Endoscopic anatomy of the oculomotor nerve: defining the blind spot during endoscopic skull base surgery

Usefulness of Opening the Diaphragma Sellae Before Transecting Interclinoidal Ligament for Endoscopic Endonasal Transoculomotor Triangle Approach: Technical Nuances and Surgical Outcomes

OBJECTIVE

Opening the oculomotor triangle (OT) and removing the posterior fossa lesion by endoscopic endonasal approach (EEA) is challenging for even an experienced endoscopic neurosurgeon. We summarize the treatment experience and technical nuances with EEA for resection of pituitary neuroendocrine tumors and cavernous sinus (CS) meningiomas invading through the OT.

METHODS

Between 2018 and 2022, 8 patients, comprising 5 with pituitary neuroendocrine tumors (3 with nonfunctioning and 2 with somatotroph tumors with increased levels of growth hormone) and 3 CS meningiomas, were treated using an endoscopic endonasal transoculomotor triangle approach. The critical surgical technique is continuously opening the diaphragma sellae from medial to lateral toward the interclinoidal ligament and transecting it to enlarge the OT. We evaluated preoperative tumor size, previous surgical history, preoperative symptoms, extent of tumor resection, histopathology, and postoperative complications for all patients.

RESULTS

The gross total resection (defined as complete removal) in 3 patients (38%), near-total resection (defined as >95% removal) in 4 patients (50%), and subtotal resection (defined as ≤90% removal) in 1 patient (12%) and gross total resection of tumor invading through the OT was achieved in all patients through pure EEA. Two of 3 patients with visual deficits in nonfunctioning pituitary neuroendocrine tumors improved, and the other remained stable postoperatively. One patient showed transient oculomotor nerve palsy. The growth hormone level of the 2 patients with somatotroph tumors declined to normal. For 3 patients with CS meningiomas, cranial nerve palsy improved in 2 patients, whereas the other patient developed increased facial numbness after surgery.

CONCLUSIONS

The endoscopic endonasal transoculomotor triangle approach is an efficient surgical option for tumors with CS invasion and OT penetration.

The Oculomotor Cistern and Its Role in the Management of Pituitary Lesions: An Anatomical, Radiographic, and Clinical Scoping Review

BACKGROUND

The oculomotor cistern (OMC) is a cerebrospinal fluid space bound by meningeal layers that surrounds the oculomotor nerve as it crosses the oculomotor triangle to reach the lateral wall of the cavernous sinus at the level of the anterior clinoid process. Although several anatomical and radiological studies are available, its anatomy and relationship with pituitary adenomas (PAs) are still matter of discussion.

OBJECTIVE

The aim of the study is to provide an updated and focused overview of the OMC, highlighting the different perspectives and descriptions from anatomical, radiological, and clinical points of view.

METHODS

A scoping review was conducted up to 29th October 2022, according to PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) criteria. PubMed, Web of Science, Scopus databases, and correlated citations were investigated.

RESULTS

Of the 562 records identified, 22 were included in the present analysis. There were 13, 5, and 4 anatomo-surgical, radiological, and clinical studies, respectively. Though there is general consensus on its definition, data are variable on different features of OMC. Defects or absence of dural layers adjacent to the oculomotor nerve were described in only 4 papers. The transition from meningeal to neural layers is still unclear. PAs with OMC involvement are poorly studied and have unique clinical characteristics. To date, 21 patients have been described; the reported prevalence of OMC involvement by PAs ranges from 4.1% to 14.6%.

CONCLUSIONS

Clarifying the OMC features with further systematic studies may not only broaden theoretical knowledge but also have implications on endoscopic transnasal pituitary surgery.

Bony landmarks in the endoscopic endonasal transoculomotor approach

The endoscopic endonasal transoculomotor approach (EETA) has been recently described as a doorway to access the parapeduncular space and treat pituitary adenomas with oculomotor extension. Intraoperative identification of the oculomotor triangle endonasally is challenging and dissection can put the internal carotid artery (ICA) at risk. The aim of the present study is to find reliable landmarks that identify the oculomotor triangle (OCMT) during the EETA and protect the ICA from injury. Several lines were defined for calculations. Among them, one oblique line that extends from the inferior margin of the lateral orbital canal recess to the vidian canal was named the clinoid-to-vidian line (CVL), while a vertical line that extends over the most medial point of the paraclival ICA was titled the sagittal paraclival line (SPL). Anatomic relationships between the OCMT to these lines were assessed in 7 cadaveric heads. The intersecting point between the CVL and SPL is located within 2 mm of the center of the OCMT (mean 0.8 ± 0.5 mm), and 1.1 ± 0.8 mm medially and above the parasellar ICA. CVL and SPL are reliable landmarks during the EETA that can both protect the parasellar ICA and anatomically orientate to the blind spot that corresponds with the OCMT. We recommend starting dissection medial and superior to the CVL-SPL intersecting point, and carry the dissection laterally thereafter to avoid inadvertent injury of the ICA.

