Imaging findings of cochlear nerve deficiency

BACKGROUND AND PURPOSE: High-resolution T2-weighted fast spin-echo MR imaging provides excellent depiction of the cisternal and intracanalicular segments of the vestibulocochlear and facial nerves. Absence or reduction in caliber of the cochlear nerve (deficiency) has been described in association with congenital sensorineural hearing loss (SNHL). Depiction of cochlear nerve integrity may be important for diagnosis and management of SNHL. METHODS: We retrospectively reviewed high-resolution T2-weighted fast spin-echo MR images of 22 patients examined for SNHL who had deficiency of the cochlear nerve. Images were evaluated for the presence and comparative size of the component nerves (facial, cochlear, superior vestibular, and inferior vestibular nerves), relative size of the internal auditory canal (IAC), and any associated inner ear abnormalities. The clinical history, results of the clinical examination, and audiometric findings were reviewed for each patient. RESULTS: Deficiency of the cochlear nerve was observed in 12 patients with congenital SNHL and in 10 patients with acquired SNHL. Hypoplasia of the IAC was observed in association with congenital deficiency of the cochlear nerve in 11 of 12 patients. Deficiency of the cochlear nerve was observed in association with acoustic schwannoma in two cases and with acquired labyrinthine abnormalities in seven cases. Hypoplasia of the IAC was not observed in association with acquired SNHL. CONCLUSION: Deficiency of the cochlear nerve can be shown by high-resolution T2-weighted fast spin-echo MR imaging. Deficiency may be observed in association with congenital or acquired SNHL and may be important in the assessment of patients for cochlear implantation. Hypoplasia of the IAC is an indicator of congenital cochlear nerve deficiency.     

前庭神经炎的颈-眼诱发肌源电位临床研究

 目的 评估前庭神经炎(vestibular neuritis,VN)的临床分类及前庭上神经(superior vestibular nerve,SVN)和下神经(inferior vestibular nerve,IVN)的受累情况。方法 选择本院60例诊断为前庭神经炎的患者(前庭神经炎组)和30例健康人(健康对照组)行颈肌前庭诱发肌源电位(ervical vestibular evoked myogenic potential,cVEMP)、眼肌前庭诱发肌源电位(ocular vestibular evoked myogenic potential,oVEMP)、前庭双温试验检查。双温试验用于评估水平半规管,oVEMP用于评估椭圆囊及前庭上神经功能,cVEMP用于评估球囊及前庭下神经功能。结果 前庭神经炎组中,前庭上神经炎46例,前庭下神经炎12例,全前庭神经炎2例,VEMPs异常率较对照组明显增高,两组相比异常率差异有统计学意义(P＜0.05)。前庭上神经患者患侧oVEMP潜伏期与健康对照组比较,差异无统计学意义,振幅及不对称比差异有统计学意义,而健侧与健康对照组比较,差异无统计学意义,双温试验与健康对照组差异有统计学意义;前庭下神经炎患者oVEMP潜伏期及振幅与健康对照组差异均无统计学意义;前庭下神经炎患者oVEMP振幅及不对称比与对照组比较,差异无统计学意义。前庭双温试验CP值与前庭神经无明显相关。前庭双温试验前庭cVEMP异常的患者oVEMP及前庭双温试验结果正常时代表前庭下神经。结论 前庭神经炎主要表现前庭上神经炎,部分可累及前庭下神经,cVEMP和oVEMP及双温试验提供更详细的前庭神经损伤定位。     

Intracanalicular meningioma mimicking vestibular schwannoma

Summary: Three cases of intracanalicular meningioma mimicking vestibular schwannoma are presented. In each case, a contrast-enhancing mass filling the internal auditory canal was identified on MR images and was originally diagnosed as a vestibular schwannoma. Although it is difficult to differentiate definitively between these lesions preoperatively, imaging findings inconsistent with a diagnosis of vestibular schwannoma can be identified. Preoperative identification of intracanalicular meningiomas permits alterations in surgical planning that allow for the more complete resection of these rare tumors.     

