Refining the predictive value of preoperative apparent diffusion coefficient (ADC) by whole-tumor analysis for facial nerve outcomes in vestibular schwannomas.

BACKGROUND: Apparent diffusion coefficient (ADC) in MRI has been shown to correlate with postoperative House-Brackmann (HB) scores in patients with vestibular schwannoma despite limited methodology. To rectify limitations of single region of interest (ROI) sampling, we hypothesize that whole-tumor ADC histogram analysis will refine the predictive value of this preoperative biomarker related to postoperative facial nerve function. METHODS: Of 155 patients who underwent resection of vestibular schwannoma (2014-2020), 125 patients were included with requisite clinical and radiographic data. After volumetric analysis and whole-tumor ADC histogram, regression tree analysis identified ADC cutoff for significant differences in HB grade. Outcomes were extent of resection, facial nerve function, hospital length of stay (LOS), and complications. RESULTS: Regression tree analysis defined three quantitative ADC groups (× 10-6 mm2/s) as high (> 2248.77; HB 1.7), mid (1468.44-2248.77; HB 3.1), and low (< 1468.44; HB 2.3) range (p 0.04). The mid-range ADC group had significantly worse postoperative HB scores and longer hospital LOS. Large tumor volume was independently predictive of lower rates of gross total resection (p <0.0001), higher postoperative HB score (p 0.002), higher rate of complications (p 0.04), and longer LOS (p 0.003). CONCLUSIONS: Whole-tumor histogram yielded a robust regression tree analysis that defined three ADC groups with significantly different facial nerve outcomes. This likely reflects tumor heterogeneity better than solid-tumor ROI sampling. Whole-tumor ADC warrants further study as a useful radiographic biomarker in patients with vestibular schwannoma who are considering surgical resection.

Direct visualization of intraparotid facial nerve assisting in parotid tumor resection.

Precise recognition of the intraparotid facial nerve (IFN) is crucial during parotid tumor resection. We aimed to explore the application effect of direct visualization of the IFN in parotid tumor resection. Fifteen patients with parotid tumors were enrolled in this study and underwent specific radiological scanning in which the IFNs were displayed as high-intensity images. After image segmentation, IFN could be preoperatively directly visualized. Mixed reality combined with surgical navigation were applied to intraoperatively directly visualize the segmentation results as real-time three-dimensional holograms, guiding the surgeons in IFN dissection and tumor resection. Radiological visibility of the IFN, accuracy of image segmentation and postoperative facial nerve function were analyzed. The trunks of IFN were directly visible in radiological images for all patients. Of 37 landmark points on the IFN, 36 were accurately segmented. Four patients were classified as House-Brackmann Grade I postoperatively. Two patients with malignancies had postoperative long-standing facial paralysis. Direct visualization of IFN was a feasible novel method with high accuracy that could assist in recognition of IFN and therefore potentially improve the treatment outcome of parotid tumor resection.

[Analysis of clinical manifestations and imaging features of facial nerve schwannomas].

Objective:To explore the clinical manifestations and imaging characteristics, and to clarify the imaging value in the diagnosis of facial nerve schwannomas. Methods:Retrospectively analyze the data of 23 patients with facial nerve schwannomas confirmed by surgery and pathology in the Department of Otorhinolaryngology of the First Affiliated Hospital of the Air Force Military Medical University from September 2020 to September 2022, including 8 males and 15 females, aged 18-66 years old. Summarize and analyze their clinical symptoms, specialized examinations, and imaging findings. Results:The clinical manifestations were facial nerve paralysis in 15 cases（2 cases of HB Ⅳ, 6 cases of HB Ⅴ, 7 cases of HB Ⅵ）, hearing loss in 14 cases（5 cases of conductive deafness, 2 cases of mixed deafness, and 7 cases of severe sensorineural hearing loss）, 8 cases tinnitus, 7 cases ear pain, 4 cases dizziness, 4 cases headache, 2 cases ear pus, and parotid gland tumors in 6 cases presenting as local masses. Endoscopic examination revealed 8 cases of external ear canal tumors and 3 cases of intratympanic tumors. Combining temporal bone HRCT, MRI enhanced scanning, and CPR imaging techniques, 1 case involved the internal auditory canal segment, 2 cases in the tympanic segment, 6 cases in the parotid gland area. A total of 14 cases involved two or more segments of the internal auditory canal segment, the labyrinthine segment, geniculate ganglion, the tympanic segment, and the mastoid segment. When the tumors were large, adjacent structures were involved. It was found that 8 cases invaded the external auditory canal and tympanic cavity, ossicles were displaced or bony destruction; 3 cases invaded the jugular foramen area, and 1 case grew to the middle cranial fossa region with temporal lobe brain parenchymal compression. Conclusion:The clinical manifestations of facial nerve schwannomas are diverse. The combination of various imaging techniques will be conducive to topical and qualitative diagnosis and provide an important basis for treatment strategies.

