Internal Auditory Canal Tumors Research Articles

Internal auditory canal tumor presented on [18F]AlF-FAPI-74 and [18F]AlF-PSMA-BCH PET/CT in a prostate cancer patient.

Internal auditory canal tumor presented on [18F]AlF-FAPI-74 and [18F]AlF-PSMA-BCH PET/CT in a prostate cancer patient.

Facial nerve protection in surgery for rare tumors of the internal auditory canal

Objective:To explore strategies for preserving facial nerve function during surgeries for rare tumors of the internal auditory canal. Methods:A total of 235 cases of internal auditory canal tumors treated between 2010 and 2023 were included, encompassing vestibular schwannomas, cavernous hemangiomas, meningiomas, and other rare tumors. Various data, including clinical presentations, imaging classifications, and treatment processes, were meticulously analyzed to delineate the characteristics of rare tumors and assess pre-and postoperative facial nerve function. Results:Among all internal auditory canal tumors, vestibular schwannomas accounted for 91.9%. In rare tumors, facial nerve schwannomas constituted 5.3%, cavernous hemangiomas 26.3%, meningiomas 15.8%, and arterial aneurysms 10.5%. Significantly, patients with cavernous hemangiomas displayed pronounced invasion of the facial nerve by the tumor, in contrast to other tumor types where clear boundaries with the facial nerve were maintained. During surgery, individualized approaches and strategies for facial nerve protection were implemented for different tumor types, involving intraoperative dissection, tumor excision, and facial nerve reconstruction. Conclusion:Preservation of the facial nerve is crucial in the surgical management of rare tumors of the internal auditory canal. Accurate preoperative diagnosis, appropriate timing of surgery, selective surgical approaches, and meticulous intraoperative techniques can maximize the protection of facial nerve function. Personalized treatment plans and strategies for facial nerve functional reconstruction are anticipated to enhance surgical success rates, reduce the risk of postoperative facial nerve dysfunction, and ultimately improve the quality of life for patients.

Comparing Linear and Volumetric Tumor Measurements During Observation of Growing Sporadic Vestibular Schwannomas.

To assess the correlation between linear and volumetric changes in vestibular schwannomas (VS). Retrospective imaging review was performed on patients diagnosed with sporadic VS from 2000 to 2019 who demonstrated linear growth on observation with serial magnetic resonance imaging (MRI). Two large tertiary care centers. Changes in diameter on serial MRI scans, measured by 1995 American Academy of Otolaryngology-Head and Neck Surgeryguidelines, were compared to changes in volume, calculated by segmentation. Ninety-two patients had VS confined to the internal auditory canal (IAC) with 236 MRIs analyzed, and 108 patients had VS involving the cerebellopontine angle (CPA) with 193 MRIs analyzed. The Spearman rank correlation coefficients between changes in diameter and volume for IAC and CPA tumors were 0.43 (p < .001) and 0.65 (p < .001), respectively. Linear diameter increases of 1 to <2 mm corresponded to a median volume change of 32% (interquartile range [IQR]: 6%-86%) for IAC tumors, compared to 23% (IQR: 13%-40%) for CPA tumors. Linear diameter increases of 2 to <3 mm (ie, the minimum linear diameter change classically considered "true growth") corresponded to a median volume change of 42% (IQR: 23%-100%) and 47% (IQR: 26%-69%) for IAC and CPA tumors, respectively. Changes in linear diameter significantly correlated with changes in volume for IAC and CPA tumors, although diameter changes that did not meet the definition of linear growth (<2 mm) had corresponding median volume changes in excess of 20% for both IAC and CPA tumors.

Analysis of the effect of neuroendoscopy-assisted microscopy in the treatment of Large (Koos grade IV) vestibular schwannoma.