Dumbbell schwannomas of the internal auditory canal

BACKGROUND AND PURPOSE: Benign tumors of the internal auditory canal (IAC) may leave the confines of the IAC fundus and extend into inner ear structures, forming a dumbbell-shaped lesion. It is important to differentiate dumbbell lesions, which include facial and vestibulocochlear schwannomas, from simple intracanalicular schwannomas, as surgical techniques and prognostic implications are affected. In this article, the imaging and clinical features of these dumbbell schwannomas are described. METHODS: A dumbbell lesion of the IAC is defined as a mass with two bulbous segments, one in the IAC fundus and the other in the membranous labyrinth of the inner ear or the geniculate ganglion of the facial nerve canal, spanned by an isthmus. Twenty-four patients with dumbbell lesions of the IAC had their clinical and imaging data retrospectively reviewed. Images were evaluated for contour of the mass and extension into the membranous labyrinth or geniculate ganglion. RESULTS: Ten of 24 lesions were facial nerve dumbbell lesions. Characteristic features included an enhancing "tail" along the labyrinthine segment of the facial nerve and enlargement of the facial nerve canal. Dumbbell schwannomas of the vestibulocochlear nerve (14/24) included transmodiolar (8/14), which extended into the cochlea, transmacular (2/14), which extended into the vestibule, and combined transmodiolar/transmacular (4/14) types. CONCLUSION: Simple intracanalicular schwannomas can be differentiated from transmodiolar, transmacular, and facial nerve schwannomas with postcontrast and high-resolution fast spin-echo T2-weighted MR imaging. Temporal bone CT is reserved for presurgical planning in the dumbbell facial nerve schwannoma group.     

MR detection of tumor in the internal auditory canal

The MR appearance of 15 tumors within or near the internal auditory canal was analyzed in detail and compared with the subsequent surgical observations. In most cases, nonenhanced MR showed the precise extent of the intracanalicular and extracanalicular tumor despite minor variations in appearance. In a case of facial nerve neurinoma, the extent to which the tumor invaded the canal was underestimated by MR. Gadolinium-DTPA enhancement is expected to eliminate uncertainties in MR imaging of the internal auditory canal.     

Spatial relationship between vestibular schwannoma and facial nerve on three-dimensional T2-weighted fast spin-echo MR images

BACKGROUND AND PURPOSE: During surgical removal of a vestibular schwannoma, correct identification of the facial nerve is necessary for its preservation and continuing function. We prospectively analyzed the spatial relationship between vestibular schwannomas and the facial nerve using 3D T2-weighted and postcontrast T1-weighted spin-echo (SE) MR imaging. METHODS: Twenty-two patients with a unilateral vestibular schwannoma were examined with MR imaging. The position and spatial relationship of the facial nerve to adjacent tumor within the internal auditory canal (IAC) and cerebellopontine angle cistern (CPA) were assessed on multiplanar reformatted 3D T2-weighted fast spin-echo (FSE) images and on postcontrast transverse and coronal T1-weighted SE images. The entrance of the nerve into the bony canal at the meatal foramen and the nerve root exit zone along the brain stem were used as landmarks to follow the nerve course proximally and distally on all images. RESULTS: The spatial relationship between vestibular schwannoma and facial nerve could not be detected on postcontrast T1-weighted SE images. In 86% of the patients, the position of the nerve in relation to the tumor was discernible on multiplanar reformatted 3D T2-weighted FSE images. In tumors with a maximal diameter up to 10 mm, the entire nerve course was visible; in tumors with a diameter of 11 to 24 mm, only segments of the facial nerve were visible; and in tumors larger than 25 mm, the facial nerve could not be seen, owing to focal nerve thinning and obliteration of landmarks within the IAC and CPA. CONCLUSION: Identification of the facial nerve and its position relative to an adjacent vestibular schwannoma is possible on multiplanar reformatted 3D T2-weighted FSE images but not on postcontrast T1-weighted SE images. Detection of this spatial relationship depends on the tumor's size and location.     

