Petrous Apex Meningioma
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Petrous apex meningiomas are located along the anterior extent of the petrous temporal bone. These tumors originate at or above the internal acoustic canal (IAC) and impinge on cranial nerves (CNs) VII-VIII and the brainstem. As the tumor expands, it can invade the Meckel’s cave and subsequently impinge on CN V and the temporal lobe.
Meningiomas of the posterior petrous bone have been classified into four groups according to the modified Desgeorges and Sterkers classification: posterior petrous, meatus and IAC, petrous apex without invasion of the IAC, and cerebellopontine angle with invasion of the IAC. Most petrous apex meningiomas do not infiltrate the IAC.
Although these tumors are generally benign, the lack of capacitance within the posterior fossa increases the incidence of significant consequences caused by brainstem or cranial nerve compression. It is this proximity to critical structures that makes management of these tumors challenging.
Petrous apex meningiomas are ambiguous entities because they have been classified along with petroclival and cerebellopontine angle meningiomas. Petroclival meningiomas typically displace CN V laterally, whereas petrous apex meningiomas mobilize this nerve medially. I have dedicated a chapter to the discussion of petrous apex meningiomas in addition to the chapters for petroclival and cerebellopontine angle meningiomas.
Based on the complex neurostructural anatomy adjacent to the anterior segment of the petrous bone, presenting signs and symptoms are variable. The clinical spectrum includes headaches, cranial nerve palsies (IV-X), trigeminal neuralgia, facial hypesthesia, hearing loss, vertigo, and long tract signs from pyramidal tract compression.
The typical magnetic resonance (MR) imaging demonstrates the size and location of the mass and estimates it extent of vascularity. The tumor’s relationship to and encasement of the brainstem, cranial nerves, temporal bone, cavernous sinus, and related vasculature are assessed. Edema in the brainstem parenchyma signifies pial invasion and a high risk of new postoperative neurologic deterioration caused by a lack of intact pial dissection planes intraoperatively. Under these circumstances, subtotal decompressive surgery is advised. A computed tomography (CT) scan will identify hyperostosis of the adjacent temporal bone.
A complete preoperative detailed assessment of neurologic function, particularly functions related to the cranial nerves that are likely to be affected, is essential to establish the patient’s baseline functional status. An audiogram is part of this evaluation. The outcomes of these baseline studies, especially those assessing hearing, can impact the selection of the appropriate surgical approach.
For more details about the evaluation of petrous apex meningiomas, please refer to the petroclival meningioma chapter.
Preoperative Considerations and Selection of the Surgical Approach
The choice of approach for resection of extra-axial petrous apex tumors depends on the location of the predominant bulk of the mass. I typically employ the retrosigmoid/lateral supracerebellar corridor as part of the transtentorial approach. Other options to consider include the subtemporal approach combined with an apical petrosectomy. Large tumors are best exposed via a two-staged operation (posterior fossa followed by subtemporal surgery).
The retrosigmoid suprameatal approach allows petrous apex drilling above CN V and expands the operative corridor further. I favor the posterior fossa corridors with extended modifications into the subtemporal space in order to avoid temporal lobe retraction, especially on the dominant side. However, the extent of supratentorial tumor or compromise and encasement of the surrounding structures can render the subtemporal approach combined with an apical petrosectomy a more strategically appropriate choice.
Preoperative embolization of tumor-feeding vessels can be a reasonable consideration in highly vascular tumors
Intraoperative neuronavigation using MRI and CT (for possible suprameatal osteotomy) is beneficial. Moreover, somatosensory evoked potentials (SSEPs) and brainstem auditory evoked responses (BAERs) monitoring are valuable to facilitate desirable outcomes.
The anatomy of the petrous ridge and the tentorial incisura is discussed in the chapter on petroclival meningiomas. The suprameatal modification of the transtentorial approach may be beneficial for reaching a portion of the meningioma hidden behind the petrous ridge.
The suprameatal osteotomy via the retrosigmoid approach can potentially prove advantageous for exposure of tumors that are primarily within the cerebellopontine angle and that also extend into the middle cranial fossa around the Meckel's cave. This osteotomy may obviate the need for a supratentorial craniotomy. The suprameatal osteotomy is mentioned here for completeness, but I rarely resort to this modification.
RESECTION OF PETROUS APEX MENINIGOMA
As mentioned previously, the combined retrosigmoid and supracerebellar transtentorial approach with a potential need for suprameatal drilling of the petrous apex is highly appealing to me because this is the least disruptive and safest approach to the petrous apex as long as the tumor does not extend anteriorly to near the cerebral peduncle.
The anterior reach of this approach along the petrous ridge is limited and the working distance is long. This technically demanding approach for a petrous apex meningioma is discussed in detail below, but further specifics are available in the Paramedian Supracerebellar Transtentorial chapter.
I present a selection of intraoperative images from the patient in Figure 1 before proceeding with the discussion of technical tenets.
Closure and Postoperative Considerations
The tentorium is not reconstructed. Bone wax is used to occlude the air cells if the petrous apex was partially removed via drilling. Closure is performed in the standard fashion.
Pearls and Pitfalls
- Devascularization of the tumor along the petrous apex and tentorium is the key step in facilitating effective tumor debulking and safe mobilization of the tumor capsule away from the vital neurovascular structures within a relatively bloodless and visible operative field.
Contributor: Andrew R. Conger, MD, MS
Bogaev C, Sekhar LN. Petrovlical meningiomas, in Atlas of Neurosurgical Techniques: Brain, 1st ed. New York: Thieme Medical Publishers, 2006.
Peyre M, Bozorg-Grayeli A, Rey A, Sterkers O, Kalamarides M. Posterior petrous bone meningiomas: surgical experience in 53 patients and literature review. Neurosurg Rev. 2012;35:53-66.
Samii M, Gerganov VM. Cerebellopontine angle meningiomas, in DeMonte F, McDermott MW, Al-Mefty O. (eds): Al-Mefty’s Meningiomas. 2nd ed. New York: Thieme Medical Publishers, 2011.
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