The Orbitozygomatic-Combined Supra- and Infratentorial Approach: Technical Note
Michael T. Lawton, MD
C. Phillip Daspit, MD†
Robert F. Spetzler, MD
Division of Neurological Surgery and Neuro-Otology† Barrow Neurological Institute, Mercy Healthcare Arizona, Phoenix, Arizona
The orbitozygomatic-combined approach was applied in the case of a 60 year-old man with a large meningioma that spanned the anterior, middle, and posterior cranial fossae. The exposure provided by this approach enabled a radical resection of the tumor with preservation of all involved cranial nerves and vascular structures, and contributed to an excellent outcome. Compared to the standard combined approach, the additional anterior exposure of the orbitozygomatic-combined approach improved the safety and facility of tumor resection. This approach is ideal for lesions located at the center of the skull base that extend into all three cranial fossae and across the midline.
Key Words: combined supra- and infratentorial approach, meningioma, orbitozygomatic approach, skull base tumor, transcochlear approach
A critical component of many skull base approaches is the safe removal of the petrous bone.[1-3,5-7,12-15,18,21,22,25,26,28] Petrosectomy opens a corridor of exposure to the center of the skull base. The transpetrosal approaches are familiar to most neurosurgeons and include the retrolabyrinthine, translabyrin-thine[5,13,21] and transcochlear[14,26] approaches. Still, exposure gained from these approaches can be limited at the region of interest medially or it can be inadequate for larger lesions. Therefore, transpetrosal approaches have been used in combination with other approaches to gain even more exposure. For example, the combined supra- and infratentorial approach joins the subtemporal and transpetrosal exposures to access the upper and middle clivus.[7,12,25,2] The far-lateral combined supra- and infratentorial approach (combined-combined approach)[3,4] adds to them the far-lateral exposure[11,23,24,27] to access the entire clivus. We continue to experiment with combination approaches. One modification that has proven useful is the orbitozygomatic-combined supra- and infratentorial approach. Our experience with this modification is reported.
Figure 1. (A) Axial and (B) coronal T1-weighted magnetic resonance (MR) images with gadolinium enhancement demonstrate an enhancing tumor that fills the right middle fossa medially, infiltrates both cavernous sinuses, and encases both optic nerves and internal carotid arteries. (C) Sagittal T1-weighted MR image with gadolinium enhancement shows that the tumor extends over the petrous ridge down to the pontomedullary junction.
A 60-year-old male presented to the emergency room after a generalized tonic-clonic seizure. His only additional complaint was diplopia on right lateral gaze during the preceding month. His neurological examination was otherwise normal. In the medial right middle cranial fossa, magnetic resonance (MR) imaging demonstrated a 6 x 5 x 5-cm skull base tumor that enhanced homogeneously (Fig. 1). It extended anteriorly into the sella, sphenoid sinus, suprasellar cistern, and both right and left cavernous sinuses, and it encased both internal carotid arteries. Posteriorly, the tumor extended down to the pontomedullary junction, into the cerebellopontine angle and compressed the pons, right cerebellar peduncles, and right cerebral peduncle.
Figure 2. Intraoperative photograph shows the large dural surface exposed after right frontotemporoparietal craniotomy,orbitozygomatic osteotomy, and petrosectomy. Note the transposed facial nerve (arrow). (B) ISG wand (ISG Technologies, Inc., Mississauga, Ontario, Canada) display shows the trajectory to the tumor through the petrosectomy defect (lower right). (C) The anterior exposure provided by this approach enables safe dissection of the optic chiasm and tracts. Intraoperative (D) photograph and (E) illustration show the internal carotid artery and the second, third, fourth, fifth, and seventh cranial nerves dissected from the tumor. ICA = internal carotid artery, CN II = optic nerve, CN III = oculomotor nerve, CN IV = trochlear nerve, CN V = trigeminal nerve, and CN VII = facial nerve.
An orbitozygomatic-combined supra- and infratentorial approach with transcochlear petrosectomy was performed. Tumor encased the optic nerves, optic chiasm, pituitary stalk, internal carotid arteries, and the oculomotor, trochlear, trigeminal and abducent nerves and displaced the basilar artery and the facial and vestibulocochlear nerves. These neurovascular structures were dissected from the tumor, and all cranial nerves were left intact (Fig. 2). Resection of tumor in the cavernous sinus and sella was not attempted. Postoperative images demonstrated substantial tumor resection (Fig. 3). Meningioma was diagnosed by pathologic examination.
Postoperatively, the patient awoke with deficits of the oculomotor, facial, and vestibulocochlear nerves. He developed a communicating hydrocephalus that required a ventriculoperitoneal shunt. He made an excellent recovery. At a 1-year follow-up examination, function of the oculomotor nerve was normal and function of the facial nerve was almost normal.
The patient is positioned supine with the head turned away from the lesion, bringing the midline parallel to the floor and inclined slightly downward. To expose the mastoid bone fully, the head is flexed to bring the chin to the contralateral shoulder. The skin incision begins at the mastoid tip, curves around the ear, and ends in the midline anteriorly at the hairline. The external auditory canal is transected and oversewn in two layers—a maneuver that allows the flap to be retracted anteriorly to the periosteum of the temporomandibular joint.
Petrosectomy is performed first. A basic mastoidectomy with complete removal of the bone covering the sigmoid sinus and dura of the posterior and middle fossae exposes the sinodural angle. The sigmoid sinus is unroofed inferiorly to the jugular bulb. The facial nerve is skeletonized along its mastoid segment and all three semicircular canals are removed. The internal auditory canal is skeletonized from the porus acousticus medially to Bill’s bar laterally. The wall of the posterior external auditory canal is taken down, and the ossicles and tympanic membrane are removed. The tympanic segment of the facial nerve is then exposed anteriorly to the geniculate ganglion. The greater superficial petrosal nerve is transected anteriorly at its origin from the geniculate ganglion, and the facial nerve is dissected from its bony canal and transposed posteriorly. The cochlea is drilled out completely. When the drilling is finished, the petrosectomy extends superiorly to the superior petrosal sinus and dura of the middle fossa floor, inferiorly to the jugular bulb and inferior petrosal sinus, anteriorly to the internal carotid artery, and medially to the carotid siphon and Meckel’s cave.