This article aimed to investigate the effects of the endoscopic-assisted microsurgery technique on the resection of large (Koos grade IV) vestibular schwannoma (VS) and provide a prognosis analysis of the patients. A retrospective analysis of the use of the endoscopic-assisted microsurgery technique in 16 cases of large vestibular schwannoma surgery was carried out. Intraoperative nerve electrophysiological monitoring was conducted to explore the effect of neuroendoscopy on the resection of internal auditory canal tumors, protection of the facial nerve, and minimizing postoperative complications. Tumors were completely removed in all 16 cases, and the facial nerve was anatomically preserved in 14 cases (87.5%). There was no postoperative cerebrospinal fluid leakage and no intracranial infection complications occurred.Following the House-Brackmann (H-B) grading system, post-operative facial nerve function was grade I in 5 cases, grade II in 6 cases, grade III in 3 cases, and grade V in 2 cases. As a result, the preservation rate of facial nerve function (H-B grade I-II) was 68.8%. All 16 patients were followed up for 3 to 24 months, and no tumor recurrence was found on enhanced MRI. Using the endoscopic-assisted microsurgery technique in the retrosigmoid approach has many advantages over the microscopic-only approach. When compared to the microscopy-only approach, the endoscope can provide a wide-angle surgical field superior to that of a microscope in areas such as the internal auditory canal in the resection of large VS, minimize iatrogenic injuries, ensure complete removal of internal auditory canal tumors, and well as reducing postoperative complications such as cerebrospinal fluid leakage and the loss of facial and auditory nerve functions.

Metastatic Bilateral Internal Auditory Canal Invasion Mimicking Neurofibromatosis Type 2

Bilateral internal auditory canal (IAC) tumors are usually pathognomonic for vestibular schwannomas in the setting of neurofibromatosis type 2 (NF2). Descriptions of bilateral nonschwannomatous IAC tumors, such as metastasis that may mimic NF2, are limited to case reports. Here, we report a case of unusual metastatic bilateral IAC tumor originating from the ovary with a rapidly progressive pattern, which we initially suspected to be NF2.

Initial Observation among Patients with Vestibular Schwannoma.

Introduction Vestibular schwannomas (VS) are slow growing tumors. Although there are a wide variety of available treatment options, these tumors are often initially observed. We aimed to establish the presenting symptoms and outcomes of patients treated with initial observation at our institution. Methods The medical records of patients with radiographically diagnosed VS were reviewed from 1989 to 2018. Actuarial estimates of radiographic tumor control and freedom of local therapy were calculated and compared using Cox regression analyses. Results A total of 360 patients were diagnosed with VS at our institution from 1989 through 2018 with a median age of 59.9 years. After radiographic diagnosis, 243 patients (67.5%) opted for initial observation. Local control at 1, 5, and 10 years was 91, 67, and 58%, respectively. On multivariable analysis, factors associated with shorter time to radiographic tumor progression included younger patient age ( p = 0.016) and tumors with an extracanalicular component ( p = 0.032). Regarding time until definitive treatment only larger baseline American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) tumor size predicted for earlier initiation of therapy ( p < 0.001), although this was restricted to tumors with an extracanalicular component ( p = 0.004), as opposed to purely internal auditory canal tumors ( p = 0.839). Conclusion Many patients who were initially observed continued to have satisfactory local control rates at 10 years. In patients with extracanalicular tumors, larger AAO-HNS tumor measurements were associated with earlier radiographic tumor progression and shorter time to local therapy, with 7 mm serving as a potential threshold value for extracanalicular tumors. Younger patients and tumors with primarily an extracanalicular portion may warrant closer observation.

Audiologic Natural History of Small Volume Cochleovestibular Schwannomas in Neurofibromatosis Type 2.

To characterize the audiometric natural progression in patient-ears with small volume (<1,000 mm), treatment-naïve cochleovestibular schwannomas (CVSs) in Neurofibromatosis Type 2 (NF2). Prospective, longitudinal cohort study. Quaternary medical research institute. One hundred eleven ears in 71 NF2 patients with small, treatment-naïve CVSs observed from July 2006 to July 2016. Serial audiometric testing, including pure tone audiometry, speech audiometry, and magnetic resonance imaging (MRI). Four-frequency pure tone average (4f-PTA) of 0.5, 1, 2, and 4 kHz and word recognition score (WRS) were recorded. Their changes were compared with MRI changes in CVS volume over time. Times to significant hearing loss (10 dB loss in 4f-PTA) and WRS based on 95% critical difference were measured. Linear regression analysis showed a significant correlation with baseline hearing level (4f-PTA) and internal auditory canal (IAC) tumor volume to annual hearing decrease rate (AHDR) (p = 0.003, p = 0.0004). Hearing level at baseline and tumor volume correlate with AHDR while tumor volume growth rate does not. Two-way analysis of variance found significant differences in AHDR, risk of significant hearing loss, and risk of critical difference in WRS based on baseline hearing level (abnormal or normal) and IAC tumor volume (greater or less than 200 mm). Subjects with normal baseline hearing and small IAC tumor component had a low AHDR and low risk of significant hearing loss and may warrant conservative management while the presence of baseline hearing loss and large IAC volume resulted in higher ADHR and greater risk for further hearing loss and may benefit from early treatment interventions.

