The value of T2(*)-weighted MR images for the diagnosis of acoustic neuromas

Surgical management for large vestibular schwannomas: a systematic review, meta-analysis, and consensus statement on behalf of the EANS skull base section

BACKGROUND AND OBJECTIVE

The optimal management of large vestibular schwannomas continues to be debated. We constituted a task force comprising the members of the EANS skull base committee along with international experts to derive recommendations for the management of this problem from a European perspective.

MATERIAL AND METHODS

A systematic review of MEDLINE database, in compliance with the PRISMA guidelines, was performed. A subgroup analysis screening all surgical series published within the last 20 years (January 2000 to March 2020) was performed. Weighted summary rates for tumor resection, oncological control, and facial nerve preservation were determined using meta-analysis models. This data along with contemporary practice patterns were discussed within the task force to generate consensual recommendations regarding preoperative evaluations, optimal surgical strategy, and follow-up management.

RESULTS

Tumor classification grades should be systematically used in the perioperative management of patients, with large vestibular schwannomas (VS) defined as > 30 mm in the largest extrameatal diameter. Grading scales for pre- and postoperative hearing (AAO-HNS or GR) and facial nerve function (HB) are to be used for reporting functional outcome. There is a lack of consensus to support the superiority of any surgical strategy with respect to extent of resection and use of adjuvant radiosurgery. Intraoperative neuromonitoring needs to be routinely used to preserve neural function. Recommendations for postoperative clinico-radiological evaluations have been elucidated based on the surgical strategy employed.

CONCLUSION

The main goal of management of large vestibular schwannomas should focus on maintaining/improving quality of life (QoL), making every attempt at facial/cochlear nerve functional preservation while ensuring optimal oncological control, thereby allowing to meet patient expectations. Despite the fact that this analysis yielded only a few Class B evidences and mostly expert opinions, it will guide practitioners to manage these patients and form the basis for future clinical trials.

Oculomotor schwannoma causing a progressive complete third-nerve palsy

A 69-year-old woman presented with an 8-month history of diplopia and examination findings consistent with a right third-nerve palsy. Head MRI identified the presence of a 5.8 mm, nodular, isointense lesion in the suprasellar cistern, which demonstrated enhancement with gadolinium contrast. The lesion did not show any evidence of growth over a 3-month follow-up period. These MRI findings, alongside the clinical features, suggest oculomotor nerve schwannoma. Oculomotor schwannomas are a rare cause of third-nerve palsy. The presenting features and management options for oculomotor schwannomas are discussed to provide a framework for the diagnosis and management of these patients.

Non-contrast magnetic resonance imaging for monitoring patients with acoustic neuroma

Objective

To assess the feasibility of non-contrast T2-weighted magnetic resonance imaging as compared to T1-weighted post-contrast magnetic resonance imaging for detecting acoustic neuroma growth.

Methods

Adult patients with acoustic neuroma who underwent at least three magnetic resonance imaging scans of the internal auditory canals with and without contrast in the past nine years were identified. T1- and T2-weighted images were reviewed by three neuroradiologists, and tumour size was measured. Accuracy of the measurements on T2-weighted images was defined as a difference of less than or equal to 2 mm from the measurement on T1-weighted images.

Results

A total of 107 magnetic resonance imaging scans of 26 patients were reviewed. Measurements on T2-weighted magnetic resonance imaging scans were 88 per cent accurate. Measurements on T2-weighted images differed from measurements on T1-weighted images by an average of 1.27 mm, or 10.4 per cent of the total size. The specificity of T2-weighted images was 88.2 per cent and the sensitivity was 77.8 per cent.

Conclusion

The T2-weighted sequences are fairly accurate in measuring acoustic neuroma size and identifying growth if one keeps in mind the caveats associated with the tumour characteristics or location.

High resolution T2 MRI in the diagnosis of cerebellopontine angle and internal auditory canal lesions

High resolution T2 magnetic resonance imaging (MRI) can provide exquisite detail of internal auditory canal (IAC) and cerebellopontine angle (CPA) lesions. In this retrospective case series, blinded imaging sequences were delivered to three radiologists and compared with previously archived clinical reads that were non-blinded and incorporated both T1+C and T2 sequences together. This article demonstrates high sensitivity and specificity for high resolution T2 MRI particularly with lesions >5mm. This suggests a role for high resolution T2 MRI as an initial screening sequence or as a surveillance sequence.

