Intracavernous Carotid Artery Research Articles

Cavernous Carotid Aneurysm Presenting as Direct Carotid-Cavernous Fistula with Contralateral Ocular Symptoms: A Rare Case Report

ABSTRACT Carotid-cavernous fistula (CCF) resulting from intracavernous carotid artery aneurysms is uncommon. However, if rupture does occur, it can lead to a CCF, which causes sudden onset of unilateral ophthalmoplegia. In this report, we present a case of a ruptured giant intracavernous carotid artery aneurysm leading to a direct CCF with contralateral ocular features. The aim is to discuss the distinctiveness of this case and the most challenging aspects of identifying similar cases. A woman in her sixties developed a sudden direct CCF, resulting in proptosis in the opposite eye. Magnetic resonance angiography revealed that the left cavernous sinus (CS) and superior ophthalmic vein were dilated, whereas the right side was unaffected. However, digital subtraction angiography (DSA) revealed a large aneurysm in the right cavernous internal carotid artery (ICA) and a direct connection between the right ICA and CS, with venous drainage exclusively occurring in the opposite direction via the intercavernous sinus. To address the issue, the aneurysm and fistula underwent Coil and Onyx embolisation, successfully closing the fistula and leading to a regression in the orbital symptom. This presents a unique scenario of an unexpected unilateral CCF with contralateral symptoms in a direct CCF, which demands immediate attention. It is crucial to remain alert for CCF and verify the diagnosis through DSA when dealing with such patients to avoid severe outcomes. Prompt identification and intervention can enhance the patient’s chances of a positive outcome.

Variants of the Anterior Subtemporal Approach to the Gasserian Ganglion and Related Structures: An Anatomical Study With Relevant Implications for Keyhole Surgery

The advantages and limitations of different craniotomy positions and approach trajectories to the gasserian ganglion (GG) and related structures using an anterior subtemporal approach have not been studied systematically. Knowledge of these features is of importance when planning keyhole anterior subtemporal (kAST) approaches to the GG to optimize access and minimize risks. Eight formalin-fixed heads were used bilaterally to assess temporal lobe retraction (TLR), trigeminal exposure, and relevant anatomical aspects of extra- and transdural classic anterior subtemporal (CLAST) approaches compared with slightly dorsally and ventrally allocated corridors. TLR to the GG and foramen ovale was found to be lower via the CLAST approach (P < 0.001). Using the ventral variant, TLR to access the foramen rotundum was minimized (P < 0.001). The overall TLR was maximal using the dorsal variant (P < 0.001) owing to interposition of the arcuate eminence. An extradural CLAST approach required wide exposure of the greater petrosal nerve (GPN) and middle meningeal artery (MMA) sacrifice. Both maneuvers were spared using a transdural approach. Using CLAST, medial dissection >39 mm can enter the Parkinson triangle, jeopardizing the intracavernous internal carotid artery. The ventral variant enabled access to the anterior portion of the GG and foramen ovale without the need for MMA sacrifice or GPN dissection. The CLAST approach provides high versatility to approach the trigeminal plexus, minimizing TLR. However, an extradural approach jeopardizes the GPN and requires MMA sacrifice. The risk of cavernous sinus violation exists when progressing medially beyond 4 cm. The ventral variant has some advantages to access the ventral structures and avoid MMA and GPN manipulation. In contrast, the usefulness of the dorsal variant is rather limited owing to the greater TLR required.

Microsurgical Treatment of a Giant Intracavernous Carotid Artery Aneurysm in a Pediatric Patient. Case Report and Literature Review

Introduction: Intracranial aneurysms in pediatric age represent 4 - 5% of all cases, and 20% are giant (&gt;25mm). The main sites of occurrence are ICA and MCA; about 55% - 72.5% of cases present rupture and secondary SAH with a 10% - 23% mortality. Case Description: We report the case of a previously healthy nine-year-old woman that initiated severe right retroocular pain and holocraneal headache. Her relatives detected paresis of the III, IV, and VI cranial nerves three days later. After evaluation, an MRI showed the presence of a giant aneurysm in the cavernous portion of the internal carotid artery (ICA) with a mass effect. The patient was treated surgically through a high-flow bypass using a radial artery graft and trapping of the aneurysm. The patient had an uneventful postoperative course and was discharged three days after the operation to continue in follow-up at the outpatient clinic. Discussion: The options for treatment are endovascular treatment through flow diverters or stenting and coiling, with the risk of incomplete occlusion or thrombosis. On the other hand, the goal of surgery is the permanent occlusion through the proximal closure of the ICA if a balloon occlusion test shows good collateral circulation or by trapping the aneurysm combined with a high-flow bypass if the collateral circulation is not good or absent. Conclusion: Even when the surgical option was successful in this case, there is no consensus about the best treatment; the selection of the method to use in these aneurysms depends on the center´s experience when confronting this rare entity.

