Preoperative hearing function shows wide variations among patients diagnosed with vestibular schwannoma. Besides the preoperative tumor size there are other factors that influence the preoperative hearing function that are frequently discussed. A comprehensive analysis of a large cohort of vestibular schwannomas has the potential to describe new insights and influence the preoperative management. We analyzed clinical factors, imaging data and the expression of the proliferation marker MIB1 as potential influencing factors on the preoperative hearing function in a retrospective cohort of 523 primary sporadic vestibular schwannomas. The results of the preoperative audiometry were quantified using the Gardner-Robertson Score. Uni- and multivariate analyses were performed. Serviceable hearing (Gardner-Robertson class 1 or 2) was documented in 391 patients (74.8%). Factors associated with non-serviceable hearing (Gardner-Robertson class 3-5) were patients of older age (p < 0.0001), larger preoperative tumor volume (p = 0.0013) and widening of the internal acoustic meatus compared to the healthy side (p = 0.0353). Gender and differences in the expression of the proliferation marker MIB1 had no influence on preoperative hearing. In the multivariate nominal logistic regression older age (OR 27.60 (CI 9.17-87.18), p < 0.0001), larger preoperative tumor volume (OR 20.20 (CI 3.43-128.58), p = 0.0011) and widening of the internal acoustic canal (OR 7.86 (CI 1.77-35.46), p = 0.0079) remained independent factors associated with non-serviceable hearing. Widening of the internal acoustic canal is an independent factor for non-serviceable preoperative hearing in vestibular schwannoma patients together with older age and larger preoperative tumor volume.

OBJECTIVE: This study aims to assess the anatomical possibilities of the jugular bulb (JB).
METHODS: Fifty archived CBCT scans were analyzed.
RESULTS: The average distance between the internal acoustic canal (IAC) and the JB was 7.97 mm on both sides (Right: SD = 2.56 mm, range 3.16-13.3 mm; Left: SD = 2.5 mm, range 2.9-13.6 mm). JB walls\' pneumatization was classified into eight patterns. Deep petrosal cells (DPCs) prevailed in the lateral wall of the JB. The absence of pneumatization (NP) was commonly found on the left side. The presence of infralabyrinthine and hypotympanic cells varied. Less common types included accessory occipital cells (AOCs), posteromedial tracts (PMTs), and basi-occipital cells (BOCs), which determined a consistent variation of the lateral wall pneumatization patterns. Pneumatization of the medial wall was not observed in 50 right sides and 49 left sides. The inferior wall analysis revealed symmetry in AOC distribution and a predominant occurrence of NP. Cases with hypotympanum (HT) in the lateral wall showed a statistically significant IAC-JB distance increase by an average of 4.67 mm compared to NPs. Specific pneumatizations, particularly HT on the lateral side, have a significant effect on the IAC-JB distance, showing a clear pattern of increasing distance from DPC to NP and then to HT. A significant distance increase in HT pneumatization was noted. There were also recorded instances of JB hypoplasia and hyperplasia, JB diverticula, dehiscent JBs, and high JBs.
CONCLUSIONS: This study establishes a novel classification of JB pneumatizations to aid in the understanding of the temporal bone anatomy.

Introduction  The wide range of anatomical variability of the structures of the middle cranial fossa (MCF) and the lack of reliable surgical landmarks contribute to a high level of complications in the surgical treatment of vestibular schwannomas. We hypothesized that the cranial phenotype influences the shape of the MCF, the orientation of the pyramid of the temporal bone, and the relative topography of the internal acoustic canal (IAC). Methods  The skull base structures were studied on 54 embalmed cadavers and 60 magnetic resonance images of the head and neck by photo modeling, dissection, and three-dimensional analysis techniques. By the value of the cranial index, all specimens were subdivided into dolichocephalic, mesocephalic, and brachycephalic groups for comparison of variables. Results  The length of the superior border of the temporal pyramid (SB), the apex to squama distance, and the width of the MCF all peaked in the brachycephalic group. The value of the angle between the SB and the axis of the acoustic canal varied from 33 to 58 degrees; it peaked in the dolichocephalic group and showed its smaller value in the brachycephalic one. The pyramid to squama angle had reversed distribution and dominated in the brachycephalic group. Conclusion  The cranial phenotype influences the shape of the MCF, temporal pyramid, and IAC. Presented in this article data help specialists operating on the vestibular schwannoma to localize the IAC based on the individual shape of a skull.

