The small petrosal approach was found to be useful and safe as an alternative technique for selective removal of the lesion in the middle portion of the mediobasal temporal region 1).
The combined petrosal approach is a suitable technique for the resection of medium-to-large petroclival meningiomas (PCMs), and suited for patients with serviceable hearing on the side of the lesion.
This approach enhances petroclival exposure and the degree of tumor resection, especially in the area of the petroclival junction, middle clivus, apical petrous bone, posterior cavernous sinus, and Meckel's cave. The combined petrosal approach also allows better visualization of the contralateral side and the ventral brainstem, which facilitates safe dissection of the tumor from the brainstem, the basilar artery, and the perforators. If a patient has an early draining bridging vein to the tentorial sinus (before it reaches the transverse-sigmoid junction) or a prominent sigmoid sinus and jugular bulb, the combined petrosal approach provides significant working space 2).
Multiple technical modifications have been reported to increase the surgical corridor, including the method of dural and tentorial opening.
The petrosal approach is based on sectioning the superior petrosal sinus (SPS) and the tentorium. However, the venous anatomy in certain situations forbids this maneuver.
Sparing of the SPS or cutting of the tentorium is an effective means for cases in which the venous anatomy mandates preservation of these structures 3).
Anterior transpetrosal approach (ATPA) is a less aggressive skull base approach and could provide sufficient exposure for the petroclival region and has additional advantages for a selected group of petroclival meningiomas (PCMs) 4).
It is the most appropriate approach for petroclival meningiomas, which are typically located from the dorsum sellae to the upper border of the internal acoustic meatus (IAM). Although neurosurgeons can resect over this area if the tumor is detached from the dura, tumors within the indication area for petroclival meningiomas is insufficient for the selection of the ATP approach because it can be difficult to evaluate whether the tumor is attached or only touching the dura 5).
The anterior transpetrosal approach (ATPA) stands out as a method for granting entry into the upper and middle clival areas.
Identification and protection of the cochlea during anterior petrosectomy is key to prevent hearing loss. Currently, there is no optimal method to infer the position of the cochlea in relation to the Kawase quadrangle, therefore damage to the cochlea during anterior petrosectomy remains a substantial risk.
An anterior transpetrosal approach (ATPA) is suitable for treating upper petroclival lesions. However, the limit of the ATPA is reached when the tumor extends posterolaterally over the internal auditory canal (IAC) along the petrous edge. In such cases, ligation of the posterior part of the superior petrosal sinus (SPS) is necessary. To overcome this limitation, Shibao et al. combined the ATPA with a partial posterior petrosectomy in 8 patients who had petroclival meningiomas extending posterolaterally over the IAC 7)
They are extensions of the basic middle fossa approach.
The middle fossa approaches spare the lateral petrous bone and involve resection of the medial petrous bone to various degrees. All of the middle fossa approaches are designed to preserve hearing. Extensions of the middle fossa approaches involve resection of bone within the Kawase triangle and division of the tentorium to provide exposure of the posterior fossa.
Borghei-Razavi et al. reviewed pre- and postoperative Multi-Slice CT scan (1mm thickness) of patients with petroclival meningioma between Jan 2009 and Sep 2013 in which anterior petrosectomy was performed to access the posterior fossa part of the tumor. The distances between drilling start and finish edge to the vital anatomical skull base structures such as internal auditory canal (IAC) and superior semicircular canal and petrous apex (petrous part of the carotid artery) were measured and analyzed.
Drilling entrance length is directly related with tumor size. The distances between anatomical structures and drilling points decrease with increasing tumor size, but it always remains a safe margin between drilling points and IAC, internal carotid artery (ICA), and semicircular canals in axial and coronal views.
The Kawase triangle is shown to be a safe anatomical landmark for anterior petrosectomy. The described landmarks avoid damage to the vital anatomical structures during access to the posterior fossa through middle fossa, despite temporal bone anatomical variations and different tumor sizes 8).