MR imaging of epidermoids at the cerebellopontine angle.

The most common location of intracranial epidermoid is the cerebellopontine angle (CPA). The present study compared the visibility of epidermoid at the CPA in various pulse sequences. Seven patients with epidermoid at the CPA underwent conventional MR imaging (T(1)-, T(2)- and proton density-weighted imaging) as well as diffusion-weighted echo-planar imaging. Fast fluid-attenuated inversion recovery (FLAIR) sequences, magnetization transfer contrast (MTC) sequences, and MR cisternography were employed for selected patients. The signal intensity of the lesions relative to cerebrospinal fluid (CSF), the degree of lesion demarcation and the displacement of surrounding structures were evaluated. Proton density-weighted imaging depicted the lesions as hyper-intense to CSF with clearer delineation than T(1)- and T(2)-weighted imaging. Diffusion-weighted imaging depicted all lesions as strongly hyper-intense relative to CSF and brain tissue. FLAIR sequences depicted the lesions with mixed signal intensities but with poor-to-medium demarcation. MTC imaging increased delineation of the lesions to some degree. MR cisternography depicted the lesions as hypo-intense to CSF and clearly showed the anatomical relation to neighboring nerves and vessels. We concluded that diffusion-weighted imaging could specifically reveal an epidermoid at the CPA as a strongly hyper-intense lesion, and that MR cisternography is mandatory for preoperative planning.     

Air-CT cisternography and canalography for small acoustic neuromas

Disenchantment with the limitations, and in some cases the morbidity, of currently used radiologic techniques for the demonstration or exclusion of small acoustic neuromas prompted development of an examination using small amounts of intrathecal air and computed tomography (CT). A prospective study was designed to evaluate air CT cisternography/canalography, wherein patients with the clinical symptoms of acoustic neuroma but with negative enhanced CT, were evaluated by metrizamide CT cisternography followed by air CT cisternography/canalography. Pantopaque cisternography was then performed as a control procedure. Four patients had surgically proven tumors. In 13 others, accumulated evidence indicated no tumors were present. Results suggest that air-CT cisternography is superior to all other diagnostic methods in defining small acoustic neuromas, and may exclude an intracanalicular lesion without the potential hazards of Pantopaque cisternography or high concentration metrizamide tomocisternography. With air-CT cisternography, there were no errors in this series.     

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.     

Magnetic resonance findings in 92 acoustic neuromas.

A retrospective analysis of the MR findings in 92 cases of acoustic neuromas is presented. The method of examination included in all cases intravenous injection of Gadolinium (Gd-DTPA or DOTA) with realization of sections in the axial and coronal planes. In 21 cases native MR studies were performed in the axial plane, before Gadolinium injection, with T1WI (n = 21), and T2WI (n = 6) images. Tumors were strictly intracanalar in 19 cases (20.7%), only localized in the cerebellopontine angle (CPA) in 5 cases (5.4%), and in 68 cases (73.9%) the tumors had intra- and extracanalar components. In this last group of lesions, 63.2% completely filled the internal auditory canal (IAC), and 36.8% occupied the internal portion of the IAC. In most cases (85.3%) the mean diameter of the CPA component was less than or equal to 2.5 cm. Lesions were more frequently homogeneous (58.8%) after Gd i.v.-enhancement. Heterogeneity was noted mainly in large lesions (greater than 2.5 cm: 100%). In all cases but one, the tumors were round, or oval-shaped, well-delineated, and did not present significant contact with the petrous bone. In 80.9% of CPA lesions, the center of the tumor was posteriorly excentered in relation to the internal auditory canal, whereas it was centered in 16.2% of cases. Widening of the IAC was observed in 51.1% of cases. In 45.2% of tumors of the CPA, smoothing of the posterior edge of the porus was visible.     

Magnetic resonance imaging in the evaluation of the brainstem

Magnetic resonance (MR) images of the brainstem region from 100 normal or asymptomatic individuals were reviewed in addition to those of 17 patients with intra-axial brainstem lesions and 15 patients with extra-axial masses around the brainstem. MR was able to demonstrate consistently the normal anatomy of the brainstem and adjacent cisterns, though the distinction between gray and white matter was seldom possible with the present technology. Masses in and around the brainstem were all accurately identified on MR and its sensitivity was superior to that of x-ray computed tomography (CT). These study results show that despite its technical limitations, MR is presently the examination of choice for the evaluation of brainstem abnormalities and eventually it will undoubtedly replace metrizamide CT cisternography.     

