Faculty Bibliography

BACKGROUND: Nonvestibular schwannomas of the skull base often represent a challenge owing to their anatomic location. With improved techniques in endoscopic endonasal skull base surgery, resection of various ventral skull base tumors, including schwannomas, has become possible. OBJECTIVE: To assess the outcomes of using endoscopic endonasal approach (EEA) for nonvestibular schwannomas of the skull base. METHODS: Seventeen patients operated on for skull base schwannomas by EEA at the University of Pittsburgh Medical Center from 2003 to 2009 were reviewed. RESULTS: Three patients underwent combined approaches with retromastoid craniectomy (n = 2) and orbitopterional craniotomy (n = 1). Three patients underwent multistage EEA. The rest received a single EEA operation. Data on degree of resection were found for 15 patients. Gross total resection (n = 9) and near-total (>90%) resection (n = 3) were achieved in 12 patients (80%). There were no tumor recurrences or postoperative cerebrospinal fluid leaks. In 3 of 7 patients with preoperative sensory deficits of trigeminal nerve distribution, there were partial improvements. Patients with preoperative reduced vision (n = 1) and cranial nerve VI or III palsies (n = 3) also showed improvement. Five patients had new postoperative trigeminal nerve deficits: 2 had sensory deficits only, 1 had motor deficit only, and 2 had both motor and sensory deficits. Three of these patients had partial improvement, but 3 developed corneal neurotrophic keratopathy. CONCLUSION: An EEA provides adequate access for nonvestibular schwannomas invading the skull base, allowing a high degree of resection with a low rate of complications.

The authors have applied high-definition fiber tracking (HDFT) to the resection of an intraparenchymal dermoid cyst by using a minimally invasive endoscopic port. The lesion was located within the mesial frontal lobe, septal area, hypothalamus, and suprasellar recess. Using high-dimensional (256 directions) diffusion imaging, more than 250,000 fiber tracts were imaged before and after surgery. Trajectory planning using HDFT in a computer model was used to facilitate cannulation of the cyst with the endoscopic port. Analysis of the proposed initial surgical route was overlaid onto the fiber tracts and was predicted to produce substantial disruption to prefrontal projection fibers (anterior limb of the internal capsule) and the cingulum. Adjustment of the cannulation entry point 1 cm medially was predicted to cross the corpus callosum instead of the anterior limb of the internal capsule or the cingulum. Following cyst resection performed using endoscopic port surgery, postoperative imaging demonstrated accurate cannulation of the lesion, with improved quantitative signal from both the anterior limb of the internal capsule and the cingulum. The observed fiber preservation from the cingulum and the anterior limb of the internal capsule, with minor injury to the corpus callosum, was in close agreement with preoperative trajectory modeling. Comparison of pre- and postoperative HDFT data facilitated quantification of the benefits and costs of the surgical trajectory. Future studies will help to determine whether HDFT combined with endoscopic port surgery facilitates anatomical and functional preservation in such challenging cases.

BACKGROUND: Understanding the course of the most medially located parasellar cranial nerve, the abducens, becomes critical when performing an expanded endonasal approach. OBJECTIVE: We report an anatomoclinical study of the abducens nerve and describe relevant surgical nuances to avoid its injury. METHODS: Ten anatomic specimens were dissected using endoscopes attached to an high-definition camera. A series of anatomic measurements and relationships of the abducens nerve were noted. Illustrative clinical cases are described to translate those findings into practice. RESULTS: Cisternal, interdural, gulfar, and cavernous segments of the abducens were identified intracranially. The mean distance from the vertebrobasilar junction (VBJ) to the pontomedullary sulcus (PMS) was 4 mm; horizontal distance between both abducens nerves at the PMS was 10 mm, and between both abducens at the interdural segment was 18.5 mm. The upper limit of the lacerum segment of the internal carotid artery was at the same level of the dural entry point of the sixth cranial nerve posteriorly. The sellar floor at the sphenoid sinus marks the level of the gulfar segment in the craniocaudal axis. At the superior orbital fissure, the abducens nerve and V2 were at an average vertical distance of 11.5 mm. CONCLUSION: Anatomic landmarks to localize the abducens nerve intraoperatively, such as the VBJ for the transclival approach, the lacerum segment of the carotid, and the sellar floor for the medial petrous apex approach, and V2 for Meckel's cave approach, are reliable and complementary to the use of intraoperative electrophysiological monitoring.

