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 74March, 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 w