Combined supra-infrasellar approach to pituitary macroadenoma with oculomotor cistern extension: surgical strategy and experience

BACKGROUND

Oculomotor cistern extension (OMCE) of pituitary adenoma through the oculomotor triangle may be one of the major characteristics of multi-lobulated adenoma. The OMCE may be hard to remove only through the endonasal approach.

METHOD

We applied the simultaneous combined supra-infrasellar approach to remove pituitary adenoma with relatively large OMCE. Four (7.3%) of 55 consecutive patients with initially operated pituitary macroadenoma (> 10 mm) had OMCE. The combined supra-infrasellar approach was adopted in two cases with relatively large OMCE.

RESULTS

The simultaneous combined supra-infrasellar approach was performed with the transcranial microscopic transsylvian anterior temporal approach and the nasal endoscopic approach. The medial main mass was removed through the nasal side. The lateral OMCE was also removed through the nasal side by pushing the tumor in the sellar direction from the transcranial side. The oculomotor nerve was confirmed with electrical nerve stimulation. The main medial mass and the OMCE were mostly removed in both cases. Remnant tumor in the cavernous sinus was treated by gamma knife radiosurgery. Endoscopic transsphenoidal removal was performed in the other two cases with relatively small OMCE.

CONCLUSIONS

Pituitary macroadenomas with OMCE are a newly recognized form of progression with important implications for surgical strategy. The combined supra-infrasellar approach performed with the transcranial microscopic transsylvian anterior temporal approach using electrical nerve stimulation and the nasal endoscopic approach may be useful for this type of multi-lobulated pituitary adenoma.

Endoscopic endonasal transoculomotor triangle approach for adenomas invading the parapeduncular space: surgical anatomy, technical nuances, and case series

OBJECTIVE

Pituitary adenomas may extend into the parapeduncular space by invading through the roof of the cavernous sinus. Currently, a transcranial approach is the preferred choice, with or without the combination of an endonasal approach. In this paper the authors present a novel surgical approach that takes advantage of the natural corridor provided by the tumor to further open the oculomotor triangle and resect tumor extension into the parapeduncular space.

METHODS

Six injected specimens were used to demonstrate in detail the surgical anatomy related to the approach. Four cases in which the proposed approach was used were retrospectively reviewed.

RESULTS

From a technical perspective, the first step involves accessing the superior compartment of the cavernous sinus. The interclinoid ligament should be identified and the dura forming the oculomotor triangle exposed. The oculomotor dural opening may be then extended posteriorly toward the posterior petroclinoidal ligament and inferolaterally toward the anterior petroclinoidal ligament. The oculomotor nerve should then be identified; in this series it was displaced superomedially in all 4 cases. The posterior communicating artery should also be identified to avoid its injury. In all 4 cases, the tumor invading the parapeduncular space was completely removed. There were no vascular injuries and only 1 patient had a partial oculomotor nerve palsy that completely resolved in 2 weeks.

CONCLUSIONS

The endoscopic endonasal transoculomotor approach is an original alternative for removal of tumor extension into the parapeduncular space in a single procedure. The surgical corridor is increased by opening the dura of the oculomotor triangle and by working below and lateral to the cisternal segment of the oculomotor nerve.

Endoscopic endonasal surgery for pituitary adenomas extending to the oculomotor cistern

BACKGROUND

Extension of a pituitary adenoma to the oculomotor cistern harbors the risk of oculomotor nerve impairment and further extension into the interpeduncular cistern. The role of endoscopic endonasal surgery for those lesions was investigated.

METHODS

The medical records were retrospectively analyzed. Attention was paid to the oculomotor nerve function and removal rate of the tumor within the oculomotor and interpeduncular cisterns.

RESULTS

Six patients were eligible for the study, including 2 with oculomotor nerve palsy. The tumor from the oculomotor and interpeduncular cistern was removed in all except on one side of the case with bilateral tumor extension. The oculomotor nerve palsy demonstrated partial recovery in both cases during the 3-month follow-up.

