経錐体骨到達法を行う上で注意すべき静脈路—術後の静脈環流障害を予防するために

Venous System Playing a Key Role in Transpetrosal Approach

I．はじめに

　頭蓋底手術法のひとつである経錐体骨到達法transpetrosal approach（以下TPA）を用いることにより，斜台部や脳幹腹側の病変に対する手術が比較的安全に行えるようになっだ^{3,6,15,18,19）}．一般に頭蓋底手術にともない血管性合併症は5-18％に発生する^2,16,24）．しかし血管性合併症の原因は，ほとんど動脈性であると考えられ，静脈性合併症は注目されることが少なかった^{2,3,16,18,24）}．TPAについても，静脈性合併症を来たしにくいことが特徴とされ^{3,6,15,19,23）}，合併症予防の観点から，静脈について検討した報告は稀である^4,7,20）．digital subtraction angiography（DSA）装置のなかった頃，われわれはTPAにより静脈性梗塞を来たした1例を経験し，TPAによる静脈環流障害の重要性に気づいた．静脈性合併症を予防するため，現在われわれはTPAによる手術を予定している症例には，術前にDSAを用いた静脈路の検討を行っている．TPAでは，上錐体静脈洞横断・中頭蓋底硬膜やテントの切開・S状静脈洞圧排などが行われることから，上錐体静脈洞・横静脈洞・S状静脈洞（以下STS）合流部付近の静脈路が重要と考えられる．今回はTPAによる静脈性梗塞の1例を報告し，15例のDSAによる脳血管写を用いて，TPAを行う上で注意すべきSTS合流部付近の静脈路の特徴について検討した．

A case with a large vertebrobasilar junction aneurysm developed a venous infarction in the temporallobe after an operation using the transpetrosal approach. Although little of the literature has been con-cerned with venous complications after the transpetrosal approach, the case prompted us to study thevenous system as playing a key role in the transpetrosal approach.

Analyzing 30 carotid and 15 vertebral angiograms of 15 patients who underwent preoperative cerebralangiography using digital subtraction angiography (DSA), we investigated the venous system near thejunction of the superior petrosal sinus, the transverse sinus and the sigmoid sinus (STS junction) whichmay play a key role in the transpetrosal approach.

Drainage pathways of the superficial middle cerebral vein (SMCV) were classified into four types; sphe-noparietal, sphenobasal, sphenopetrosal and undeveloped. In the sphenopetrosal type (4/30 : 13%), thedrainage of SMCV passes back along the floor of the middle fossa to drain into the transverse sinus. Thelateral temporal vein (LTV) and the temporobasal vein (TBV) drain into the transverse sinus. The LTVemptied into the transverse sinus either directly (20/30: 67%) or indirectly through the tentorial sinus(10/30: 33%). The entry of the LTV into the transverse sinus (venous point) was usually located in thelateral third of the transverse sinus (14/20: 70%), but sometimes in the middle third (6/20: 30%). TheTBV, observed in 8/30 (27%), also often emptied into the tentorial sinus to drain into the transverse sinus.Atresia of a unilateral transverse sinus and a large LTV emptying into the distal sigmoid sinus wasobserved in 2/15 cases.

The venous system near the STS junction may be interrupted by the incision of the tentorium and themiddle fossa dura mater and by the retraction of the sigmoid sinus. Since the transpetrosal approach may cause venous complication by compromising the venous systemnear the STS junction, it is necessary to evaluate of the venous system preoperatively using DSA and toset up a surgical strategy preserving the venous system.