Neurophysiologic Monitoring of Oculomotor Nerves During Transorbital Surgery: Proof of Concept and Anatomic Demonstration.

BACKGROUND AND OBJECTIVES: Transorbital neuroendoscopic surgery (TONES) is continuously evolving and gaining terrain in approaching different skull base pathologies. The objective of this study was to present our methodology for introducing recording electrodes, which includes a new transconjunctival pathway, to monitor the extraocular muscle function during TONES. METHODS: A translational observational study was performed from an anatomic demonstration focused on the transconjunctival electrode placement technique to a descriptive analysis in our series of 6 patients operated using TONES in association with intraoperative neurophysiologic monitoring of the oculomotor nerves from 2017 to 2023. The stepwise anatomic demonstration for the electrode placement and correct positioning in the target muscle was realized through cadaveric dissection. The descriptive analysis evaluated viability (obtention of the electromyography in each cranial nerve [CN] monitored), security (complications), and compatibility (interference with TONES). RESULTS: In our series of 6 patients, 16 CNs were correctly monitored: 6 (100%) CNs III, 5 (83.3%) CNs VI, and 5 (83.3%) CNs IV. Spontaneous electromyography was registered correctly, and compound muscle action potential using triggered electromyography was obtained for anatomic confirmation of structures (1 CN III and VI). No complications nor interference with the surgical procedure were detected. CONCLUSION: The methodology for introducing the recording electrodes was viable, secure, and compatible with TONES.

Pituitary adenoma with oculomotor cistern extension: membranous anatomy and clinical application.

BACKGROUND: The anatomical basis of pituitary adenomas (PAs) with oculomotor cistern (OC) extension as a growth corridor is overlooked in the literature. In this paper, the authors use the technique of epoxy sheet plastination to study the membranous structure of the OC and validate the results by retrospective analysis of patients with OC extension. METHODS: Eighteen specimens were used to study the membranous anatomy surrounding the OC using the epoxy sheet plastination technique. Thirty-four patients with OC extension were retrospectively reviewed. RESULTS: The OC consisted of two thin membranous layers. The inner layer was extended by the arachnoid layer from the posterior fossa, and the lateral layer consisted of the dura mater sinking from the roof of the cavernous sinus. The oculomotor nerve is more likely to displace with a superolateral trajectory due to the weakness of the posterior dura and the relatively large space in the medial and posterior trajectories, which is consistent with the intraoperative observations. Among the anatomical factors that affect the PA by OC extension, we found that the relative position of the internal carotid artery (ICA) and posterior clinoid process may lead to the narrowing of the OC. Of 34 cases, 28 patients achieved total resection. Among 24 preoperative patients with oculomotor nerve palsy, 16 cases were relieved to varying degrees postoperatively. There was no ICA injury or severe intracranial infection found in any of the patients. CONCLUSIONS: Extension into the OC is influenced by two anatomical factors: a weak point in the dura in the posterior OC and a potential space beyond this region of the dura. Meticulous knowledge of the membranous anatomy in endoscopic endonasal surgery is required to safely and effectively resect PA with OC extension.

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.

Malignant nerve sheath tumor of oculomotor nerve in a pediatric patient.

Malignant nerve sheath tumors are extremely rare pathologies. They tend to occur within peripheral nerves and have close association of neurofibromatosis disease. Here, we present the second case of MNST of oculomotor nerve in literature. The patient was a 2-year-old girl with left sided oculomotor nerve palsy. After resection, the patient immediately had chemotherapy and radiotherapy. One year after surgery disease progressed with extensive intracranial seedings, and she passed away.

Surgical anatomy and nuances of the expanded endonasal transdorsum sellae and posterior clinoidectomy approach to the interpeduncular and prepontine cisterns: a stepwise cadaveric dissection of various pituitary gland transpositions.