[This corrects the article DOI: 10.3389/fonc.2021.774462.].

OBJECTIVE: To explore the role of neuroendoscope assistance during surgical resection of the intracanalicular portion of vestibular schwannomas via the retrosigmoid approach and the subsequent early facial nerve outcomes.
METHODS: Patients of vestibular schwannoma with intracanalicular extensions undergoing retrosigmoid dissection at a single institution were retrospectively analyzed in this study. Several surgical techniques were applied to ensure maximal and safe removal of tumors. Tumors extending less than 10 mm into the internal acoustic canal (IAC) were classified as Grade A, while those extending over 10 mm into IAC were taken as Grade B. Neuroendoscope was applied at the end of microscopic phase to search for potential remnants for Grade B tumors. Absolute tumor extension was defined and measured. House and Brackmann (HB) scale was used to evaluate immediate CN VII outcomes.
RESULTS: Of the 61 patients, there were 38 females and 23 males. A total of 18 (29.51%) cases were Koos Grade II, 12 (19.67%) cases Koos Grade III, and 31 (50.82%) cases Koos Grade IV. There were 38 cases (62.30%) of Grade A and 23 cases (37.70%) of Grade B. Gross total resection was achieved in 60 cases (98.36%). Four cases of intracanalicular remnants were detected and completely removed under endoscopic visualizations. There was a significantly higher proportion (17%, p = 0.02) of intracanalicular remnants in Grade B than Grade A. CN VII and VIII were anatomically preserved in all cases. A total of 55 cases (90.16%) retained good (HB Grades 1 and 2) facial nerve outcomes.
CONCLUSIONS: In Grade B vestibular schwannomas, after maximal microsurgical removal, endoscopic evaluation of the intracanalicular portion revealed residual tumors in 17% of the patients. Hence endoscopic evaluation of the potential intracanalicular remnants for tumor extending over 10 mm within IAC (Grade B) is recommended.

Cerebellopontine angle (CPA) and internal auditory canal (IAC) lipomas are rare, benign tumors comprising 0.08% of all intracranial tumors and can be mistaken for other, more common lesions of the CPA/IAC such as vestibular schwannoma. The purpose of this study was to review the literature and assess the evolution of CPA/IAC lipoma diagnosis and management. In addition, we present 17 new lipomas, matching the largest known case series of this rare tumor.
Retrospective case series and systematic review.
Systematic review of the literature was performed using PubMed and Google Scholar. References from identified articles were also reviewed to identify potential additional manuscripts. Manuscripts and abstracts were reviewed to identify unique cases. For the case series, the charts of all CPA/IAC lipoma patients seen at a single institution from 2006-2019 were manually reviewed. Logistic regression and chi-squared analysis were performed where appropriate.
A total of 219 unique lipomas have been reported in the literature, including 17 presented in this study. Surgical management has been performed in 46% of cases and has been conducted less often in recent decades, likely due to improved radiographic diagnostic capabilities and understanding of surgical outcomes. Surgical management is associated with worse neurologic outcomes (P = .002) and has become less common in recent decades. Although growth is unlikely, it has been demonstrated in patients into their 30s.
Accurate radiographic diagnosis is imperative for appropriate patient management, as CPA/IAC lipomas should typically be managed through observation and serial imaging whereas vestibular schwannomas and other CPA/IAC lesions may require microsurgical or radiosurgical intervention depending on growth and symptomatology. Laryngoscope, 131:2081-2087, 2021.