A Case of Large Intracavernous Internal Carotid Artery Aneurysm with Acute Spontaneous Thrombosis and Parent Artery Pseudo-occlusion

A Case of Large Intracavernous Internal Carotid Artery Aneurysm with Acute Spontaneous Thrombosis and Parent Artery Pseudo-occlusion

P18.11.A Active beam scanning proton therapy for large skull base benign meningiomas: long-term results

Abstract Purpose To report long-term results of active beam scanning proton therapy (PT) for large skull base benign meningiomas Material and Methods Eighty-two patients (pts) with large skull base meningiomas were treated with PT between April 2015 and December 2021. Median age was 62 years (range, 48-82) while KPS ranged between 60 and 100 (median 90); 60 were female (73%), and 22 were male (27%). Thirty-two pts (39%) had histologically proven World Health Organization (WHO) Grade I tumors. In remaining pts diagnosis was based on the typical imaging appearance of benign meningioma. All patients received PT for residual, progressive or non-operable lesions. Newly diagnosed tumors received total dose of 50 GyRBE (RBE: relative biologic effectiveness) while progressing meningiomas 54 GyRBE. All the treatments were delivered at 2 GyRBE per fraction. All pts were treated with active beam scanning PT using 3 fields with single field optimization technique. Treatment planning was based on morphological magnetic resonance imaging (MRI) with contrast enhancement medium administration. All pts received also 68-Ga-DOTATOC-PET. Gross tumor volume ranged from 21 to 64 cc. Toxicity was assessed according to Common Terminology Criteria for Adverse Events version 4.0. Median follow-up time was 40 months (range, 3-83). Results All pts completed the treatment without breaks. Registered acute side effects include grade 1 (19%) and grade 2 (8%) skin erythema, grade 1 (5%) and grade 2 (5%) alopecia, grade 1 (40%) fatigue, grade 1 (5%) and grade 2 (10%) conjunctivitis, grade 1 (10%) pain, grade 1 (5%) blurred vision, grade 1 (10%) headache, and grade 2 (5%) skin hyperpigmentation. One pts (1%) experienced grade 3 pain. There were no further grade 3 or higher acute toxicities. Registered late side effects include grade 1 (2%) and grade 2 (5%) alopecia, grade 1 (21%) fatigue, grade 1 (5%) and grade 2 (5%) headache, grade 1 (6%) dizziness, grade 1 (3%) blurred vision, grade 1 (3%) and grade 2 (6%) pain, grade 1 (2%) dry eye, and grade 1 (5%) skin hyperpigmentation. Two pts (2%) experienced grade 3 pain. Two further pts (2%) experienced grade 3 optic neuropathy. There were no further grade 3 or higher late toxicities. During follow-up one pts (1%) with cavernous sinus meningioma experienced complete obstruction of intracavernous carotid artery with mild transient symptoms that resolved in few days and brain tissue ischemia detected at MRI (grade 2). Before irradiation this pts already had a meningioma-related near-complete obstruction of the intracavernous carotid artery and received a vascular surgery evaluation. Currently, absolute tumor control is 99%. Moreover, relief of symptoms recorded before irradiation occurred in 40% of pts. Conclusion PT is safe and effective treatment for pts with large skull base benign meningiomas.

The medial wall and medial compartment of the cavernous sinus: an anatomic study using plastinated histological sections

The medial wall of the cavernous sinus (CS) has a significant role in evaluation and treatment of pituitary adenomas. This study was conducted to clarify the fine architecture of the medial wall and medial compartment of the CS at both macro- and micro-levels in twenty-one human cadaveric heads by using the epoxy sheet plastination technique. The sellar part medial wall is an intact dural layer that separates the CS from the pituitary gland. This dural wall adhered to the diaphragma sellae and the periosteum of the sella turcica to form fibrous triangles. Eight micro-protrusions of the pituitary gland were found at both sides of that wall. The thickness of the sellar part medial wall at its central portion was significantly thinner than that at the other surrounding portions. From the superior view, tortuous intracavernous carotid arteries can be divided into outward bending type and inward bending type. The inward bending intracavernous carotid was apt to bent towards the central part of the sellar part medial wall, where there were usually wide and short fibrous bands with more densely stained connective tissues between them. The micro-protrusion of the pituitary gland in the medial wall of the CS could provide an anatomical basis for the occult tumor invasion and the recurrence of residual tumor. Different bending facing states of tortuous intracavernous carotid arteries in the lateral direction may be a factor of the determination of the direction of growth of pituitary tumors.