Sudden sensorineural hearing loss associated with inner ear lesions detected by magnetic resonance imaging

Although recent advances in magnetic resonance imaging (MRI) techniques have contributed to the detection of tiny lesions in the internal auditory canal (IAC) that may be responsible for sudden sensorineural hearing loss (SSNHL), there have been relatively few studies on the clinical characteristics of intra-labyrinthine hemorrhage (ILH) and labyrinthitis versus those regarding IAC tumors. Our purpose was to investigate the frequency of those IAC lesions on MRI and their clinical characteristics. Initial MRIs of 200 patients with SSNHL (93 men, 107 women; mean age = 48.61 years, range: 18–84 years), as well as detailed clinical histories, audiological examinations, and thyroid function, lipid battery, and serological tests (for viral agents and autoimmune disease), were performed. All patients were hospitalized at the time of diagnosis of SSNHL and were administered the same treatment protocol. Patients were divided into idiopathic and secondary groups according to their MRI results. After discharge, they underwent follow-up audiometry and clinical examination at predetermined intervals (2 weeks, 1, 2, 4, and 6 months, and 1 and 2 years). Propensity score-matching and receiver operating characteristics curves of the initial parameters were used for estimating clinical characteristics. Of the 200 patients, 25 (12.55%) who had abnormal findings suggesting inner ear lesions on MRI were assigned to the secondary SSNHL group; within this group, 10 patients (10/200, 5%) had a tumor invading the IAC, 7 (7/200, 3.5%) had ILH, 6 (6/200, 3%) had labyrinthitis, and 2 (1%) had a structural deformity of the IAC. The secondary group showed significantly poor recovery of hearing function compared with that in the idiopathic group. Patients with ILH or labyrinthitis showed prognoses that were equally poor as those of patients with tumors in the secondary group. Additionally, patients with such lesions showed significant canal paresis on the lesion side at an early stage and a high prevalence of benign paroxysmal positional vertigo (BPPV). In conclusion, the prevalence of non-tumorous lesions on MRI represents common findings and showed a poorer treatment response than that of vestibular Schwannoma in patients with SSNHL. Abnormal canal paresis (cut-off value of 35% on the lesioned side, sensitivity 65.2% and specificity 67%), spontaneous nystagmus directed to the contralesional side, and positional vertigo would be the clinical presentation of SSNHL with IAC lesions, in which the presence of acute prolonged vertigo or positional vertigo compatible with BPPV suggests the possibility of a non-tumorous lesion, such as ILH or a labyrinthitis rather than an IAC tumor.

P11.10 Atypical teratoid/rhabdoid tumor in the internal auditory canal

AbstractOBJECTIVE: The case of a thirteen-year-old woman showing an atypical teratoid/rhabdoid tumor (AT/RT) primarily occurred in the internal auditory canal was presented. Results: There was a delay in diagnosing AT/RT because of the first histological diagnosis of benign neurofibroma. If we had changed the surgical approach to one which was middle cranial fossa-based or translabyrinthine in the second or third operation, we might have reached an earlier final diagnosis. Although we faced a dilemma about whether to sacrifice facial nerve function for dissection of the tumor, we should have considered the possibility of malignancy at an earlier stage. CONCLUSION: This is a case report of AT/RT in the internal auditory canal presenting with progressive hearing loss as the initial symptom. Although no previous reports of AT/RT primarily occurring in the internal auditory canal are existent, this rare form of the disease should be considered in future evaluations as a differential diagnosis for internal auditory canal tumor.

Efficacy and outcomes of facial nerve-sparing treatment approach to cerebellopontine angle meningiomas.

