Preoperative simulation of the running course of the abducens nerve in a large petroclival meningioma: a case report and literature review.

One of the most important and useful pieces of information in the preoperative evaluation of a large petroclival meningioma is the running course of the abducens nerve. The abducens nerve is small and has a long intracranial course, making it prone to compression by the tumor at various anatomical points. In relatively large tumors, it is difficult to confirm the entire course of the abducens nerve, even by heavy T2-thin slice imaging. We report a case of successful preoperative estimation of the course of the abducens nerve that aided in its complete preservation during the resection of a large petroclival tumor.

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.

Predictors of Surgical Outcomes in Patients with Abducens Nerve Schwannoma: A Comprehensive Systematic Review and a Case Report.

BACKGROUND: Abducens nerve (AN) schwannomas are extremely rare tumors. Clinical characteristics and factors that influence postoperative outcomes are not well defined. OBJECTIVE: To characterize clinical features of AN schwannomas and predictors of surgical outcomes. METHODS: PRISMA-guided systematic review of the literature on AN schwannomas was performed. Subsequently, univariate and multivariate regression analyses were performed to identify the predictive value of variables that influence postoperative outcomes. RESULTS: A total of 42 studies with 55 patients were evaluated. The mean age at presentation was 43.9 ± 14.6 years. The most common presenting symptom was cranial nerve VI palsy (69.1%). Cavernous sinus (49.1%) and prepontine cistern (36.3%) were the most commonly involved locations. Complete recovery after surgery was seen in 36.3% at a median follow-up of 28.4 ± 25.8 months. Preoperative AN palsy (P < 0.001), suboccipital approach (P = 0.007), and subtotal resection of tumor (P = 0.044) were significant protective factors for postoperative complications. Prepontine location and postoperative complications were poor prognostic indicators of AN recovery (odds ratio [OR], 0.10, P = 0.030 and OR, 0.10, P = 0.028, respectively). Subtotal resection was significantly correlated with higher odds of AN recovery (OR, 6.06; P = 0.040). CONCLUSIONS: AN schwannomas are rare but serious tumors that can cause significant morbidity, with only approximately one third of patients showing complete recovery after surgery. The suboccipital approach was a protective factor for postoperative complications, especially when combined with subtotal resection. Knowledge of these factors along with tumor characteristics helps optimize surgical planning and preoperative counseling.

Surgical treatment for combined hemifacial spasm and atypical trigeminal neuralgia caused by a tortuous basilar artery. Case report and review of the literature.

Simultaneous hemifacial spasm (HFS) and trigeminal neuralgia caused by cranial nerve (CN) compression from a tortuous basilar artery (BA) is very rare. We report a case of a 66-year-old man who presented with both HFS and "atypical" trigeminal neuralgia. The patient had a tortuous BA compressing both CN V and VII. The patient underwent microvascular decompression after failing conservative medical management. To the best of our knowledge this is the first reported case of both HFS and "atypical" trigeminal neuralgia that were both successfully treated by surgical intervention. We report the management of this rare combination and review the literature.

Microsurgical anatomy of the abducens nerve.

The aim of this study is to demonstrate and review the detailed microsurgical anatomy of the abducens nerve and surrounding structures along its entire course and to provide its topographic measurements. Ten cadaveric heads were examined using ×3 to ×40 magnification after the arteries and veins were injected with colored silicone. Both sides of each cadaveric head were dissected using different skull base approaches to demonstrate the entire course of the abducens nerve from the pontomedullary sulcus to the lateral rectus muscle. The anatomy of the petroclival area and the cavernous sinus through which the abducens nerve passes are complex due to the high density of critically important neural and vascular structures. The abducens nerve has angulations and fixation points along its course that put the nerve at risk in many clinical situations. From a surgical viewpoint, the petrous tubercle of the petrous apex is an intraoperative landmark to avoid damage to the abducens nerve. The abducens nerve is quite different from the other nerves. No other cranial nerve has a long intradural path with angulations and fixations such as the abducens nerve in petroclival venous confluence. A precise knowledge of the relationship between the abducens nerve and surrounding structures has allowed neurosurgeon to approach the clivus, petroclival area, cavernous sinus, and superior orbital fissure without surgical complications.