An unusual presentation of “Mirror-Image” bilateral giant carotid cavernous aneurysms: Case report and review of the literature

The almost asymptomatic “mirror-image” bilateral giant intracavernous carotid artery aneurysms are not common and its successful conservative management without further neurological complications is rarely reported. We report a case of a 64-year-old woman, admitted with a rapidly progressive headache, with no other signs or symptoms associated. The Head CT-Scan shows bilateral parasellar round hyperdense lesions and the Magnetic resonance angiography discloses bilateral giant intracavernous carotid artery aneurysms in detail. The clinical presentation of these types of lesions depends on their mass effect on the surrounding neurovascular structures. So, possibly no mass effect on any structure, then no obvious expected symptoms. A patient with these conditions and without neurological deficit should not be rushed to surgery or endovascular treatment.

Microsurgical Anatomy of the Inferomedial Paraclival Triangle: Contents, Topographical Relationships and Anatomical Variations.

The inferomedial triangle is one of the two surgical triangles in the paraclival subregion of the skull base. It is delineated by the posterior clinoid process, the dural entrance of the trochlear nerve and the dural entrance of the abducens nerve. The aim of the present article is to describe the anatomical variations within the inferomedial triangle. Measurements of the triangle’s borders and area were supplemented by detailed observations of the topographical anatomy and various arrangements of its contents. Nine adult cadaveric heads (18 sides) and 28 sagittal head sections were studied. The mean area of the inferomedial triangle was estimated to be 60.7 mm2. The mean lengths of its medial, lateral and superior borders were 16.1 mm, 11.9 mm and 10.4 mm, respectively. The dorsal meningeal artery was identified within the inferomedial triangle in 37 out of 46 sides (80.4%). A well-developed petrosphenoidal ligament of Grüber was identified within the triangle on 36 sides (78.3%). Although some structures were variable, the constant contents of the inferomedial triangle were the posterior petroclinoid dural fold, the upper end of the petroclival suture, the gulfar segment of the abducens nerve and the posterior genu of the intracavernous internal carotid artery.

Temporary Clipping of the Intracavernous Internal Carotid Artery: A Novel Technique for Proximal Control.

Securing proximal control in complex paraclinoid aneurysm surgery through traditional techniques may be challenging and risky in certain situations. Advancements of anatomical knowledge of the cavernous sinus (CS) and hemostasis have made it more accessible as a surgical option. To describe the technique of temporary clipping of the horizontal segment of the intracavernous internal carotid artery (IC-ICA) in preparation for permanent clipping of complex paraclinoid aneurysms. Through an extradural pretemporal approach, the lateral wall of the CS is exposed. The dura between the trochlear nerve and V1 is opened, and access is made to the horizontal segment of the IC-ICA. After circumferential dissection, the temporary clip can be introduced to the artery, and the extradural clinoidectomy can be continued under secured proximal control. Seven patients with complex paraclinoid aneurysms were treated between May 2013 and May 2016 by the senior author. Temporary clipping of the IC-ICA was performed in all cases. Average time to achieve proximal control was 22.6 min (22.6±13.8). One patient developed transient oculomotor palsy postoperatively. There were no other complications. When the exposed clinoidal segment of the internal carotid artery does not offer sufficient proximal space for temporary clipping, the extradural approach can be extended to the horizontal portion of the IC-ICA. In our experience, this technique is a quick, reliable, and safe alternative to the classical modalities of temporary occlusion.

