Endoscopic precaruncular medial transorbital and endonasal multiport approaches to the contralateral skull base: a clinicoanatomical study.

OBJECTIVE: Minimally invasive endoscopic endonasal multiport approaches create additional visualization angles to treat skull base pathologies. The sublabial contralateral transmaxillary (CTM) approach and superior eyelid lateral transorbital approach, frequently used nowadays, have been referred to as the "third port" when used alongside the endoscopic endonasal approach (EEA). The endoscopic precaruncular contralateral medial transorbital (cMTO) corridor, on the other hand, is an underrecognized but unique port that has been used to repair CSF rhinorrhea originating from the lateral sphenoid sinus recess. However, no anatomical feasibility studies or clinical experience exists to assess its benefits and demonstrate its potential role in multiport endoscopic access to the other contralateral skull base areas. In this study, the authors explored the application and potential utility of multiport EEA combined with the endoscopic cMTO approach (EEA/cMTO) to three target areas of the contralateral skull base: lateral recess of sphenoid sinus (LRSS), petrous apex (PA) and petroclival region, and retrocarotid clinoidocavernous space (CCS). METHODS: Ten cadaveric specimens (20 sides) were dissected bilaterally under stereotactic navigation guidance to access contralateral LRSS via EEA/cMTO. The PA and petroclival region and retrocarotid CCS were exposed via EEA alone, EEA/cMTO, and EEA combined with the sublabial CTM approach (EEA/CTM). Qualitative and quantitative assessments, including working distance and visualization angle to the PA, were recorded. Clinical application of EEA/cMTO is demonstrated in a lateral sphenoid sinus CSF leak repair. RESULTS: During the qualitative assessment, multiport EEA/cMTO provides superior visualization from a high vantage point and better instrument maneuverability than multiport EEA/CTM for the PA and retrocarotid CCS, while maintaining a similar lateral trajectory. The cMTO approach has significantly shorter working distances to all three target areas compared with the CTM approach and EEA. The mean distances to the LRSS, PA, and retrocarotid CCS were 50.69 ± 4.28 mm (p < 0.05), 67.11 ± 5.05 mm (p < 0.001), and 50.32 ± 3.6 mm (p < 0.001), respectively. The mean visualization angles to the PA obtained by multiport EEA/cMTO and EEA/CTM were 28.4° ± 3.27° and 24.42° ± 5.02° (p < 0.005), respectively. CONCLUSIONS: Multiport EEA/cMTO to the contralateral LRSS offers the advantage of preserving the pterygopalatine fossa contents and the vidian nerve, which are frequently sacrificed during a transpterygoid approach. This approach also offers superior visualization and better instrument maneuverability compared with EEA/CTM for targeting the petroclival region and retrocarotid CCS.

Assessing the feasibility of the transmastoid infralabyrinthine approach without decompression of the jugular bulb to the extradural part of the petrous apex and petroclival junction prior to surgery.

BACKGROUND AND OBJECTIVE: This study aims to define specific measurements on cranial high-resolution computed tomography (HRCT) images prior to surgery to prove the feasibility of the navigated transmastoid infralabyrinthine approach (TI-A) without rerouting of the facial nerve (FN) and decompression of the jugular bulb (JB) in accessing the extradural-intrapetrous part of petrous bone lesions located at the petrous apex and petroclival junction. MATERIALS AND METHODS: Vertical and horizontal distances of the infralabyrinthine space were measured on cranial HRCT images prior to dissection. Subsequently, the area of access was measured on dissected human cadaveric specimens. Infralabyrinthine access to the extradural part of the petrous apex and petroclival junction was evaluated on dissected specimens by two independent raters. Finally, the vertical and horizontal distances were correlated with the area of access. RESULTS: Fourteen human cadaveric specimens were dissected bilaterally. In 54% of cases, the two independent raters determined appropriate access to the petrous apex and petroclival junction. A highly significant positive correlation (r = 0.99) was observed between the areas of access and the vertical distances. Vertical distances above 5.2 mm were considered to permit suitable infralabyrinthine access to the extradural area of the petrous apex and petroclival junction. CONCLUSIONS: Prior to surgery, vertical infralabyrinthine distances on HRCT images above 5.2 mm provide suitable infralabyrinthine access to lesions located extradurally at the petrous apex and petroclival junction via the TI-A without rerouting of the FN and without decompression of the JB.