Microsurgical anatomy of the abducens nerve.

OBJECTIVE: To clarify the oriented classification, relationships, and variations of the abducens nerve and provide a detailed description of its microsurgical anatomic features. METHODS: A microsurgical anatomic dissection of the abducens nerve was performed in 100 specimens obtained from 50 adult cadaveric heads fixed in formalin and two adult cadaveric heads stained with hematoxylin and eosin for histological examination. Important neurovascular and structural relationships of the abducens nerve were observed. RESULTS: The abducens nerve was divided into five segments (cisternal, petroclival, internal carotid artery, fissural, and intraconal). It coursed in the petroclival venous confluence and there was a complex anatomic relationship. Two new types of abducens nerve variations were found. In one type, the duplicated nerve is split into two branches for a limited length in the cavernous sinus (CS). The other is a complex type, which has a complex course and pattern. This type of duplicated abducens nerve has a communicating branch in the cistern and numerous fasciculi in the CS. In addition, the two branches do not accompany each other for the entire course in the CS. CONCLUSION: The vulnerability of the abducens nerve results from diverse factors. The inferolateral trunk, which arises from the intracavernous segment of carotid artery (also called the artery of the inferior CS), is an important landmark for finding the abducens nerve and sympathetic nerve. Variations of the abducens nerve are not rare. Keeping variations of the nerve in mind is important during skull base operations and transvenous endovascular interventions. Understanding the relationship of the abducens nerve with adjacent structures will help us in preparing for safe surgery.

Increased MIB-1 Labeling Index Is Associated with Abducens Nerve Morbidity in Primary Sporadic Petroclival Meningioma Surgery: Beyond Location and Approach.

Abducens nerve palsy is a severe dysfunction after petroclival meningioma (PC MNG) surgery. The objective of this investigation was to analyze abducens nerve outcomes in patients who underwent the retrosigmoid approach in relation to the MIB-1 index. Thirty-two patients with primary sporadic PC MNG were retrospectively analyzed. Mean follow-up was 28.0 months. Analysis of the MIB-1 index was performed to evaluate the abducens nerve outcome. An optimal MIB-1 index cut-off value (<4/≥4) in the association with postoperative CN VI palsy was determined by ROC analysis (AUC: 0.74, 95% CI: 0.57−0.92). A new-onset CN VI palsy was present in 7 cases (21.88%) and was significantly associated with an increased MIB-1 index (≥4%, p = 0.025) and a peritumoral edema in the brachium pontis (p = 0.047) which might be caused by the increased growth rate. Tumor volume, cavernous sinus infiltration, auditory canal invasion, and Simpson grading were not associated with new CN VI deficits. Six (85.7%) of the 7 patients with both an increased MIB-1 index (≥4%) and new abducens nerve palsy still had a CN VI deficit at the 12-month follow-up. A peritumoral edema caused by a highly proliferative PC MNG with an elevated MIB-1 index (≥4%) is associated with postoperative abducens nerve deficits.

Can Ophthalmologic Examination Predict Abducens Nerve Recovery After Endoscopic Skull Base Surgery?