BACKGROUND: Excelsior knowledge of endoscopic anatomy and techniques to remove the natural barriers preventing full endonasal access to the interpeduncular and prepontine cisterns determines the ease of transposing the pituitary gland (hypophysiopexy) preserving the glandular function without manipulating the optic apparatus and the oculomotor nerves. METHODS: Throughout stepwise cadaveric dissections, we describe the expanded endonasal approach (EEA) to the interpeduncular and prepontine cisterns with special references to the intricate anatomy of the region and techniques for hypophysiopexy and posterior clinoidectomies. CONCLUSION: This article illustrates sellar-diaphragmatic dural incisions and various "pituitary gland transpositions" techniques performed via extradural (lifting the gland still covered by both dural layers), interdural (transcavernous), and intradural (between the medial wall of the cavernous sinus and the pituitary tunica) to access the prepontine and interpeduncular cisterns.

Endodermal Cyst Arising from the Oculomotor Nerve: A Case Report Outlining the Novel Insertion of Cysto-subarachnoid Shunt for Refractory Disease.

BACKGROUND: Endodermal cysts of the oculomotor nerve are rare presentations. Only case reports are available to help guide clinicians with managing this rare entity. CASE DESCRIPTION: A 3-year-old boy presented with an acute on chronic left oculomotor nerve palsy due to a left interpeduncular cistern cyst found on magnetic resonance imaging. He underwent a left pterional craniotomy and fenestration of the histologically proven endodermal cyst and had initial improvement at the 2-month review. He subsequently developed clinical and radiologic evidence of recurrence and was treated surgically with a refenestration and insertion of a cysto-subarachnoid shunt through a trans-sylvian approach. At 6-month follow-up, there was complete resolution of the oculomotor nerve palsy with interval development of oculomotor synkinesis. CONCLUSIONS: Magnetic resonance imaging is an essential modality in the follow-up of these patients postoperatively in the setting of unchanged or deteriorated neurology. Fenestration of the cyst is appropriate first-line surgical management; however, a cysto-subarachnoid shunt is a safe consideration in recurrent, symptomatic cysts and provides sustained symptom resolution.

Transnasal prelacrimal approach to the inferior intraconal space: a feasibility study.

BACKGROUND: Endonasal access to the inferomedial and inferolateral intraconal space via the orbital floor has not been reported. The primary purpose of this study was to assess the feasibility of accessing the inferior intraconal space through the orbital floor via a transnasal prelacrimal approach. Secondarily, it aims to highlight anatomical relationships of neurovascular structures in this space, as a requirement to prevent complications. METHODS: Six cadaveric heads (12 sides) were dissected using a transnasal prelacrimal approach. The orbital floor, medial to the infraorbital canal, was removed and the periorbita opened to expose the inferior rectus muscle. The inferomedial and inferolateral intraconal space was accessed alongside the medial and lateral border of inferior rectus muscle, respectively. Various anatomical relationships of adjacent neurovascular structures were recorded, and the distances among the recti muscles and optic nerve were also measured. RESULTS: The infraorbital nerve is located at the inferolateral aspect of inferior rectus muscle. In the inferomedial intraconal space, we identified the inferomedial muscular trunk of the ophthalmic artery, optic nerve, and branches of the oculomotor nerve; whereas the inferolateral intraconal space contained the inferolateral muscular trunk of ophthalmic artery, branches of the oculomotor and nasociliary nerve, and abducens nerve. Distances from the medial, inferior, and lateral recti muscles to the optic nerve were (mean ± standard deviation) 4.70 ± 1.18 mm, 5.60 ± 0.93 mm, and 7.98 ± 1.99 mm, respectively. Distances from the inferior rectus muscle to the inferior borders of medial and lateral recti muscles were 4.45 ± 1.23 mm and 8.77 ± 1.80 mm. CONCLUSION: It is feasible to access the inferior intraconal space through the orbital floor via a transnasal prelacrimal approach. The access may be subdivided into inferomedial and inferolateral corridors according to the entry point at the medial or lateral border of the inferior rectus muscle. Neurovascular structures in the inferior intraconal space are visualized directly, which should enhance their preservation.

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.

Cerebral Aneurysm Arising from Variant Posterior Communicating Artery Lying Lateral to Oculomotor Nerve.

