通过外耳道顶切除颞下内肿瘤.pdf

J Neurosurg 74 520 522 1991 Removal of the roof of the external auditory meatus in approaching the tentorial notch through a low temporal craniotomy Technical note MARC P SINt OU M D D Sc BIoL AND JEAN Luc FOBi M D Department of Neurological Surgery HOp a Neurologique University of Lyon Lyon France u Improved access to the tentorial notch can be obtained by removal of the roof of the external auditory meatus in association with a low temporal craniotomy This approach decreases temporal lobe retraction and the risk of venous infarction This method was perfected in the surgical laboratory on five cadavers and was successfully performed in a patient with a giant aneurysm of the posterior cerebral artery KEY WORDS subtemporal approach 9 tentorial notch 9 external auditory meatus 9 aneurysm giant 9 posterior cerebral artery T HE classical approach to the tentorial notch and to the peduncular region including the posterior cerebral artery PCA and its P2 and P3 seg ments is by the subtemporal route The absence of a cistern in the subtemporal region often leads to signifi cant temporal lobe retraction which may result in the sacrifice of the vein of Labb6 and other bridging veins to the transverse and tentorial sinuses To decrease temporal lobe retraction and the risks of edema and venous infarction an approach to the tentorial notch has been developed which involves removal of the roof of the external auditory meatus in association with a low temporal craniotomy We have perfected this com bined approach in the surgical laboratory bilaterally on five cadavers Table l and have performed it in a patient with a giant aneurysm of the PCA at the P2 P3 junction Operative Technique The patient is placed in the lateral position with the head in a three pin headholder and tilted 15 down A vertical anterior skin incision is made just anterior to the tragus to avoid damaging the frontal branch of the facial nerve a posterior incision is carried down to the mastoid process The scalp flap and the helix of the ear are reflected inferiorly until the soft external auditory meatus is reached this structure is gently detached from its bone roof The temporal muscle is incised in a cruciform fashion and reflected inferiorly A low tem poral 4 0 3 0 cm craniotomy is performed just above the external auditory meatus The dura mater of the temporal fossa is detached from the skull base as well as the soft external auditory meatus The roof of the external auditory meatus is removed at a second stage with a sagittal vibrating saw Fig 1A and its temporal and zygomatic edges are drilled off to provide more room The mastoid cells if opened must be carefully occluded with bone wax The dura is opened and re flected inferiorly Under the surgical microscope the temporal lobe is gently retracted with two narrow Sugita retractors Special care is taken not to tear the vein of Labb6 and the other bridging veins to the transverse and tentorial sinuses The pyramidal space with an external base gained by removal of the roof of the external auditory meatus provides additional room for better vision and manipulation of the microsurgical instruments Fig 1B After the surgical procedure has been completed in our clinical case after clipping a giant P2 P3 aneurysm Fig 2 the dura is closed with continuous stitches Thereafter the roof of the external meatus and the temporal bone flap are fixed with wires The skin is then closed and a pledget is packed within the external auditory meatus to avoid the risk of cica tricial stenosis 520 J Neurosurg Volume 74 March 1991 Low craniotomy to the tentorial notch FIG 1 Operative drawings A The patient lies in the lateral position with the head tilted 15 down The skin flap and the helix of the ear are reflected inferiorly and a low temporal craniotomy is performed The roof of the external auditory meatus on the fight side is then removed with a sagittal vibrating saw directed toward the soft external auditory meatus which is protected as well as the dura mater B Coronal section comparing the surgical field using the subtemporal approach and temporal craniotomy alone 17 4 with that obtained by removal of the roof of the external auditory