The trans-sylvian trans-petrosal "half & half" approach-a how I do it.

BACKGROUND: Petroclival meningiomas are one of the most challenging tumors to be operated in the realm of neurosurgery. Many approaches have been developed over the years. METHOD: The authors describe the Half & Half (H&H) approach whose main indication is petroclival meningiomas with suprasellar extension. The part of the tumor located above CN III and in the retrochiasmatic space is addressed through a trans-sylvian, while the petroclival portion is through an extradural anterior petrosectomy approach. The wide surgical corridor given by this approach allows extensive tumor resection while avoiding the risk associated with the manipulation of intracavernous neurovascular structures. CONCLUSION: The H&H approach is an effective strategy to maximize the safe resection of petroclival meningiomas.

Combined microscope-endoscopy resection of petrous bone cholesteatoma with temporary facial nerve transposition versus nontransposition.

PURPOSE: The narrow supralabyrinthine space affects surgical procedures. To study the effect of temporary transposition of geniculate ganglion of facial nerve versus nontransposition on lesion recurrence and facial nerve function in patients with petrous bone cholesteatoma. METHODS: A total of 18 patients with petrous bone cholesteatoma involving the facial nerve were treated in our hospital from November 2016 to March 2023. The main surgical method is the extended supralabyrinthine approach assisted by a microscope and an endoscope. We collected and retrospectively analyzed their medical records. RESULTS: Temporary facial nerve transposition was performed in five patients, and nontransposition was performed in 13 patients. Cholesteatoma recurred in three patients with facial nerve nontransposition, whereas none in patients with facial nerve transposition. In this study, except for one case with a second operation, postoperative facial paralysis in other cases was improved to varying degrees, and there was no significant difference between the two groups. CONCLUSION: Temporary transposition of geniculate ganglion of facial nerve will not affect the postoperative nerve function of patients and can reduce the possibility of cholesteatoma recurrence of the petrous bone.

Microsurgical transcranial approaches to the posterior surface of petrosal portion of the temporal bone: quantitative analysis of surgical volumes and exposed areas.

Different microsurgical transcranial approaches (MTAs) have been described to expose the posterior surface of the petrous bone (PPB). A quantitative, anatomical comparison of the most used MTAs, for specific areas of the PPB, is not available. Anatomical dissections were performed on five formalin-fixed, latex-injected cadaver heads (10 sides). Six MTAs were analyzed: Kawase approach (KWA), retrosigmoid approach (RSA), retrosigmoid approach with suprameatal extension (RSAS), retrolabyrinthine approach (RLA), translabyrinthine approach (TLA), and transcochlear approach (TCA). Surgical volumes and exposed areas of each approach were quantified with a dedicated neuronavigation system (ApproachViewer, part of GTx-Eyes II, University Health Network, Toronto, Canada) and adjuvant software (ITK-SNAP and Autodesk Meshmixer 3.5). Areas and volumes were compared using linear mixed models. TCA provided the best exposure of Trautmann's triangle and the retromeatal, suprameatal, meatal, and premeatal regions. RSAs provided the best exposure of the inframeatal region, with RSAS gaining significant exposure of the suprameatal region. KWA had the highest surgical volume, and RLA the lowest. Transpetrosal approaches offer the widest exposure of PPB proportionally to their invasiveness. Retrosigmoid approaches, which get to the studied region through a postero-lateral path, are paramount for the exposure of the inframeatal and suprameatal region and, given the adequate exposure of the remaining PPB, represent an effective approach for the cerebellopontine angle (CPA). These anatomical findings must be considered with approach-related morbidity and the pathological features in order to choose the most appropriate approach in clinical practice.

