Extended Posterior Petrosectomy
There are several variations of the posterior transpetrosal approach (posterior petrosectomy or presigmoid approach) that differ in the magnitude of petrous pyramid osteotomy.
The progressive degrees of bone removal of the otic capsule provide some advantages, mostly for gaining further access to the anterolateral brainstem and medial clivus. When combined with a subtemporal approach, the posterior petrosectomy expands the exposure as high as CN IV and as low as the jugular tubercle.
In this chapter, I will describe the techniques for extended posterior petrosectomy. Please refer to the chapter on conservative posterior petrosectomy for general considerations and the initial stages of exposure.
Indications for Extended Posterior Petrosectomy
In some cases involving small and soft tumors, conservative petrosectomy followed by aggressive intracapsular tumor decompression provides adequate working angles to reach the anterior brainstem without significant brain retraction. These working angles obviate the need for a more extensive osteotomy as described in the following section.
I believe the extended retrosigmoid route provides a reasonable operative corridor for accessing some petroclival tumors, including epidermoid and soft or small to moderate size meningiomas without supratentorial extension. However, multicompartmental fibrous, vascular, and/or partially calcified petroclival meningiomas with both supratentorial and infratentorial extensions require extended operative angles and space for dissection of neurovascular structures. In these circumstances, the extended petrosal approach is preferred.
A detailed understanding of the mastoid bone and otic capsule is important for petrous bone drilling.
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EXTENDED POSTERIOR PETROSAL APPROACH
For the initial steps of this procedure, please refer to the chapter on conservative posterior petrosectomy.
The sigmoid sinus is unroofed inferiorly and the air cells of the mastoid tip are drilled away, exposing the inferior segment of the sigmoid sinus and digastric ridge. The facial nerve courses from the inferior edge of the lateral semicircular canal toward 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.
After the trajectory of the facial nerve has been identified, the positions of the superior and posterior semicircular canals are confirmed through further drilling. These canals are covered by dense cortical bone.
At higher magnification, the bony labyrinth is skeletonized using a diamond burr. Next, the bone covering the presigmoid dura at the sinodural angle is removed, exposing Trautmann’s triangle, an area of 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. Please refer to the chapter on conservative posterior petrosectomy for further details on the anatomy of the Trautmann’s triangle.
During the retrolabyrinthine approach, hearing preservation is the goal. The bony labyrinth must not be violated. If an accidental disruption of the bone occurs but the membranous labyrinth remains intact, a small amount of bone wax or fascia can be used to cover the defect. However, if both the bony and membranous components of the labyrinth are transected, a small piece of muscle must be inserted in the defect to prevent peri- and endolymph leakage; there is high risk of not only hearing loss, but also vertigo.
The dural opening should maximize the intradural operative trajectory.
Following surgical treatment of the pathology at hand, closure begins. The dura is approximated primarily, but “watertight” closure is not feasible and additional measures minimize the risk of postoperative cerebrospinal fluid leakage. All exposed air cells are meticulously waxed and strips of adipose tissue or fascia lata are placed through and over the dural defect to seal the fistula.
Additionally, the vascularized periosteal flap that was harvested during exposure is used to cover and fill the defect in the dura. The bone flap is replaced and secured using miniplates and the rest of closure is conducted in a standard fashion.
The lumbar drain is used to drain 8cc/hour of cerebrospinal fluid for 48 hours after surgery. Patients are mobilized as soon as possible.
Pearls and Pitfalls
- An intimate familiarity with the anatomy of the temporal bone, including the mastoid process, is necessary for safe completion of presigmoid osteotomy.
- Judicious use of extended posterior petrosal approach is prudent to avoid unnecessarily long operative sessions and the associated risks.
For additional illustrations of combined transpetrosal-middle fossa approaches, please refer to the Jackler Atlas by clicking on the image below:
For additional illustrations of jugular foramen approaches, please refer to the Jackler Atlas by clicking on the image below:
For additional illustrations of the translabyrinthine approach, please refer to the Jackler Atlas by clicking on the image below:
Miller CG, van Loveren HR, Keller JT, Pensak M, el-Kalliny M, Tew JM. Transpetrosal approach: surgical anatomy and technique. Neurosurgery. 1993; 33: 461–469; discussion 469.
Sincoff EH, McMenomey SO, Delashaw JB. Posterior transpetrosal approach: less is more. Neurosurgery. 2007; 60(2 Suppl 1): ONS 53–58; discussion ONS 58–59.
Horgan MA, Delashaw JB, Schwartz MS, Kellogg JX, Spektor S, McMenomey SO. Transcrusal approach to the petroclival region with hearing preservation. Technical note and illustrative cases. J Neurosurg. 2001; 94: 660–666.
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