Localization of the Vertical Part of the Facial Nerve in the High-Resolution Computed Tomography During Pediatric Cochlear Implantation.

BACKGROUND: This study proposed a classification of the vertical portion of the facial nerve (VPFN) location, incorporating the previous classifications regarding the posterior-to-anterior and medial-to-lateral dimensions. We also evaluated the implication of this proposed classification on the round window visibility during pediatric cochlear implantation (CI). METHODS: It was a retrospective multicenter observational cohort study. This study included 334 cases that underwent CI between 2015 and 2022 at multiple referral institutes. Two physicians evaluated the preoperative computed tomography images of 334 patients and determined the radiological type of the VPFN. These types were matched with intraoperative round window accessibility. RESULTS: The Spearman's correlation coefficient showed a strong correlation between the proposed VPFN type and the intraoperative round window visibility, as the P-value was <.001. CONCLUSION: This classification could provide the surgeon preoperatively with the precise location of the VPFN in the lateral-to-medial and posterior-to-anterior dimensions. Furthermore, this location classification of the VPFN was significantly correlated with intraoperative round window accessibility, with an accuracy of 90.42%. Therefore, types C and D were expected to have difficult accessibility into the round window, and more surgical interventions were needed to modify the posterior tympanotomy or use other approaches.

Diagnostic Challenges and Imaging Considerations for Intraparotid Facial Nerve Schwannoma: A Case Report and Literature Review.

BACKGROUND A mass in the parotid gland usually indicates parotid gland neoplasia. Warthin tumors or pleomorphic adenomas are common differential diagnoses. Less frequently, other differential diagnoses and sites of origin are considered. Schwannomas are rare, benign tumors in the head and neck region. Even more rarely, these tumors occur in the intraparotid course of the facial nerve. In the following, we report about 2 patients in whom a mass in the right parotid gland was found incidentally during magnetic resonance imaging (MRI). CASE REPORT We reviewed data from the literature on intraparotid facial nerve schwannomas (IPFNS) and compared them with those from our cases. The focus was on data such as clinical history, clinical symptoms, electroneurography, and various imaging modalities, such as ultrasonography and MRI combined with diffusion-weighted imaging. CONCLUSIONS It is challenging to distinguish facial nerve schwannomas from other neoplasms. Patient's history, clinical symptoms, MRI examination with diffusion-weighted imaging, and high-resolution ultrasound imaging are decisive factors for diagnosis and should be performed when IPFNS is suspected. Diagnosis and therapy for IPFNS remain challenging. A wait-and-scan approach could be an option for patients with small tumors and good facial nerve function. On the other hand, patients with advanced tumors associated with limited facial nerve function can benefit from surgical approaches or stereotactic radiosurgery.

Evaluating magnetic resonance imaging characteristics and risk factors for hemifacial spasm.

PURPOSE: The specific neurovascular compression (NVC) event responsible for the symptomatic manifestation of hemifacial spasm (HFS) remains difficult to assess accurately using magnetic resonance imaging (MRI). We aim to evaluate the MRI characteristics of HFS. METHOD: We retrospectively included patients with HFS and divided them into a test group (n = 186) and a validation group (n = 28). The presence, severity, and offending vessel type of NVC in each portion, and the orientation of the offending vessel around the facial nerve, were recorded. Conditional logistic regression analyses were performed to evaluate correlations using test group. The validation group was used to verify whether our findings improved diagnostic performance. RESULTS: Deformity in the proximal cisternal segment was significantly correlated with HFS occurrence (odds ratio [OR]: 256.58, p = .002), whereas contact was not (p = .233). Both contact and deformity in the root detachment point (OR: 19.98 and 37.22, p < .001 and p = .013, respectively) or attached segment (OR: 4.99 and 252.52, p = .001 and p < .001, respectively) were significantly correlated with HFS occurrence. Our findings improved specificity, positive predictive value, and accuracy of diagnosis than conventional diagnostic methods. The vertebral artery predominantly compress the facial nerve in the inferior-anterior position, the anterior inferior cerebellar artery predominantly in the inferior position, the posterior inferior cerebellar artery predominantly in the inferior position, vein predominantly in the posterior-superior position. CONCLUSIONS: This study further demonstrates that within the susceptible portion of facial nerve, different portions of the nerve respond differently to NVC. Each offending vessel has its own preferred conflict orientation. Our study offers reference for neurosurgeons in diagnosis and treatment.

