Massive arachnoid granulation in the transverse sinuses on CT myelogram

Giant arachnoid granulations have been previously reported in the literature, with the largest documented measuring 6 cm and usually associated with significant clinical symptoms. Herein, we present a patient with a massive, irregular-shaped arachnoid granulation occupying both transverse sinuses, a finding that has not yet been reported. The patient, who had a history of transvenous CSF-venous fistula (CVF) embolization, presented with persistent left occipital headaches. Digital subtraction myelography (DSM) to investigate a residual or recurrent CVF yielded negative results. Contrast enhanced brain MRI showed a nonenhancing lobulated lesion in the expected location of, but distinct from the transverse sinuses. The patient was later started on indomethacin, which completely resolved his headaches, consistent with the diagnosis of hemicrania continua. This indicated that the arachnoid granulation was an incidental finding despite its unusual size.