Combined petrosal approach: a systematic review and meta-analysis of surgical complications.

Transpetrosal approaches are known to be associated with a significant risk of complications, including CSF leak, facial palsy, hearing impairment, venous injury, and/or temporal lobe injury. We aimed to evaluate the morbidity of the standard combined petrosal approach (CPA), defined as a combination of the posterior (retrolabyrinthine) and the anterior petrosal approach. We performed a systematic review and meta-analysis of articles reporting on clinical series of patients operated on for petroclival meningiomas through CPA. Studies that used the terminology "combined petrosal approach" without matching the aforementioned definition were excluded as well as clinical series that included less than 5 patients. A total of 8 studies were included involving 160 patients. The pooled complication rates were 3% (95% CI, 0.5-5.6) for CSF leak, 8.6% (95% CI, 4.1-13.2%) for facial palsy, 8.2% (95% CI, 3.9-12.6%) for hearing impairment, 2.8% (95% CI, 0.9-6.5%) for venous complications, and finally 4.8% (95%, 1.2-8.4%) for temporal lobe injury. Contrary to the general belief, CPA is associated with an acceptable rate of complications, especially when compared to alternative approaches to the petroclival area. In view of the major advantages like shorter trajectory, multiple angles of surgical attack, and early tumor devascularization, CPA remains an important tool in the armamentarium of the skull base surgeon.

How I do it: intradural anterior petrosectomy.

BACKGROUND: The anterior transpetrosal approach (ATPA) is a cranial base approach for addressing upper petroclival or lateral pontine lesions. It is fundamentally an epidural procedure involving the drilling of the petrous apex. However, this approach has significant procedure-related morbidity, and the surgeon must perform a complete petrosectomy, as the intradural structures are not in view during the drilling. For selected cases, a rationale exists for choosing a tailor-made intradural anterior petrosectomy (IAP). METHOD: This article describes the relevant surgical anatomy and the different surgical steps of the IAP. CONCLUSION: IAP represents a feasible alternative to the standard ATPA with the advantage of minimizing the extent of petrous bone removal to the individual need.

Combined retrosigmoid and middle fossa approach for a small, superiorly located petroclival meningioma: how I do it.

BACKGROUND: Petroclival meningiomas pose significant surgical challenges because of their deep location and complex surrounding neurovasculature. The use of multiple surgical approaches can optimize safe tumor removal from multiple anatomic compartments. METHOD: We describe a patient with a growing superior petroclival meningioma centered at the posterior clinoid with extension into Meckel's cave that was successfully removed with a combined retrosigmoid and subtemporal middle fossa approach. This strategy avoided the need for anterior petrous bone drilling and tentorial splitting. CONCLUSION: A combined retrosigmoid and subtemporal middle fossa approach can provide safe access to tumors spanning the supra- and infratentorial compartments.

Surgical Considerations in Addressing Cholesterol Granuloma of the Petrous Apex through an Infracochlear Approach.

Cholesterol granuloma of the petrous bone is a foreign body giant cell reaction to cholesterol deposits with symptoms including hearing loss, vestibular dysfunction, and cranial nerve deficit as a result of cystic mass compression. Surgical treatment is often difficult to plan due to limited access to the lesion and possible injury to surrounding structures. We report on a case of petrous apex cholesterol granuloma drainage through an infracochlear approach. A 27-year-old female patient presented with acute diplopia due to left-sided abducens paralysis. Multislice computed tomography (MSCT) and magnetic resonance (MR) imaging described a 3.5-cm well-marginated lesion in petrous bone apex, compressing the left abducens nerve at the point of entry into the cavernous sinus, corresponding to cholesterol granuloma. The patients was surgically treated through a transcanal infracochlear approach, since preserving the external and middle ear conduction mechanisms was paramount for the patient. The patient was discharged on the second postoperative day and diplopia resolved within 5 days postoperatively. Six months after the surgery, her hearing on the left side is normal, and she remains symptom-free. This case underpins the value of preoperative planning when approaching the petrous apex, an anatomically complex area due to abundance of important neurovascular structures crowded in a narrow and confined region.

