Figure 1: Mastoidectomy, retrolabyrinthine, partial labyrinthine, translabyrinthine, and transcochlear approaches have been demonstrated. The mastoid bone and its superficial anatomy are shown in the left upper photo. The spine of Henle is at the posterosuperior margin of the external meatus and superficial to the deep lateral semicircular canal and junction of the tympanic and mastoid segments of the facial nerve. The supramastoid crest approximates the level of the transverse and sigmoid sinuses. In the right upper photo, mastoidectomy has exposed the middle fossa dura, the sigmoid sinus and the jugular bulb; these structures form the borders of the presigmoid dura where intradural operative trajectory is centered. The sinodural angle is where the sigmoid sinus meets the middle fossa dura.

In the left middle image, the retrolabyrinthine exposure is complete and the dura has been excised to reveal cranial nerves V to X within the cerebellopontine angle. In the right middle image, the translabyrinthine approach allows a more ventral view of the brainstem. Furthermore, the meatal and labyrinthine segments of the facial nerve are apparent. In the left lower image, the facial nerve has been transposed posteriorly for removal of the cochlea in the transcochlear approach. The semicircular canals and vestibule have also been removed. In the right lower image, removal of the cochlea allows resection of the remainder of the petrous apex, facilitating an unhindered view of the anterior brainstem (images courtesy of AL Rhoton, Jr).

Figure 2: Surgical steps for a right-sided posterior petrosal or presigmoid approach combined with a subtemporal extension are demonstrated. The mastoidectomy will reveal the presigmoid dura, and the extent of drilling of the dense cortical bone housing the semicircular canals determines the difference between the standard (conservative) and extended posterior petrosal approaches (upper images). The relevant anatomy of the temporal bone is depicted in the right upper image. The tympanic segment of the facial nerve travels inferior to the lateral canal. The initial dural exposure is demonstrated (left lower image). The vein of Labbé is protected during dural incisions (right lower image)(images courtesy of AL Rhoton, Jr). Please note that the demonstrated retrolabyrinthine approach in these photos requires more aggressive bone resection (similar to the one for the extended posterior petrosectomy) than the approach illustrated in the operative sketches below (images courtesy of AL Rhoton, Jr).

Figure 3: The location of a right-sided Trautmann’s triangle (marked by the hashed line) and its relationship to the surrounding structures is shown. Removal of the bone over this triangle is the principle maneuver executed during the petrosal approach.

Figure 4: Extradural (left image) and intradural (right image) exposures through a left-sided posterior petrosectomy or presigmoid osteotomy are shown (images courtesy of AL Rhoton, Jr).

Figure 5: Patient position, skull clamp fixation, and skin incision are illustrated. The locations of the burr holes and craniotomy in relation to the dural venous sinuses are evident. The vertex of the head is tilted slightly toward the floor until the zygoma is the highest point on the operative field. The skull clamp pins are positioned so the pins stay away from the outlines of the incision. I place the single pin anteriorly over the frontal area and the two-pin rocker arm low on the occipital bone and parallel to the sagittal plane.

The usual incision for posterior petrosectomy starts at the level of the zygoma, approximately 1 cm anterior to the tragus. It circles 3-4 cm above the ear, and descends 4 cm behind the mastoid process, exposing the suboccipital bone. The extent of temporal bone work can be tailored based on the extension of the tumor into the middle fossa.

Figure 6: The scalp flap is reflected anteroinferiorly and the natural plane between the temporalis fascia and galea is developed. The pericranium and temporal fascia is incised along the edges of the incision and separated from the muscle. This pericranial flap is further dissected beyond the superior nuchal line in continuity with the sternocleidomastoid muscle, which is released from its insertion on the mastoid bone. This technique provides a large, vascularized fascial/pericranial flap that can be used for skull base reconstruction at the end of the operation.

The temporal muscle is then detached from the bone and also reflected anteroinferiorly. Other muscle attachments on the mastoid and superior nuchal line are also released to gain exposure for the suboccipital craniotomy.

Figure 7: The craniotomy for posterior petrosal approach includes both a temporal and a suboccipital component. I make four burr holes, two sets on each side of the transverse sinus. The first burr hole is placed immediately medial and inferior to the asterion. This burr hole gives access to the infratentorial compartment.

The second burr hole is made at the junction of the squamous and parietomastoid sutures (upper and middle images). This burr hole provides access to the supratentorial compartment. The space between these two burr holes contains the transverse-sigmoid junction. A second set of burr holes is placed more medially above and below the superior nuchal line, flanking the transverse sinus.

A high-speed drill with a foot attachment is used to elevate subtemporal and suboccipital-retromastoid craniotomies. I avoid the use of the footplate attachment over the dural sinuses since these sinuses are often embedded in the inner surface of the skull bone and tenaciously adherent. The anatomy of the sutures in the region is further depicted in the lower image (images courtesy of AL Rhoton, Jr).

Figure 8: I “eggshell” the bone between the burr holes and overlying the venous sinuses using a side-cutting burr (B1 without a footplate). I then slowly detach the sinus wall from the inner skull table and remove the remaining bone over the sinuses using a Kerrison rongeur (inset).

The bone flap is then carefully elevated. Minor injuries to the venous sinus can usually be covered and not aggressively packed with hemostatic material (Surgicel Fibrillar, Ethicon, Somerville, NJ). Larger tears require primary repair using a local dural flap. Again, the lumen of the sinus should not be packed to avoid its thrombosis. The osteotomy over the mastoid bone can be less straightforward, requiring the use of a round side-cutting burr.