Major salivary gland masses: comparison of MR imaging and CT

Computed tomography (CT) and magnetic resonance (MR) imaging studies were done prospectively in 21 unselected patients in whom 28 major salivary glands had pathologic changes. Blinded and final readings were used to establish the relationship of the lesion to the plane of the facial nerve (parotid masses), whether the lesion was intrinsic to the gland, and whether the lesion was aggressive. In the blinded reading, CT was superior to MR imaging in eight instances; in the final reading, however, with clinical information available, CT was superior in four cases of inflammatory salivary gland "masses." CT and MR imaging provided the same diagnostic information in all cases of salivary gland neoplasms. T1- and T2-weighted images proved of equal value in detection of salivary gland lesions, and use of both provided no additional specificity. In most cases, T1-weighted images alone provided the information necessary for surgical management. MR imaging is a reasonable first choice if a neoplasm is likely; the potential for improved tissue contrast at the margins of a tumor may be particularly useful. If a mass may be of inflammatory origin, contrast material-enhanced CT is a more reasonable first choice.     

MR imaging of osteogenic and Ewing's sarcoma

Twenty patients with biopsy-proven osteogenic (11 cases) or Ewing's (nine cases) sarcoma were evaluated by MR imaging on a 0.15-T resistive unit to determine the value of MR in the diagnosis and treatment of these two neoplasms and to develop the best protocol for MR imaging. In all 20 cases, MR identified tumor spread into bone marrow, and it was superior to CT in five cases. Extension of tumor into the soft tissues adjacent to bone was shown better by MR than CT in six cases. Improved anatomic information from MR is the result of the ability to image in the axial, coronal, and sagittal planes. Compared with CT, MR identifies cortical disease but has inferior spatial resolution and defines calcium poorly. MR can be used to monitor tumor response to chemotherapy, and the relationship of tumor to adjacent vasculature can be determined without the use of contrast agents. Two pulse sequences are necessary for maximum display of disease, since, in general, tumor involvement of the bone marrow is best assessed on T1-weighted sequences, and tumor involvement of the soft tissue is best seen on T2-weighted sequences. Additional information about bone-marrow involvement, soft-tissue tumor extent, and the relationship of tumor to blood vessels makes MR a valuable adjunct to CT in the evaluation of these neoplasms.     

Bone tumors: magnetic resonance imaging versus computed tomography

The magnetic resonance (MR) imaging characteristics of bone tumors are described and the clinical utility of MR imaging in patient evaluation is reported. Fifty-two patients with skeletal lesions were examined with a Picker MR imager (0.15-T resistive magnet). Twenty-five patients had primary malignancies, seven had benign bone neoplasms, 15 had skeletal metastases, and five had neoplasm simulators. Forty-five patients had CT scans available for comparison. For demonstrating the extent of tumor in marrow, MR was superior to CT in 33% of cases, about equal to CT in 64%, and inferior to CT in 2%. For delineating the extent of tumor in soft tissue, MR was superior to CT in 38% of cases and about equal to CT in 62%. CT was superior in all cases for demonstrating calcific deposits and pathologic fractures. In four patients with metal prostheses or surgical clips, MR was superior to CT in documenting recurrent tumor because of artifactual degradation of the CT image. Direct sagittal and coronal images from MR permit accurate assessment of the relationship of tumor to adjacent normal structures, including the physis, joints, and neurovascular structures. MR is useful in the evaluation of bone tumors: it is of greatest value in evaluations of the peripheral skeleton, the medullary canal, soft tissues, and postoperative tumor recurrence. With a 0.15-T magnet, MR is less useful in the evaluation of the axial skeleton and cortical bone.     

