1. Subarachnoid hemorrhage (SAH) doesn't always present as the "worst ever" headache. Don't most of our patients say their headache is the worst headache anyway? Be suspicious of the diagnosis if your patient has acute onset of an unusual or atypical headache. Diagnoses starts with the history.
2. The neuro exam may be completely normal in some cases, especially early on.
3. The headache due to SAH may get better with analgesics. This is a huge pitfall. Don't rule this diagnosis out if analgesics help.
4. The CT scan may be negative. Enough said.
5. Be careful with interpretation of the CSF. We all want the number of red cells in tube 4 to be zero. Be careful with this. Although the rbcs may have dropped by 50% from tubes 1 to 4, the diagnosis hasn't been excluded unless the cells clear completely. Although there have been some case reports of SAH with rbcs < 100, this is pretty uncommon.
6. CT Angiography and/or MRI with FLAIR is not a substitute for the lumbar puncture.
