Dissection of the Petrosal Presigmoid-Retrolabyrinthine Approach for the Petroclival Region on a Cadaver: 2-Dimensional Operative Video

Skull base epidermoid tumors, meningiomas, and schwannomas can be accessed by different techniques depending on the location and size of the lesion. Small lesions located anterior to the internal acoustic meatus (IAM) can be accessed via the subtemporal approach, and lesions located posterior to the IAM can be approached via retrosigmoid craniotomy. However, expansive lesions that are located anterior to the IAM and extend posteriorly toward the lower clivus can be accessed via the petrosal approach. The petrosal approach (presigmoid-retrolabyrinthine) is centered on the petrous ridge of the temporal bone and is mainly performed for intradural lesions located at the clivus and petroclivus junction area. Patients with intact hearing can benefit from this technique, as the labyrinth is untouched and yet the middle and posterior fossa compartments are connected. Additionally, extension of the lesion from the suprasellar area/cavernous sinus to the foramen magnum can be dissected and removed. There are variations of the petrosal approach, such as translabyrinthine, transotic, and transchoclear, with which hearing cannot be preserved, and the “transcrusal” approach, wherein posterior and superior semicircular canals are sacrificed yet hearing preserved. The endolymphatic duct is usually transected and not reapproximated. Neurotology input is always helpful when dealing with inner ear structures. This complex approach demands exhaustive practice with temporal bone dissection in a cadaver laboratory. Although this approach can be extended anteriorly, combination with an anterior petrosal approach permits more rostral exposure. In this video, we demonstrate the stepwise dissection of the posterior petrosal approach only, showing procedure nuances in a cadaver.1-8Used with permission from Barrow Neurological Institute, Phoenix, Arizona.

The Transcrusal Approach

OBJECTIVE This study reviewed the experience and outcomes of 1 surgical team (L.S.P., S.P.L.) using the transcrusal approach. METHODS Ten-year retrospective review of 17 consecutive patients requiring transcrusal exposure of the petrous apex and upper brainstem was performed. The main outcome measures included hearing and facial nerve preservation as measured by standard audiography and postoperative assessment using the House-Brackmann scale. RESULTS Operative indications included meningioma (5 patients), epidermoid/dermoid cyst (3 patients), trigeminal schwannoma (3 patients), giant or large upper basilar artery aneurysm (3 patients), pontine cavernoma (1 patient), chondrosarcoma (1 patient), and clival melanocytoma (1 patient). Average tumor size was 3.6 cm. Complete resection was achieved in 50% of patients with petroclival tumors. Follow-up data were obtained for 14 patients at 20 ± 4 months. Serviceable hearing was preserved in 58%. Sixty-four percent of patients demonstrated House-Brackmann stage I facial nerve function. Two patients died perioperatively (brainstem infarction). Two patients became hemiparetic, with 1 improving substantially. CSF leaks developed in 3 patients. Forty-seven percent of patients demonstrated cranial nerve V deficits. Forty-one percent of patients demonstrated deficits of cranial nerve III, IV, or VI. Vertigo, vestibular disturbance, hydrocephalus, temporal lobe contusion, or hematoma did not develop in any patients. CONCLUSION The transcrusal approach provides adequate exposure for most petroclival lesions and giant aneurysms of the upper basilar artery while offering the possibility of hearing preservation. Like all approaches to large tumors and aneurysms in this region, there is a significant risk of morbidity and mortality. However, this approach is an excellent alternative to other techniques that necessitate deliberate sacrifice of ipsilateral hearing.

Transcrusal approach to the petroclival region with hearing preservation

✓ As a term, the “petrosal approach” to the petroclival region has a variety of meanings. The authors define a common nomenclature based on historical contributions and add new terminology to describe a technique of hearing preservation that allows for greater exposure of the petroclival region. The degree of temporal bone dissection defines five stages of operation. The authors used the second or “transcrusal” stage, in which the posterior and superior semicircular canals are sacrificed while preserving hearing, in six consecutive cases. Use of a common terminology ensures better understanding among surgeons. In the authors' hands, hearing has been successfully preserved in six patients after partial labyrinthectomy.

Classification and quantification of the petrosal approach to the petroclival region

Object. The petrosal approach to the petroclival region has been used by a variety of authors in various ways and the terminology has become quite confusing. A systematic assessment of the benefits and limitations of each approach is also lacking. The authors classify their approach to the middle and upper clivus, review the applications for each, and test their hypotheses on a cadaver model by using frameless stereotactic guidance.Methods. The petrosal approach to the upper and middle clivus is divided into four increasingly morbidity-producing steps: retrolabyrinthine, transcrusal (partial labyrinthectomy), transotic, and transcochlear approaches. Four latexinjected cadaveric heads (eight sides) underwent dissection in which frameless stereotactic guidance was used. An area of exposure 10 cm superficial to a central target (working area) was calculated. The area and length of clival exposure with each subsequent dissection was also calculated.The retrolabyrinthine approach spares hearing and facial function but provides for only a small window of upper clival exposure. The view afforded by what we have called the transcrusal approach provides for up to four times this exposure. The transotic and transcochlear procedures, although producing more morbidity, add little in terms of a larger clival window. However, with each step, the surgical freedom for manipulation of instruments increases.Conclusions. The petrosal approach to the upper and middle clivus is useful but should be used judiciously, because levels of morbidity can be high. The retrolabyrinthine approach has limited utility. For tumors without bone invasion, the transcrusal approach provides a much more versatile exposure with an excellent chance of hearing and facial nerve preservation. The transotic approach provides for greater versatility in treating lesions but clival exposure is not greatly enhanced. Transcochlear exposure adds little in terms of intradural exposure and should be reserved for cases in which access to the petrous carotid artery is necessary.