[Image Diagnosis for Hemifacial Spasm].

Cisternography using heavy T2-weighted images from 3-Tesla magnetic resonance imaging(MRI)and three-dimensional time-of-flight MR angiography(3D TOF MRA)is useful for identifying conflicting vessels in primary hemifacial spasm(HFS). Cisternography provides high-signal images of the cerebrospinal fluid and low-signal images of the cranial nerves and cerebral blood vessels, whereas 3D TOF MRA provides high-signal images with only vascular information. The combination of these two methods increases the identification rate of conflicting vessels. The neurovascular conflict(NVC)site in HFS is where the facial nerve exits the brainstem. However, on MRI, the true NVC site is often more proximal than the facial nerve attachment to the brainstem. On preoperative MRI, it is important to not miss the blood vessels surrounding the proximal portion of the facial nerve. If multiple compression vessels or deep vessels are located in the supraolivary fossette, they may be missed. Coronal section imaging and multiplanar reconstruction(MPR)minimize the chances of missing a compression vessel. Preoperative MRI and CT can also provide various other information, such as volume of the cerebellum, presence of emissary veins, shape of the petrosal bone, and size of the flocculus.

Significant tumor compression of the middle cerebellar peduncle is associated with worse facial nerve outcomes and lower extent of resection in surgery for medium-sized vestibular schwannomas - A radiographic analysis of a case series.

BACKGROUND AND OBJECTIVE: Optimizing the extent of resection (EOR) and facial nerve outcomes (FNO) remain a challenge in medium to large vestibular schwannomas (VS). Currently, tumor size has been the only consistently reported factor predicting FNO and EOR. Here, we sought to evaluate whether the degree of the tumor's compression on the middle cerebellar peduncle (PC) influences FNO and EOR in medium to large VS. METHODS: This retrospective case series included 99 patients who underwent surgical resection of their VSs from 2014 to 2022. Preoperative MR imaging was used to measure the degree of PC. Patient medical records were queried to determine the EOR and FNO. RESULTS: Patients with unfavorable FNO (HB 3 +) immediately post-op had significantly greater PC than those with favorable FNO (19.9 vs. 15.4 mm, P = .047). This significance was not observed at the last follow-up but there was a trend. When medium-sized tumors (15-30 mm) were analyzed separately, patients with unfavorable FNO immediate post-op and at last follow-up had significantly greater PC than their favorable counterparts (14.1 vs 8.7 mm). Significantly greater PC was also observed in patients who underwent subtotal resection (20.7 mm) compared to near (14.3 mm) and gross total resection (10.8 mm). Multivariate analyses confirmed these findings in medium-sized tumors, but not large-sized tumors. CONCLUSION: The degree of PC as measured on preoperative imaging can predict FNO and EOR in medium-sized vestibular schwannomas. Medium-sized tumors with > 15 mm of PC likely will have worse FNO and lower EOR.

How to face the hemifacial spasm: challenges and misconceptions.

Hemifacial spasm (HFS) is characterised by intermittent, brief or sustained, repetitive contractions of the muscles innervated by one facial nerve. It is one of the most frequent movement disorders affecting the face. However common and allegedly straightforward to diagnose, it might reveal as a challenge for clinicians in various situations. Indeed, it often needs prior exclusion of many other movement disorders affecting the face, with frequent phenomenological overlaps with blepharospasm, post-facial palsy, facial motor tics, etc. The clinical diagnosis shall be supported by modern brain imaging techniques, and sometimes electromyography, as some particular aetiologies may require specific treatment. Primary forms are associated with vascular compression of the ipsilateral seventh cranial nerve, whereas secondary forms can be caused by any injury occurring on the facial nerve course. This article proposes a global and organised approach to the diagnosis, and the ensuing therapeutic options, as many practitioners still use some inefficient medications when they encounter a case of facial spasm.

Evaluation of facial nerve perineural spread from cutaneous squamous cell carcinoma using 3T MR neurography.