OBJECTIVE Advanced microsurgical techniques contribute to reduced morbidity and improved surgical management of meningiomas arising within the cerebellopontine angle (CPA). However, the goal of surgery has evolved to preserve the quality of the patient's life, even if it means leaving residual tumor. Concurrently, Gamma Knife radiosurgery (GKRS) has become an acceptable and effective treatment modality for newly diagnosed, recurrent, or progressive meningiomas of the CPA. The authors review their institutional experience with CPA meningiomas treated with GKRS, surgery, or a combination of surgery and GKRS. They specifically focus on rates of facial nerve preservation and characterize specific anatomical features of tumor location with respect to the internal auditory canal (IAC). METHODS Medical records of 76 patients with radiographic evidence or a postoperative diagnosis of CPA meningioma, treated by a single surgeon between 1992 and 2016, were retrospectively reviewed. Patients with CPA meningiomas smaller than 2.5 cm in greatest dimension were treated with GKRS, while patients with tumors 2.5 cm or larger underwent facial nerve-sparing microsurgical resection where appropriate. Various patient, clinical, and tumor data were gathered. Anatomical features of the tumor origin as seen on preoperative imaging confirmed by intraoperative investigation were evaluated for prognostic significance. Facial nerve preservation rates were evaluated. RESULTS According to our treatment paradigm, 51 (67.1%) patients underwent microsurgical resection and 25 (32.9%) patients underwent GKRS. Gross-total resection (GTR) was achieved in 34 (66.7%) patients, and subtotal resection (STR) in 17 (33.3%) patients. Tumors recurred in 12 (23.5%) patients initially treated surgically, requiring additional surgery and/or GKRS. Facial nerve function was unchanged or improved in 68 (89.5%) patients. Worsening facial nerve function occurred in 8 (10.5%) patients, all of whom had undergone microsurgical resection. Upfront treatment with GKRS for CPA meningiomas smaller than 2.5 cm was associated with preservation of facial nerve function in all patients over a median follow-up of 46 months, regardless of IAC invasion and tumor origin. Anatomical origin was associated with extent of resection but did not correlate with postoperative facial nerve function. Tumor size, extent of resection, and the presence of an arachnoid plane separating the tumor and the contents of the IAC were associated with postoperative facial nerve outcomes. CONCLUSIONS CPA meningiomas remain challenging lesions to treat, given their proximity to critical neurovascular structures. GKRS is a safe and effective option for managing CPA meningiomas smaller than 2.5 cm without associated mass effect or acute neurological symptoms. Maximal safe resection with preservation of neurological function can be performed for tumors 2.5 cm or larger without significant risk of facial nerve dysfunction, and, when combined with GKRS for recurrence and/or progression, provides excellent disease control. Anatomical features of the tumor origin offer critical insights for optimizing facial nerve preservation in this cohort.

Defining the Limits of Endoscopic Access to Internal Auditory Canal.

To quantify surgical access to the internal auditory canal (IAC) using an exclusively endoscopic transcanal approach (EETA) and investigate surgically relevant relationships with neurovascular and osseous landmarks of the temporal bone. Anatomical dissection of two paired temporal bones and 15 unpaired temporal bones was performed using an exclusively endoscopic approach to IAC. The dissection proceeded until the cerebellopontine angle (CPA) could be accessed. Following dissection, all the specimens were subjected to computed tomography (CT) imaging. Anatomage InVivo5 software was used to analyze the CT scans and record measurements. CPA access and visualization of the labyrinthine segment of the facial nerve were achieved in all specimens. The mean distances from the carotid artery, jugular bulb, and middle fossa to the surgical opening (or fundostomy) of IAC were 4.1±1.5, 6.4±2.5, and 5.5±1.9 mm, respectively. The mean cross-sectional areas of the fundostomy and tympanic ring were 30.8±10.4 and 67.7±11.3 mm2. The mean distances from the osteo-cartilaginous junction and tympanic ring to the porus acusticus were 29±2.6 and 21±2.3 mm, respectively. Transcanal access to the entire IAC can be safely achieved using an exclusively endoscopic approach. Generous removal of the cochlear promontory can be accomplished while a safe distance is maintained from key neurovascular structures. EETA to IAC offers a minimally invasive alternative to patients without serviceable hearing for intrameatal and medial IAC tumors. Increased knowledge of crucial anatomical relationships involved in this approach will facilitate acceptance and utilization.

Is the cause of sensorineural hearing loss in patients with facial schwannomas multifactorial?

