A 57-year-old woman presents to the emergency department with new-onset seizures. She was witnessed by her husband to have a generalized seizure lasting approximately 1 minute. She has smoked 1 pack of cigarettes a day for over 40 years. In the past 3 months, she has lost 25 lb in weight. On examination, she appears thin and nervous but findings on her neurologic examination are otherwise essentially within normal limits. Plain radiographs of the chest obtained in the emergency department show a 4-cm nodule in the upper lobe of her right lung. To exclude cerebral metastasis as a cause of her seizure, what should the next test requested be?

An adult with new onset seizures is considered to have a brain tumor until proved otherwise. The best test available to detect metastatic deposits in the brain is the MRI with intravenous contrast. MRI is exquisitely sensitive in diagnosing brain metastasis, sometimes detecting them by the brain edema they induce even when the lesion itself is too small to be seen. The EEG may likely show the presence of seizure activity and even localize it to a particular region of the brain; it will not, however, answer the question of what pathologic process is responsible. Also, in this case, because a mass lesion is expected, performing a spinal tap is relatively contraindicated for the fear of inducing uncal herniation in a patient who may have increased ICP.