Intracavernous Internal Carotid Artery Aneurysm Presenting as Acute Diplopia: A Case Report

IntroductionDiplopia is an uncommon emergency department (ED) complaint representing only 0.1% of visits, but it has a large differential. One cause is a cranial nerve palsy, which may be from a benign or life-threatening process.Case ReportA 69-year-old female presented to the ED with two days of diplopia and dizziness. The physical exam revealed a sixth cranial nerve palsy isolated to the left eye. Imaging demonstrated an intracavernous internal carotid artery aneurysm. The patient was treated with embolization by neurointerventional radiology.DiscussionThe evaluation of diplopia is initially divided into monocular, usually from a lens problem, or binocular, indicating an extraocular process. Microangiopathic disease is the most common cause of sixth nerve palsy; however, more serious etiologies may be present, such as an intracavernous internal carotid artery aneurysm, as in the patient described. Imaging modalities may include computed tomography or magnetic resonance imaging.ConclusionSome causes of sixth nerve palsy are benign, while others will require more urgent attention, such as consideration of an intracavernous internal carotid artery aneurysm.

Cavernous sinus and abducens nerve in human fetuses near term.

A long tortuous course of the abducens nerve (ABN) crossing a highly curved siphon of the internal carotid artery is of interest to neurosurgeons for cavernous sinus surgery. Although a "straight" intracavernous carotid artery in fetuses can change into an adult-like siphon in infants, there is no information on when or how the unique course of ABN is established. Histological observations of 18 near-term fetuses (12 specimens of frontal sections and 6 specimens of sagittal sections) demonstrated the following: (I) the ABN consistently took a straight course crossing the lateral side of an almost straight intracavernous carotid artery; (II) the straight course was maintained when sympathetic nerves joined; (III) few parasellar veins of the developing cavernous sinus separated the ABN from the ophthalmic nerve; and (IV) immediately before the developing tendinous annulus for a common origin of extraocular recti, the ABN bent laterally to avoid a passage of the thick oculomotor nerve. Since the present observations strongly suggested morphologies at birth and in infants, major angulations of the ABN as well as the well-known course independent of the other nerves in the cavernous sinus seemed to be established during childhood. In the human body, the ABN might be a limited example showing a drastic postnatal change in course. Consequently, it might be important to know the unique course of ABN before performing endovascular interventions and skull base surgery for petroclival and cavernous sinus lesions without causing inadvertent neurovascular injuries to neonates or infants.

Bilateral Giant Opthalmic Carotid Artery Aneurysms Presenting as Unilateral Diplopia: A Case Report

Introduction: The etiology of giant aneurysms is multifactorial. It becomes symptomatic in 9/100.000, most frequently in the fifth and sixth decades of the life. Intracavernous carotid artery aneurysms (ICAAs) represent less than 1% of intracranial aneurysms and show a slight female predominance. Case-Report: We report an interesting case of bilateral ICAA in 42-year-old female presented as acute diplopia and emphasize the need of a thorough systemic evaluation in young patients with diplopia and treated with endovascular coil embolization. A 42-year-old woman was admitted to the neurology department suffering from the unilateral diplopia. Neurological examination showed the left sixth cranial nerve palsy and had no further general motor or sensory symptoms. Digital Subtraction Angiogram (DSA) showed bilateral ophthalmic artery aneurysm. The patient was treated with endovascular loose packing coil embolization and Derivo 3.5x30mm flow diverter stent. Conclusion: It should be kept in mind that intracavernous carotid artery aneurysms may be bilateral in patients with unilateral cranial nerve symptoms.

The Size and Shape of the C4 Segment of the Intracavernous Carotid Artery Intermediate to the Petrolingual Ligament and the Abducens Nerve: Implications for Neurosurgery

Neurosurgical management of the neurovascular structures encompassed within the cavernous sinus may be aided by improved understanding of neurovascular anatomical relationships. Therefore, this study assessed the morphometry of the C4 segment of the intracavernous carotid artery as it relates to the petrolingual ligament and abducens nerve in cadavers. A total of 40 sides were assessed (18 female and 22 male sides). The area of the carotid artery intermediate to the petrolingual ligament and the abducens averaged 17.56±10.86mm2 (Mean±SD). The anterior and posterior distances from the petrolingual ligament to the abducens nerve averaged 3.12±1.72mm and 3.17±1.58mm, respectively. Further, unpaired T‐tests revealed no significant differences between sexes with regard to the area (p = 0.82), anterior distance (p = 0.96), and posterior distance (p=0.94). Further, three morphotypes for the window between the petrolingual ligament and abducencs were identified; namely, quadrilateral (n=30), triangular (n=8), and atretic (n=2). The results of this study will help improve the approach to lesions including C4 aneurysms and local tumors including those of the abducens.Support or Funding InformationFunding: WV Research Challenge Fund [HEPC.dsr.17.06]This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Convergent strabismus fixus after bilateral abducens nerve palsies due to aneurysms