INTRODUCTION: Perineural spread (PNS) is a rare but potentially fatal consequence of cutaneous squamous cell carcinoma (cSCC) of the head and neck. We aimed to evaluate the accuracy of 3T MR neurography in detecting and defining the extent of facial nerve (VII) PNS from cSCC, and highlight characteristic radiological features in peripheral branches to improve early diagnosis. METHODS: Single-institution retrospective review of 38 patients with clinical, radiological, and/or histopathological findings consistent with VII PNS from cSCC who underwent pre-operative 3T MR neurography. RESULTS: Compared to histopathology (gold standard), 3T MR neurography had a sensitivity of 89% and positive predictive value of 97%. In true-positive cases (n = 33), zonal extent was correctly identified in 100%. Seventy-nine% had simultaneous trigeminal nerve (V) PNS, mostly involving the auriculotemporal branch of the mandibular nerve (64%). When the causative lesion was absent (n = 23), the extra-temporal VII demonstrated asymmetrical enhancement alone (n = 6), bulky expansion (n = 8), or extra-neural spread (n = 9). Peripheral VII branch involvement, particularly the buccal and zygomatic, was readily identified using known anatomical landmarks. CONCLUSION: 3T MR neurography is highly accurate in evaluating VII PNS from cSCC, and thus should be specifically requested by physicians if suspicious for disease. Coexistent V PNS was common, highlighting the need to examine V branches to allow complete treatment planning. The unique radiological patterns identified showcases disease progression. As early detection improves patient outcomes, the radiologist must look for peripheral VII involvement in specific anatomical areas, which is within the capabilities of 3T MR neurography.

The clinical availability of facial nerve enhancement in temporal bone MRI for the patients of idiopathic acute peripheral facial palsy.

PURPOSE: This study is to evaluate the duration of facial nerve enhancement in gadolinium-enhanced temporal bone MRI after the onset of acute facial palsy. METHODS: Gd-enhanced MRI imagines were examined in 13 patients with idiopathic acute facial palsy within 14 days after the onset. The degree of facial nerve function was measured according to the House-Brackmann (H-B) grading system at their first visit at outpatient clinic. The follow-up MRI was taken about 16.5 months (7-24 months) after onset of disease. The degree of facial nerve enhancement was measured with signal intensity (SI) which was quantitatively analyzed using the region-of-interest (ROI) measurements for each segment of the facial nerve. SI was statistically analyzed by comparing SI values of contralateral site and ipsilateral site using the paired t test with SPSS program. RESULTS: The gadolinium enhancement was statistically increased at labyrinthine segment and geniculate ganglion area of facial nerve at initial temporal bone MRI. The gadolinium enhancement was statistically decreased at all the segments of facial nerve except tympanic segment (p < 0.05) at follow-up MRI. CONCLUSIONS: The facial nerve enhancement in Gd-enhanced MRI images prolonged more than 21 months of the onset. The newly developed pathologic lesions of acute facial palsy especially occur at the site of labyrinthine and geniculate ganglion.

The value of radiographic features in predicting postoperative facial nerve function in vestibular schwannoma patients: A retrospective study and nomogram analysis.

OBJECTIVE: The purpose of this study was to identify significant prognostic factors associated with facial paralysis after vestibular schwannoma (VS) surgery and develop a novel nomogram for predicting facial nerve (FN) outcomes. METHODS: Retrospective data were retrieved from 355 patients who underwent microsurgery via the retrosigmoid approach for VS between December 2017 and December 2022. Univariate and multivariate logistic regression analysis were used to construct a radiographic features-based nomogram to predict the risk of facial paralysis after surgery. RESULTS: Following a thorough screening process, a total of 185 participants were included. The univariate and multivariate logistic regression analysis revealed that tumor size (p = 0.005), fundal fluid cap (FFC) sign (p = 0.014), cerebrospinal fluid cleft (CSFC) sign (p < 0.001), and expansion of affected side of internal auditory canal (IAC) (p = 0.033) were independent factors. A nomogram model was constructed based on these indicators. When applied to the validation cohort, the nomogram demonstrated good discrimination and favorable calibration. Then we generated a web-based calculator to facilitate clinical application. CONCLUSION: Tumor size, FFC and CSFC sign, and the expansion of the IAC, serve as good predictors of postoperative FN outcomes. Based on these factors, the nomogram model demonstrates good predictive performance.

Predicting value for incomplete recovery in Bell's palsy of facial nerve ultrasound versus nerve conduction study.