飞行员前庭下神经炎一例（摘要）

飞行员的空间定向障碍是引起许多致命性飞行事故的首要原因。空间定向是本体、前庭和视觉输入整合的结果。前庭神经炎（VN）可能导致飞行员突然的空中失能。VN一般通过单侧冷热反应丧失所显示的前庭功能丧失表现得到诊断。但是冷热试验只测试前庭上神经的功能,单纯前庭下神经受损的患者可能会漏诊。我们报告了一个海军飞行员病例,其症状显示是前庭神经炎,但冷热试验正常,而单侧前庭诱发肌源性电位（VEMP）缺失,我们认为该飞行员患有单纯的前庭下神经炎。     

CT and MR imaging of craniopharyngioma

We reviewed imaging findings of CT and MR imaging in 20 cases of surgically confirmed craniopharyngioma in an attempt to determine their relation to patterns of tumor extent. The relationship between these patterns and the frequency of preoperative CT diagnosis and MR imaging diagnosis according to the surgical diagnosis were determined. The CT technique was superior to MR imaging in the detection of calcification. The MR imaging technique was superior to CT for determining tumor extent and provided valuable information about the relationships of the tumor to surrounding structures. Thus, CT and MR imaging have complementary roles in the diagnosis of craniopharyngiomas. In cases of possible craniopharyngioma, noncontrast sagittal T1-weighted images may enable the identification of the normal pituitary, possibly leading to the correct diagnosis. Received 6 November 1995; Revision received 9 August 1996; Accepted 14 October 1996     

Tumors and tumor-like lesions of peripheral nerves

The diagnosis of a peripheral nerve tumor can often be suggested on imaging. Direct continuity with a neural structure or location along a typical nerve distribution, shape, and intrinsic magnetic resonance (MR) signal characteristics represent the most important signs in this regard. Although several nonneoplastic nerve lesions can be specifically diagnosed by MR imaging, benign and malignant neoplasms of peripheral nerves can usually not be distinguished with confidence. This article reviews the MR imaging appearance, clinical and pathological features of schwannoma, localized neurofibroma, plexiform neurofibroma, intraneural perineurioma, fibrolipomatous hamartoma, nerve sheath ganglion, traumatic neuroma, malignant peripheral nerve sheath tumor, and secondary malignant neoplasms of peripheral nerves. Typical findings are illustrated on the basis of histologically confirmed cases.     

Displacement of the facial nerve course by vestibular schwannoma: preoperative visualization using diffusion tensor tractography

PURPOSE: To preoperatively visualize the course of the facial nerve, which is displaced by vestibular schwannoma, using diffusion tensor (DT) tractography, and to evaluate the agreement with surgical findings. MATERIALS AND METHODS: The subjects were eight patients with vestibular schwannoma who had undergone removal surgery. DT MR images were obtained and tracts that were considered to represent the facial nerve were constructed. We assessed the success rate for tract construction and evaluated the agreement between tractography findings and surgery. RESULTS: We obtained a tract that connected the internal auditory meatus and brainstem, and was considered to represent the facial nerve in seven of eight cases. The course of the constructed tract agreed with surgical findings in five of these seven cases. One exception was a case in which the tumor was too large to enable intraoperative observation of the facial nerve; however, the facial nerve appeared to be displaced anteriorly at intracapsular resection, in agreement with tractography. In the other case, the schwannoma was mostly cystic. CONCLUSION: Tractographs constructed using MR tensor images enabled us to identify tracts considered to represent facial nerves. We consider DT tractography to be a useful tool for preoperatively predicting facial nerve displacement in vestibular schwannoma.     

Magnetic resonance imaging in the diagnosis and staging of renal and perirenal neoplasms

Thirty-one adult patients underwent magnetic resonance (MR) imaging after CT scans had demonstrated findings consistent with renal cell carcinoma. MR images were interpreted prospectively and independently of the CT findings. Because the CT scanning was performed at multiple institutions by many examiners, this study was not a direct comparison of CT versus MR. The preoperative diagnoses and staging of the neoplasms, as judged by MR, were compared with those obtained at laparotomy (n = 28), autopsy (n = 1), or biopsy (n = 2). Correct preoperative diagnoses were rendered in 31 patients (100%) on the basis of MR findings. The anatomic staging of 27 renal cell carcinomas was correctly performed by MR in 26 patients (86%). When compared with results of previous studies of the value of CT in the diagnosis and staging of renal neoplasms, MR appears to have several advantages in determination of the origin of the mass; the evaluation of vascular patency; the detection of perihilar lymph node metastases; and the evaluation of direct tumor invasion of adjacent organs. MR is sensitive in determining the extent of tumor thrombus and in evaluating invasion of the inferior vena caval wall. MR should assume an important role in the diagnosis and staging of renal neoplasms.     

