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Every year, about 30,000 people in the U.S. develop a subarachnoid hemorrhage, a bleeding on the surface of the brain often caused by a ruptured aneurysm, or weak spot in a blood vessel.

The main symptom of a subarachnoid hemorrhage is a vicious headache, which also happens to be one of the most common symptoms of any kind reported to emergency room doctors. In one of the largest studies of its kind, Dr. Stephan A. Mayer and colleagues reported in a recent issue of the Journal of the American Medical Association, that all too often, patients who have a subarachnoid hemorrhage are sent home with a diagnosis of a migraine, tension headache, or other less-serious condition.

Immediate aneurysm repair is particularly crucial because rebleeding occurs in 26% to 73% of patients within days or weeks after the initial rupture if the aneurysm is left untreated, said Dr. Mayer, Associate Professor of Clinical Neurology and Neurosurgery in the Division of Stroke and Critical Care Neurology at Columbia University College of Physicians and Surgeons and Director of the Neurological Intensive Care Unit at NewYork-Presbyterian/Columbia. A patient can rapidly deteriorate if treatment isn't initiated immediately.

Dr. Mayer and his team looked at 482 subarachnoid hemorrhage patients admitted to the Neurological Intensive Care Unit at NewYork-Presbyterian/Columbia between 1996 and 2001. The hospital is a tertiary care center that receives patients diagnosed elsewhere.

Dr. Mayer found that 12% of all patients initially had a diagnosis other than subarachnoid hemorrhage, and that this occurred more often in some types of patients than others.

For example, the risk of having a diagnosis other than subarachnoid hemorrhage was nearly 11 times higher in those with a normal mental status at their first exam, five times higher for those with a smaller amount of bleeding and three times higher for those with an aneurysm on the right side of the brain.

Patients with brain hemorrhage can have sudden thunderclap headaches, loss of consciousness, vomiting, neck or back pain, signs of bleeding in the retina of the eye, and recent headaches that have lasted for days at a time.

Patients who were less fluent in English, unmarried or who had less than 12 years of education were more likely to have had a delay in the diagnosis of subarachnoid hemorrhage. Patients who told their doctor they had had headaches in the past were also more likely to have such a delay.

Doctors may assume incorrectly that recent headaches are a sign of more benign conditions such as migraine or tension headaches, said Dr. Mayer. The most common initial diagnosis in 36% of all delayed-diagnosis cases was migraine.

The new study found it took a median of four days before a patient with a diagnosis of migraine or other condition was correctly diagnosed with brain hemorrhage. And 39% of such patients developed neurological complications before they were diagnosed, including 12% who experienced rebleeding.

While a 12% rate of delayed diagnosis is high, other studies have found up to 51% of patients can have a diagnosis of headache or other condition before their subarachnoid hemorrhage is recognized, said Dr. Mayer.

Overall, the patients who initially had an alternate diagnosis fared just as well as those diagnosed immediately. However, this is misleading, because patients with less severe symptoms should fare much better than those who do poorly from the beginning.

While past studies have suggested a delayed diagnosis can occur when subtle results on lab tests or CT scans are missed, we found that CT scans weren't performed often enough , said Dr. Mayer. Performing more CT scans, particularly on those with symptoms suggestive of a subarachnoid hemorrhage,could help prevent delayed diagnosis.

Co-authors of the study include Robert Kowalski, M.S. (lead author), Jan Claassen, M.D., Kurt Kreiter, M.D., Joseph Bates, M.A., Noeleen Ostapkovich, M.S., and E. Sander Connolly, M.D.

The study was funded by a grant from the American Heart Association.