A CLUSTER HEADACHE MIMIC: CT-NEGATIVE SUBARACHNOID HEMORRHAGE FROM MCA ANEURYSM

CT-NEGATIVE SUBARACHNOID HEMORRHAGE FROM MCA ANEURYSM

Abstract

  Abstract Introduction: Primary cluster headache is a debilitating trigeminal autonomic cephalalgia. While diagnostic criteria are well-established, secondary structural lesions can closely mimic this phenotype, posing a significant diagnostic challenge in emergency settings. Case Presentation: A 51-year-old woman presented with sudden-onset, severe, unilateral right temporal headache clinically mimicking a primary cluster headache. Initial emergency non-contrast computed tomography (NCCT) demonstrated no acute intracranial abnormalities. Due to persistent symptoms, a subsequent brain MRI was performed. Multi-sequence MRI revealed a small saccular aneurysm arising from the M1 segment of the right middle cerebral artery (MCA). Accompanying right temporal sulcal hyperintensities on FLAIR and subtle hyperintensity on T1-weighted imaging confirmed a localized, late subacute subarachnoid hemorrhage (SAH). Discussion: This case illustrates a critical clinical pitfall driven by time-dependent radiologic attenuation, where transitional subacute blood becomes isodense on NCCT. The structural mimicry could be explained by mechanical irritation or a minor leak from the MCA aneurysm stimulating the closely adjacent ophthalmic branch (V1) of the trigeminal nerve, triggering the trigeminovascular pain pathway. Conclusion: Multi-sequence MRI is indispensable for ruling out occult, life-threatening secondary vascular pathologies when strong clinical suspicion persists despite negative initial CT findings.