Giant arachnoid granulation: Differential diagnosis of acute headache

SUMMARYWe present a case of intense, rapidly evolving headache clinically mimicking meningitis, subarachnoid haemorrhage or venous sinus thrombosis. Clinical examination, standard blood work and central nervous system studies were non‐contributory and effectively ruled out these diagnoses. Cranial multidetector CT studies before and after application of intravenous contrast medium performed prior to lumbar tap disclosed a non‐enhancing ovoid mass filling the superior sagittal sinus. This lesion posed a differential to venous sinus thrombosis, but ultimately fulfilled the criteria of a giant arachnoid granulation. The imaging characteristics and differential diagnosis of giant arachnoid granulations are discussed.