BACKGROUND: In most cases, the posterior communicating artery (PCoA) lies medial to the oculomotor nerve. In this report, a rare case of a ruptured cerebral aneurysm arising from a variant PCoA lying lateral to the oculomotor nerve is described. CASE DESCRIPTION: A 41-year-old woman who had a history of surgical clipping of a right PCoA aneurysm 13 years earlier developed a subarachnoid hemorrhage due to a ruptured left true PCoA aneurysm. Three-dimensional computed tomography angiography showed a small saccular aneurysm arising from the PCoA itself. She underwent surgical clipping via a left frontotemporal craniotomy. Interestingly, the PCoA lay lateral to the oculomotor nerve, and the aneurysm dome projected medially and compressed the oculomotor nerve medially. A slightly angled fenestrated miniclip was applied across the PCoA, followed by reconstruction of the PCoA medial wall and simultaneous obliteration of the aneurysm. Complete aneurysm obliteration and good patency of both the PCoA and perforating arteries were confirmed intraoperatively by indocyanine green videoangiography. The patient's postoperative course was uneventful, and the patient was discharged with no neurologic deficits. CONCLUSIONS: Recognizing this anatomic variant is helpful in minimizing the potential complications in microsurgical management around the PCoA and oculomotor nerve. Lateral localization of the P1-2 junction might affect this rare anatomic variant.

Third nerve decompression by anterior petroclinoid ligament opening after clipping of posterior communicating artery aneurysm-How I do it.

BACKGROUND: Posterior communicating artery aneurysms sometimes present with partial or complete oculomotor nerve palsy, due to direct oculomotor nerve compression, irritation by subarachnoid blood, or both. Superiority of surgical clipping over endovascular coiling in terms of postoperative outcome is still controversial. METHOD: Direct oculomotor nerve decompression by opening of the anterior petroclinoid ligament during aneurysm clipping is performed as a simple and feasible surgical maneuver which allows to improve the decompression effect obtained by aneurysm exclusion. CONCLUSION: Anterior petroclinoid ligament opening permits to achieve a better oculomotor nerve decompression. Its efficiency on the recovery of the deficit needs to be proved by larger series.

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.

Usefulness of intraoperative electromyographic monitoring of oculomotor and abducens nerves during skull base surgery.

BACKGROUND: Intraoperative neurophysiologic monitoring of the extraocular cranial nerve (EOCN) is not commonly performed because of technical difficulty and risk, reliability of the result and predictability of the postoperative function of the EOCN. METHODS: We performed oculomotor nerve (CN III) and abducens nerve (CN VI) intraoperative monitoring in patients with skull base surgery by recording the spontaneous muscle activity (SMA) and compound muscle action potential (CMAP). Two types of needle electrodes of different length were percutaneously inserted into the extraocular muscles with the free-hand technique. We studied the relationships between the SMA and CMAP and postoperative function of CN III and CN VI. RESULTS: A total of 23 patients were included. Nineteen oculomotor nerves and 22 abducens nerves were monitored during surgery, respectively. Neurotonic discharge had a positive predictive value of less than 50% and negative predictive value of more than 80% for postoperative CN III and CN VI dysfunction. The latency of patients with postoperative CN III dysfunction was 2.79 ± 0.13 ms, longer than that with intact CN III function (1.73 ± 0.11 ms). One patient had transient CN VI dysfunction, whose CMAP latency (2.54 ms) was longer than that of intact CN VI function (2.11 ± 0.38 ms). There was no statistically significant difference between patients with paresis and with intact function. CONCLUSIONS: The method of intraoperative monitoring of EOCNs described here is safe and useful to record responses of SMA and CMAP. Neurotonic discharge seems to have limited value in predicting the postoperative function of CN III and CN VI. The onset latency of CMAP longer than 2.5 ms after tumor removal is probably relevant to postoperative CN III and CN VI dysfunction. However, a definite quantitative relationship has not been found between the amplitude and stimulation intensity of CMAP and the postoperative outcome of CN III and CN VI.

Microsurgical Anatomy of the Oculomotor Nerve.

