The Skull Base Team at Penn Medicine is performing advanced minimally invasive surgeries to manage tumors in inaccessible areas of the skull base.
Certain regions of the skull base are a challenge for surgical access by virtue of their depth, anatomic complexity, and proximity to the optic tracts, cranial nerves, and internal carotid artery, among other vital neurovascular structures. Tumors arising in these areas are particularly destructive for their tendency for compression, adherence, and bony infiltration. Reaching and resecting these growths present significant complexities to neurosurgical practice, and safe access to this region has become an area of specialization for the surgeons at Penn Neurosurgery and Penn Otorhinolaryngology.
The petrous apex (PA) offers a particularly challenging environment for tumor resection, for two principal reasons. First, the PA is deep-seated, and bordered by a collection of sinuses and conduits for vital structures, including the posterior cavernous sinus, Meckel’s cave, internal acoustic canal, the petrous portion of the internal carotid artery (ICA), and the inferior petrosal sinus. Second, frequent invaders of the PA include chordomas and chondrosarcomas, which are among the most resilient, invasive, and destructive skull base tumors.
Traditional surgical approaches to the PA include anterolateral transpetrous middle fossa and lateral translabyrinthine procedures, all of which involve invasive exposures with a heightened risk for injury to neurovascular structures. The middle fossa approach is limited by the need for temporal lobe retraction and working around the petrous carotid artery. Translabyrinthine approaches requires navigating the regions of the cochlea, labyrinth, and facial nerve, heightening the concern for hearing, balance, and facial nerve dysfunction.
The endoscopic endonasal approach offers some advantage over traditional approaches accessing the PA for the treatment of central tumors, but the lateral extent of this approach has previously been limited by the ICA. Furthermore, comfort with the endoscope and the endonasal corridor require specialized training and complementary surgical teams.
Contralateral Transmaxillary Surgery for Skull Base Tumors
At Penn Neurosurgery, the management of deep-seated skull base tumors is motivated by the application of recent advances in surgical technique designed to yield a combination of benefits. These include direct access to the target region, minimizing risk to surrounding structures, avoidance of manipulative or potentially destructive procedures (e.g., brain retraction, cranial nerve manipulation), gross total resection of the tumor, and effective wound closure. The newer contralateral transmaxillary approach to the PA, for example, takes advantage of the paranasal sinuses to offer improved surgical trajectory relative to the ICA, minimizing risk to the vessel. Moreover, the procedure can be combined with endoscopic endonasal surgery to increase the lateral extent of access from the anterior trajectory including access to lesions behind the petrous ICA through a minimally invasive approach.
Case Study
Figure 1: Endoscopic endonasal approach combined with contralateral transmaxillary middle fossa surgery to remove a deep-seated right chondrosarcoma involving the middle and posterior fossae, petrous apex, clivus, and petrous segment of the internal carotid artery.
Mrs. R, a 64-year-old woman, was referred to Penn Neurosciences from an outside institution following biopsy for a deep-seated right petrous apex and petroclival lesion that on pathology was determined to be a chondrosarcoma. Preoperative imaging of the tumor demonstrated involvement of the middle and posterior fossae, petrous apex, clivus, and the petrous segment of the internal carotid artery. Mrs. R’s presenting symptoms included diplopia and sixth nerve palsy.
At Penn Medicine, surgery for skull base tumors involves the collaboration of skull base specialists from the Divisions of Neurosurgery and Otorhinolaryngology-Head and Neck Surgery. Thus, a surgical plan for Mrs. R was developed Christina Jackson, MD, of Penn Neurosurgery, Nithin Adappa, MD, and Michael Kohanski, MD, PhD, of Penn ENT. Together, the team determined that the best way to achieve complete resection of the tumor while minimizing surgical risk and morbidity was an expanded endoscopic endonasal approach combined with contralateral transmaxillary middle fossa surgery followed by a vascularized pedicled nasoseptal flap for reconstruction (Figure 1). A discussion of the benefits and risks of surgery then took place with Mrs. R, who expressed her understanding and a wish to proceed.
The Procedure - Following standard surgical preparation, the stereotactic surgical navigation and image guidance system was calibrated, and used throughout the surgery. An extended left-sided pedicled vascularized nasoseptal flap was then created, followed by bony exposure using a high speed drill to access the tumor, beginning with the removal of portions of the septum, sphenoethmoid bone and turbinates, to allow bimanual access through the nasal corridor. A Caldwell-luc procedure was then performed to gain access to the contralateral maxillary sinus, followed by widening of the anterior and medial maxillary wall. A transpterygoid approach involving removal of the posterior wall of the maxillary sinus followed, exposing the pterygopalatine and middle cranial fossae. Subsequently, the internal maxillary artery was ligated and identification and exposure of critical neurovasculature structures (including the carotid artery and 6th nerve) was established under the guidance of intra-operative microdoppler, neuronavigation, and neuromonitoring.
Continued exposure of the middle and inferior clivus revealed tumor-involved bone. Removal of this bone found soft tumor filling the cavity along the right lateral clivus, petrous apex, and petroclival synchondrosis posterior to the right paraclival and petrous carotid.
Figure 2: Complete resection of a soft tumor in the petrous apex and petroclival synchondrosis posterior to the right paraclival and petrous carotid via combined contralateral transmaxillary and endonasal approaches. Safe resection was ensured using meticulous microsurgical techniques, frequent stimulation of cranial nerves, and doppler of the carotid artery.
To further reveal the lateral aspect of the tumor and allow mobilization of the carotid artery, further drilling was performed to expose the right paraclival and petrous carotid artery and the right 6th nerve. Endoscopic resection of the tumor was then initiated through the combined contralateral transmaxillary and bilateral nasal corridors, allowing visualizing and access to the tumor behind the carotid artery (Figure 2). Safe resection of the tumor was ensured using meticulous microsurgical techniques, frequent stimulation of cranial nerves, and doppler of the carotid artery. The tumor was then carefully peeled away from the carotids.
Tumor resection continued inferiorly and laterally using an angled endoscope, drilling away diseased bone as it was encountered until the inferior petrosal sinus was encountered. The final pieces of the tumor were carefully dissected off of the horizontal segment of the petrous carotid artery. Complete resection of the tumor was achieved and confirmed by endoscopy. There was no invasion of the dura and no evidence of CSF leak. The carotid was dopplered, revealing substantial flow. Warm irrigation allowed meticulous hemostasis. Reconstruction was then accomplished by rotating the pedicled nasoseptal flap to cover the entire defect area, including the exposed carotid artery and right pterygopalatine fossa. The graft was then secured with surgical glue.
Following standard procedures for post-procedural safety, Mrs. R was extubated and transported to the ICU in stable condition, where she recovered without issue. After an overnight in-hospital stay for observation, she was discharged home on post operative day one in excellent condition. She resumed regular activities and work two weeks after her surgery.
About the Center for Cranial Base Surgery at Penn Medicine
The Center for Cranial Base Surgery has a rich history as a leader in the treatment of complex lesions through the use of modern techniques such as minimally invasive endonasal surgery, transoral robotic surgery (TORS), 3-D navigation planning, microscopic and laser techniques, and ongoing research studies and clinical trials. With the advent of these procedures, many tumors that were once considered inaccessible can now be successfully treated.
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