INTRODUCTION: The transclival endoscopic endonasal approach was used to completely remove a prepontine neuroenteric cyst in two different patients. CASE REPORTS: Full clinical improvement without postoperative complication was achieved in both cases. The postoperative hospital stay was limited to 2 and 3 days. DISCUSSION: In comparison to posterolateral skull base approaches, the transclival endoscopic endonasal approach allows direct access to the prepontine cistern without unnecessary manipulation of neurovascular structures at the cerebellopontine angle. In contrast to transoral surgery, patients may have decreased risk of infection and can be fed orally immediately without the risks of palatal and oropharyngeal dehiscence. CONCLUSION: Neuronavigation technology, strict adherence to microsurgical principles, and significant endoneurosurgical experience are strongly recommended when approaching these challenging lesions.

OBJECTIVE: The endoscopic endonasal transclival approach is a valid alternative for treatment of lesions in the clivus. The major limitation of this approach is a significant lateral extension of the tumor. We aim to identify a safe corridor through the occipital condyle to provide more lateral exposure of the foramen magnum. METHODS: Sixteen parameters were measured in 25 adult skulls to analyze the exact extension of a safe corridor through the condyle. Endonasal endoscopic anatomic dissections were carried out in nine colored latex-injected heads. RESULTS: Drilling at the lateral inferior clival area exposed two compartments divided by the hypoglossal canal: the jugular tubercle (superior) and the condylar (inferior). Completion of a unilateral ventromedial condyle resection opens a 3.5 mm (transverse length) * 10 mm (vertical length) lateral surgical corridor, facilitating direct access to the vertebral artery at its dural entry point into the posterior fossa. The supracondylar groove is a reliable landmark for locating the hypoglossal canal in relation to the condyle. The hypoglossal canal is used as the posterior limit of the condyle removal to preserve more than half of the condylar mass. The transjugular tubercle approach is accomplished by drilling above the hypoglossal canal, and increases the vertical length of the lateral surgical corridor by 8 mm, allowing for visualization of the distal cisternal segment of the lower cranial nerves. CONCLUSION: The transcondylar and transjugular tubercle "far medial" expansions of the endoscopic endonasal approach to the inferior third of the clivus provide a unique surgical corridor to the ventrolateral surface of the ponto- and cervicomedullary junctions.

OBJECT: Rathke cleft cysts (RCCs) are benign lesions that can be diagnosed as an incidental finding associated with headaches, pituitary dysfunction, or vision deterioration. Typically, they occur in a sellar or suprasellar location. The aim of this study was to review the clinical presentation and outcomes associated with endoscopic endonasal resection of these lesions. METHODS: The authors retrospectively reviewed a series of 35 patients with a diagnosis of RCC after endoscopic endonasal resection at the University of Pittsburgh between January 1998 and July 2008. RESULTS: All 35 patients underwent a purely endoscopic endonasal approach (EEA). The average patient age was 34 years (range 12-67 years), and the average follow-up was 19 months (range 1-60 months). Clinical follow-up data were available for 32 patients, and radiographic follow-up data were accessible for 33 patients. All of the patients underwent complete removal of the cyst contents, and according to radiography studies 2 patients had a recurrence, neither of which required reoperation. The mean cyst volume was 1052.7 mm(3) (range 114-6044 mm(3)). Headache was a presenting symptom in 26 (81.2%) of 32 patients, with 25 (96.1%) of 26 having postoperative improvement in their headaches. Fifteen (57.7%) of the 26 patients had complete pain resolution, and 10 (38.5%) had a > 50% reduction in their pain scores. Six (18.8%) of 32 patients initially presented with pituitary dysfunction, although 2 (33.3%) had postoperative improvement. Three (9.4%) of 32 patients had temporary pituitary dysfunction postoperatively, although there was no permanent pituitary dysfunction. Neither were there any intraoperative complications, postoperative CSF leaks, or new neurological deficits. The average hospital stay was 1.8 days (range 1-5 days). CONCLUSIONS: The EEA is a safe and effective approach in the treatment of RCCs. None of the patients in this study experienced any worsening of their preoperative symptoms or pituitary function, and 96% of the patients who had presented with headache experienced complete or significant pain relief following treatment.