OBJECTIVES: While abducens nerve palsy (ANP) is a known risk in the setting of some endoscopic endonasal skull base surgery (ESBS), frequency and prognosis of post-operative palsy remain unknown. Our goals were to determine the frequency and prognosis of ANP after high-risk ESBS, and identify factors associated with recovery. METHODS: Retrospective case series of all patients with pathology at highest risk for abducens nerve injury (pituitary adenoma, chordoma, meningioma, chondrosarcoma, cholesterol granuloma) generated a list of patients with abducens nerve palsy after ESBS performed from 2011-2016. A validated ophthalmologic clinical grading scale measuring lateral rectus duction from 0 to -5 (full motion to inability to reach midline) was measured at multiple time points to assess recovery of ANP. RESULTS: Of 655 patients who underwent ESBS with increased risk of abducens injury, 40 (6.1%) post-operative palsies were identified and 39 patients with dedicated examination at multiple time points were included in subsequent analysis. Complete resolution was noted in 25 patients (64%) within 12 months. While 19 of 23 (83%) with a partial palsy had complete resolution, only six of 16 (38%) with a complete palsy resolved entirely (P = .005; Fisher's exact test). All six patients with delayed onset of palsy resolved (P = .070; Fisher's exact test). Meningioma and chordoma had higher rates of both temporary and permanent post-operative ANP (P < .0001; Fisher's exact). CONCLUSIONS: The frequency of post-operative ANP following ESBS is low, even in high-risk tumors. While only a minority of complete abducens nerve palsies recover, patients with partial or delayed palsy post-operatively are likely to recover function without intervention. LEVEL OF EVIDENCE: IV Laryngoscope, 131:513-517, 2021.

Microanatomical study of the intracranial abducens nerve: clinical interest and surgical perspective.

AIM: The microanatomy of the abducens nerve (AN) is important for clinical reasons and surgical approaches as it is located in the petroclival region. The incidence of branching and duplication of the abducens nerve are unknown and mechanisms relating to paralysis of the nerve in indirect conditions are yet to be clarified. MATERIAL AND METHODS: Microanatomical details (anatomical observations and morphometric measurements) of the AN were obtained from 20 cadaveric skull bases (40 specimens). RESULTS: 55% of the intracranial abducens nerves had branching, with type 2 and 3 branching occurring in 10%. The nerve coursed below the petrosphenoidal ligament in all but one, and was located at the lateral third below the ligament in 82.5% of the specimens. The mean AN diameter was 1.3±0.2 mm, and the mean diameter of the dural entrance pore was 1.8±0.3 mm, the right being significantly larger than the left. The mean distance of the AN from the posterior clinoid process was 8.4±2.5 mm and from the petrous apex 3.6±2.1 mm. CONCLUSION: Branching of the AN was present in a significant number of specimens; the branching pattern at the cavernous segment may be called "pseudobranching". The AN is at risk for paresis in indirect conditions because of its angles and fixations on its course.

Health-related quality of life evaluation in patients undergoing cavernous nerve reconstruction during radical prostatectomy.

OBJECTIVE: Nerve-grafting surgery after resection of neuro-vascular bundles during radical prostatectomy is one of the promising resolutions for dilemma between cancer control and functional preservation. The objective of this study is to evaluate the effect of nerve-grafting surgery on health-related quality of life (HRQOL) in localized prostate cancer patients with special interest in the influence of sexual dysfunction on mental status. METHODS: A total of 88 patients followed for a minimum of 12 months after surgery with a median follow-up of 48 months were enrolled in this study. Of those, 24 patients underwent unilateral nerve-sparing with contralateral nerve-grafting or bilateral nerve-grafting and 64 patients underwent prostatectomy without nerve-sparing procedure. HRQOL assessed with the Japanese version of Extended Prostate Cancer Index Composite (EPIC) and Medical Outcomes Study 8 Items Short Form Health Survey (SF-8) was analyzed cross-sectionally. RESULTS: Patients in nerve-grafting group who recovered potency demonstrated higher sexual function scores compared with those without nerve-sparing procedure (P = 0.022 and 0.001 in 25-48 and 49 months or later, respectively). However, sexual bother scores in nerve-grafting group who recovered potency were lower than those without nerve-sparing procedure throughout the observation periods (P = 0.012 in 49 months or later). CONCLUSIONS: Cavernous nerve reconstruction provided recovery of erectile dysfunction in substantial proportion of patients, which resulted in favorable physical HRQOL. Majority of these patients, however, did not seem to be satisfied with their sexual function, which caused sustained sexual bother feeling.

