**Core Concept**
The question is testing the knowledge of the most common intracranial tumor in adults, which requires an understanding of the epidemiology of brain tumors. In adults, the majority of intracranial tumors are secondary (metastatic) lesions, rather than primary brain tumors.

**Why the Correct Answer is Right**
Metastatic brain tumors are the most common intracranial tumors in adults, accounting for approximately 50-70% of all primary brain tumors. This is due to the high incidence of systemic cancers, such as breast, lung, and melanoma, which can metastasize to the brain. The most common sources of brain metastases are breast cancer (20-30%), lung cancer (20-30%), and melanoma (5-10%). The blood-brain barrier is disrupted in metastatic lesions, allowing cancer cells to infiltrate the brain tissue.

**Why Each Wrong Option is Incorrect**
* **Option A:** Astrocytoma is a type of primary brain tumor, specifically a glioma, which is more common in children and young adults.
* **Option C:** Meningioma is another type of primary brain tumor, which is more common in women and typically arises from the meninges, the protective membranes surrounding the brain and spinal cord.
* **Option D:** Oligodendroglioma is a rare type of primary brain tumor, which is often associated with a good prognosis and is usually found in the cerebral hemispheres.

**Clinical Pearl / High-Yield Fact**
The location and presentation of brain metastases can be variable, but they often present with symptoms such as headache, seizures, and focal neurological deficits. A high index of suspicion is required for early diagnosis, and imaging studies such as MRI or CT scans are essential for confirming the diagnosis.

✓ Correct Answer: B. Metastases