Surgical Management of Posterior Petrous Meningiomas
Posterior petrous meningiomas (commonly termed posterior pyramid meningiomas and/or meningiomas of the posterior surface of the petrous pyramid) are the most common meningiomas of the posterior cranial fossa. They are located along the posterior surface of the temporal bone in the region of the cerebellopontine angle. They often mimic vestibular schwannomas, both clinically and on neuroimaging studies. Common clinical symptoms include hearing loss, cerebellar ataxia, and trigeminal neuropathy. The site of dural origin determines the direction of cranial nerve displacement. Total resection can be achieved in most cases with a low morbidity rate and an excellent prognosis. The authors review the surgical management of posterior petrous meningiomas.
Posterior fossa meningiomas comprise approximately 10% of all intracranial meningiomas. Castellano and Ruggiero reviewed Olivecrona's experience with treating posterior fossa meningiomas and classified them based on the site of dural attachment. They described the location as cerebellar convexity (10%), tentorium (30%), posterior surface of the petrous bone (42%), clivus (11%), or foramen magnum (4%). Based on their extensive microsurgical experience, Yas¸argil, et al., proposed a new classification of posterior fossa meningiomas: 1) clival; 2) petroclival; 3) sphenopetroclival; 4) foramen magnum; and 5) CPA. The authors pointed out the difficulty in grouping meningiomas into precise topographic areas because in some cases they are transitional.
There is lack of a uniform consensus on the definition of posterior petrous meningiomas; thus, it is difficult to compare data in the various published series. The lesions are frequently termed "CPA meningiomas" in the literature, which describes the tumor as occupying the CPA cistern. We believe, however, that this term is inaccurate, and does not precisely describe the point of dural attachment and predict the direction of cranial nerve displacement, which can significantly determine surgery-induced morbidity.
In their series Samii and Ammirati used the term "posterior pyramid meningiomas" and defined them as tumors whose main direction of growth brings them in contact with the posterior pyramid, irrespective of their site of dural attachment. They also designated those located anterior and those posterior to the internal acoustic meatus. Of the 56 lesions in their series, however, 18 arose from the tentorium, three from the clivus, and one from the jugular foramen. There were only nine cases in which the dural attachments originated from the petrous bone (six lesions anterior to and three lesions posterior to the internal acoustic meatus).
Al-Mefty described a group of CPA meningiomas as "petrosal meningiomas" that originated on the posterior surface of the petrous bone and divided them into two categories: tumors originating anterior to the internal auditory meatus and those originating posterior to it. Based on topography and displacement patterns of neurovascular structures, Bricolo and Turazzi classified meningiomas with dural attachments arising from the posterior surface of the petrous bone "posterior to the internal acoustic meatus as posterior petrous meningiomas." Lesions situated anterior to the internal acoustic meatus were named "anterior petrous meningiomas" (Fig. 1 left). In their experience, anterior petrous meningiomas tended to displace seventh and eighth cranial nerves posteriorly, whereas posterior petrous meningiomas displaced the nerves anteriorly. The anterior petrous meningiomas were more difficult to remove because the cranial nerves were situated between the surgeon and the tumor.
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Illustrations. Left: Illustration depicting the potential sites of dural attachment on the posterior skull base: 1) petroclival; 2) anterior petrous; 3) posterior petrous; 4) jugular foramen; and 5) foramen magnum. (From Bricolo and Turazzi; used with permission). Right: Petroclival meningiomas have dural attachments that originate at or medial to the skull base foramina of the fifth through 11th cranial nerves (shaded region). In contrast, posterior petrous meningiomas have dural attachments that arise lateral to these cranial nerve foramina. From Couldwell, et al., 1996; used with permission.
In this review, we define posterior petrous meningiomas as tumors with basal dural attachments originating on the petrous bone posterior to the internal auditory meatus and lateral to the skull base foramina of the fifth through 11th cranial nerves. These tumors may project to the CPA and mimic VSs, displacing neurovascular structures. The chance of totally removing posterior petrous meningiomas is excellent without significant morbidity as opposed to petroclival meningiomas. Petroclival meningiomas whose dural attachments emanate at or medial to the skull base foramina of the fifth through 11th cranial nerves (Fig. 1 right) place the cranial nerves between the surgeon and the tumor, and are thus associated with significantly higher rates of surgical morbidity, primarily as a result of cranial neuropathies and vascular injury to the brainstem perforating vessels.