The oculomotor nerve supplies the extraocular muscles. It also supplies the ciliary and sphincter pupillae muscles through the ciliary ganglion. The nerve fibers leave the midbrain through the most medial part of the cerebral peduncle and enter the interpeduncular cistern. After the oculomotor nerve emerges from the interpeduncular fossa, it enters the cavernous sinus slightly lateral and anterior to the dorsum sellae. It enters the orbit through the superior orbital fissure, after exiting the cavernous sinus, to innervate the extraocular muscles. Therefore, knowledge of the detailed anatomy and pathway of the oculomotor nerve is critical for the management of lesions located in the middle cranial fossa and the clival, cavernous, and orbital regions. This review describes the microsurgical anatomy of the oculomotor nerve and presents pictures illustrating this nerve and its surrounding connective and neurovascular structures. Clin. Anat. 30:21-31, 2017. © 2016 Wiley Periodicals, Inc.

Evaluation of Surgical Strategy Based on the Intraoperative Superior Oblique Tendon Traction Test.

PURPOSE: To clarify the efficacy of a surgical strategy based on the superior oblique tendon traction test. METHODS: A retrospective chart review was performed between January 2002 and June 2015. During that period, a single inferior oblique muscle (IO) myectomy and a combined IO myectomy and superior oblique muscle (SO) tuck procedure were performed based on SO tendon looseness as revealed by a traction test. The surgical effects of both procedures and the number of operations were analyzed. RESULTS: Sixty-five cases were retrieved. Seventy-four surgeries were required. The IO myectomy and simultaneous groups included 48 and 17 cases, respectively. Pre-operative vertical deviation was significantly lower in the IO myectomy (11.8 prism diopters) than in the simultaneous (27.2 prism diopters; Mann-Whitney U-test, P < 0.001) group. The mean induced changes were 9.4 prism diopters and 21.6 prism diopters in the IO myectomy and simultaneous groups, respectively, and the postoperative vertical deviation was not significantly different. On average, 1.13 and 1.18 surgeries per patient were performed in the IO myectomy and simultaneous groups, respectively. CONCLUSION: The simultaneous surgery of inferior oblique myectomy and superior oblique tuck is safe and effective for treating large angle of congenital/idiopathic superior oblique palsy with a lax superior oblique tendon, as determined by the traction test.

Tarsoaponeurectomy as an alternative in difficult blepharoptosis cases.

BACKGROUND: The purpose of this study was to evaluate the results of tarsoaponeurectomy in patients with unsuccessful results after repetitive surgery or who developed post-traumatic blepharoptosis. METHODS: The files of 107 patients (136 eyes) on whom surgery was performed between January 2010 and December 2014 due to blepharoptosis were scanned retrospectively. Among these patients, the files and operational notes of eight patients who underwent surgery through the method of tarsoaponeurectomy were examined in detail. The epidemiological data, indication for surgery, previous ptosis and/or eyelid surgeries and trauma histories, preoperative and postoperative measurement data (palpebral space (PS), margin reflex distance (MRD1, MRD2), levator muscle function (LMF)) of the patients were recorded. The follow-up time of the patients was 7 to 34 months with an average of 16 months. RESULTS: A total of eight patients consisting of three females and five males were included in the study. The age range was 19 to 63 years with an average of 39 ± 16.2 years. Four patients had traumatic ptosis history whereas four patients had previous multiple levator procedure surgery history. Those patients with a history of ptosis had undergone surgery with levator procedure at least two times. Additionally, one patient had upper eyelid entropion, one had anophthalmic socket syndrome, and one had exposure keratopathy and traumatic dilated pupil. Seven patients had ptosis in the left eye whereas one patient had ptosis in the right eye. All patients were given a tarsoaponeurectomy as the basic surgical procedure while the patient with entropion was given a tarsal fracture and ear cartilage grafting as additional surgery. Two patients with vertical notching were also given a vertical blepharotomy through which a strip of tarsus was removed. CONCLUSIONS: Tarsoaponeurectomy is an alternative method for oculoplastic surgeons used to deal with patients on whom sufficient and desired results have not been achieved despite repetitive surgery and in post-traumatic cases where levator muscle and aponeurosis cannot be dissociated peroperatively.

Endoscopic endonasal surgical approach to the oculomotor trigone from the cavernous sinus.

