Magnetic Resonance Appearance of the Inner Ear After Hearing-Preservation Surgery

Postoperative Cochlear Obliteration after Retrosigmoid Approach in Patients with Vestibular Schwannoma

Objective  Vestibular schwannomas (VSNs) account for the vast majority of lesions located in the cerebellopontine angle (CPA). The goals of VSN surgery are possible total tumor removal, intact facial nerve function, and preservation of cochlear nerve function. In cases of pre- or postoperative deafness, restoration of hearing with auditory brainstem implant (ABI) or cochlear implant (CI) is a promising treatment option with normally better results in CI than in ABI. The aim of this retrospective study is to evaluate cochlear ossification or obliteration secondary to a retrosigmoid approach, which is important for later CI, especially in single-sided deafness. Materials and Methods  We retrospectively reviewed data from our suboccipital retrosigmoid operation database for the period from January 2008 to February 2015. A total of 65 patients with VSN could be analyzed retrospectively. The patient's data (age, gender, side of operation, tumor entities, and the duration of follow-up) were evaluated. The most recent T2-weigted MRI exams were taken into account for the evaluation of cochlea. To compare left and right sides, the coronal reformatted images were reconstructed in a symmetrical way. Results  Twenty-two out of 65 (33%) patients had cochlear obliteration in our survey. The cochlear obliteration was more common in females (44 vs. 20% in males). The median follow-up was 28 months. The size and the intrameatal extension of tumors could not be considered as factors influencing the cochlear obliteration rate. According to our survey, 33% of suboccipital approaches manifested cochlear obliteration to some extent. It was more common in females. The intrameatal extension of tumors played statistically no role in the occurrence of postoperative cochlear obliteration. Whether the prohibition of cochlear ossification can be best achieved by retrosigmoid approaches, compared to other approaches to the CPA, or not could be a subject of future studies.

Cochlear Patency After Translabyrinthine Vestibular Schwannoma Surgery

OBJECTIVES

To determine the temporal occurrence of fluid signal changes on T2-weighted magnetic resonance imaging (T2MRI) that occur in the cochlear lumen after translabyrinthine surgery.

STUDY DESIGN

Retrospective case control study.

SETTING

Tertiary referral neurotology center.

SUBJECTS AND METHODS

Seventy-one patients were identified who underwent translabyrinthine removal of a vestibular schwannoma between 2010 and 2014; of these 49 were included as they had postoperative T2 MRI at 6, 18, and 48 months available postsurgery. Magnetic resonance imaging scans were scored base on fluid signal changes within the cochlea.

RESULTS

In total, 147 magnetic resonance imaging scans were reviewed on 49 patients. In the cohort analysis 86% of patients showed evidence of fluid signal changes 48 months postoperatively. Ninety-five percent of patients who went on to demonstrate loss of fluid signal at 48 months had already shown changes at 6 months postsurgery. The majority of cochlea signal changes identified at 6 months were minor (72% Grade 1) while at 48 months this had progressed to severe (71% Grade 2 or 3). Of the patients with a normal cochlea at 6 months 78% maintained a normal cochlea to the 48-month scan.

CONCLUSION

Cochlear signal changes suggestive of fibrosis occurred in most patients following translabyrinthine removal of vestibular schwannoma. Given the early onset of cochlear fluid signal changes on T2MRI, and the progression of these changes on subsequence imaging, cochlear implantation would ideally need to be performed either simultaneous to translabyrinthine surgery or as an early second-stage procedure to maximize the chance of a successful electrode insertion, or one can consider a placeholder as well.

The Management and Imaging of Vestibular Schwannomas

Vestibular schwannomas are the most common cerebellopontine angle tumor. During the past century, the management goals of vestibular schwannomas have shifted from total resection to functional preservation. Current treatment options include surgical resection, stereotactic radiosurgery, and observation. Imaging has become a crucial part of the initial screening, evaluation, and follow-up assessment of vestibular schwannomas. Recognizing and understanding the management objectives, various treatment modalities, expected posttreatment findings, and complications allows the radiologist to play an essential role in a multidisciplinary team by providing key findings relevant to treatment planning and outcome assessment. The authors provide a comprehensive discussion of the surgical management, role of radiation therapy and observation, imaging differential, and pre- and posttreatment imaging findings of vestibular schwannomas.

An allograft mouse model for the study of hearing loss secondary to vestibular schwannoma growth

Vestibular schwannoma is a benign neoplasm arising from the Schwann cell sheath of the auditory-vestibular nerve. It most commonly affects both sides in the genetic condition Neurofibromatosis type 2, causing progressive high frequency sensorineural hearing loss. Here, we describe a microsurgical technique and stereotactic coordinates for schwannoma cell grafting in the vestibular nerve region that recapitulates local tumor growth in the cerebellopontine angle and inner auditory canal with resulting hearing loss. Tumor growth was monitored by bioluminescence and MRI in vivo imaging, and hearing assessed by auditory brainstem responses. These techniques, by potentially enabling orthotopic grafting of a variety of cell lines will allow studies on the pathogenesis of tumor-related hearing loss and preclinical drug evaluation, including hearing endpoints, for NF2-related and sporadic schwannomas.

Cochlear obliteration after translabyrinthine vestibular schwannoma surgery

The objective of the study was to determine the temporal occurrence of cochlear obliteration following translabyrinthine vestibular schwannoma resection. A retrospective chart review, cross-sectional study, and sequential analysis of the time series were performed. The retrospective study included patients undergoing translabyrinthine resection for stage T1-T2 vestibular schwannoma from 2007 to 2010 without prior therapy and postoperative follow-up including MRI of the brain and the cerebellopontine angle. Already 3 months after surgery a radiographic labyrinthine change was observed in 66.7 %, a partial obstruction in 50 %, and an obstruction limited to the saccule in 16.7 %. Only 33.3 % of the patients showed an unchanged inner ear. In consideration of early cochlear obstruction after translabyrinthine vestibular schwannoma resection, temporary follow-up is necessary. Since the indications for cochlear implantation (CI) have been extended, especially concerning patients with single-side deafness, a simultaneous or early second-stage CI after tumour removal should be discussed.