The cerebellopontine angle and internal auditory canal: neurovascular anatomy on gas CT cisternograms

We reviewed 103 normal gas CT cisternograms to delineate the appearance of normal neurovascular structures in the cerebellopontine angle (CPA) and internal auditory canal (IAC). Cranial nerves VII and VIII were identified in the CPA in 97% of cases, either separately (53%) or as a bundle (44%). Intracanalicular branches of the VIIIth cranial nerve were identified in 20% of cases, and cranial nerve V was visualized in the CPA in 14%. The characteristic vascular loop, usually the anterior inferior cerebellar artery, was visible in 35% of cases, and, in 22% of visualized cases, was in an intracanalicular location. The internal auditory artery was questionably visualized in one case. In 10% of cases, greater than 66% of the IAC was occupied by the neurovascular bundle. Familiarity with the normal anatomy and variants seen on gas CT cisternograms is necessary to prevent false-positive interpretations.     

Diagnostic imaging of Budd-Chiari syndrome in adults and children

Budd-Chiari syndrome is caused by the obstruction of the hepatic veins or of the inferior vena cava. It is characterized by the classic symptomatological triad: ascites, hepatomegaly, and abdominal pain. In 2/3 cases its etiology remains unknown. Budd-Chiari syndrome may be associated with polycythemia vera, neoplasms, chronic leukemia, congenital abnormalities, hypercoagulation conditions, pregnancy, oral contraceptives, and constrictive pericarditis. Even though its clinical diagnosis is difficult, radiology plays a decisive role with US, CT, MR imaging and, above all, angiography; the latter, together with liver biopsy, generally provides with an unquestionable diagnosis. Through the definition of stage of the disease, of level (intrahepatic, venous, caval, cardiac), of type (intrinsic or extrinsic), and degree of both obstruction and consequent development of collateral channels, radiology determines which patients should undergo a medical or a surgical treatment. In some case, percutaneous angioplasty can be performed. Four cases of Budd-Chiari syndrome, including two children, were investigated with US, CT, angiography, and liver biopsy; MR imaging was also employed in one case. The underlying cause was identified in 3 patients: constrictive pericarditis of probable congenital origin and web occlusion of the inferior vena cava near the right atrium in the 2 children; hepatic vein thrombosis due to essential thrombocythemia in the third case. In the fourth patient, thrombosis of the inferior vena cava and hepatic veins was unexplained. The diagnosis was established by means of liver biopsy and phlebography of the hepatic veins. Good diagnostic information was also supplied by non-invasive techniques, such as US, CT, and MR imaging.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bell palsy: quantitative analysis of MR imaging data as a method of predicting outcome

PURPOSE: To assess the prognostic value of quantitative analyses of region-of-interest (ROI) magnetic resonance (MR) imaging data in patients with acute facial nerve palsy. MATERIALS AND METHODS: In a single-blinded study, MR images were obtained in 39 patients (32 men and seven women; age range, 18-75 years; average age, 37.9 years) with acute facial nerve palsy. MR images were obtained before the 6th day of illness, on the first day of standard inpatient treatment with high-dose steroids. Signal intensity (SI) was measured at ROIs in each of five segments (internal auditory canal [IAC]; geniculate ganglion; and labyrinth, tympanic, and mastoid segments) of the intratemporal portion of the facial nerve and quantitatively analyzed. The SI measurements in the five segments were summed and divided by 100 to provide a basis for establishing an MR imaging index. SI increases and MR imaging indexes were compared with available clinical findings and electrophysiologic data. RESULTS: Data for all 39 patients could be analyzed. The MR imaging index was significantly higher in patients with poor outcomes than in patients with favorable outcomes (specificity, 97%; sensitivity, 75%; P <.01). The SI increases in the IAC were significantly different between patients who progressed to full recovery (mean increase, 45.7%) and patients who developed chronic facial paralysis (mean increase, 156.5%) (sensitivity, 100%; specificity, 97%; P <.001). The results of differentiating between patients with good and those with poor outcomes on the basis of SI measurements in the IAC were found to be in complete agreement with electrophysiologic data. CONCLUSION: Quantitative analysis of ROI MR imaging data is a valid method of predicting the outcome of acute facial nerve palsy during the first days after onset of symptoms and thus at a time when it is not yet possible to obtain valuable prognostic information by using electrophysiologic methods.     