Anatomic Study of Petrous Bone and Its Surrounding Structures in the Extended Anterior Transpetrosal Approach.

Extended anterior transpetrosal approach (ATPA) includes drilling the petrous bone to achieve maximal exposure of the petroclival region. Injuring of surrounding neurovascular structures, such as the internal carotid artery (ICA), during the procedure may result in severe complications. In this study, we aimed to use computer topographic images to provide comprehensive anatomic information on the petrous bone and surrounding structures to help surgeons during the extended ATPA. Computer topographic angiography images of 110 individuals were reviewed, and measurements were performed on coronal, sagittal, and axial planes following multiplanar reformation. The petrous apex and sagittal midline were used to locate the anterior, middle, and posterior parts of the petrous bone and petrosal segment of the ICA during the ATPA. The thicknesses of the petrous bone were 3.28±0.71, 3.53±0.88, and 7.02±1.11 mm at the petrous apex, trigeminal impression, and internal opening of internal auditory canal (IAC) positions, respectively. The distances between the petrous apex to the trigeminal impression, internal opening of the IAC, auris interna, and labyrinth were 7.39±1.62, 15.95±2.48, 17.39±2.39, and 29.00±3.18 mm, respectively. Furthermore, the petrosal segment of the ICA was located at the above landmarks on the petrous bone. Our findings provide anatomic information on the petrous bone and surrounding structures during the extended ATPA procedure based on fixed anatomic landmarks so as to achieve maximal exposure and reduce the number of complications.

Scratching in the minefield: using intertriangles line to safely perform anterior petrosectomy.

PURPOSE: The transpetrosal-transtentorial approach provides a practical and safe surgical corridor for the treatment of petroclival region lesions. Any inaccuracies while performing this surgical technique can result in catastrophic results; nevertheless, this can be prevented under the guidance of a detailed anatomical orientation. An "intertriangles line" was defined to preserve the internal auditory canal (IAC) and cochlea during extradural bone drilling. METHODS: The anatomical study consisted of two groups: the cadaveric head and the skull group. A literature-based landmark and criteria list was created to examine the borders of the Kawase triangle/space and evaluate the anatomical structures that may be at risk during drilling for anterior petrosectomy. RESULTS: A total of 20 cadaveric head sides and 30 dried skull sides were examined. The rhomboid area was divided into two triangles with a common the intertriangles line. In all dissections, the IAC was found to be localized posterior to the "intertriangle line". A minimum distance of 1 mm for the Internal Carotid artery and 2 mm for the IAC can serve as threshold values to be considered by the surgeon during drilling for petrosectomy. CONCLUSIONS: Kawase's area resembles a minefield, in which every step and manipulation should be considered. A minimal but effective resection of the cranial base is needed to increase safety and decrease morbidity during skull base surgery. Furthermore, this study investigated accessible and prominent landmarks to establish a feasible area of triangles and define the intertriangles line to guide the neurosurgeon under microscope and avoid IAC injury.

How I do it? Resection of residual petrous apex chordoma with combined endoscopic endonasal and contralateral transmaxillary approaches.

BACKGROUND: The petrous apex is one of the most challenging areas of the skull base to access. METHOD: We present a case of residual petrous apex chordoma posterolateral to the paraclival segment of the internal carotid artery (ICA) resected with combined endoscopic endonasal and contralateral transmaxillary (CTM) approaches, without lateralization of the ICA. CONCLUSION: This case demonstrates the value of the CTM corridor in resecting petrous apex lesions that are posterolateral to the paraclival segment of the ICA.

Lariboisiere Hospital pre-operative surgical checklist to improve safety during transpetrosal approaches.