Postoperative imaging of vestibular schwannomas

Symptomatic vestibular schwannomas can be treated with resection (translabyrinthine, retrosigmoid [suboccipital], or middle cranial fossa approaches) or stereotactic radiosurgery. When appropriate, auditory brainstem stimulators can also be implanted in patients with current or impending hearing loss due to bilateral vestibular schwannomas. Imaging plays a prominent role in determining management following these procedures. In this article, the expected postoperative imaging appearances are depicted. The radiological features of complications are also reviewed, including recurrent tumor, fat graft necrosis, CSF leakage, infection, hydrocephalus, cerebral infarction, venous sinus thrombosis, hemorrhage, and temporal lobe and cerebellar contusions.

Diagnosis and therapy of vestibular schwannoma

MRI studies are of paramount importance for diagnosis and follow-up measurements during conservative and postinterventional management of vestibular schwannomas (VS). MRI findings that convey important information for hearing-preservation VS surgery are: length of tumor-cochlear nerve contact, involvement of the internal auditory canal, incomplete filling of internal auditory canal, tumor size less than 15 mm and the intralabyrinthine signal intensity on 3DFT-CISS gradient-echo images. Functional neuro-otologic studies of facial nerve function, hearing and vestibular/balance function provide a valuable means of assessment of the actual impairment of the functional status of the VS patient. Intraoperative monitoring of facial nerve function and hearing has been refined, resulting in improved final postoperative facial nerve and hearing outcomes in VS patients treated with microsurgery. Long-term results reported by teams practicing stereotactic radiosurgery or fractionated stereotactic radiotherapy have been very encouraging. On the other hand, conservative management appears to be a viable option for a select group of VS patients. The refinement of surgical technique has rendered surgery safer and less invasive, resulting in better functional outcomes. Steroid use is currently used postinterventionally to improve final hearing outcome, although with questionable effectiveness. Physical rehabilitation programs are applied to accelerate vestibular functional recovery postoperatively and there is weak evidence that early physical rehabilitation may improve the final facial nerve outcome. Quality-of-life measures have emerged as important determinants of final therapeutic decision-making. More studies with high levels of evidence are needed to support clinical decisions.

Visualization of inner ear disorders with MRI in vivo: from animal models to human application

CONCLUSION

The inner ear membranous permeability and leakiness and endolymphatic hydrops can be visualized using gadolinium-enhanced MRI in both rodents and man. Intratympanic administration of contrast agent gives greater perilymphatic loading of gadolinium.

OBJECTIVES

Visualization of different types of inner ear dysfunction in MRI with intravenous or intratympanic administration of contrast agent.

MATERIALS AND METHODS

In the animal study, gadolinium was administered intravenously or intratympanically and imaged with 4.7 T MRI. In man, gadolinium was delivered intratympanically and studied with 1.5 T or 3 T MRI.

RESULTS

In the animals, intravenous delivery of gadolinium demonstrated uptake in the perilymph of normal inner ears. The cochlear modiolus appeared to be a critical site for the secretion of perilymph and the location of fluid communication between the perilymphatic scalae. Intense noise exposure and immune reaction caused cochlear injury and accelerated gadolinium passage through the blood-perilymph and blood-endolymph barriers. In man, perilymphatic uptake of gadolinium was only observed in the impaired inner ear when administered intravenously. However, the signal-to-noise ratio of images was improved when gadolinium was delivered intratympanically. MRI demonstrated endolymphatic hydrops in both animal models and patients with Meniere's disease.

Pathology of the vestibulocochlear nerve

Imaging of the vestibulocochlear nerve has evolved dramatically over the past few decades. The imaging specialist now is involved in the diagnosis of far more diagnostic entities than ever before. With this increased involvement comes the responsibility to increase collective knowledge regarding the pathophysiology of these diagnostic entities. This article is organized in a conventional way and covers congenital deformity of the internal auditory canal, neoplastic and pseudoneoplastic lesions, with special detailed emphasis on schwannoma of the eight cranial nerves (acoustic neuroma), nonneoplastic IAC/CPA pathology, including vascular loops, and numerous additional differential diagnostic entities, with particular emphasis on non-neoplastic meningeal disease. Lesions of the auditory pathway and an overview of cochlear implant surgery are also included in this discussion.

Anatomic study of maximum intensity projection of the membranous labyrinth and the internal auditory meatus - MRI scan in 16 Chinese adults

CONCLUSION

Three-dimensional reconstruction of maximum intensity projection (MIP) might document objectively, stereoscopically and directly the minute structures of the membranous labyrinth and internal auditory meatus. In this study, we establish magnetic resonance imaging (MRI) measurement criteria of the inner ear in Chinese adults.

OBJECTIVE

The goal of this study was to provide an anatomic basis for otolosurgery and neurosurgery in Chinese adults.

MATERIALS AND METHODS

Sixteen healthy volunteer subjects were scanned by a GE-signa 1.5T MRI scanner. All original images were transferred to an MRI workstation and all the structures of the inner ear were reconstructed, rotated at various angles and measured with an MIP program.

RESULTS

Anatomic structures of the membranous labyrinth and internal auditory meatus were well demonstrated in MIP images in all volunteers. All inner ear structures including utricle, saccule, cochlear duct, internal auditory meatus and three semicircular ducts produced high intensity signals.