Clinical Pathways
Clinical Pathways
Perform LP
Perform LP

Perform LP

View The Full Pathway

Decision

What are the results?

Normal CSF

(Class II)

  • Consider workup for alternative diagnosis
  • Provide analgesia and reassurance
  • Discharge with outpatient follow-up

Xanthochromia Present

Other

  • Traumatic tap
  • Unable to obtain CSF sample
  • Persistence of RBCs in all tubes

Background

Lumbar Puncture

The most significant change to the 2019 ACEP Clinical Policy in the evaluation of adult patients with acute headache is the recommendation on whether an LP is needed. If findings on noncontrast head CT are positive for sSAH, then an LP is not needed. In patients with suspected sSAH with a negative noncontrast CT, the ACEP guidelines support omitting the LP in some patients as described below, although this is not supported in the 2012 AHA/ASA guidelines.

The best evidence supporting the value of LP comes from studies that included older generation CT scanners or more-delayed presentations. A prospective study of 592 neurologically intact ED patients with acute headache attempted to determine if the combination of negative CT and negative LP was sufficient to rule out SAH. Of the 61 patients with SAH, 6 cases (10%) were diagnosed on the basis of positive CSF results after a normal cranial CT scan. Another prospective study of 107 adult ED patients found a diagnosis of sSAH in 18 patients, 2 of which were missed by CT (2% miss rate, 95% confidence interval [CI] up to 8.8%). Furthermore, a 1994 prospective study of 27 patients with acute headache found SAH in 9 patients, 5 cases of which were missed by CT. Additional retrospective studies, each with >100 SAH patients, found 2% to 7% of cases were missed by CT but seen on LP and confirmed by angiography. In an in-depth evidence-based analysis of these studies, a neurologically normal patient with a negative head CT could still have as much as a 7% chance of SAH. The studies presented used third-generation CT scanner technology with mean presentation times up to 60 hours from symptom onset.

The current body of literature suggests that there may be a role for a CT-only approach in patients who present within 6 hours of headache onset. Although previously reported sensitivities of early-generation CT scans were inadequate to rule out sSAH effectively, newer-generation CTs have shown more reliable results. A large meta-analysis by Dubosh et al of 8907 patients found the overall sensitivity of CT to diagnose sSAH within 6 hours to be 98.7% with a specificity of 99.9% if the CT scanner was a third generation or higher, the interpreting physician was an attending radiologist, patients had a headache of known time of onset, a normal neurologic examination, and a normal hematocrit level.

Given the life-threatening nature of SAH and the fact that CT is not 100% sensitive for SAH, for patients in whom sSAH is suspected despite a normal CT, an LP is recommended to increase the sensitivity of the diagnostic algorithm. In addition, LP may diagnose or suggest other conditions that cannot be detected by CT, such as benign intracranial hypertension, cerebral venous sinus thrombosis, spontaneous intracranial hypotension, and meningitis.

Primary Computed Tomographic Angiography

Direct imaging of the cerebral vessels in conjunction with a neurosurgical consultation can confirm the presence of an aneurysm. CTA has the diagnostic advantage of being noninvasive and is readily available in most EDs. El Khaldi et al prospectively enrolled patients with a head CT that was positive for sSAH and performed a CTA, followed by digital subtraction angiography (DSA) if the CTA was negative for aneurysm. In this study, the CTA was able to identify 133 out of 134 aneurysms, a sensitivity of 99.7%. A meta-analysis by Menke et al evaluated 3643 patients with SAH and found CTA had a sensitivity of 97.2% in diagnosing cerebral aneurysms when compared with DSA. Additionally, a methodological review supported a CTA approach in neurologically intact patients presenting within 48 hours of symptom onset.

CTA sensitivity decreases for aneurysms <4 mm in size  and carries the risk of contrast-induced nephropathy, especially if DSA is performed after CTA. In addition, the CTA may discover incidental aneurysms that may confound identification of the cause of the headache. The 2012 AHA/ASA guidelines recommended CTA as part of the workup for aneurysm but not as the primary diagnostic tool. In a patient diagnosed with sSAH, a nondiagnostic CTA should be followed up with a DSA (except possibly in the case of perimesencephalic hemorrhage).

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References

Evidence-based medicine requires a critical appraisal of the literature based upon study methodology and number of subjects. Not all references are equally robust. The findings of a large, prospective, random-ized, and blinded trial should carry more weight than a case report.

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