Occipital sinusに直接流入する後頭蓋窩静脈を伴った退形成性上衣腫の1手術例

A Surgical Case of Anaplastic Ependymoma Involving a Bridging Vein that Drained Directly into the Occipital Sinus

Ⅰ．はじめに

　後頭蓋窩の静脈解剖を理解しておくことは実際に手術を行う上で重要となるが，このバリエーションは複雑であり，記された文献も未だ少ない．Huangら^3-5)は，後頭蓋窩の静脈還流を①superior or galenic draining group，②anterior or petrosal draining group，③posterior or tentorial draining groupの3つのグループに分類している．①は小脳半球上面や虫部上部，中脳を還流し，主にGalen大静脈に流入する静脈群であり，②は脳幹部（橋，延髄）や小脳半球前面または外側部を還流し，③は小脳虫部下部，小脳半球の後下面を上行し，confluence of sinuses，straight sinus，transverse sinusなどに流入することが知られている．第四脳室周囲の静脈群はanterior or petrosal draining groupに分類され，バリエーションは多様であり，上方ではpetrosal veinに流入し，下方ではsigmoid sinusに流入するものが多いが，marginal sinusに流入する場合もある．

　今回われわれは，延髄背側，第四脳室からの静脈が架橋静脈を介して直接occipital sinus（OS）に流入した1例を経験したので報告する．

　INTRODUCTION:The draining veins of the brain stem and cerebellum commonly drain into the petrosal vein and sigmoid sinus, and often drain into the marginal sinus in the caudal part of the posterior fossa. Here, we report a rare case of anaplastic ependymoma involving a bridging vein that drained directly into the occipital sinus.

　CASE DESCRIPTION:A 6-year-old boy was admitted to our hospital with a 1-month history of nausea, headache, and dizziness. Magnetic resonance imaging（MRI）revealed a markedly enhanced fourth ventricular tumor and obstructive hydrocephalus. Surgical removal was performed via a midline suboccipital approach. When opening the dura, we observed a bridging vein that directly connected the brain stem and the tumor with the occipital sinus. Therefore, the Y-shaped dura mater incision was not inverted, and the tumor was totally removed while preserving the draining vein. After the operation, the patient's clinical course was uneventful. The pathological diagnosis was anaplastic ependymoma（WHO grade Ⅲ). Subsequently, the patient received radiotherapy and was discharged without any neurological deficits 9 weeks after the operation. At 10 months after the initial surgery, the tumor recurred on the fourth ventricle floor. Thus, we performed a second surgical procedure and noted that the bridging vein had regressed.

　CONCLUSION:We report a rare draining vein that directly connected the brain stem to the occipital sinus. The tumor was removed without sacrificing this vein. Since the draining system of the posterior fossa is sometimes very complicated, we need to pay attention to it during the pre- and intra-operative periods.