A Case of Sylvian Hematoma Enlarging 3 Days after Neck Clipping for the Ruptured Anterior Communicating Artery Aneurysm, in the Contralateral Sylvian Fissure to the Operative Approach

We report a case of sylvian hematoma enlarging 3 days after neck clipping for a ruptured anterior communicating artery aneurysm, in the contralateral sylvian fissure to the operative approach. This 65-year-old man was admitted with sudden loss of consciousness by ambulance. Angiography revealed a saccular aneurysm at the anterior communicating artery complex, measuring 2.3×2.4 mm and pointing inferiorly. The aneurysmal neck was successfully clipped by using the right pterional approach. To minimize predictable vasospasm, the hematoma in the left sylvian stem was removed. Postoperative CT scan showed a considerable decrease in hematoma in the basal cistern, but a slight decrease in the vertical portion of the left sylvian fissure. The patient’s consciousness gradually recovered, but deteriorated again 3 days after the operation. CT scan showed a large high-density area in the sylvian fissure suggesting unexpected enlargement of sylvian hematoma. A left fronto-temporal craniotomy was performed. When the subpial hematoma around the sylvial fissure was removed, a large amount of bloody cerebrospinal fluid (CSF) flowed out. The cavity containing bloody fluid was located in the temporal lobe. Postoperative course was uneventful. He recovered well, but moderate sensory aphasia remained. Sylvian hematoma is rarely associated with ruptured anterior communicating artery aneurysms. Furthermore, there has been no report describing delayed onset sylvian hematoma as far as we are aware. The following mechanism was considered to explain this very rare condition. Removal of subarachnoid hematoma in the left sylvian fissure made a recovery of CSF flow up to the limen insulae, but CSF appeared to be blocked from entering the distal sylvian fissure by the thick subpial sylvian hematoma. Instead of normal CSF flow route, CSF may enter into the weakened subpial space to allow accumulation of bloody CSF in the temporal lobe. Subpial hematoma may act as a one-way valve.