Magnetic resonance spectroscopy features of Heschl's gyri in patients with unilateral acoustic neuroma: preliminary study

RATIONALE AND OBJECTIVES

To evaluate neurochemical alterations in Heschl's gyri and determine the most affected side in case of unilateral acoustic neuroma using magnetic resonance spectroscopy (MRS).

MATERIALS AND METHODS

Fifteen patients with unilateral acoustic neuroma were studied. Following routine cranial MRI sequences, MRS of Heschl's gyri on tumor and nontumor sides was obtained. MRS metabolite values of both Heschl's gyri were statistically compared.

RESULTS

The values of N-acetylaspartate (NAA) and Cr on nontumor side Heschl's gyrus (HG) were significantly lower than that on tumor side.

CONCLUSIONS

We found nontumor side HG more affected with lower NAA and Cr values, suggesting neuronal damage and decreased energy metabolism compared to the tumoral side.

Role of magnetic resonance imaging in evaluation of cerebellopontine angle schwannomas

The aim of the present study was to evaluate the role of Magnetic Resonance Imaging (MRI) to localize and characterize the MR imaging features of cerebellopontine angle schwannomas and to compare with surgical/histopathological findings. It was a prospective study which included 19 patients, who presented with signs and symptoms s/o any lesion in the CP angle and were referred to the radiology department for MRI. All patients included in the study were subjected to detailed clinical history and physical examination following which MRI was carried out on Philips Gyroscan Achieva 1.5 Tesla unit and the standard protocol consisted of T1WI, T2WI, DWI and FLAIR images in axial, sagittal and coronal planes. Hearing abnormality was the most common presenting complaint in patients with CP angle schwannoma's followed by headache and tinnitus. Vestibulocochlear nerve was the most commonly involved nerve in patients with these lesions followed by involvement of trigeminal nerve. MRI was erroneous in giving provisional diagnosis of schwannoma in one case, which on subsequent surgery and histopathology was found to be a meningioma. The sensitivity of MRI for correctly diagnosing vestibular schwannoma was 100 % and specificity was 92.86 % with a positive predictive value of 94.12 % and accuracy of 96.67 %. MRI is considered as an excellent noninvasive investigation for CP angle schwannoma's. It can identify the site and extension of the lesions as well as the characteristic signal. Apart from diagnosing, MR imaging plays an important role in stratifying patients into appropriate treatment options.

Do we really still need an open surgery for treatment of patients with vestibular schwannomas?

BACKGROUND

Gamma Knife surgery (GKS) should be considered a standard treatment option for small and medium-sized vestibular schwannomas (VSs). It results in a tumor control rate similar to that seen with microsurgery and provides better preservation of facial nerve function and hearing.

METHODS

From December 2002 to April 2011, a total of 260 patients with VS underwent GKS using Leksell Gamma Knife model 4C with an automatic positioning system. There were 30 Koos stage I tumors, 112 stage II, 100 stage III, and 18 stage IV. All patients were treated with the use of high-resolution magnetic resonance imaging; creation of the highly precise conformal and selective multi-isocenter dose planning with small collimators, carefully sparing adjacent cranial nerves of any excessive irradiation; and creation of a wide 80 % isodose area within the tumor while applying a low marginal dose (mean 11.9 Gy) at the 50 % isodose line.

RESULTS

Among 182 patients who were followed for more than 3 years after treatment, the tumor control and shrinkage rates were 98.4 % and 76.4 %, respectively. Volume reduction of >50 % was marked in 54.9 % of VSs. Preservation of facial nerve function and hearing at the pretreatment level was noted in 97.8 % and 87.9 %, respectively. There was marked improvement of facial nerve function and hearing after GKS in 2.2 % and 3.8 %, respectively. There was no major morbidity.

CONCLUSION

Due to contemporary technological and methodological achievements GKS can be focused not only on growth control but on shrinking the VS, with possible reversal of the neurological deficit.

