Summary

Patients with signs of elevated intracranial pressure (ICP) or other risk factors for brain herniation require a head CT before performing a lumbar puncture.

At-a-glance

Risk Factor	Description
Age > 60	Increased risk of intracranial lesions 14
Immunocompromised	Higher risk for CNS infections or mass lesions 14
History of CNS Disease	Prior stroke, mass, or other CNS pathology increases risk 1
Recent Seizure (<1 week)	Can be an indicator of increased ICP or mass effect 14
Altered Mental Status/Decreased Level of Consciousness	Inability to answer two consecutive questions or follow commands reliably 1
Focal Neurological Deficits	Lateralizing signs suggesting a mass lesion or other structural abnormality 4
Papilledema and Other Signs of Elevated ICP	Direct evidence of raised intracranial pressure that contraindicates immediate LP 4

Explanation

A head CT prior to LP is indicated when there is any concern for increased ICP or risk factors for brain herniation. According to WikEM, LP without CT is generally safe if the patient is under 60, immunocompetent, has no history of CNS disease, no recent seizures, and has a normal neurological exam ¹. Conversely, patients who fail these criteria—such as those older than 60, immunocompromised, with a history of CNS pathology, recent seizures, altered mental status, or focal deficits—should have a head CT prior to LP. Additionally, the “TAP AS IF” mnemonic (Trauma, Age >60, Papilledema, Altered mental status, Seizure, Immunocompromised, Focal deficits) from ALiEM reinforces this approach ⁴.

This approach minimizes the risk of causing a catastrophic herniation in patients with intracranial mass effect or other structural abnormalities.