meatus 27 9 FIG 2 A Preoperative computerized tomography scan with contrast enhancement demonstrating an aneurysm of the right posterior cerebral artery PCA occupying the lateral part of the quadrigeminal cistern B Preoperative vertebro basilar angiogram lateral view showing the aneurysm arising from the right PCA at the P2 P3 junction C Postoperative vertebrobasilar angiogram lateral view showing the neck of the aneurysm successfully occluded with two clips Discussion With subtemporal craniotomy alone the angle of vision needed to identify the PCA in its P2 P3 segment under the surgical microscope was on average 17 4 This field was increased to an average of 27 9 when J Neurosurg Volume 74 March 1991 521 M P Sindou and J L Fob6 TABLE I Visual angle obtained in bilateral approaches thrive cadavers Cadaver l Cadaver 2 Cadaver 3 Cadaver 4 Cadaver 5 Operative Approach Rt Lt Rt Lt Rt Lt Rt Lt Rt Lt without REAM removal 15 16 18 19 9 10 26 25 18 18 with REAM removal 22 24 33 32 20 22 39 38 24 25 Vision of surgical field comparing the approach with removal of the roof of the external auditory meatus REAM in association with a low temporal craniotomy witt a temporal eraniotomy alone the roof of the external auditory meatus was removed Table 1 on average providing an additional 10 5 to the field of vision that is 60 34 more than with the subtemporal approach alone Fig 1B These measure ments were performed in the surgical laboratory on five fresh cadavers The surgical field included the PCA in its P2 P segment the retracted temporal lobe and the soft external auditory meatus This approach reduces the need for brain retraction and decreases the danger of sacrificing venous drainage of the temporal lobe It allows access to the posterolateral part of the tentorial notch 6 the peduncular and quadrigeminal cisterns and the PCA 2 in its P2 P3 segment This technique does entail certain surgical risks some of them related to the temporal approach others related to removal of the roof of the external auditory meatus Injury of the frontal branch of the facial nerve can be avoided if the cutaneous incision passes close enough to the tragus If the mastoid cells are opened they must be carefully occluded with bone wax Drilling of the arcuate eminence if done must be superficial to avoid injury to the superior semicircular canal 7 Cicatricial stenosis of the external auditory meatus must be pre vented by meticulous fixation of its roof and temporary packing of a pledger inside the meatus Subtemporal craniotomy with removal of the roof of the canal could be a significant aid in obtaining access to tumors located in the vicinity of the lateral part of the tentorial notch and to arteriovenous malfor mations or aneurysms with a vascular supply from the P2 P3 segment of the PCA 2 5 It could also be valuable in reaching the peduncular portion of the PCA or the superior cerebellar artery as a site for an extracranial intracranial bypass s 9 Acknowledgments We thank Dr Jorge Jarolin for the medical illustrations Dr Jessika Mann for assistance with the English version of the text and Professor Bouchet head of the Department of Anatomy We also thank Dr Robert G Grossman for editing help References 1 Ausman JI Lee MC Chater N et al Superficial temporal artery to superior cerebellar artery anastomosis for distal basilar artery stenosis Surg Neurol 12 277 282 1979 2 Chang HS Fukushima T Takakura K et al Aneurysms of the posterior cerebral artery report of ten cases Neu rosurgery 19 1006 1011 1986 3 Drake CG The treatment of aneurysms of the posterior circulation Clin Neurosurg 26 96 144 1979 4 Fukamachi A Hirato M Wakao T et al Giant serpentine aneurysm of the posterior cerebral artery Neurosurgery 11 271 276 1982 5 Keravel Y Sindou M Aneurysms of posterior cerebral artery in Keravel Y Sindou M eds Giant Intracranial Aneurysms ed 1 Heidelberg Springer Verlag 1988 pp 65 66 6 Ono M Ono M Rhoton AL Jr et al Microsurgical anatomy of the region of the tentorial incisura J Neu rosurg 60 365 399 1984 7 Pait TG Zeal A Harris FS et al Microsurgical anatomy and dissection of the temporal bone Surg Neurol 8 363 391 1977 8 Sundt TM Jr Campbell JK Houser OW Transpositions and anastomoses