Figure 9: The second component of this approach is an almost complete mastoidectomy. The first step is decortication of the mastoid surface using a high-speed cutting burr and continuous suction irrigation. Troughs are created to outline the superior and anterior limits of the mastoidectomy. The superior trough extends from the zygomatic root to the asterion, just inferior to the infratemporal line.

The anterior trough extends from the posterior rim of the external auditory meatus down to the mastoid tip. The mastoid air cells are removed within these limits. Drilling should take place at an even depth throughout the process of drilling. The cortical bone over the sigmoid sinus is identified as the air cells are removed. My neuro-otologist usually performs this part of the procedure.

Figure 10: Once the sigmoid sinus is fully skeletonized, additional air cells anterior to the sigmoid sinus are removed to expose the dura of the middle and posterior fossae. Small islands of thin adherent cortical bone are left on the sinus to minimize injury to this important venous structure. Bone removal is continued until the middle fossa dura is exposed. Smaller cutting burrs are employed as mastoidectomy proceeds and the deeper structures are reached.

The sigmoid sinus is followed inferiorly to near the jugular bulb, exposing the inferior segment of the sigmoid sinus and digastric ridge. The facial nerve courses along the inferior edge of the lateral semicircular canal into the stylomastoid foramen located just anterior to the digastric ridge. The facial nerve is embedded in the cortical bone of the fallopian canal. There is no need to skeletonize the facial nerve unless exposure of the jugular foramen is desired. The sigmoid sinus is now unroofed from its confluence with the superior petrosal sinus superiorly all the way to the level of the jugular bulb inferiorly. Patients with a “high-riding” jugular bulb will provide a limited presigmoid working window and alternative operative corridors besides the posterior petrosal route should be considered.

Figure 11: Removal of the bone over the Trautmann’s triangle is shown. The bone covering the presigmoid dura at the sinodural angle is removed (upper image), exposing the Trautmann’s triangle. This triangle is an area of the posterior fossa dura bounded inferiorly by the jugular bulb, superiorly by the superior petrosal sinus, anteriorly by the bony labyrinth, and posteriorly by the sigmoid sinus (hashed area in the middle and inferior images).

Bone resection anterior to the sigmoid sinus can progress forward until the cortical bone over the posterior semicircular canals is encountered. Aggressive drilling around the jugular bulb is unnecessary and can lead to injury of the jugular bulb or facial nerve. Once I have achieved exposure of the Trautmann’s triangle, the conservative retrolabyrinthine petrosectomy is considered complete.

Figure 12: Next, the posterior fossa dura is incised, anterior and parallel to the sigmoid sinus, extending from the jugular bulb to the superior petrosal sinus. The endolymphatic sac will be visible inferior to the posterior semicircular canal as a white, thick area of the dura. This structure is usually the anterior limit of the dural exposure and should be preserved to avoid hearing loss. If the dural incision violates the endolymphatic sac, the patient’s hearing may still remain intact if the endolymphatic duct is spared.

Figure 13: The second segment of the dural incision follows the floor of the temporal fossa and is continued posteriorly to the level of the superior petrosal sinus. To prevent injury to the vein of Labbé, I cut the dura in small increments and inspect the subdural space for the entry point of the vein into the transverse or superior petrosal sinuses.

Figure 14: The superior petrosal sinus is now isolated, coagulated, or ligated with Weck clips. The point where the sinus is divided must be anterior to the insertion point of the temporal lobe’s draining veins (including the vein of Labbé) to preserve their outflow into the transverse-sigmoid sinuses. If the vein of Labbé crosses the area of exposure, it can be partially untethered, mobilized, and protected.

Preoperative assessment of the temporal lobe’s venous drainage patterns using CT/catheter angiography or magnetic resonance venography is beneficial in tailoring the safe zones for tentorial transection. If the superior petrosal sinus is intimately involved with the venous drainage of the region, an incision along the tentorium medial to the superior petrosal sinus will spare this sinus and allow an operative corridor, albeit limited, to the petroclival region around the sinus.

Figure 15: After the superior petrosal sinus is divided, the dural incision is continued on the tentorium parallel to the posterior edge of the petrous pyramid toward the tentorial incisura. It is often tempting to incise the tentorium more posteriorly because of the wider exposure in that region. Completing the dural incision more posteriorly (and not along the petrous pyramid) will lead to a tentorial flap along the ridge that may limit the surgical corridor.

Figure 16: Before the medial edge of the tentorium is transected, CN IV must be identified to the point where it enters the dura. To protect this nerve, I cut the tentorium posterior to the point where the nerve enters the tentorial edge.

Figure 17: The posterior tentorial flap is then elevated with the temporal lobe and held in place using a retractor blade. Another retractor blade holds the cerebellum inferiorly. The presigmoid dura, temporal dura, and tentorium are retracted using retention sutures. Note that the sutures are placed as deep as possible and close to the petrous edge to maximize exposure.

Figure 18: Gentle posterior retraction of the sigmoid sinus allows a direct panoramic view of the anterolateral brainstem and the origins of the cranial nerves along the petroclival space. As mentioned above, more extensive bone resection of the labyrinth is usually not necessary to remove lesions along the anterolateral brainstem because the operator can typically expand the operative corridor through lesional intracapsular decompression.