Diagnosing Serious "Cannot Miss" Causes of Non-traumatic Headache-Thunderclap Headache and Beyond.

Headache accounts for 2% to 3% of emergency department visits annually. While the vast majority of these patients have a primary, non-serious cause, a small proportion of these patients have a "cannot miss" secondary cause that if misdiagnosed or have a delay in diagnosis, result in poor patient outcomes. The majority of serious diagnoses include subarachnoid hemorrhage, other types of intracranial hemorrhage including subdural hematoma, strokes, meningitis, and other non-neurologic etiologies. It is important for emergency physicians to identify through a careful history, physical examination, and consideration of epidemiologic factors which patients require extensive testing.