Lateral ventricular neoplasms of the brain: differential diagnosis based on clinical, CT, and MR findings

The differential diagnosis of lateral ventricular tumors was explored by retrospective analysis of 47 pathologically proved cases identified by CT and/or MR imaging. Third ventricular tumors adjacent to the foramen of Monro (e.g., colloid cysts) were excluded. Forty-six patients underwent CT, and eight had MR imaging. The most common neoplasms were choroid plexus papilloma (10 cases) and meningioma (nine cases). Other common neoplasms included subependymoma (six cases), subependymal giant cell astrocytoma (five cases), and metastasis/lymphoma (four cases). Important features for differential diagnosis included age of the patient, the tumor's location within the lateral ventricle, and density on CT before IV administration of contrast material. Fifty percent of the tumors were in the ventricular atrium. All intraventricular tumor types (except subependymoma) showed contrast enhancement. MR was most useful in evaluating tumor location, size, and extent, but it did not help in eliminating alternative diagnoses. On the basis of patients' ages, specific tumor location, and the appearance on CT scans or MR images, an algorithm for differential diagnosis of lateral ventricular tumors was developed.     

Cystic neoplasms of the pancreas: comparison of MR imaging with CT

Cystic neoplasms of the pancreas are divided into two major groups: microcystic adenomas and mucinous cystic neoplasms. Five microcystic adenomas and seven mucinous cystic neoplasms (three cystadenomas and four cystadenocarcinomas) were examined with both magnetic resonance (MR) imaging and computed tomography (CT). The cystic content was differentiated more easily with MR imaging than with CT. It was homogeneous in four of the five microcystic adenomas, all of which had lobulated borders best seen on T2-weighted images. The mucinous cystadenomas and cystadenocarcinomas were all composed of multiple compartments that varied in signal intensity. The septa, shape, and wall thickness were demonstrated on T1- and/or T2-weighted MR images almost as well as on CT scans. Overall, MR imaging was equal or slightly superior to CT in the diagnosis of pancreatic cystic neoplasms, except in its limited ability to demonstrate calcifications of the tumor wall and septa.     

Lateral ventricular neoplasms of the brain: differential diagnosis based on clinical, CT, and MR findings

The differential diagnosis of lateral ventricular tumors was explored by retrospective analysis of 47 pathologically proved cases identified by CT and/or MR imaging. Third ventricular tumors adjacent to the foramen of Monro (e.g., colloid cysts) were excluded. Forty-six patients underwent CT, and eight had MR imaging. The most common neoplasms were choroid plexus papilloma (10 cases) and meningioma (nine cases). Other common neoplasms included subependymoma (six cases), subependymal giant cell astrocytoma (five cases), and metastasis/lymphoma (four cases). Important features for differential diagnosis included age of the patient, the tumor's location within the lateral ventricle, and density on CT before IV administration of contrast material. Fifty percent of the tumors were in the ventricular atrium. All intraventricular tumor types (except subependymoma) showed contrast enhancement. MR was most useful in evaluating tumor location, size, and extent, but it did not help in eliminating alternative diagnoses. On the basis of patients' ages, specific tumor location, and the appearance on CT scans or MR images, an algorithm for differential diagnosis of lateral ventricular tumors was developed.