Oculomotor Trigone Research Articles

Transorbital approach to the cavernous sinus: an anatomical study of the related cranial nerves.

The cavernous sinus (CS) is a demanding surgical territory, given its deep location and the involvement of multiple neurovascular structures. Subjected to recurrent discussion on the optimal surgical access, the endoscopic transorbital approach has been recently proposed as a feasible route for selected lesions in the lateral CS. Still, for this technique to safely evolve and consolidate, a comprehensive anatomical description of involved cranial nerves, dural ligaments, and arterial relations is needed. Detailed anatomical description of the CS, the course of III, IV, VI, and V cranial nerves, and C3-C7 segments of the carotid artery, all described from the ventrolateral endoscopic transorbital perspective. Five embalmed human cadaveric heads (10 sides) were dissected. An endoscopic transorbital approach with lateral orbital rim removal, anterior clinoidectomy, and petrosectomy was performed. The course of the upper cranial nerves was followed from their apparent origin in the brainstem, through the middle fossa or cavernous sinus, and up to their entrance to the orbit. Neuronavigation was used to follow the course of the nerves and to measure their length of surgical exposure. The transorbital approach allowed us to visualize the lateral wall of the CS, with cranial nerves III, IV, V1-3, and VI. Anterior clinoidectomy and opening of the frontal dura and the oculomotor triangle revealed the complete course of the III nerve, an average of 37 (±2) mm in length. Opening the trigeminal pore and cutting the tentorium permitted to follow the IV nerve from its course around the cerebral peduncle up to the orbit, an average of 54 (±4) mm. Opening the infratrochlear triangle revealed the VI nerve intracavernously and under Gruber's ligament, and the extended petrosectomy allowed us to see its cisternal portion (27 ± 6 mm). The trigeminal root was completely visible and so were its three branches (46 ± 2, 34 ± 3, and 31 ± 1 mm, respectively). Comprehensive anatomic knowledge and extensive surgical expertise are required when addressing the CS. The transorbital corridor exposes most of the cisternal and the complete cavernous course of involved cranial nerves. This anatomical article helps understanding relations of neural, vascular, and dural structures involved in the CS approach, essential to culminating the learning process of transorbital surgery.

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

Opening the oculomotor triangle 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 oculomotor triangle (OT). Between 2018 and 2022, eight cases, including five pituitary neuroendocrine tumors (PitNET) including three nonfunctioning and two somatotroph tumors with elevated 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 towards the interclinoidal ligament (ICL) 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. The GTR(gross total resection)- defined as complete removal in 3 patients (38%), near-total resection(NTR) - defined as >95% removal in 4 patients (50%), and subtotal resection (STR)- defined as up to 90 % removal in one patient (12%)and gross-total resection of tumor invading through the OT was achieved in all patients through pure EEA. Two of three patients with visual deficit in Non-Functioning-PitNET improved, and the other remained stable postoperatively. One patient showed transient oculomotor nerve palsy. The Growth Hormone level of the two patients with somatotroph tumors declined to normal. For three patients with CS meningiomas, cranial nerve palsy improved in two patients, while the other patient developed increased facial numbness after surgery. Endoscopic endonasal transoculomotor triangle approach is an efficient surgical option for the tumor with CS invasion and OT penetration.

Endoscopic Endonasal Transsphenoidal Transcavernous Transoculomotor Triangle Approach for Resection of an Invasive Pituitary Adenoma Extending Into the Parapeduncular Space Through the Cavernous Sinus.

A subset of invasive pituitary adenomas invade not only the medial wall of the cavernous sinus but can progress superiorly through the cavernous sinus roof at the oculomotor triangle and reach the subarachnoid parapeduncular space. We describe a series of 2 of 3 cases where an endoscopic endonasal approach was used to reach the parapeduncular space through the oculomotor triangle for tumor decompression. Images of the third case are presented. Case 1: We present a 2-dimensional surgical video of a recurrent corticotroph adenoma post gamma knife radiotherapy which was invading the left cavernous sinus and extending into the left parapeduncular space. Histopathological examination revealed densely granulated corticotrophin adenoma. The patient had reduction in the serum cortisol level postoperatively and was induced into remission medically. Postoperative third nerve palsy recovered partially, and sixth nerve palsy recovered completely at the 3-month follow-up. Case 2 : A case of recurrent silent corticotrophin adenoma invading the right parapeduncular space through the right cavernous sinus was operated through the same approach as case 1. Only a subtotal excision of the tumor in the cisternal space was possible. The patient developed a complete right third cranial palsy in the immediate postoperative period with near total recovery at the 6-month follow-up. Endoscopic endonasal approach to the parapeduncular space through a transcavernous transoculomotor route is reasonably safe and effective, as long as key anatomic landmarks and structures are identified and preserved while using natural tumor corridors to achieve tumor clearance.