Current treatment strategy for vestibular schwannoma: image-guided robotic microradiosurgery

Object

Gamma Knife surgery (GKS) is becoming a standard treatment for vestibular schwannoma (VS); it is ranked with microsurgery from the perspective of tumor control and audiofacial nerve function preservation. A new treatment technique that will improve the tumor shrinkage ratio, shorten the patient's recovery time, and even recover some cranial nerve function is described.

Methods

Along with advances in the GKS system, the authors have developed magnetic resonance imaging sequences specific to particular treatments. These newly developed sequences provide much clearer visualization of the distribution of the cranial nerves, especially in the area from the cisterns to the internal acoustic meatus. Magnetic resonance images have been fused with computed tomography scans to facilitate better delineation of the anatomical relationships. These dose-planning images allow for a higher isodose line (80%) inside the tumor. The aim is to shrink the tumor and not just to control it. To date 130 patients have been treated with GKS in conjunction with this new technique. Of the 130, 91 patients were observed for more than 12 months. The tumor shrinkage rate was 65.9% (76% for patients with > 24 months of follow up), the facial nerve preservation rate was 98.9%, the hearing preservation rate was 92.3%, and four (4%) of 91 patients recovered hearing function. Transient tumor enlargement was observed in most cases, but no severe complications were found.

Conclusions

Although these results are preliminary, they would appear to represent a potential breakthrough in the treatment of VS. Longer follow-up periods and additional cases will firmly establish this method as an absolute treatment option for patients with a VS.

Screening for cerebellopontine angle tumors: is a CISS sufficient?

This study attempted to evaluate the reliability of ultra-thin T2-weighted imaging with a constructive interference in steady state (CISS) sequence as a screening method for tumors in the cerebellopontine angle. A retrospective study of 200 CISS examinations was made by five investigators. The examinations were inspected on plain film supported by clinical information. The interobserver agreement in the detection of lesions was analyzed. Fourteen cases (50% of the contrast-enhancing lesions) were rated pathological by all five readers. One case of subarachnoid lymphoma infiltration was overlooked by all five readers. Overall, six pathological lesions (median = 6, range 1-9) were not identified. The interobserver agreement for all pathological lesions was moderate (kappa=0.53; 95% CI, 0.43-0.62). The mean sensitivity was 77.8% (range 72.0-96.3%), and the mean specificity was 97.6% (range 94.8-100%). The median sensitivity for pathological lesions concerning only patients with acute sensorineural hearing loss (n=148, patients with 20 contrast-enhancing cases) was 86.6% (range 80-100%), and median specificity was 95.2% (range 84.4-96.9%) with a moderate interobserver agreement (kappa=0.55; 95% CI, 0.44-0.66). In our opinion the CISS sequence is a valuable addition to the examination of the cerebellopontine angle but lacks sufficient reliability for the detection of tumors of small size or of tumors adjacent to brain parenchyma or the temporal bone.

MR imaging of cranial nerve lesions using six different high-resolution T1- and T2(*)-weighted 3D and 2D sequences

PURPOSE

To find a suitable high-resolution MR protocol for the visualization of lesions of all 12 cranial nerves.

MATERIAL AND METHODS

Thirty-eight pathologically changed cranial nerves (17 patients) were studied with MR imaging at 1.5 T using 3D T2*-weighted CISS, T1-weighted 3D MP-RAGE (without and with i.v. contrast medium), T2-weighted 3D TSE, T2-weighted 2D TSE and T1-weighted fat saturation 2D TSE sequences. Visibility of the 38 lesions of the 12 cranial nerves in each sequence was evaluated by consensus of two radiologists using an evaluation scale from 1 (excellently visible) to 4 (not visible).

RESULTS

The 3D CISS sequence provided the best resolution of the cranial nerves and their lesions when surrounded by CSF. In nerves which were not surrounded by CSF, the 2D T1-weighted contrast-enhanced fat suppression technique was the best sequence.

CONCLUSIONS

A combination of 3D CISS, the 2D T1-weighted fat suppressed sequence and a 3D contrast-enhanced MP-RAGE proved to be the most useful sequence to visualize all lesions of the cranial nerves. For the determination of enhancement, an additional 3D MP-RAGE sequence without contrast medium is required. This sequence is also very sensitive for the detection of hemorrhage.