BACKGROUND: Transpetrosal approaches are technically complex and require a complete understanding of surgical and radiological anatomy. A careful evaluation of pre-operative magnetic resonance imaging and computed tomography scan is mandatory, because anatomical or pathological variations are common and may increase the risk of complications related with the approach. METHODS: Pre-operative characteristics of venous and petrous bone anatomy were analysed and correlated with intraoperative findings, using injected magnetic resonance imaging and thin-slices computed tomography scan. These data regularly checked before each transpetrosal approach were progressively included in the presented checklist. RESULTS: Transpetrosal approaches have been used in 101 patients. Items included in the checklist were petrous bone pneumatization, angle between petrous apex and clivus, dehiscence of petrous carotid artery, dehiscence of geniculate ganglion, distance between superior semicircular canal and middle fossa floor, distance between cochlea and middle fossa floor, sigmoid sinus dominance, transverse sigmoid sinus junction depth to the outer cortical bone, jugular bulb height (high or low), location of the vein of Labbé, characteristics of superior petrosal vein complex. CONCLUSION: The presented checklist provides a systematic scheme of consultation of characteristic of venous and petrous bone anatomy for transpetrosal approaches. In our experience, the use of this checklist reduces the risk of complications related with approach, by minimizing the neglect of crucial information.

The mini-combined transpetrosal approach: an anatomical study and comparison with the combined transpetrosal approach.

BACKGROUND: The combined transpetrosal approach (CTPA) is a versatile technique suitable for challenging skull base pathologies. Despite the advantages provided by a wide surgical exposure, the soft tissue trauma, complex and time-consuming bony work, and cosmetic issues make it far from patient expectations. In this study, the authors describe a less invasive modification of the CTPA, the mini-combined transpetrosal approach (mini-CTPA), and perform a quantitative comparison between these two approaches. METHODS: Five human specimens were used for this study. CTPA was performed on one side and mini-CTPA on the opposite side. The surgical freedom, petroclival and brainstem area of exposure, and maneuverability for 6 anatomical targets, provided by the CTPA and mini-CTPA, were calculated and statistically compared. The bony volumes corresponding to each anterior petrosectomy were also measured and compared. Three clinical cases with an operative video are also reported to illustrate the effectiveness of the approach. RESULTS: The question-mark skin incision done along the muscle attachments permits an optimal cosmetic result. Even though the limited incision, the smaller craniotomy, and the less extensive bone drilling of mini-CTPA provide a smaller area of surgical freedom, the areas of exposure of petroclival region and brainstem were not statistically different between the two approaches. The antero-posterior maneuverability for the oculomotor foramen (OF), Meckel's cave (MC) and the REZ of trigeminal nerve, and the supero-inferior maneuverability for OF, MC, Dorello's canal, and REZ of CN VII are significantly reduced by the smaller opening. The bony volume of anterior petrosectomy resulted similar among the approaches. CONCLUSIONS: The mini-CTPA is an interesting alternative to the CTPA, providing comparable surgical exposure both for petroclival region and for brainstem. Although the lesser soft tissue dissection and bony opening decrease the surgical maneuverability, the mini-CTPA may reduce surgical time, potential approach-related morbidities, and improve cosmetic and functional outcomes for the patients.

Management of postoperative CSF rhinorrhea after retrosigmoid craniotomy: how I do it.

BACKGROUND: Cerebrospinal fluid (CSF) rhinorrhea as a complication of retrosigmoid craniotomy does not occur often today. This complication is primarily associated with the petrous bone drilling during surgery. METHOD: The management of this complication is shown by the example of the patient with a trigeminal schwannoma located in posterior cranial fossa operated through resrisigmoid craniotomy. Three steps of management and surgical stages of petrous bone plasty are shown. CONCLUSION: CSF rhinorrhea after retrosigmoid craniotomy is a preventable complication: petrous bone pneumatization should be evaluated preoperatively. If the air cells are open, primary plasty of the defect should be performed.

A two-stage combined anterolateral and endoscopic endonasal approach to the petroclival region: an anatomical study and clinical application.