Petroclival Clinoidal Folds and Arachnoidal Membranes of the Anteromedial Incisural Space: Clinical Anatomy for Neuro Critical Care.

A systematic and narrative literature review was performed, focusing attention on the anatomy of the area located at the junction of the sphenoid and the basal portion of the temporal bone (petrous bone, petrous apex, upper petro-clival region) encircled by the free edge of the tentorium, the insertion of the tentorium itself to the petrous apex and the anterior and posterior clinoid processes that give rise to three distinct dural folds or ligaments: the anterior petroclinoid ligament, the posterior petroclinoid ligament and the interclinoid ligament. These dural folds constitute the posterior portion of the roof of the cavernous sinus denominated "the oculomotor triangle". The main purpose of this review study was to describe this anatomical region, particularly in the light of the relationships between the anterior margin of the free edge of the tentorium and the above-mentioned components of the sphenoid and petrous bone.

THU101 A Challenging Case Of Recurrent Suprasellar Epidermoid Cyst With Visual Field Deficits

Abstract Disclosure: S. Ahsun: None. A. Atri: None. R. Bhat: None. C. eaton: None. N. Blocher: None. A challenging case of recurrent suprasellar epidermoid cyst with visual field deficits. Introduction: Intracranial epidermoid cysts account for approximately 1% of all intracranial tumors. The most common location of occurrence is cerebellopontine angle. Suprasellar region is the second most common location. We present a case for suprasellar epidermoid cyst with visual field deficits. Case Presentation: A 52 y/o female presented to an ophthalmologist for blurring of vision and was found to have bitemporal hemianopia. MRI of the brain showed a large suprasellar mass of 6.9x4.2x3.3 cm with extension into the surrounding structures. A portion of the cyst wall was hemorrhagic. There was significant mass-effect on the optic chiasm and bilateral optic tracts. Patient underwent elective craniotomy with left frontotemporal approach. A characteristic pearly wide epidermoid capsule was visualized through the oculomotor triangle. The optic nerve was noted to be quite distorted in its course, exiting from the optic canal and being pushed superiorly by the epidermoid tumor. Accessible tumor capsule was resected, however due to the dense adhesions of the epidermoid cyst to the surrounding vasculature and the optic nerves, complete resection was not attempted. Postoperatively, patient developed right-sided hemiparesis due to an acute infarct. Patient also developed some dementia, hyperphagia and aggressive behavior following her surgery. She started her rehabilitation therapy but had persistent dementia and cognitive decline. Repeat vision testing showed right superior homonymous hemianopia. MRI of the brain a year after the initial surgery showed growth of the residual cyst and some obstructive hydrocephalus but without any symptoms. She underwent a second debulking procedure that was successful with complete excision of the residual tumor but the patient had delayed recovery. She subsequently underwent tracheostomy and PEG tube placement and was transferred to the rehabilitation facility. She is now awake but still nonverbal. Patient also developed panhypopituitarism and is currently on the replacement for cortisol and thyroid hormone. She is also on DDAVP for her diabetes insipidus which seems to be permanent in her case. Conclusion: This case highlights some important facts: 1. Epidermoid cysts are challenging from the management standpoint. Only 50-80% can be resected completely. Incomplete removal increases the chances for recurrence which are variable at 1-54%. 2. Even in cases of recurrent growth repeat surgery should only be performed if patient has significant symptoms from the tumor. 3.As per the literature patients with adjuvant radiotherapy have improved outcomes. As in our case radiotherapy should have been considered in the setting of recurrence of the tumor. 4.Endoscopic endonasal approach is a new modality that has shown a very low rate of complications after resection. Presentation: Thursday, June 15, 2023

A New Perspective on the Cavernous Sinus as Seen through Multiple Surgical Corridors: Anatomical Study Comparing the Transorbital, Endonasal, and Transcranial Routes and the Relative Coterminous Spatial Regions.

