From the Guidelines
A head CT scan should be performed before a lumbar puncture in patients with suspected increased intracranial pressure or specific risk factors, as indicated by clinical signs such as altered mental status, focal neurological deficits, or papilledema, as suggested by the most recent and highest quality study 1.
Indications for Head CT Scan Before Lumbar Puncture
The main indications for a head CT scan before a lumbar puncture include:
- Altered mental status or reduced level of consciousness, particularly a Glasgow Coma Score (GCS) of 12 or less 1
- Focal neurological deficits
- New onset seizures
- Papilledema on fundoscopic examination
- History of central nervous system disease
- Recent head trauma
Rationale
Getting a CT scan in these cases is crucial to rule out intracranial mass lesions or severe brain swelling, which can increase the risk of brain herniation when cerebrospinal fluid pressure is reduced during a lumbar puncture 1. By identifying such risks beforehand, physicians can prevent potentially life-threatening complications and ensure the safety of the procedure. However, it is essential to note that performing a CT scan before a lumbar puncture can lead to delays in antibiotic treatment, which may increase mortality 1. Therefore, a CT scan should only be performed if there are clinical signs suggestive of a shift of brain compartments.
Clinical Assessment
Clinical assessment rather than CT scanning should be used to determine the safety of performing a lumbar puncture 1. The decision to perform a CT scan before a lumbar puncture should be based on the patient's clinical presentation and risk factors, rather than routine imaging for all patients with suspected meningitis or encephalitis.
From the Research
Indications for Head Computed Tomography (CT) Scan Before Lumbar Puncture (LP)
- A head CT scan is indicated before performing a lumbar puncture (LP) in certain situations, including:
- Suspected subarachnoid hemorrhage, especially if the headache occurred more than 6 hours prior to patient presentation 2
- Adults with suspected meningitis who have certain clinical features, such as an age of at least 60 years, immunocompromise, a history of central nervous system disease, and a history of seizure within one week before presentation, as well as neurologic abnormalities 3
- Patients with suspected bacterial meningitis who are at risk for intracranial mass effect lesions, based on decision rules or clinical gestalt 4
- The decision to perform a head CT scan before LP should be based on individual patient risk factors and clinical presentation, rather than routine practice 5, 4, 6
- Clinical features that can be used to identify patients who are unlikely to have abnormal findings on CT of the head include a normal level of consciousness, no history of central nervous system disease, and no neurologic abnormalities 3
- The use of decision rules to selectively perform CT on only those individuals most likely to have intracranial mass effect lesions has not undergone validation, and physicians should exercise caution when interpreting these rules 4
Clinical Features and CT Scan Results
- The presence of certain clinical features, such as an abnormal level of consciousness, gaze palsy, and facial palsy, can increase the likelihood of abnormal findings on CT of the head 3
- A normal CT scan does not completely rule out the possibility of subarachnoid hemorrhage or other intracranial abnormalities, and clinical judgment should be used to determine the need for further evaluation 2, 3
- The negative predictive value of a normal CT scan can be high, especially in patients with no clinical signs or symptoms of intracranial abnormalities 5
Timing and Antibiotic Therapy
- In patients with suspected bacterial meningitis, antibiotic therapy should be initiated promptly, and the decision to perform a head CT scan should not delay antibiotic administration 4
- The timing of LP and CT scan should be individualized based on patient risk factors and clinical presentation, and the potential benefits and risks of each procedure should be carefully considered 6