OBJECT: The pretemporal transcavernous anterior petrosal (PTAP) approach and the combined petrosal (CP) approach have been used to resect petroclival meningiomas (PCMs). In this cadaveric anatomical study, a two-stage combined PTAP and endoscopic endonasal far medial (EEFM) approach (the PTAPE approach) was compared morphometrically to the CP approach. A case study provides a clinical example of using the PTAPE approach to treat a patient with a PCM. The key elements of the approach selection process are outlined. METHODS: Five cadaveric specimens underwent a CP approach and 5 underwent a PTAPE approach. The area of drilled clivus, length of multiple cranial nerves (CNs), and the area of brain stem exposure were measured, reported as means (standard deviations) by group, and compared. RESULTS: The total area of the clivus drilled in the PTAPE group (695.3 [121.7] mm2) was greater than in the CP group (88.7 [17.06] mm2, P < 0.01). Longer segments of CN VI were exposed via the PTAPE than the CP approach (35.6 [9.07] vs. 16.3 [6.02] mm, P < 0.01). CN XII (8.8 [1.06] mm) was exposed only in the PTAPE group. Above the pontomedullary sulcus, the total area of brain stem exposed was greater with the PTAPE than the CP approach (1003.4 [219.5] mm2 vs. 437.6 [83.7] mm2, P < 0.01). Similarly, the total exposure of the medulla was greater after the PTAPE than the CP exposure (240.2 [57.06] mm2 vs. 48.1 [19.9] mm2, P < 0.01). CONCLUSION: A combined open-endoscopic paradigm is proposed for managing large PCMs. This approach incorporates the EEFM approach to address the limitations of the PTAP and the CP approach in a systematic fashion. Understanding the anatomical findings of this study will aid in tailoring surgical approaches to patients with these complex lesions.

Petrous bone cholesteatoma: our experience of 20 years and management of two giant cases affecting rhinopharynx.

PURPOSE: To demonstrate our experience in the treatment of petrous bone cholesteatoma (PBC). METHODS: Data of PBC patients in our hospital from January 2000 to December 2019 were collected. Surgical approaches and facial function were mainly discussed and compared with the literature. The management of 2 giant PBC cases affecting rhinopharynx has been demonstrated. RESULTS: The supralabyrinthine type was the most frequent type followed by the massive type. There were 5 cases with cholesteatoma extending into the clivus (2 cases), sphenoid (1 case) and rhinopharynx (2 cases). The translabyrinthine approach (40%) was our most frequently used approach followed by the middle fossa approach (36%) and the transmastoid approach (11%). There were 10 cases managed with the assistance of endoscope, including 3 cases with cholesteatoma extending into clivus, sphenoid and rhinopharynx separately. Obliteration of the cavity was performed in 70.3% (135/192) cases; 3 of them recurred. For the 2 giant PBC cases affecting rhinopharynx, traditional microscopic surgery assisted with transnasal endoscope was performed. The reduced exposure was beneficial for postoperative recovery, and the approach in the nasal cavity provided a permanent drainage for postoperative examination. CONCLUSION: Otologic endoscope combined with traditional microscopic surgery could reduce the exposure in surgery. For extremely extended cases of PBC, supplementary transnasal endoscopic approach deserves to be considered for the traditional temporal bone approach.

Prevention of cerebrospinal fluid leak after vestibular schwannoma surgery: a case-series focus on mastoid air cells' partition.