Background: The cavernous sinus (CS) is a highly vulnerable anatomical space, mainly due to the neurovascular structures that it contains; therefore, a detailed knowledge of its anatomy is mandatory for surgical unlocking. In this study, we compared the anatomy of this region from different endoscopic and microsurgical operative corridors, further focusing on the corresponding anatomic landmarks encountered along these routes. Furthermore, we tried to define the safe entry zones to this venous space from these three different operative corridors, and to provide indications regarding the optimal approach according to the lesion's location. Methods: Five embalmed and injected adult cadaveric specimens (10 sides) separately underwent dissection and exposure of the CS via superior eyelid endoscopic transorbital (SETOA), extended endoscopic endonasal transsphenoidal-transethmoidal (EEEA), and microsurgical transcranial fronto-temporo-orbito-zygomatic (FTOZ) approaches. The anatomical landmarks and the content of this venous space were described and compared from these surgical perspectives. Results: The oculomotor triangle can be clearly exposed only by the FTOZ approach. Unlike EEEA, for the exposure of the clinoid triangle content, the anterior clinoid process removal is required for FTOZ and SETOA. The supra- and infratrochlear as well as the anteromedial and anterolateral triangles can be exposed by all three corridors. The most recently introduced SETOA allowed for the exposure of the entire lateral wall of the CS without entering its neurovascular structures and part of the posterior wall; furthermore, thanks to its anteroposterior trajectory, it allowed for the disclosure of the posterior ascending segment of the cavernous ICA with the related sympathetic plexus through the Mullan's triangle, in a minimally invasive fashion. Through the anterolateral triangle, the transorbital corridor allowed us to expose the lateral 180 degrees of the Vidian nerve and artery in the homonymous canal, the anterolateral aspect of the lacerum segment of the ICA at the transition zone from the petrous horizontal to the ascending posterior cavernous segment, surrounded by the carotid sympathetic plexus, and the medial Meckel's cave. Conclusions: Different regions of the cavernous sinus are better exposed by different surgical corridors. The relationship of the tumor with cranial nerves in the lateral wall guides the selection of the approach to cavernous sinus lesions. The transorbital endoscopic approach can be considered to be a safe and minimally invasive complementary surgical corridor to the well-established transcranial and endoscopic endonasal routes for the exposure of selected lesions of the cavernous sinus. Nevertheless, peer knowledge of the anatomy and a surgical learning curve are required.

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

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

Added Predictive Values of Proton Density Magnetic Resonance Imaging on Posterior Communicating Artery Aneurysms and Surrounding Soft Tissues with Simple Classification.

Deciphering the anatomy of posterior communicating artery (PCoA) aneurysms in relation to surrounding structures is essential to determine adjuvant surgical procedures. However, it is difficult to predict surgical structures through preoperative imaging studies. We aimed to present anatomical structures using preoperative high-resolution three-dimensional proton densityweighted turbo spin-echo magnetic resonance (PDMR) imaging with simple classification. From January 2020 to April 2022, 30 patients underwent PDMR before microsurgical clipping for unruptured PCoA aneurysms in a single tertiary institute. We retrospectively reviewed the radiographic images and operative data of these patients. The structural relationship described by PDMR and intraoperative findings were compared. Subsequently, we classified aneurysms into two groups and analyzed the rate of adjuvant surgical procedures and contact with the surrounding structures. Correlations between preoperative PDMR predictions and actual intraoperative findings for PCoA aneurysm contact to the oculomotor nerve, temporal uncus, and anterior petroclinoid fold (APCF) reported a diagnostic accuracy of 0.90, 0.87, and 0.90, respectively. In 12 patients (40.0%), an aneurysm dome was located on the plane of the oculomotor triangle and was classified as the infratentorial type. Compared to the supratentorial type PCoA aneurysm, adjuvant procedures were required more frequently (66.7% vs. 22.2%, p=0.024) for infratentorial type PCoA aneurysm clipping. Preoperative PCoA aneurysm categorization using PDMR can be helpful for predicting surgical complexity and planning of microsurgical clipping.

Morphometric analysis of oculomotor triangle in dry human skulls and its clinical applications.

The oculomotor triangle is denoted as the "Triangle of Hakuba" or the "Hakuba's Triangle." This oculomotor triangle is a significant anatomical landmark. Oculomotor nerve, abducens nerve and part of the internal carotid artery (ICA) lie in this triangle. The determination of this analysis is to calculate the oculomotor triangle in dry processed skull bones of the south Indian population and its clinical significance. Fifty-one processed skulls of human origin were received from Anatomy Department, Basic Medical Sciences, Saveetha Dental College. Length from anterior-clinoid process (ACP) to posterior-clinoid process (PCP), length from PCP to APEX, and length from ACP to APEX were measured. Paired samples t-test was considered to analyze the values between the right triangle with the left triangle. From the measurements taken, the mean for the left side of the oculomotor triangle, ACP to PCP was 8.0591 ± 0.52 mm and the right side was 7.5482 ± 0.52 mm. The mean left side of the oculomotor triangle, measured from PCP to APEX was 6.73 ± 0.48 mm and the right side was 6.55 ± 0.72 mm. The mean of the left side of the oculomotor triangle, measured from ACP to APEX was 15.94 ± 0.682 mm and the right side was 16.21 ± 0.747 mm. Through this paired triangle of the cranial cavity, the horizontal section of ICA may be correlated with numerous vascular-related pathological considerations.

