Study of comparative surgical exposure to the petroclival region using patient-specific, petroclival meningioma virtual reality models

OBJECTIVE Despite advancement of surgical techniques, the attachments of petroclival meningiomas near the central clival depression (CCD) remain difficult to visualize. With existing methods, the amount of tumor near the CCD that is inaccessible through various approaches cannot be compared. Tumors distort the brainstem, changing the size of the operative corridor for some but not all approaches; therefore, using cadavers with normal posterior fossae makes it impossible to compare different approaches to the tumor. The authors used virtual reality (VR) models created from the imaging data of patients to compare various surgical approaches that have otherwise been incomparable in previous studies. METHODS CT and MRI data obtained in 15 patients with petroclival meningiomas were used to create anatomically accurate 3D VR models. For each model, various surgical approaches were performed, and the surgical freedom to 6 targets of the regions were measured. Furthermore, portions of the tumor that were visually blocked by the brainstem or bony structures were segmented and recorded as blinded volumes for comparison. RESULTS The extended retrosigmoid approach generated excellent exposure of the petroclival region, but for most specimens, there was inaccessible tumor volume adjacent to the brainstem (mean 641.3 mm3, SE 161.8). In contrast, the brainstem sides of the tumors were well-visualized by all the transpetrosal approaches. The blinded volume of the tumor was largest for the retrolabyrinthine approach, and this was statistically significant compared with all other approaches (mean 2381.3 mm3, SE 185.4). CONCLUSIONS The authors performed a novel laboratory study by using patient CT and MRI data to generate 3D virtual models to compare surgical approaches. Since it is impossible to perform various approaches in separate surgeries in patients for comparison, VR represents a viable alternative for such comparative investigations.

Retrosigmoid transhorizontal fissure approach to lateral pontine cavernous malformation: comparison to transpetrosal presigmoid retrolabyrinthine approach

OBJECTIVE The retrosigmoid (RS) approach is a classic route used to access deep-seated brainstem cavernous malformation (CM). The angle of access is limited, so alternatives such as the transpetrosal presigmoid retrolabyrinthine (TPPR) approach have been used to overcome this limitation. Here, the authors evaluated a modification to the RS approach, horizontal fissure dissection by using the RS transhorizontal (RSTH) approach. METHODS Relevant clinical parameters were evaluated in 9 patients who underwent resection of lateral pontine CM. Cadaveric dissection was performed to compare the TPPR approach and the RSTH approach. RESULTS Five patients underwent the TPPR approach, and 4 underwent the RSTH approach. Dissection of the horizontal fissure allowed for access to the infratrigeminal safe entry zone, with a direct trajectory to the middle cerebellar peduncle similar to that used in TPPR exposure. Operative time was longer in the TPPR group. All patients had a modified Rankin Scale score ≤ 2 at the last follow-up. Cadaveric dissection confirmed increased anteroposterior working angle and middle cerebellar peduncle exposure with the addition of horizontal fissure dissection. CONCLUSIONS The RSTH approach leads to a direct lateral path to lateral pontine CM, with similar efficacy and shorter operative time compared with more extensive skull base exposure. The RSTH approach could be considered a valid alternative for resection of selected pontine CM.

Anatomic Assessment of the Limits of an Endoscopically Assisted Retrolabyrinthine Approach to the Internal Auditory Canal

Objective Data regarding the surgical advantages and anatomic constraints of a hearing-preserving endoscopic-assisted retrolabyrinthine approach to the IAC are scarce. This study aimed to define the minimum amount of retrosigmoid dural exposure necessary for endoscopic exposure of the IAC and the surgical freedom of motion afforded by this approach. Methods Presigmoid retrolabyrinthine approaches were performed on fresh cadaveric heads. The IAC was exposed under endoscopic guidance. The retrosigmoid posterior fossa dura was decompressed until the fundus of the IAC was exposed. Surgical freedom of motion at the fundus was calculated after both retrolabyrinthine and translabyrinthine approaches. Results The IAC was entirely exposed in nine specimens with a median length of 12 mm (range: 10–13 mm). Complete IAC exposure could be achieved with 1 cm of retrosigmoid dural exposure in eight of nine mastoids. For the retrolabyrinthine approach, the median anterior–posterior surgical freedom was 13 degrees (range: 6–23 degrees) compared with 46 degrees (range: 36–53 degrees) for the translabyrinthine approach (p = 0.014). For the retrolabyrinthine approach, the median superior–inferior surgical freedom was 40 degrees (range 33–46 degrees) compared with 47 degrees (range: 42–51 degrees) for the translabyrinthine approach (p = 0.022). Conclusion Using endoscopic assistance, the retrolabyrinthine approach can expose the entire IAC. We recommend at least 1.5 cm of retrosigmoid posterior fossa dura exposure for this approach. Although this strategy provides significantly less instrument freedom of motion in both the horizontal and vertical axes than the translabyrinthine approach, it may be appropriate for carefully selected patients with intact hearing and small-to–medium sized tumors involving the IAC.

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.