Abducens nerve schwannoma mimicking intrinsic brainstem tumor.

Schwannomas of the abducens nerve are extremely rare tumors affecting cavernous, cisternal or both segments of sixth cranial nerve. Clinical features and neuroradiological imagery are frequently insufficient to reach an accurate pre-operative diagnosis. We report a patient with a cystic tumor with ring-like contrast enhancement at the right anterior pontomesencephalic junction. Radical excision was performed via anterior transpetrosal approach and showed an extrinsic tumor originating from the sixth nerve. A postoperative sixth nerve palsy had disappeared completely 9 months after the surgery. The correct diagnosis of an abducens nerve schwannoma is established by the intraoperative finding of a tumor attachment to the sixth nerve and by histopathological analysis. The various differential diagnoses, the clinical and radiological features of this diagnosis and management are issues discussed in this illustrated review.

Clinical course of abducens nerve palsy associated with skull base tumours.

BACKGROUND: The clinical course of abducens nerve palsy associated with skull base tumour is rarely reported. In this study, we examined the post-operative course of abducens nerve palsies associated with various skull base tumours. METHOD: Between January 2003 and December 2006, 240 patients with various skull base tumours underwent surgery at Kyushu University Hospital. Among them, nine patients presented with abducens nerve palsies (ten nerves) following surgery. The conditions included two pituitary adenomas, two trigeminal schwannomas and five meningiomas. We evaluated the function of the abducens nerves in these patients on admission, at discharge, and periodically in the outpatient clinic. FINDINGS: Four of the abducens nerve palsies already existed prior to surgery, and six of them developed post-operatively. In the four patients with pituitary adenomas and trigeminal schwannomas, all nerves were anatomically preserved and showed complete recovery of function within 6 months after surgery. In contrast, only two of the six palsies in patients with skull base meningiomas showed complete recovery. In three patients with petro-clival meningiomas, the abducens nerves were completely transected during surgery, and one was reconstructed using fibrin glue. This patient remarkably recovered from the abducens nerve palsy within 2 years. CONCLUSIONS: The abducens nerve palsies in pituitary adenomas and trigeminal schwannomas showed a better clinical course compared to those in skull base meningiomas. The abducens nerve palsies that occur with skull base meningiomas are less likely to recover. Nevertheless, it is important to preserve the nerves and to perform surgical repair if the nerve is transected.

Surgical Treatment of Spontaneous Internal Carotid Artery Dissection with Abducent Nerve Palsy: Case Report and Review of Literature.

BACKGROUND: Sixth-nerve palsy often develops as a result of trauma, neoplasm, or vascular disease affecting the pons. Less commonly, this palsy can be caused by pathology of the internal carotid artery in the cavernous sinus region. Here, we describe a rare case of spontaneous dissection of the internal carotid artery in the cavernous sinus accompanied by acute sixth nerve palsy that was successfully treated with surgery. CASE DESCRIPTION: An 18-year-old man presented suddenly and spontaneously with isolated abducent nerve palsy. His magnetic resonance angiography identified a dissection of the right internal carotid artery in the cavernous sinus. We successfully treated it with high-flow bypass and ligation of the internal carotid artery (ICA). CONCLUSIONS: Intracavernous ICA dissection is a possible cause of sixth nerve palsy. While most cases likely result from compromised arterial blood supply to the affected nerve, compression of the cranial nerves by the expanded artery can occur in some cases. Surgical treatment is a safe and effective option for relieving nerve compression after intracavernous ICA dissection.

Abducens Nerve Schwannoma: A Case Report and Literature Review.