Facial nerve schwannomas (FNSs) and vestibular nerve schwannomas (VNSs) may occupy similar locations in the internal auditory canal (IAC). Risk factors for hearing loss in patients with FNS are unknown. Similar to VNSs, we hypothesize that the size and location of FNSs do not correlate with hearing loss. Retrospective cohort study and otopathology case review. A single institution retrospective review of all patients diagnosed with FNS was performed. Demographic data, tumor size and location, severity and type of hearing loss, and facial nerve function were analyzed. Otopathologic review of a case of FNS was also performed. Thirty-three patients with FNS were identified. Mean age was 44 years, and 61% (n = 21) were female. Nine patients had tumors involving the IAC facial nerve, whereas 24 had distal tumors without IAC involvement. Eleven patients (33%) had hearing loss, and 55% of patients with sensorineural hearing loss (SNHL) had tympanic segment tumors without IAC involvement. The presence of SNHL was not associated with IAC tumor location (P = 0.21). Maximal dimensions of FNSs were 3 mm to 42 mm, without correlation between size and SNHL severity (r = -0.017, P = 0.926). Otopathologic review of an untreated 5-mm IAC FNS demonstrated disproportionate spiral ganglion and hair cell loss within the ipsilateral cochlea compared to the contralateral ear. Tympanic segment FNS without IAC involvement may result in SNHL. Tumor size is not associated with the presence or severity of SNHL. Otopathologic review suggests degenerative cochlear changes in FNS. Mechanisms for SNHL in schwannomas are likely multifactorial and may be unrelated to cochlear nerve compression. 4. Laryngoscope, 127:1676-1682, 2017.

Vestibular Schwannomas: Do Linear and Volumetric Parameters on MRI Correlate With Hearing Loss?

To determine if two-dimensional and volumetric imaging parameters in vestibular schwannomas (VS) correlate with hearing loss at presentation. Retrospective. Forty-one cases of pathologically confirmed sporadic VS were analyzed. Maximal tumor dimensions in anteroposterior (AP), coronal (ML), and craniocaudal (CC) dimensions were obtained along with tumor-fundus distance and internal auditory canal (IAC) porus diameters. Volumetric analysis was done on 37 cases. Tumors volumes were calculated through both 3-D volumetric and ABC/2 [AP × ML × CC/2] methodology. With the 3-D method, total tumor volume (TTV), and cerebellopontine angle (CPA) tumor volume were separately calculated and IAC volumes obtained by subtracting CPA tumor volumes from TTV. Pure tone average (PTA) and speech discrimination scores (SDS) were correlated with tumor dimensions. Non-volumetric analysis was performed on 41 tumors. The AP and ML dimensions correlated with both PTA and SDS (p < 0.05). No significant correlations were seen between hearing loss and tumor-fundus distance or porus diameters. The tumor volume calculated through ABC/2 methodology correlated with PTA and SDS (p < 0.05). The 3-D TTV and CPA volumes only correlated with PTA. IAC tumor volumes did not correlate with hearing loss. Maximal AP and ML dimensions are the only non-volumetric variables, which significantly correlate with hearing loss. Tumor volume calculated through ABC/2 method significantly correlates with hearing impairment while the 3-D TTV and CPA tumor volumes only correlated significantly with PTA scores but not SDS scores.

Optical Coherence Tomography Navigated Surgery for Different Internal Auditory Canal Tumor Approaches

Optical Coherence Tomography Navigated Surgery for Different Internal Auditory Canal Tumor Approaches

Neurofibromatosis 2 invasion of the internal auditory canal wall: clinical significance.

To describe the infiltration of severe phenotype ("Wishart") neurofibromatosis type 2 (NF2)-related vestibular nerve schwannomas (VSs) into the internal auditory canal wall in contrast to sporadic VS and the milder ("Gardner") phenotype NF2-related VS. Retrospective case series involving microscopic examination and review of clinical history. Temporal bone laboratory, harboring 849 documented pairs of decalcified, formalin-fixed, celloidin-embedded, sectioned human temporal bones (hTBs) with clinical history. Histologic sections from 56 patients who had been treated by the House Clinic for VS and who had pledged their temporal bones were identified in the data base of the laboratory. Twenty-four hTBs were from individuals with NF2.Each series of sections was examined microscopically for evidence of invasion of the walls of the internal auditory canal (IAC), hearing thresholds, speech discrimination, score (SDS), and tumor recurrence. Infiltration of the walls of the IAC by small buds of VS was found in 17 of the 24 NF2 hTBs. The only 2 NF2 without invasion were from an elderly patient with the milder (Gardner) form of NF2. Ten of the 12 NF2 patients had undergone surgery for the removal of their tumor, but residual tumor remained in the bone surrounding the IAC. Invasive VS were associated with poorer hearing thresholds at 250, 500, 1,000, and 2,000 Hz and lower SDS score. A relationship between invasion and recurrence was not statistically significant. The majority of IAC tumors associated with the severe "Wishart" phenotype demonstrate bone invasion within the IAC. Invasion of bone was associated with poorer hearing. The invasive nature of NF2-associated tumors may partially explain their higher recurrence rate after resection. Surgeons managing NF2-related VS should be aware of the small infiltrations of the wall of the IAC when removing these tumors to minimize recurrence.

