Evaluating thunderclap headache

Purpose of review Thunderclap headache (TCH) is an abrupt-onset of severe headache that needs to be thoroughly investigated because the most common secondary cause is subarachnoid hemorrhage (SAH). There has been no consensus guideline regarding the diagnostic workup. This review aims to provide an update on the evaluation of TCH. Recent findings The most important update in the 2019 American College of Emergency Physicians guideline for evaluation of acute headache in the emergency department is that negative noncontrast brain computed tomography (CT) findings within 6 h from ictus essentially excludes SAH. Additionally, the updated guideline recommends that after a negative brain CT, CT angiogram is a reasonable alternative to lumbar puncture if clinical suspicion of an intracranial source of SAH is high. An important update of reversible vasoconstriction syndrome (RCVS), the second most common etiology of TCH, is the RCVS2 score development based on clinical and radiological features, providing high specificity and sensitivity for distinguishing RCVS from other intracranial arteriopathies. Although the evaluation of TCH is exhaustive, the potentially catastrophic consequence of a missed diagnosis of sentinel headache justifies the efforts. Awareness of the clinical features and application of diagnostic tools specific for different pathological conditions can facilitate the diagnostic workup.