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.

Trochlear cistern of the cavernous sinus: an anatomical study using magnetic resonance imaging.

The present study aimed to explore the trochlear cistern (TC) of the cavernous sinus using magnetic resonance imaging (MRI). Following conventional MRI examination, a total of 73 patients underwent the constructive interference steady-state (CISS) sequence in thin-sliced coronal sections. Moreover, three injected cadaver heads were dissected. In the cadaver specimens, the extent of the TC was difficult to identify on any dissected side. On the CISS images, the TC was identified in 98.6% on the right side and 94.5% on the left, while transmitting the trochlear nerve (TN) was identified in 83.6% on the right and 79.5% on the left. Most TNs were delineated as a single trunk, while duplication of the nerve was found in 3% of cases. The TC, commonly located inferior or inferolateral aspect of the oculomotor trigone. The size and extent of TC were highly variable. The TN location in the TC was also variable and was identified throughout the upper, middle, and lower parts of the TC. Moreover, relationships between the TC and Meckel's cave were highly variable. TC shows morphological variability. The coronal CISS sequence is useful for exploring TC and TN in clinical practices.

Carotid Artery Mobilization to Increase the Working Zone Area in Optic Carotid Triangle and Carotid Oculomotor Triangle (A Technical Note of Proximal and Distal Dural Ring Release)

Optic carotid and carotid oculomotor triangles are the main corridors for reaching sellar and parasellar lesions...

Oculomotor nerve palsy in pituitary apoplexy associated with pituitary adenoma: a radiological analysis with fast imaging employing with steady-state acquisition.

Oculomotor nerve palsy (ONP) occasionally occurs in cases of pituitary apoplexy (PA) associated with pituitary adenoma, but its mechanism remains unclear. Intracranial nerves are clearly visualized by fast-imaging employing with steady-state acquisition (FIESTA). Here, we assessed the oculomotor nerve compression in patients with PA associated with pituitary adenoma using FIESTA. Twenty-eight cases of PA, with or without ONP, were retrospectively reviewed. All patients had undergone preoperative FIESTA. Two neuroradiologists, unaware of the patient's clinical symptoms, evaluated the presence and location of oculomotor nerve compression due to the tumor. Thirteen of the twenty-eight PA cases were associated with ONP. Tumor size and degree of cavernous sinus invasion were not significantly different between the ONP and non-ONP groups. Even in the ONP group, 8/13 (62%) tumors did not show cavernous sinus invasion. Via FIESTA, the presence of oculomotor nerve compression was confirmed in 11/13 (85%) and 5/15 (33%) cases in the ONP and non-ONP groups, respectively (p = 0.008). The radiologists' diagnoses of laterality of nerve compression (right or left) were consistent with the patient's affected eye. In the ONP group, the location of the nerve compression was located at the entry point to the cavernous sinus, the so-called oculomotor triangle, in 9/11 (82%) cases and intra cavernous sinus in 2/11 (18%) cases. Compression at the oculomotor triangle is considered the main cause of ONP with PA in pituitary adenomas.

Pituitary adenoma with posterior area invasion of cavernous sinus: surgical anatomy, approach, and outcomes

We found a series of Knosp grade 3A-4 pituitary adenomas in the posterior areas of the cavernous sinus (CS), a triangular-like structure on axial MRI. In this study, we dissected the surrounding neurovascular structure, discussed the surgical approach, and analyzed outcomes for patients with this invasion into this area. Eight embalmed adult cadaveric specimens were prepared for this study to demonstrate in detail the surgical anatomy related to this triangular-like structure. We used the "two points and one line" method to determine the surgical approach, and 35 cases with this area invasion were retrospectively reviewed. According to the endoscopic and microsurgical anatomy, the triangular-like structure appearing on the axial MRI is correlated with a square-based pyramid structure in the CS, and the upper surface is the posterior portion of the oculomotor triangle. A total of 37 posterior areas of the CS were involved in 35 patients. The accuracy of the "two points and one line" method in predicting the surgical approach is 86.5% (32/37). All three patients with Knosp 3A underwent gross total resection (GTR). Twenty (62.5%) patients with Knosp 4 underwent GTR, 9 (28.1%) patients underwent subtotal resection, and 3 (9.4%) patients underwent partial resection. Preoperative symptoms were alleviated to varying degrees, and no worsening occurred. Postoperative complications included two (5.7%) cases of cerebrospinal fluid leakage, one (2.9%) case of meningitis, two (5.7%) cases of permanent diabetes insipidus, and three (8.6%) cases of transient cranial nerve palsy. The "two points and one line" method is of great value in predicting the surgical approach of pituitary adenomas with CS invasion. The anatomic description of this particular square-based pyramid structure in the CS refines the understanding of pituitary adenomas with CS invasion.

