Which imaging study should be obtained prior to LP when there is concern for a mass lesion?

• A. MRI brain
• B. Head CT
• C. Chest X-ray
• D. Abdominal CT

Answer: (B)

Before performing lumbar puncture when there is concern for a mass lesion, you must rule out raised intracranial pressure or brain herniation risk. A non-contrast head CT is the imaging study of choice because it can quickly detect mass effect, midline shift, hydrocephalus, or hemorrhage that would make LP dangerous. It’s fast, widely available, and can be done at the bedside in many settings, which is crucial in acute contexts.

If the CT is negative but clinical suspicion remains high, MRI can be used for more detailed assessment, since it is more sensitive for subtle or smaller lesions, though it takes longer and is less practical emergently. Imaging of the chest or abdomen does not evaluate intracranial pathology, so it would not inform the risk of LP in this scenario.