In the absence of the classic signs and symptoms, SAH may be misdiagnosed. The frequency of misdiagnosis may be up to 50% in patients presenting for their first visit to a physician. The main reasons for misdiagnosis include failure to obtain the appropriate imaging study (i.e., head CT) in 73% of cases and failure to perform, or correctly interpret the results of, a lumbar puncture in 23% of cases. Patients who are misdiagnosed are usually found to be less ill and have normal neurologic examination. However, it is important to realize that neurologic complications eventually occur in up to 50% of patients with delayed diagnosis and are associated with an increased risk of death and disability. Every patient presenting with a severe and unusual headache should be evaluated for SAH. Headache may be the only presenting complaint in up to 40% of patients and may abate completely
within minutes or hours (so-called sentinel or thunderclap headaches or “warning leaks”). Emergent evaluation of sentinel headaches is required since patients may experience a major SAH within 3 weeks.