Hematogenous spread most common. Skull metastases rarely invade CNS; may compress adjacent brain or cranial nerves or obstruct intracranial venous sinuses. Primary tumors that commonly metastasize to the nervous system are listed in Table 189-1. Brain metastases are well demarcated by MRI and enhance with gadolinium. Ring enhancement is nonspecific; differential diagnosis includes brain abscess, radiation necrosis, toxoplasmosis, granulomas, tuberculosis, sarcoidosis, demyelinating lesions, primary brain tumors, CNS lymphoma, stroke, hemorrhage, and trauma. Screen for occult cancer: examine skin and thyroid gland; blood carcinoembryonic antigen (CEA) and liver function tests; CT of chest, abdomen, and pelvis. In approximately 10% of pts, a systemic cancer may present with brain metastases; biopsy of primary tumor or accessible brain metastasis is needed to plan treatment. Treatment with glucocorticoids, anticonvulsants, RT, or surgery. Whole-brain RT is often given because multiple microscopic tumor deposits are likely throughout the brain; stereotaxic radiosurgery is of benefit in pts with three or fewer metastases demonstrated by MRI. If a single metastasis is found, it may be surgically excised followed by whole-brain RT. Systemic chemotherapy may produce dramatic responses in rare cases of a highly chemosensitive tumor type such as germ cell tumors or small-cell lung cancer harboring specific epidermal growth factor receptor (EGFR) mutations that sensitize them to EGFR inhibitors.