BACKGROUND: Abducens nerve function seldom shows complete recovery after removal of abducens nerve schwannoma. No cases with unclear course of the abducens nerve during surgery have been reported to achieve complete recovery of nerve function. CASE DESCRIPTION: We report the case of a 44-year-old woman who presented with occasional dysgeusia without abducens nerve paresis. Magnetic resonance imaging showed a solid tumor about 2 cm in diameter at the left cerebellopontine cistern. Cranial nerves except the abducens nerve appeared intact. The tumor was removed via suboccipital craniotomy. The abducens nerve was totally invisible on the surface of the tumor throughout the procedure. Only short segments of abducens nerve were identifiable at around Dorello's canal and the root exit zone. The tumor was resected by subcapsular dissection, and part of the tumor capsule was preserved as a scaffold for nerve generation, although whether any abducens nerve was included remained uncertain. Histopathologic examination confirmed World Health Organization grade I schwannoma. Postoperatively, the patient presented with complete left abducens nerve paresis and diplopia, but abducens nerve function began to improve 3 months later and had completely recovered within 16 months after surgery. CONCLUSIONS: This represents the first description of abducens nerve schwannoma in which the course of the abducens nerve was intraoperatively unclear but complete recovery was achieved. In such cases, intentional subcapsular dissection may potentiate functional recovery.

Isolated intraorbital schwannoma arising from the abducens nerve.

CASE REPORT: A case of isolated schwannoma of the orbit, arising from the terminal branches of the abducens nerve to the lateral rectus muscle, is reported. The patient presented with a painless proptosis of the left eye. DISCUSSION: Preoperative diagnosis of benign intraorbital neoplasm was made by means of CT and MR scans; the mass was radically excised through a microsurgical lateral orbitotomy and the pathological examination revealed a schwannoma. Features of orbital schwannoma are described, together with some details concerning the surgical strategy and the history of the evolution of the lateral orbitotomy.

Neurovascular compression of the abducent nerve causing abducent palsy treated by microvascular decompression. Case report.

Isolated abducent palsy is a symptom that can be caused by many different intracranial pathological conditions. In this report the authors describe the case of a patient who suffered isolated abducent palsy resulting from vascular compression of the sixth cranial nerve; surgical treatment consisted of microvascular decompression (MVD). This 56-year-old man presented with short-lasting episodes of a pulling sensation at the lateral side of his right eye associated with intermittent diplopia, followed by a progressive palsy of the abducent nerve and constant diplopia. Magnetic resonance imaging revealed a neurovascular contact of a dolichoectatic basilar artery with the abducent nerve. The patient underwent surgery consisting of a combined supra- and infratentorial presigmoid approach and subsequent MVD of the abducent nerve. Postoperatively, the abducent nerve palsy resolved within days, and the patient remains free of symptoms with a follow-up time of 4 years. This is the first report of a neurovascular compression of the abducent nerve treated successfully by MVD.

Factors Associated with Abducens Nerve Recovery in Patients Undergoing Surgical Resection of Sixth Nerve Schwannoma: A Systematic Review and Case Illustration.

BACKGROUND: Limited or no literature exists identifying factors associated with functional nerve recovery in patients undergoing resection of sixth cranial nerve (CN VI) schwannomas. METHODS: A systematic review of literature was performed on CN VI schwannomas that were treated surgically. Synthesizing the findings pooled from the literature, we investigated associations of patient demographics and clinical characteristics with postsurgical CN VI functional recovery in multivariable regression models. In addition, we present the findings of an adolescent woman surgically managed for intracavernous CN VI schwannoma. Complete encasement of the cavernous segment of the internal carotid artery is unique to our case. RESULTS: We synthesized data of 32 patients from 29 studies, and our index case. Overall, the mean age of the patients was 44.0 ± 16.5 years, and approximately 52% (n = 17) were female. Most tumors were left-sided (n = 18; 54.5%), with an average size of 3.46 ± 1.71 cm. The most common location was cisternal (n = 11; 33%), followed by cavernous sinus (CS) proper (n = 9; 27%), cisterocavernous (n = 8; 24%), orbital (n = 4; 12%) and caverno-orbital (n = 1; 3%). CN VI recovery was reported in less than half the cohort (n = 14; 45%). Tumor extension in the CS was significantly associated with lesser likelihood (odds ratio [OR], 0.07; 95% confidence interval [CI], 0.01-0.98; P = 0.048) of postsurgical CN VI recovery. Although female gender (OR, 0.86; 95% CI, 0.07-10.09; P = 0.906), large tumor size (>2.5 cm) (OR, 0.45; 95% CI, 0.07-2.89; P = 0.397), and solid consistency (OR, 0.37; 95% CI, 0.03-4.19; P = 0.421) were associated with lesser odds for recovery, these were not statistically significant. Likewise, although gross total resection (OR, 6.28; 95% CI, 0.33-118.25; P = 0.220) was associated with higher odds of nerve recovery, the estimates were statistically insignificant. CONCLUSIONS: CS involvement is associated with lesser odds for functional nerve recovery in patients undergoing surgical resection for CN VI schwannoma.

