple myeloma, among others.