OBJECTIVE: This longitudinal study aims at assessing the predictive value of facial nerve high-resolution ultrasound (HRUS) for incomplete clinical recovery in patients with Bell's palsy, the most common facial nerve disease. METHODS: We prospectively enrolled 34 consecutive patients with Bell's palsy. All patients underwent neurophysiological testing (including facial nerve conduction study) and HRUS evaluations 10-15 days (T1), one month (T2), and three months (T3) after the onset of Bell's palsy. Patients who did not experience complete recovery within three months were also evaluated after six months (T4). We have then compared the accuracy of HRUS with that of the facial nerve conduction study in predicting incomplete clinical recovery at three and six months. RESULTS: At T1, the facial nerve diameter, as assessed with HRUS, was larger on the affected side than on the normal side, particularly in patients with incomplete recovery at T2, T3 and T4. ROC curve analysis, however, showed that the facial nerve diameter at T1 had a lower predictive value than the facial nerve conduction study for an incomplete clinical recovery at three (T3) and six (T4) months. Still, the facial nerve diameter asymmetry, as assessed with HRUS, had a relatively high negative predictive value (thus indicating a strong association between normal HRUS examination and a good prognosis). CONCLUSIONS: Although HRUS shows abnormally increased facial nerve diameter in patients in the acute phase of Bell's palsy, the predictive value of this technique for incomplete clinical recovery at three and six months is lower than that of the nerve conduction study. SIGNIFICANCE: Nerve ultrasound has a low predictive value for incomplete clinical recovery in patients with Bell's Palsy.

Contrast-enhanced MRI findings of patients with acute Bell palsy within 7 days of symptom onset: A retrospective study.

The brain magnetic resonance imaging (MRI) findings seen in patients with Bell palsy are abnormal contrast enhancement of affected facial nerves. Previous studies were conducted on a few patients, mainly those who had experienced palsy for several weeks. This study investigated the diagnostic usefulness of MRI by examining MRI findings of acute Bell palsy (within 7 days of symptom onset) in a large cohort. Among the patients with Bell palsy (idiopathic unilateral facial palsy) who visited the hospital, 123 patients who underwent contrast-enhanced MRI of the internal auditory canal within 7 days of symptom onset were reviewed retrospectively. MRI examination results were investigated along with the patient's clinical symptoms and electrodiagnostic test results. Based on the MRI results, the frequency of abnormal contrast enhancement and contrast-enhanced areas were investigated. Of the 123 patients, 13 (11%) had normal brain MRI results, and 110 (89%) had abnormal findings. The frequency of abnormal contrast enhancement was not significantly associated with test timing (P = .56). Of the 110 patients with abnormal findings, 65 (59%) showed contrast enhancement in the labyrinthine segment and 36 (33%) in both the labyrinthine segment and geniculate ganglion. Most patients with Bell palsy who are in the acute phase showed abnormal contrast enhancement in their facial nerves, and similar findings were even observed in the examination conducted on the day of symptom onset. Brain MRI helps in the diagnosis of acute Bell palsy.

Application of diffusion tensor imaging of the facial nerve in preoperative planning for large vestibular schwannoma: a systematic review.

The accurate identification and preservation of the facial nerve (FN) during vestibular schwannoma (VS) surgery is crucial for maintaining facial function. Investigating the application of diffusion tensor imaging (DTI) in preoperative planning for large VS surgery is provided. PubMed, Cochrane Library, Science Direct, ISI Web of Science, Embase, and additional sources were searched to identify cohort studies about the preoperative DTI usage for the FN tracking before large VS (≥ 2.5 cm) surgery published between 1990 and 2023. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed; the Newcastle-Ottawa Scale was used to assess the risk of bias and to evaluate limitations based on selection/outcome biases. A total of 8 publications yielding 149 VS (mean size 3.66 ± 0.81 cm) were included. Surgical concordance with preoperative DTI FN tracking was 91.67% (range 85-100%). Overall DTI reliability was 88.89% (range 81.81-95.83%). Larger tumor size predicted either DTI inaccurate finding or complete DTI failure (p = 0.001). VS size above > 3.5 cm was associated with a higher risk of DTI failure (p = 0.022), with a higher risk of inaccurate DTI finding preoperatively (p = 0.033), and with a higher House-Brackman score postoperatively (p = 0.007). Application of DTI in larger VS surgery is a valuable FN identification along with electrophysiological monitoring and neuronavigation, therefore also in its preservation and in lowering risk of complications. DTI represents a valuable adjunct to electrophysiological monitoring and neuronavigation in FN identification, applicable not only for smaller, but also larger VS.

