What is the utility of CT (Computed Tomography) angiography and lumbar puncture (LP) in a patient with sudden onset severe headache?

From the Guidelines

For a patient with sudden onset severe headache, a non-contrast head CT should be performed first, followed by lumbar puncture (LP) if the CT is negative but clinical suspicion remains high, and CT angiography (CTA) may be considered to detect aneurysms and other vascular abnormalities, as recommended by the 2023 guideline for the management of patients with aneurysmal subarachnoid hemorrhage 1.

Diagnostic Approach

The diagnostic approach for a patient with sudden onset severe headache should prioritize the detection of subarachnoid hemorrhage (SAH), a potentially life-threatening condition. The following steps are recommended:

• Non-contrast head CT should be performed first, ideally within 6-12 hours of headache onset, as it is highly sensitive (nearly 100%) for detecting SAH within this time frame 1.
• If the CT is negative but clinical suspicion remains high, LP should be performed to detect xanthochromia, which develops 12 hours after bleeding and may persist for 2 weeks 1.
• CTA may be considered to detect aneurysms and other vascular abnormalities, especially if the patient presents with a diffuse basal cistern and sylvian fissure SAH pattern 1.

Rationale

The rationale for this approach is based on the high mortality rate of SAH (25-50%) and the importance of early detection and treatment. The combination of CT followed by LP if needed has a negative predictive value approaching 100% for SAH, providing necessary reassurance in this potentially life-threatening condition 1.

Key Considerations

Key considerations in the diagnostic approach include:

• The Ottawa SAH Rule, which can identify patients with a low likelihood of SAH and avoid unnecessary imaging and workup 1.
• The importance of using high-quality CT scanners and fellowship-trained, board-certified neuroradiologists to interpret the images 1.
• The potential limitations of CTA in detecting small aneurysms or other vascular lesions, and the need for digital subtraction angiography (DSA) in certain clinical settings 1.

From the Research

Utility of CT Angiography and Lumbar Puncture in Sudden Onset Severe Headache

• The utility of CT angiography and lumbar puncture (LP) in patients with sudden onset severe headache is crucial for diagnosing subarachnoid hemorrhage (SAH) 2, 3.
• A noncontrast computed tomography (CT) brain scan is the initial investigation of choice, and if negative, it is often followed by a lumbar puncture (LP) and cerebrospinal fluid (CSF) analysis to rule out SAH 2.
• The sensitivity of LP in the context of a negative CT and subsequent imaging confirming the cause of SAH was quantified in a meta-analysis, which found a combined pooled proportion of 0.383 for LP+ investigations 3.
• A retrospective observational study found that a CT scan taken within 6 hours of onset of sudden headache is sufficient for confirming or ruling out subarachnoid bleeding in patients with sudden headache who have no neurologic deficits 4.
• However, there are cases where CT angiography head may be negative, but LP can still diagnose SAH, highlighting the importance of understanding the current limitations of CT imaging and the risks and benefits of both CT and LP 5, 6.

Diagnostic Accuracy of CT Angiography and Lumbar Puncture

• The negative predictive value of a noncontrast CT of the brain is 99.8%, reducing the post-test probability of having an angiogram-positive SAH detected by LP and CSF analysis to 0.21% 2.
• The pooled data from a meta-analysis found a combined pooled proportion of 0.086 for DSA+ investigations and 0.22 for DSA/computed tomography angiography+ investigations 3.
• A case report highlighted the importance of LP in diagnosing SAH, particularly in the setting of significant anemia, despite the high sensitivity of non-contrast head CT 6.

Clinical Implications

• The management of neurologically pristine patients with sudden onset severe headache on a Clinical Decision Unit (CDU) pathway is feasible, but the decision to follow a negative CT with an LP in all cases needs careful consideration 2.
• The current clinical workflow of an LP after a negative CT head for a patient presenting with a sudden-onset severe headache is observed to have a high enough proportion to warrant its continued use despite the sensitivity of modern CT scanners of ≥97% 3.
• LP still has a role in diagnosing SAH, particularly in the setting of significant anemia, despite the high sensitivity of non-contrast head CT 6.