subarachnoid hemorrhage and CT within 6 hours

9 Aug

BMJ article (by Perry J, et al.–link below) looked at specificity/sensitivity, NPV, PPV of CT scan to dx SAH w/o an LP in non-focal and stable patients within 6 hrs.

3132 patients, 240 had SAH.

of 953 patients (121 with SAH) scanned within 6hrs of symptom onset, found a 100% sensitivity, specificity, NPV, and PPV if done w/in 6 hrs.

important to note the inclusion and exclusion criteria used (quoted from the article):

enrolled consecutive alert patients aged over 15 who presented with non-traumatic acute headache or with syncope associated with headache and underwent emergency head computed tomography as part of their diagnostic investigation.

  • defined “alert” as a Glasgow coma score of 15 (scale ranges from 3 to15, with 15 being normal),
  • “non-traumatic” as no falls or direct trauma to the head in the previous seven days,
  • “acute” as headache reaching maximum intensity in less than one hour after onset.


  • patients with onset of headache more than 14 days previously;
  • recurrent headaches (three or more headaches of similar character and intensity as presenting headache);
  • transfer from another hospital with confirmed subarachnoid haemorrhage;
  • focal neurological deficits;
  • papilloedema;
  • history of subarachnoid haemorrhage, aneurysm, ventricular shunt, or brain neoplasm.

Computed tomography was ordered at the discretion of the treating physician, who was aware of the clinical decision rule study but was advised not to alter usual care because of the study.


CT is pretty darn good (100% sensitivity/specificity/PPV/NPV) within 6hours of symptom onset for SAH (it seems reasonable to not perform an LP on patients if they meet the inclusion criteria).

Of note, anecdotally, some are reluctant to do this because they feel they have diagnosed many cases of viral meningitis with an LP.

Submitted by J. Rothstein.

Reference(s): the Perry article; picture


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