Wound breakdown after middle cranial fossa craniotomy: An unusual complication after rhytidectomy

Wound complications after middle cranial fossa craniotomy are rare. We describe a patient who underwent a left middle fossa craniotomy for resection of a small internal auditory canal tumor with subsequent development of wound breakdown and infection 1 week postoperatively. Prompting of the patient elicited a history of bilateral rhytidectomies. Wound debridement, hyperbaric oxygen therapy, dermal regeneration template placement, and prolonged antibiotic treatment were performed. Complete secondary intention healing occurred with an acceptable cosmetic outcome. Prior rhytidectomy scars must be identified and incorporated into the surgical planning prior to performing middle fossa craniotomy incisions.

Pediatric cerebellopontine angle and internal auditory canal tumors

The aim in this study was to describe the clinical presentation, differential diagnosis, and risk for neurofibromatosis Type 2 (NF2) in pediatric patients presenting with cerebellopontine angle (CPA) and internal auditory canal (IAC) tumors. The authors conducted a retrospective study at a tertiary care academic referral center. All patients with an age ≤ 18 years who had presented with an extraaxial CPA or IAC tumor between 1987 and 2012 were included in the study cohort. Data regarding symptoms, diagnosis, tumor characteristics, and NF2 status were collected and analyzed. Sixty patients (55% female, 45% male) harboring 87 tumors were identified. The mean age at diagnosis was 12.8 years (median 14.0 years, range 0.9-18.9 years). Schwannomas were the most commonly identified lesions (57 of 87 tumors, including 52 vestibular, 3 facial, and 2 trigeminal schwannomas), followed by meningiomas (5 of 87) and epidermoid cysts (4 of 87). Six malignant tumors were diagnosed, including small-cell sarcoma, squamous cell carcinoma, malignant meningioma, atypical rhabdoid-teratoid tumor, endolymphatic sac tumor, and malignant ganglioglioma. Headache, followed by hearing loss and imbalance, was the most common presenting symptom, whereas dysphagia, otalgia, and facial pain were uncommon. Neurofibromatosis Type 2 was diagnosed in 20 (61%) of 33 patients with vestibular schwannoma (VS), while the other 13 patients (39%) had sporadic tumors. Nineteen of the 20 patients with NF2 met the diagnostic criteria for that disorder on initial presentation, and 15 of them presented with bilateral VS. At the last follow-up, 19 of the 20 patients subsequently diagnosed with NF2 demonstrated bilateral VSs, whereas 1 patient with a unilateral VS and multiple other NF2-associated tumors has yet to demonstrate a contralateral VS to date. Only 1 patient presenting with an isolated unilateral VS and no family history of NF2 demonstrated a contralateral VS on subsequent radiological screening. Cerebellopontine angle and IAC tumors in the pediatric population are rare. There are several noteworthy differences between the adult and pediatric populations harboring these lesions. While VS is the most common pathology in both age groups, the lesion was found in only 60% of the pediatric patients in the present study. Unlike in adults, VSs in the pediatric population were associated with NF2 in over one-half of all cases. The majority of pediatric patients with NF2 fulfilled the diagnostic criteria at initial presentation; however, approximately 7% of patients presenting with a seemingly sporadic (no family history of NF2) unilateral VS will meet the criteria for NF2 later in life. Finally, malignancies account for a significantly higher percentage (10%) of cases among pediatric patients. These findings underscore the importance of early screening and close radiological follow-up and may be helpful in patient counseling.