Rationale:Convergent strabismus fixus is an ocular motor abnormality in which the eye is fixed in adduction. This condition is mostly associated with high myopia and is caused by a displacement of the extraocular muscles. We report a nonmyopic woman with convergent strabismus fixus due to aneurysms.Patient concerns:A 79-year-old woman complained of progressive worsening of esotropia about 50 years prior to her visit. Neuroimaging showed that the eye was not dislocated, and the extraocular muscles were not displaced. However, aneurysms were found bilaterally from the intracavernous carotid arteries and the location was on both abducens nerves.Diagnoses:Chronic bilateral abducens nerve palsies due to aneurysms.Interventions:Endovascular treatment was successfully performed for the aneurysms.Outcomes:Convergent strabismus fixus still remained.Lessons:Chronic abducens nerve palsies may develop to nonmyopic convergent strabismus fixus without displacement of extraocular muscles, and mass lesions in the brain including aneurysms should be ruled out when orbital MRI cannot explain the condition.

Complications Associated With Transsphenoidal Pituitary Surgery: Review of the Literature.

Complications Associated With Transsphenoidal Pituitary Surgery: Review of the Literature.

Pathophysiology of carotid-cavernous fistulas in vascular Ehlers-Danlos syndrome: a retrospective cohort and comprehensive review

BackgroundVascular Ehlers-Danlos syndrome (vEDS) is a rare condition characterized by connective tissue fragility. Direct spontaneous carotid-cavernous fistula (sCCF) is reportedly pathognomonic of vEDS. We conducted this study to understand the possible mechanisms of occurrence of sCCF in this subset of patients.MethodsWe conducted a retrospective analysis of a monocentric vEDS cohort along with a literature review regarding sCCF in this condition.ResultsOf 133 patients regularly followed in our centre between 2000 and 2017, 13 (9.8%) had a diagnosis of direct sCCF (92.3% female, median age 33.0 years, interquartile range (IQR) [26.0–39.5]). There were 7 Glycine missense and 6 splice-site variants but no variant leading to haploinsufficiency. The literature search identified 97 vEDS patients with direct sCCF (79.4% female, 7.2% sex not reported, median age 31.0 years, IQR [24.0–39.0]). Increased carotid circumferential wall stress, higher carotid distensibility and lower carotid intima-media thickness could contribute to a higher risk for direct sCCF in vEDS. There is no predictive factor for the occurrence of sCCF apart from female sex in vEDS.ConclusionsIn vEDS, anatomical and pathophysiological features of the intra-cavernous internal carotid artery make it prone to shunting in the cavernous sinus, due either to a spontaneous rupture or to a spontaneous dissection with pseudoaneurysm formation. Direct sCCF in seemingly healthy young individuals should be highly suggestive of vEDS and prompt further investigation.

Surgical Treatment of Carotid-cavernous Fistula Performed through the Brazilian Unified Health System

Abstract Introduction The carotid-cavernous fistula (CCF) is an abnormal communication between the arterial carotid system and the cavernous sinus. In most cases, spontaneous fistulas are due to the rupture of intracavernous carotid artery aneurisms. Traumatic fistulas occur in 0.2% of head injuries, and 75% of all CCFs are caused by automobile accidents or penetrating traumas. Objective To identify the data regarding the number of annual procedures, hospital expenses, length of hospital stay, and the number of deaths of patients admitted by the Brazilian Unified Health System (SUS, in the Portuguese acronym), in the period between 2007 and 2017, using the surgical code of the surgical treatment for CCF. Methods The present was an ecological study whose data were obtained by consulting the database provided by the Department of Computer Sciences of the Brazilian Unified Health System (Datasus, in Portuguese). Results A total of 85 surgical procedures were performed for the treatment of CCFs from January 2007 to October 2017 through the Unified Health System (SUS, in Portuguese), and there was a reduction of 71.42% in this period. The annual incidence of patients undergoing this surgical treatment during the period observed remained low, with 1 case per 13,135,714 in 2007, and 1 case per 51,925,000 in 2017. Conclusion Despite the low annual incidence of the surgical treatment of CCFs performed by the SUS in Brazil in the period of 2007–2017, based on the data obtained on the average length of stay and expenditures in hospital services, it is necessary that we develop an adequate health planning.