Knowledge of anatomy visualized endoscopically is necessary to perform endoscopic surgical procedures safely. The cavernous sinuses are complicated structures with major blood vessels and nerves seated deeply in the center of the skull base. Anatomical orientation during surgery is essential for deep and narrow skull base surgery. While performing surgery involving the cavernous sinuses, understanding of the structures identifiable via a transsphenoidal view can allow comprehension of the relationship between a lesion and the surrounding structures, thus preventing intraoperative complications. The objective of this study was to dissect the neurovascular structures in the cavernous sinus deeply inside the oculomotor trigone through a transsphenoidal view, and to determine the relationships among anatomical landmarks in the path of surgery. Ten fresh silicone-injected cadaveric heads were evaluated. Four millimeter-diameter rigid endoscopes with 0° and 30° rod-lenses were utilized to perform an endonasal transsphenoidal approach. The detailed position and course of the major components in each cavernous sinus were assessed under panoramic view. We also validated the utility of this approach by successfully excising a huge pituitary adenoma.

Compartmental endoscopic surgical anatomy of the medial intraconal orbital space.

BACKGROUND: Surgical management of intraconal pathology represents the next frontier in endoscopic endonasal surgery. Despite this, the medial intraconal space remains a relatively unexplored region, secondary to its variable and technically demanding anatomy. The purpose of this study is to define the neurovascular structures in this region and introduce a compartmentalized approach to enhance surgical planning. METHODS: This study was an institutional review board (IRB)-exempt endoscopic anatomic study in 10 cadaveric orbits. After dissection of the medial intraconal space, the pattern and trajectory of the oculomotor nerve and ophthalmic arterial arborizations were analyzed. The position of all vessels as well as the length of the oculomotor trunk and branches relative to the sphenoid face were calculated. RESULTS: A mean of 1.5 arterial branches were identified (n = 15; range, 1-4) at a mean of 8.8 mm from the sphenoid face (range, 4-15 mm). The majority of the arteries (n = 7) inserted adjacent to the midline of medial rectus. The oculomotor nerve inserted at the level of the sphenoid face and arborized with a large proximal trunk 5.5 ± 1.1 mm in length and multiple branches extending 13.2 ± 2.7 mm from the sphenoid face. The most anterior nerve and vascular pedicle were identified at 17.0 and 15.0 mm from the sphenoid face, respectively. CONCLUSION: The neurovascular supply to the medial rectus muscle describes a varied but predictable pattern. This data allows the compartmentalization of the medial intraconal space into 3 zones relative to the neurovascular supply. These zones inform the complexity of the dissection and provide a guideline for safe medial rectus retraction relative to the fixed landmark of the sphenoid face.

[Detection of oculomotor nerve compression by 3D-FIESTA MRI in a patient with pituitary apoplexy and diabetes mellitus].

We report the usefulness of 3D-FIESTA magnetic resonance imaging(MRI)for the detection of oculomotor nerve palsy in a case of pituitary apoplexy. A 69-year-old man with diabetes mellitus presented with complete left-side blepharoptosis. Computed tomography of the brain showed an intrasellar mass with hemorrhage. MRI demonstrated a pituitary adenoma with a cyst toward the left cavernous sinus, which was diagnosed as pituitary apoplexy. 3D-FIESTA revealed that the left oculomotor nerve was compressed by the cyst. He underwent trans-sphenoid tumor resection at 5 days after his hospitalization. Post-operative 3D-FIESTA MRI revealed decrease in compression of the left oculomotor nerve by the cyst. His left oculomotor palsy recovered completely within a few months. Oculomotor nerve palsy can occur due to various diseases, and 3D-FIESTA MRI is useful for detection of oculomotor nerve compression, especially in the field of parasellar lesions.

Complete reduction with traction of the infraorbital neurovascular bundle in a delayed patient with white-eyed blow-out fracture.

In case of delayed surgery, if an orbital floor fracture involves the infraorbital canal, adhesions may form between the infraorbital neurovascular bundle and herniated muscle, and manipulations to reduce the fracture may lead to unexpected bleeding due to injury of the infraorbital artery. The author reports a case of a white-eyed blow-out fracture patient, who visited our clinic one-and-a-half months after the injury. Exploration of the fracture confirmed intensive fibrosis of the infraorbital neurovascular bundle and the entrapped inferior rectus muscle at the fracture site. The author was able to reduce the muscle completely with the release of the fibrotic tissue around the nerve bundle by using a vessel loop to safely retract the neurovascular bundle upwards, and obtained good results.