This video depicts the case of a 48-yr-old female with 3 yr of progressive left hemifacial spasm (HFS) refractory to medication. Magnetic resonance imaging showed a large anterior inferior cerebellar artery (AICA) and also a labyrinthine artery loop around the facial nerve (FN) root exit zone. A large bony eminence was also noted in the superior and lateral aspects of the porous acousticus (PA). She preferred surgery if \"cure\" was possible in lieu of Botox injections. A left retro sigmoid craniotomy was performed with brainstem auditory evoked responses (BAERs) and FN monitoring along with lateral spread response (LSR) assessment. The large bony prominence was drilled in its lateral aspect. Despite this, visualization was still limited and therefore we utilized a 30-degree-angled endoscope to observe the vessels caudal and cranial to the FN. This view prompted us to then drill further at the PA to decompress the FN as well as mobilize the labyrinthine artery away from the nerve. The LSR showed a dramatic improvement when FN decompression was accomplished, and then a further improvement with arterial mobilization and Teflon pledget placement. The BAERS remained at baseline throughout. FN function and hearing were intact on postoperative clinical assessment. Her symptomatic improvement was recorded at 12 mo after surgery. This video illustrates a more complex case of microvascular decompression with skull base concepts and techniques. The patient provided consent for the procedure and use of her images and operative video for publication.

Lateral angle (LA) of the internal acoustic canal (IAC) at its opening at the surface of the petrous portion of the temporal bone is known in literature as a dimorphic measurement useful for sex assessment. However, its reliability is still debated. Moreover, no information is available about the possible relationship between LA and shape and size of the IAC. This study aims at assessing breadth, length and lateral angle of IAC on 100 CT scans belonging to subjects aged between 20 and 70 years, equally divided between males and females. Possible differences in the three measurements according to side and sex were assessed through two-way ANCOVA test, using three cranial measurements (distance between anterior and posterior nasal spine, upper facial height, bizygomatic breadth) as covariates (p < 0.05). Possible correlations among IAC measurements and with age were assessed through Pearson\'s test (p < 0.05). Results showed a significantly greater IAC breadth on the left side than on the right side; moreover, LA was significantly wider in females than in males and was positively correlated with IAC breadth in both males and females. In addition, LA was negatively correlated with age only in the female group. The study first showed that LA is strictly related to IAC morphology; moreover, it is significantly affected by masculinization of skeletal traits in females. Therefore, caution is suggested in using this measurement for sex assessment.

Background  Exostoses and osteomas are benign, insidious lesions of the bone involving the internal acoustic canal (IAC). We present two cases of IAC exostoses managed with surgical decompression and review the clinical outcomes of previously reported cases in the literature. Methods  A comprehensive search was conducted using PubMed Central, Web of Science Core Collection, and Google Scholar databases to identify previous reports of IAC exostoses and osteomas. A total of 26 reported cases were identified, and patient presenting symptoms, management strategies, and response to surgery was obtained when available. Results  Of the 13 patients who underwent surgical decompression, 8 patients had resolution of vertigo symptoms, 10 patients had improvement of tinnitus symptoms, and all patients maintained some level of serviceable hearing. Conclusion  IAC exostoses and osteomas are rare lesions that lead to insidious onset of debilitating symptoms from vestibulocochlear nerve dysfunction. Although the role of surgical decompression remains unclear, it appears that patients presenting with vertigo have more favorable response to surgical decompression as compared with those presenting with tinnitus and sensorineural hearing loss.

Salivary duct carcinoma (SDC) is a rare parotid tumor that often develops as a rapidly growing mass with a poor prognosis. It has a high rate of distant metastases, sometimes with infiltration along nerves. We describe a case of SDC that originated outside the cranium and extended into the cranium along the path of the facial nerve.
A 74-year-old man underwent magnetic resonance imaging at a local hospital, which revealed a tumor in the left internal acoustic canal; the patient was referred to our department. A left facial schwannoma was suspected, and magnetic resonance imaging was performed again 6 months later. Rapid tumor growth was confirmed, and the tumor was resected. The tumor displayed atypical epithelial cells with comedo necrosis and cribriform structure and was diagnosed as SDC. All residual intracranial tumors were removed using the middle fossa approach. The tumor, which was considered to be a primary tumor, was found near the stylomastoid foramen, and it was removed with the parotid gland. Five months after the initial surgery, metastasis to the trigeminal nerve was observed, and this was removed using a retrosigmoid approach, followed by radiation therapy.
All 4 surgical specimens of this case were presented, and the path of tumor progression was examined in detail. Although the primary lesion was small, intracranial invasion along the facial nerve occurred. SDC should be considered as a tumor that can extend into the cranium, even with a small primary lesion.