Intra cavernous aneurysm of internal carotid artery masquerading as a pituitary adenoma: a case report

BackgroundPituitary dysfunction in adults are often associated with tumors of the gland and manifests with mass effects and hypopituitarism. MRI of pituitary region often provides confirmation of the diagnosis and assists in planning neurosurgery.Case presentationA 69 years old female evaluated for chronic headache was found to have a supra-sellar mass lesion that mimicked a pituitary tumor, with biochemical evidence of hypopituitarism. Cerebral angiogram confirmed the diagnosis of an aneurysm of the intracavernous internal carotid artery. She was successfully treated with coil embolization of the aneurysm and achieved resolution of symptoms and return of biochemistries to normal.ConclusionCarotid aneurysm can mimc pituitary tumours clinically and radiologically on MRI scan. This rare possibility should be considered in evaluating supra-sellar masses to avoid catastrophic consequences.

First Application of 7-T Magnetic Resonance Imaging in Endoscopic Endonasal Surgery of Skull Base Tumors

Successful endoscopic endonasal surgery for the resection of skull base tumors is reliant on preoperative imaging to delineate pathology from the surrounding anatomy. The increased signal-to-noise ratio afforded by 7-T MRI can be used to increase spatial and contrast resolution, which may lend itself to improved imaging of the skull base. In this study, we apply a 7-T imaging protocol to patients with skull base tumors and compare the images with clinical standard of care. Images were acquired at 7 T on 11 patients with skull base lesions. Two neuroradiologists evaluated clinical 1.5-, 3-, and 7-T scans for detection of intracavernous cranial nerves and internal carotid artery (ICA) branches. Detection rates were compared. Images were used for surgical planning and uploaded to a neuronavigation platform and used to guide surgery. Image analysis yielded improved detection rates of cranial nerves and ICA branches at 7 T. The 7-T images were successfully incorporated into preoperative planning and intraoperative neuronavigation. Our study represents the first application of 7-T MRI to the full neurosurgical workflow for endoscopic endonasal surgery. We detected higher rates of cranial nerves and ICA branches at 7-T MRI compared with 3- and 1.5-T MRI, and found that integration of 7 T into surgical planning and guidance was feasible. These results suggest a potential for 7-T MRI to reduce surgical complications. Future studies comparing standardized 7-, 3-, and 1.5-T MRI protocols in a larger number of patients are warranted to determine the relative benefit of 7-T MRI for endonasal endoscopic surgical efficacy.

Endoscopic endonasal approach to the ventral brainstem: anatomical feasibility and surgical limitations.

OBJECTIVE Sporadic cases of endonasal intraaxial brainstem surgery have been reported in the recent literature. The authors endeavored to assess the feasibility and limitations of endonasal endoscopic surgery for approaching lesions in the ventral portion of the brainstem. METHODS Five human cadaveric heads were used to assess the anatomy and to record various measurements. Extended transsphenoidal and transclival approaches were performed. After exposing the brainstem, white matter dissection was attempted through this endoscopic window, and additional key measurements were taken. RESULTS The rostral exposure of the brainstem was limited by the sella. The lateral limits of the exposure were the intracavernous carotid arteries at the level of the sellar floor, the intrapetrous carotid arteries at the level of the petrous apex, and the inferior petrosal sinuses toward the basion. Caudal extension necessitated partial resection of the anterior C-1 arch and the odontoid process. The midline pons and medulla were exposed in all specimens. Trigeminal nerves were barely visible without the use of angled endoscopes. Access to the peritrigeminal safe zone for gaining entry into the brainstem is medially limited by the pyramidal tract, with a mean lateral pyramidal distance (LPD) of 4.8 ± 0.8 mm. The mean interpyramidal distance was 3.6 ± 0.5 mm, and it progressively decreased toward the pontomedullary junction. The corticospinal tracts (CSTs) coursed from deep to superficial in a craniocaudal direction. The small caliber of the medulla with very superficial CSTs left no room for a safe ventral dissection. The mean pontobasilar midline index averaged at 0.44 ± 0.1. CONCLUSIONS Endoscopic endonasal approaches are best suited for pontine intraaxial tumors when they are close to the midline and strictly anterior to the CST, or for exophytic lesions. Approaching the medulla is anatomically feasible, but the superficiality of the eloquent tracts and interposed nerves limit the safe entry zones. Pituitary transposition after sellar opening is necessary to access the mesencephalon.