BACKGROUND: Petrous bone pneumatization may be related to cerebrospinal fluid (CSF) leak secondary to vestibular schwannoma surgery. OBJECTIVE: To assess the association between petrous bone pneumatization and CSF leak in vestibular schwannoma surgery. METHODS: A retrospective study included 222 consecutive vestibular schwannoma patients treated via a retrosigmoid or translabyrinthine approach in a 17-year period in one University Hospital. Association of CSF leak and petrous bone pneumatization, as seen on CT scans, was assessed on ANOVA and Student's t or Chi-squared test in case of non-parametric distribution. RESULTS: One hundred and 75 resections were performed on a retrosigmoid approach and 47 on a translabyrinthine approach. Mean age was 53.6 ± 12.9 years. Mean follow-up was 5 years 6 months. Twenty-six patients (11.7%) showed CSF leak and 8 (3.6%) meningitis. Approach (p = 0.800), gender (p = 0.904), age (p = 0.234), body-mass index (p = 0.462), tumor stage (p = 0.681) and history of schwannoma surgery (p = 0.192) did not increase the risk of CSF leak. This risk was unrelated to mastoid pneumatization (p = 0.266). There was a highly significant correlation between internal acousticus meatus (IAM) posterior wall pneumatization and CSF leak after retrosigmoid surgery (p = 0.008). Eustachian tube packing in the translabyrinthine approach did not decrease risk of CSF leak (p = 0.571). CONCLUSION: Degree of petrous bone pneumatization was not significantly related to risk of CSF leak, but pneumatization of the posterior IAM wall increased this risk in retrosigmoid surgery. Eustachian tube packing in the translabyrinthine approach is not sufficient to prevent postoperative CSF leak. Both approaches had similar rates of CSF leaks, around 12%.

The otologic approach in the management of posterior petrous surface meningiomas.

PURPOSE: Report our experience in the management of posterior petrous surface meningiomas (PPSMs), and identify features that affect hearing, facial nerve (FN) function, and control of the disease. METHODS: Retrospective case series of 131 patients surgically managed for PPSMs. FN status, hearing and tumour radicality were assessed and compared between patients with tumours of different locations (Desgeorges classification) and internal auditory canal involvement (IAC). RESULTS: At the time of surgery 74.8% of patients had a hearing loss. Hearing was mostly unserviceable in tumors attached to the meatus. Pure tone audiometry did not correlate to IAC extension, while speech discrimination scores were statistically worse when the tumor occupied the IAC (unpaired t test, p = 0.0152). Similarly, extrameatal tumors undergoing removal by otic preserving techniques maintained postoperative hearing, whereas hearing worsened significantly in tumors involving the IAC (paired t test, p = 0.048). The FN was affected preoperatively in 11.4% of cases. Postoperative FN palsy was significantly correlated to the IAC involvement (Fisher's exact test, p = 0.0013), while it was not correlated to tumor size. According to the Desgeorges classification, a postoperative FN palsy complicated the majority of anteriorly extending tumors and, two-fifths of meatus centred tumors. 75% of posterior located tumors had a postoperative FN grade I HB. CONCLUSIONS: Since the involvement of the IAC by the tumor affects both hearing and FN function, the IAC is of primary importance in PPSMs and should be studied and addressed as much as the tumor location in the CPA.

Three-dimensional imaging for the localization of related anatomical structures during surgery on the internal auditory canal.

BACKGROUND: The Fisch infra-temporal fossa approach (Fisch's method), first proposed in 1970, is commonly used during internal auditory canal (IAC) surgery with an approach that advances through the middle cranial fossa. This study was designed to address the technical difficulties encountered in recognizing and localizing the arcuate eminence with respect to the superior semicircular canal (SSC). METHODS: Forty men and 40 women (18-57 years of age) without space-occupying lesions in the petrous part of the temporal bone were selected for the study. In total, 160 samples were obtained from both sides of the temporal bone. The temporal bone in these 160 samples was scanned using computed tomography, and a three-dimensional coordinate system was established to measure the three-dimensional coordinate values of structures adjacent to the arcuate eminence, the SSC, and the IAC. RESULTS: The results showed that the shape of the arcuate eminence is highly variable. Approximately 23.12% of samples had no obvious arcuate eminence, which prevented the use of Fisch's method to localize the SSC. The arcuate eminence was difficult to identify in 37 samples. CONCLUSIONS: Analysis samples showed that the SSC was located in a fan ring centered at the midpoint of the upper edge of the petrous portion of the temporal bone. The arcuate eminence did not correspond directly with the SSC, as the former was located posterolateral to the latter in 85.83% of samples. The angle between the SSC and the IAC ranged from 0° to 60° degrees, as reported previously by Fisch. However, the angle typically ranged from 10-30° in our study.