Likelihood of aneurysmal subarachnoid haemorrhage in patients with normal unenhanced CT, CSF xanthochromia on spectrophotometry and negative CT angiography

Background: Patients with suspected subarachnoid haemorrhage, a normal noncontrast computed tomography (CT) and cerebrospinal fluid (CSF) evidence of haemoglobin breakdown products often undergo CT angiography (CTA). If this is normal, then invasive catheter angiography may be offered. In current clinical practice, haemoglobin breakdown products are detected by spectrophotometry rather than visible xanthochromia, and CTA is performed on multidetector scanners. The aim of this study was to determine if such patients should still have a catheter angiography, given the associated risks.
Methods: Patients positive for CSF spectrophotometry (n=26) were retrospectively identified from the clinical biochemistry information system and
imaging data from the electronic radiology records were reviewed. Discharge
letters were consulted to relate the biochemistry and radiology results to the
final diagnosis.
Results: 15 patients with CT angiography were found. Nine patients had normal
CT angiography. No causative aneurysms had been missed. One patient had small, coincidental aneurysms missed on initial reading of the CTA.
Conclusion: The likelihood of a clinically significant aneurysm in a patient who is
CT negative, lumbar puncture positive and CTA negative is low. Double reporting
of negative CT angiograms may be advisable.