正円窓小窩, 内耳道への進展を認めた迷路内神経鞘腫の1例

Intralabyrinthine schwannomas (ILSs) are rare benign neoplasms arising from distal branches of the cochlear, superior vestibular, or inferior vestibular nerves. We report on a case of ILS with extensions to the round window niche and internal auditory canal (IAC) in a 47-year-old male. The patient noticed sudden hearing loss and tinnitus in his left ear at the age of 36, received steroid therapies, but was left with complete deafness. He had suffered from repetitive vertigo attacks for 6 months at 41. At 46 when he presented with deterioration of his left tinnitus, he was finally diagnosed as having ILS on enhanced MRI and constructive interference in steady-state analysis. The tumor was located in all turns of cochlea, vestibule, and the fundus of the IAC. Because follow-up MRI suggested growth of the IAC tumor, we performed total removal of the tumor via the translabyrinthine and transcanal approaches. The tumor had invaded only the cochlear nerve in the IAC and appeared in the round window niche in the middle ear. Pathological examination showed an Antoni A type schwannoma with fibrous changes of the semicircular canals. We should remember this inner

Evaluation of the vestibulo-ocular reflex using sinusoidal off-vertical axis rotation in patients with acoustic neurinoma

The vestibulo-ocular reflex (VOR) was studied to examine the utility of off-vertical axis rotation (OVAR) in the diagnosis of acoustic neurinoma. Subjects were sinusoidally rotated with eyes open in complete darkness at frequencies of 0.4 and 0.8 Hz with a maximum angular velocity of 60°/s at either earth-vertical axis rotation (EVAR) or OVAR. Thirteen patients with acoustic neurinomas were investigated. Results showed that VOR gain during OVAR at 0.8 Hz and in a 30° nose-up position in patients with internal auditory canal tumors was significantly less than the gain measured during EVAR. The VOR gain measured from all patients (including those with tumors extending to the cerebellopontine angle) was not significantly different when the patients were subjected to EVAR and OVAR. These observations were possibly due to superior vestibular nerve dysfunction. We concluded that certain stimulating parameters—patient's nose tilted up 30°; sinusoidal OVAR at 0.8 Hz and 60°/s maximum angular head velocity—were useful for evaluating vestibular function in patients suffering from an acoustic neurinoma located within the internal auditory canal.

Secondary Intracanalicular Extension of a Primary Intracochlear Schwannoma

Vestibular schwannomas represent 6 to 8% of all intracranial tumors. Verocay, along with Antoni, suggested the idea of the Schwann cell as the cell of origin, a theory that has since been confirmed by electron microscopy and immunohistochemical studies. Until recently, the commonly accepted teaching was that these tumors originate from the Schwann-glial cell junction along the nerve, an area also known as the Obersteiner-Redlich zone. This transition zone is located along the internal auditory canal (IAC) portion of the nerve, approximately 7 to 13 mm from the brainstem (1). More recently, however, numerous cadaveric and clinical studies have described tumors arising from the myelinated portion of the nerve, lateral to the transition zone (2). With recent improvements in imaging techniques, there have been an increasing number of reports describing exclusively intralabyrinthine schwannomas, not involving the more medial segments of the nerve (3). More than 50 such cases have been reported in the literature to date, the first one by Mayer as early as 1917 (3,4). While most of the earlier cases were reported at autopsy or during surgery for severe vertigo, improved imaging resolution has resulted in earlier identification of these tumors (5). Intralabyrinthine schwannomas are currently considered a separate clinical entity from those involving the IAC and cerebellopontine angle (CPA). Although initially thought to arise more commonly from the cochlear division of the nerve, a recent review of all published cases by Neff et al. (3) reveals an equal incidence between the vestibular and the cochlear varieties. Depending on the involved portion of the labyrinth, these tumors present with sensorineural or mixed hearing loss, tinnitus, and/or vestibular symptoms. The vestibular symptoms related to labyrinthine schwannomas differ from those of patients with IAC and CPA tumors in that true vertigo exists in a higher percentage of patients (6). Of interest, all of the cases of labyrinthine schwannomas reported to date have been restricted to the osseous labyrinth without involvement of the IAC. Although tumors involving both the IAC and the labyrinthine compartment have been described, most have been attributed to secondary labyrinthine extension by a primary IAC tumor rather than the converse (6). This conclusion likely reflects the fact that the IAC-CPA schwannomas are relatively common, whereas the intralabyrinthine tumors are rare. In fact, serial imaging studies that document progressive, direct tumor extension either from or into the inner ear over time are lacking. The images in Figure 1, A to D, show the axial cuts of a gadolinium-enhanced magnetic resonance imaging scan of the same patient taken during a 5-year period. They reveal a clear progression of the tumor, with medial extension from the labyrinth into the IAC.