Carlos A. David, MD*
Robert F. Spetzler, MD
*Division of Neurosurgery, University of Missouri, Columbia, Missouri
Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona
Petroclival meningiomas are formidable surgical challenges. Surgical outcomes, however, have improved as neuroimaging and surgical approaches have advanced. The surgical anatomy associated with petroclival meningiomas and the skull base approaches best suited for their resection are reviewed.
Key Words: clivus, meningiomas, petrosectomy, surgical approaches, tumors
Meningiomas of the clivus and petrous apex remain formidable surgical challenges. Characterized by slow, relentless growth, these tumors can become enormous before they become apparent clinically. The involvement of the brain stem, cranial nerves, and critical vascular structures invariably makes these tumors fatal. Before the last decade, attempts at extirpation were associated with a mortality rate greater than 50%,[4,6,10,30] leading many surgeons to conclude that these tumors were incurable.
Advances in neuroimaging with concurrent refinements in surgical technique and the development of skull base surgery have improved surgical outcomes. These tumors, however, remain a substantial surgical challenge, and significant morbidity is still associated with their surgical removal. The most important surgical advance enabling acceptable morbidity rates has been the development of approaches that maximize surgical exposure while minimizing the extent of brain retraction. Several surgical approaches, which can be used by themselves or in combination, have been devised to maximize exposure from different vantage points. The selection of a particular approach or combination is based on careful consideration of the size, location, and extent of the lesion as well as on the patient's neurological status. This article reviews the various approaches and their appropriate selection as well as the complications, management, and outcomes associated with the treatment of petroclival meningiomas.
The clivus is the segment of the skull base that adjoins the foramen magnum to the sphenoid bone. Otherwise known as the basilar part of the occipital bone (basiocciput), this thick plate of bone extends rostrally at an angle of 45° from the foramen magnum to the dorsum sellae. Early in life an articulation exists between these two regions known as the sphenoid occipital synchondrosis; this articulation usually disappears by adulthood. Laterally, the clivus meets the petrous portion of the temporal bone at the petro-occipital fissure. Together, these three bones form the skull base and middle fossa floor. The entire region is lined with a double layer of dura consisting of the endosteal and periosteal layers. Between these two layers are found various venous sinuses and plexi.
Figure 1. Artist’s representation of the anatomy of the petroclival region. The dura has been removed on the right half.
The concave intracranial surface of the clivus is lined by a thick double layer of dura that contains the basilar venous plexus. This venous plexus forms a venous confluence with the posterior cavernous sinus and the inferior petrosal sinus, which contains an osteofibrous compartment known as Dorello's canal. This canal is found at the region of the petrous apex between the two dural leaves. The abducens nerve lies within this canal, coursing toward the cavernous sinus below a strong fibrous trabecula known as the petrosphenoidal ligament or Gruber's ligament (Fig. 1). Slightly lateral to this region, along the petrous apex, is the trigeminal groove or impression. With its dural lining, this region forms Meckel's cave, the entrance of the trigeminal nerve. The trigeminal nerve, surrounded not only by a dural sheath but also by a well-developed cistern, enters this region from the posterior fossa. As the trigeminal nerve travels anteriorly, it leaves the cistern, and the individual divisions of the nerve become surrounded by dural sheaths as they travel along the middle fossa floor to their respective exiting foramina.
The petrous portion of the temporal bone houses the carotid artery as it ascends in its vertical portion before its anteromedial bend. In addition, the sigmoid sinus, jugular bulb, vestibulocochlear apparatus, and facial nerve are encased within the mastoid bone.
Figure 2. Classification scheme for preoperative planning divides the clivus into thirds. The choice of surgical approach depends on the anatomical extent of the tumor.
No ideal scheme exists for classifying petroclival meningiomas. An overall classification scheme would encompass tumor location as well as assess technical difficulty and choice of approach. Sekhar et al.  have developed a useful scheme that is based on the tumor's anatomical location along the clivus, mainly along the upper, middle, or lower clivus. A similar scheme based on both anatomical location and tumor extent permits more rational decision making regarding the optimal surgical approach. The tumors are divided into three areas (Fig. 2). Tumors of the upper third involving the petrous apex and posterior cavernous sinus are best approached via an orbitozygomatic or Kawase's approach. Tumors of the middle clival level involving the caudal extent of the internal auditory meatus to the jugular foramen are best approached via a transpetrosal route. Tumors of the lower clivus down to the foramen magnum are best approached by the far-lateral approach or combination approaches.