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

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. 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 (> 10mm) had OMCE. The combined supra-infrasellar approach was adopted in two cases with relatively large OMCE. 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. 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.

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. 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. 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. 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.

The Microsurgical Relationships between Internal Carotid-Posterior Communicating Artery Aneurysms and the Skull Base.

Objective This study aimed to review the anatomical and clinical characteristics of internal carotid-posterior communicating artery (IC-PC) aneurysms, especially those located close to the skull base. Methods The microsurgical anatomy around the posterior communicating artery (PComA) was examined in a dry skull and five formalin-fixed human cadaveric heads. The clinical characteristics of 37 patients with 39 IC-PC aneurysms, who were treated microsurgically between April 2008 and July 2016, were retrospectively reviewed. Results The anterior clinoid process (ACP), as well as the anterior petroclinoidal dural fold (APF), which forms part of the oculomotor triangle, are closely related to the origin of the PComA. Among the 39 IC-PC aneurysms, anterior clinoidectomy was performed on 4 (10.3%) and a partial resection of the APF was performed on 2 (5.1%). Both of these aneurysms projected inferior to the tentorium, or at least part of the aneurysm's dome was inferior to the tentorium. Conclusion Proximally located IC-PC aneurysms have an especially close relationship with the ACP and APF. We should be familiar with the anatomical relationship between IC-PC aneurysms and the structures of the skull base to avoid hazardous complications.

The cisternal segments of the oculomotor nerve: a magnetic resonance imaging study.

The cisternal segments of the oculomotor nerve (OMN), which courses through the interpeduncular and oculomotor cisterns (OMC) have not been well delineated on neuroimages. The present study aimed to explore the cisternal segments of the OMN using magnetic resonance (MR) imaging. A total of 92 patients were enrolled in this study. A constructive interference in steady-state sequence was performed in coronal and axial sections. On coronal images, cisternal portions of the OMN were entirely delineated in 97% on the right and in 98.5% on the left. Most of the OMCs were of a round shape, with a centrally located OMN, while 9% were ectatic with the OMN located eccentrically. In 5.3% of cases, fetal-type posterior communicating arteries (PCoAs), which coursed adjacent to the superior surfaces of the OMNs at the oculomotor triangle (OMT), were observed. On axial images, cisternal portions of the OMN were identified in all cases. The OMN segment passing through the OMT showed medial, central, and lateral courses. The PCoAs and P2 segments of the posterior cerebral artery (PCA) were adjacent to the OMNs in 17 and 19% of cases, respectively. The OMN most frequently courses in the medial part of the OMT and enters into the OMC. These findings indicate that OMN paresis can be caused by vascular compression at any site of the interpeduncular cistern and OMT.

Endoscopic anatomy of the intracisternal oculomotor nerve: a new segmentation based on the topography of the arachnoid membranes

Abstract Objective: The aim of our study was to investigate the detailed endoscopic anatomy of the intracisternal portion of the oculomotor nerve and to update the present knowledge of its related anatomy with the newest research on the topography of the arachnoid membrane system of the skull base. Methods: This study was performed on 50 fresh human cadaveric specimens post-mortem not more than 72 h. In each specimen, the intracranial arterial system was injected with red gelatin solution. We used the endoscope-controlled and endoscope-assisted microsurgical techniques applied through the minimally invasive supraorbital keyhole craniotomy to perform our dissections. Results: We divided the intracisternal oculomotor nerve into three segments in this study. These are the interpeduncular segment, located in the interpeduncular fossa and surrounded by dens arachnoid trabeculae around the thalamoperforating arteries; the tentorial segment, located between the posterior cerebral and superior cerebellar arteries and the posterior petroclinoid fold and surrounded by the elements of the clival and tentorial arachnoid membrane groups; and the trigonal segment located on the surface of the oculomotor trigone between the posterior petroclinoid fold and the dural exit of the nerve into the cavernous sinus and surrounded by the posteriorly located membranes of the carotid membrane group. Conclusions: Our findings support the more accurate understanding of the physiology of the arachnoid membrane system and the pathophysiology of space-occupying lesions in the region of the oculomotor nerve. Therefore, our results may support performing more atraumatic surgery in this area.

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.