Abstract
A 32-year-old woman was admitted with acute bi-occipital headaches at our emergency room. A head CT study without contrast agent injection was performed to exclude acute cerebral hemorrhage. It revealed a focal well delimited round lacuna in the left transverse sinus, which was confirmed after contrast material injection (Fig. A, transverse and frontal views, black arrow). This anomaly measured 4 mm in diameter, presenting a low mean density of 40 HU (lesser than normal sinus density) and was linked to the sinus upper wall by a small peduncle only visible on sagittal views (Fig. B1, white arrow). MRI series were realized to confirm the diagnosis of a “giant” arachnoid granulation bulging in the left transverse sinus and to exclude a focal thrombosis. The granulation presented a typical low T1-weigthed signal with no contrast enhancement (Fig. B2, sagittal view, white arrow), high T2-weighted signal similar to CSF (Fig. C, sagittal view, white arrow), and the peduncle in connection with the subarachnoid space was clearly visible.