Reasons for failing to make the diagnosis:
(1) misinterpretation of clinical findings
(2) misinterpretation of imaging findings
(3) mistinterpretation of CSF findings
Misinterpretations of clinical findings:
(1) failing to perform a lumbar puncture or to do so incorrectly (failing to measure opening pressure)
(2) failing to adequately evaluate someone with an unusual headache
(3) not realizing that the headache of SAH may clear spontaneously or with analgesics
(4) misdiagnosis as another condition (viral infection, sinus headache, migraine, tension headache, etc)
(5) inexperienced clinician not aware of how an unruptured aneurysm or a small bleed can present
Misinterpretation of imaging findings:
(1) not realizing that a small bleed may not be detected on a CT scan
(2) not realizing that moderate to severe anemia may reduce the sensitivity of the CT scan
(3) not realizing that a significant time interval between the onset of the headache and the performance of the CT scan may miss the bleed
(4) artifacts in the CT scan
(5) inexperienced reader
Misinterpretation of CSF findings:
(1) misdiagnosis as a traumatic tap
(2) failure to detect subtle xanthochromia (measurement in a spectrophotometer is the most sensitive method of detecting)
(3) exclusion of diagnosis on the basis of absent xanthochromia AND timing of tap when xanthochromia may be absent (< 12 hours or > 2 weeks)