CONCLUSION

The pituitary adenoma extending to the oculomotor cistern can be removed under the endoscope. Improvement of oculomotor nerve palsy can be achieved, and further tumor extension into the interpeduncular cistern can be prevented.

Pituitary macroadenomas with oculomotor cistern extension and tracking: implications for surgical management

OBJECT Oculomotor cistern extension of pituitary adenomas is an overlooked feature within the literature. In this study, 7 cases of pituitary macroadenoma with oculomotor cistern extension and tracking are highlighted, and the implications of surgical and medical management are discussed. METHODS The records of patients diagnosed with pituitary macroadenomas who underwent resection and in whom preoperative pituitary protocol MRI scans were available for review were retrospectively reviewed. The patient and tumor characteristics were reviewed along with the operative outcomes and complications. RESULTS Seven patients (4.1%) with oculomotor cistern extension and tracking were identified in a cohort of 170 patients with pituitary macroadenoma. The most common presenting symptoms were visual deficit (6 patients; 86%), apoplexy (3 patients; 43%), and oculomotor nerve palsy (3 patients; 43%). Lone oculomotor nerve palsy was seen in 2 patients without apoplexy and 1 patient with an apoplectic event. Gross-total resection was achieved via a microscopic endonasal transsphenoidal approach with or without endoscopic aid to the sella in 14%, near-total resection in 29%, and subtotal resection in 57% of patients in the data set. CONCLUSIONS Pituitary adenoma extension along the oculomotor cistern is uncommon; however, preoperatively recognizing such extension should play an important role in the surgeon's operative considerations and postoperative clinical management because this extension can limit gross-total resection using the transsphenoidal approach alone.

The oculomotor nerve: anatomic relationship with the floor of the third ventricle

PURPOSE

Endoscopic third ventriculostomy (ETV) has become first-line treatment for obstructive hydrocephalus. Many complications have been described, but the literature about oculomotor palsy after ETV is scarce. Therefore we undertook an anatomical study of the relationship of the oculomotor nerve to the floor of the third ventricle.

METHODS

Distances and angles between the third nerve and the bottom of the third ventricle were studied both in two cadaver heads and in high-definition CISS images in 16 MRI scans. The angles of the trajectories putting the nerve at risk or not were compared. Finally, in a retrospective analysis of intraoperative images the appearance of the membranous portion of the floor was defined and if visible, the distance of the third nerve to the midline was estimated by comparing with the 8-mm balloon catheter.

RESULTS

The course of the third nerve is approximately 8 mm laterally and approximately 17 mm caudally distant from the midpoint of the floor of the third ventricle. The angle of the trajectory to damage the third nerve is at least 12° greater than any safe angle of ETV trajectory through a normal burr hole.

CONCLUSIONS

The third nerve is not always visible during ETV procedures, but the angular and linear measurements imply that the risk to damage the nerve should be relatively small. Confirmation of these data in hydrocephalic patients with distorted anatomy is needed.

Extended endoscopic endonasal approach to the suprasellar parachiasmatic cisterns: anatomic study

OBJECTIVE

The objective of this study is to recognize the available endoscopic routes during approaches to the suprasellar region and the surgical endoscopic anatomy of the related neurovascular structures.

MATERIAL AND METHODS

Extended endoscopic endonasal approach to the suprasellar region (EEASR) through the planum sphenoidale was performed in five fresh adult cadavers. The anatomic characteristics of the suprasellar parachiasmatic cisterns were studied and documented following the resection of the planum sphenoidale and opening the dura to expose the anterior incisural space.

RESULTS

Two separate surgical corridors could be used during EEASR: one above and the other below the chiasm. The suprachiasmatic route exposed the gyrus recti, interhemispheric fissure, anterior cerebral artery complex, the lamina terminalis, and through this structure the anterior recess of the third ventricle. The subchiasmatic route exposed the pituitary stalk, superior hypophyseal artery, supraclinoidal internal carotid artery, origin of the ophthalmic artery, anterior choroidal artery, posterior communicating artery, uncus, optic tract, basilar artery and its bifurcation, pons, posterior cerebral artery, superior cerebellar artery, and oculomotor nerve.

CONCLUSION

The EEASR, a minimally invasive route to suprasellar parachiasmatic area, provided wide exposure of the basal cisterns. The surgical areas that were accessed through the subchiasmatic corridor could be divided into a medial part that included the interpeduncular and prepontine cisterns and a lateral part that contained carotid and sylvian cisterns superiorly and the crural and ambient cisterns inferiorly.