For us, neurosurgeons working mostly in tertiary referral centers, it seems obvious that sudden headache accompanied with nausea and sensory disturbances is a subarachnoid hemorrhage (SAH) or other hemorrhagic stroke until proven otherwise. However, even in countries like Finland, with a rather high incidence of SAH and well-equipped and well-funded public emergency medicine, we frequently encounter patients with delayed diagnosis of aneurysm rupture. Although diagnosis in our case was attained with MRI (because of private oupatient clinic setting), a conventional CT scan readily available in any hospital ER would have been brilliantly sufficient, had it crossed the mind of the unfortunate ER physician that this patient really DID have the diagnosis that first comes to mind. But what are the reasons for, and how frequent is, this kind of potentially fatal – and to us, incomprehensible – misjudgement?
Probably the most important reason – and the one perhaps difficult to appreciate from the vantage point of a referral center neurosurgeon – is that SAH is actually not a very common cause of severe headache. Perry et al. (1) have reported that in a Canadian cohort of almost 2000 patients admitted to a hospital ER for a sudden, severe headache, only 6.5% actually had SAH. Althought the cohort only included fully alert, neurologically intact patients, it is noteworthy that 79% of the cohort described their headache as “the worst they’ve ever had”. Even lower figures were seen in a recent UK study (2), where only 2.7% of ER patients with sudden, severe headache had SAH. The authors of this study also questioned the rationale for lumbar puncture to rule out SAH after normal CT scan in headache patients, since the negative predictive value of CT in this population was 99.8%.
So how common in the misdiagnosis in SAH patients? Kowalski et al reported on a US cohort of SAH patients (3), showing that 12% of the patients were initially misdiagnosed by a health care professional. Failure to perform a CT was the most common mistake in 73% of the cases. Of those misdiagnosed, 21% experienced rebleeding before adequate treatment, and this was associated with increased risk of death and severe disability after a long term follow-up. Initial health care professional-related misdiagnosis of 13% was also observed in a Japanese cohort (4), resulting in rebleeding in 26% of the patients with delayed diagnosis.
Although missed SAH diagnoses should definitely be avoided to decrease unnecessary morbidity and mortality from preventable rebleedings, the above-mentioned observations also have interesting connotations for epidemiological studies. Although high, the rebleeding risk of a ruptured aneurysm is clearly less than 100%. If up to 10-15% of SAH patients EVENTUALLY diagnosed are initially misdiagnosed, even in developed countries with adequate health care services, how many mild SAH patients who never experience a rebleeding will go unnoticed? If there are geographic differences in susceptibility to misdiagnose mild SAH, could these explain part of the observed variability of incidence of SAH?