Unilateral severe chronic periodontitis associated with ipsilateral surgical resection of cranial nerves V, VI, and VII.

BACKGROUND: The central and peripheral nervous systems participate in several local physiological and pathological processes. There is experimental evidence that the inflammatory, local immune, and wound healing responses of a tissue can be modulated by its innervation. The aim of this clinical report is to present a case of unilateral severe periodontitis associated with ipsilateral surgical resection of the fifth, sixth, and seventh cranial nerves and to discuss the possible contribution of the nervous system to periodontal pathogenesis. METHODS: A 39-year-old female patient with a history of a cerebrovascular accident caused by a right pontine arteriovenous malformation and destruction of the right fifth, sixth, and seventh cranial nerves was diagnosed with severe chronic periodontitis affecting only the right maxillary and mandibular quadrants. The patient's oral hygiene was similar for right and left sides of the mouth. Percentages of tooth surfaces carrying dental plaque were 41% and 36% for right and left sides, respectively. Non-surgical and surgical periodontal therapy was performed, and the patient was placed on a regular periodontal maintenance schedule. RESULTS: Healing following initial periodontal therapy and osseous periodontal surgery occurred without complications. Follow-up clinical findings at 1 year revealed stable periodontal health. CONCLUSIONS: This case report suggests that periodontal innervation may contribute to the regulation of local processes involved in periodontitis pathogenesis. It also suggests that periodontal therapy can be performed successfully at sites and in patients affected by paralysis.

Grüber's ligament as a useful landmark for the abducens nerve in the transnasal approach.

OBJECT: Extended endoscopic transnasal surgeries for skull base lesions have recently been performed. Some expert surgeons have attempted to remove tumors such as chordomas, meningiomas, and pituitary adenomas in the clival region using the transnasal approach and have reported abducens nerve injury as a common complication. There have been many microsurgical anatomical studies of the abducens nerve, but none of these studies has described an anatomical landmark of the abducens nerve in the transnasal approach. In this study the authors used cadaver dissections to describe Grüber's ligament as the most reliable landmark of the abducens nerve in the transnasal transclival view. METHODS: The petroclival segment of the abducens nerve was dissected in the interdural space-which is also called Dorello's canal, the petroclival venous gulf, or the sphenopetroclival venous confluence-using the transnasal approach in 20 specimens obtained from 10 adult cadaveric heads. RESULTS: The petroclival segment of the abducens nerve clearly crossed and attached to Grüber's ligament in the interdural space, as noted in the transnasal view. The average length of the dural porus to the intersection on the abducens nerve was 5.2 ± 1.0 mm. The length of the posterior clinoid process (PCP) to the intersection on Grüber's ligament was 6.4 ± 2.6 mm. The average width of Grüber's ligament at the midsection was 1.6 ± 0.5 mm. CONCLUSIONS: Grüber's ligament is considered a useful landmark, and it is visible in most adults. Thus, surgeons can find the abducens nerve safely by visualizing inferolaterally along Grüber's ligament from the PCP.