Irreversible facial nerve palsy as a revelator ofparotid gland cancer.

<br><b>Introduction:</b> Bell's palsy is still the diagnosis of exclusion. In most patients it does not progress, it is unilateral, and selflimiting. Additionally, the majority of patients recover spontaneously within 3 weeks. It is well known that all patients with irreversible facial nerve paresis (FNP) need further examinations to exclude the organic, infectious, metabolic, and autoimmunological causes of the palsy. The goal of the study was to assess the frequency of malignancies hidden under the diagnosis of "Bell's palsy".</br> <br><b>Aim:</b> We aimed to create a diagnostic algorithm to avoid failures concerning patients whose only symptom of parotid gland cancer was irreversible FNP.</br> <br><b>Material and methods:</b> We analyzed 253 consecutive patients with FNP treated in our department in the last 5 years. The subject of the study was "Bell's palsy" cases. All patients with irreversible FNP were reassessed in 6-12 months. We underlined all shortcomings in the diagnostics of those in whom malignancies were found in MRI of the neck and presented the proposal for a diagnostic algorithm to avoid missing such an entity.</br> <br><b>Results:</b> Bell's palsy was observed in 157/253 patients (62.06%), in 36/157 (22.92%) it remained permanent. In 4/36 patients (11.11%) with irreversible FNP, which constituted 2.54% of all "Bell's palsy" cases, parotid gland deep lobe mass was found in MRI. In one patient, infiltration of the skull base was diagnosed. Adenoid cystic carcinoma was confirmed in final histopathology in all cases.</br> <br><b>Conclusions:</b> Our experience has shown that irreversible FNP can be a revelator of the malignant tumor located in the deep lobe of the parotid gland. Contrast-enhanced MRI covering intra- and extracranial segments of the facial nerve should be ordered in all cases of FNP without recovery after 4 months. Repeated imaging should be considered in undiagnosed cases. The main point of our study is to underline that the assessment of the deep lobe of the parotid gland with MRI should be included in the standard diagnostic protocol in all irreversible "Bell's palsy" cases.</br>.

Analysis of mastoid portion of facial nerve course in temporal bone using computed tomography.

<b>Introduction:</b> The facial nerve (FN) follows a complex route in the temporal bone. Successful temporal bone surgery requires knowledge of its course which can be achieved using imaging methods such as computed tomography. This investigation aims to analyze the FN course in its mastoid portion and second genu and the frequency of its atypical course.</br></br> <b>Material and methods:</b> This is a retrospective study that enrolled 104 CT scans of temporal bones of patients followed up in the outpatient clinic of the Otorhinolaryngology Department of Dentistry Faculty of the Medical University of Warsaw between 2020 and 2022. FN courses were classified as straight, bulging, or letter "S"-like. Other parameters estimated: </br> • position of the second genu according to the prominence of the lateral semicircular canal (classified as lateral, medial, or middle) and its distance from a line adjacent to the lateral semicircular canal was measured;</br> • the distance between the short process of the incus and the outermost point of the second genu;</br> • the course of the mastoid portion of FN and the location of SG in comparison to the tympanic portion of n. VII. The course was later classified as lateral, medial, or middle.</br></br> <b>Results:</b> Among the 104 assessed temporal bones, the course of the mastoid portion of FN was classified as bulging in 47 cases (45.2%). Straight and letter "S"-like courses were present in 41 (39.4%) and 16 (15.4%) cases, respectively. Deviation of the second genu according to the prominence of the lateral semicircular canal was medial in 86 cases (82.7%), and middle in 4 cases (3.8%). In the rest, second genu was paramedian to the prominence of the later circular canal. The mean distance between the short process of the incus and the outermost point of SG was 4.9 mm (0.73 mm). The mastoid portion was located laterally, medially, and in the middle of the tympanic portion plane in, respectively, 4.8%, 83.7%, and 11.5%. The second genu was located laterally, medially, and in the middle of the tympanic portion plane in 1.9%, 73.1%, and 25%, respectively. In conclusion, seven temporal bones (6.7%) of five patients presented with a lateral displacement of FN in relation to the established anatomical landmarks.</br></br> <b>Conclusions:</b> Although the atypical course of FN, including the lateral displacement of the mastoid portion, is rare, screening for it is crucial before surgical exploration.