Waimei Tai, MD

Wallace et. al. presented an interesting case series of 57 patients who had negative imaging but positive lumbar puncture results who presented with worst headache of their life. In this series, 2 out of the 57 patients had a positive catheter angiogram suggested of ruptured aneurysm.  These two patients presented late (5 day from symptom onset) potentially explaining why they had negative CT scans (scant blood on CT may certainly become isodense by day 5). One patient had a vertebral dissection with pseudoaneurysm formation, while another had an ICA bifurcation aneurysm.

There was 1 patient in their series that positive erythrocytes (that did not clear with serial punctures) that had an angiogram with an incidental small aneurysm tht was not thought to be related to the symptom onset, not treated and stable on follow up studies.
Given the paucity of recent data on CSF analyses as a predictor for catheter angiograms in the SAH literature, this study is certainly helpful.

It would have been more helpful if they also reported any additional imaging studies made available (CT angiogram, MR and MR angiogram) which may have revealed some additional information. For example, MRI has been shown to be more sensitive for acute subarachnoid blood even in the setting of negative non-contrast CT and thus, may have been revealing in these patients if the clinical picture fit that of aneurysmal SAH.

Regardless, given the inherent dangers and negative sequelae of aneurysmal SAH (vs. other relatively more benign form of SAH such as perimesecephalic hemorrhage), it is important  for clinicians to keep a high vigilance for patients who present with clinical features suggestive of aneurysmal SAH, especially those who present in a delayed fashion, knowing the inherent pitfalls of non contrast CT imaging, and consider other imaging modalities (such as MRI brain with and without contrast) and CT angiogram, and catheter angiograms.