MR cisternography: a new method for the diagnosis of CSF fistulae

The aim of this study was to compare a new MRI method for detecting the existence of cerebrospinal fluid (CSF) fistulae, i. e. MR cisternography, with CT cisternography. In a prospective study, 30 patients with post-traumatic CSF fistulae were examined. The MR examinations were performed with a 1.0-T whole-body MR system, using two T2^*-weighted sequences, a 3D PSIF (time-inversed fast imaging with steady-state precession, FISP) and a 3D constructive interference steady-state (CISS) sequence. The results of MRI and CT cisternography were compared with the surgical findings. The sensitivity in detecting CSF fistulae with MR cisternography (PSIF: 89.9 %; CISS: 93.6 %) was higher than with CT cisternography (72.3 %). The sensitivity of CT cisternography at detecting CSF fistulae in patients with a size of dural lesion less than 2 mm or in patients with multiple dural lesions is significantly lower compared with the MR method. Although the localization of CSF fistulae always proved possible with MR cisternography, this could only be accomplished wih CT in 70 % of cases. The MR cisternography technique is a new examination method with a higher sensitivity for the detection of CSF fistulae than CT cisternography. The CISS technique is superior compared with PSIF and should be used in patients with high-flow CSF fistulas. Received 15 July 1996; Revision received 15 January 1997; Accepted 25 February 1997     

Intratemporal vascular tumors: detection with CT and MR imaging

The diagnostic contributions of computed tomography (CT) and magnetic resonance (MR) imaging were compared in 12 patients with benign intratemporal vascular tumors (hemangioma or vascular malformation). The tumors included six in the internal acoustic canal and six in the geniculate ganglion region. Clinical and histologic correlations were made. Two of the six patients with tumors in the internal acoustic canal underwent CT, and both required gas cisternography to show the tumor. Five patients in that group underwent MR imaging, and all five studies showed the tumor. All six patients with geniculate ganglion tumors underwent CT. Results in one study were questionable, and five showed the tumor. Five patients in this group underwent MR imaging, but the MR findings were positive in only two cases. MR imaging should therefore be performed before CT in the evaluation of facial nerve dysfunction, as it demonstrated all tumors in the internal acoustic canal and some in the geniculate ganglion region. If MR findings are negative, CT should then be performed to rule out a possible geniculate ganglion lesion.     

MR cisternography of the cerebello-pontine angle and internal auditory canal in diagnosis of intracanalicular acoustic neuroma

Summary One hundred and fifteen patients, suffering from sensorineural hearing loss were tested with a 1.5 T superconducting magnet. The authors describe utility of both T1-weighted multiple slice and T2-weighted multiple echo images for the evaluation of cerebello-pontine angle, internal auditory canal and their neurovascular content. In seventy-three cases MR cisternography was normal. The remaining forty-two cases were subdivided into twenty extracanalicular masses, eleven small intra-extracanalicular and nine purely intracanalicular lesions. All the lesions were histologically proven acoustic neuromas, except one intracanalicular mass which was a meningioma. Examination was inconclusive only in two cases and decision was then made to follow the clinical course. Advantages of MR cisternography over CT and air CT cisternography, such as absence of ionizing radiation and contrast material, easy multiplanar evaluation of the region of interest and the possibility to delineate both the cisternal and canalar extremities of the tumor mass are pointed out.     

面神经瘤的CT和MRI诊断(附六例报告)

目的 探讨CT,MRI对面神经瘤的诊断价值,方法 回顾分析了6例经手术病理证实的面神经瘤CT,MRI表现,结果 6例面神经瘤中位于颞内段4例（迷路段1例,鼓室段2例,鼓室段＋乳突段1例）,颅,内脑池段,内听段及颞内段（迷路段＋鼓室段）1例,颞内段（鼓室段＋乳突段＿并颅外肋腺段1例,肿瘤的影像学表现与肿瘤的部位有关,CT影像上,颞内段面神经瘤显示受累段面神经管扩大,破坏;中耳腔和（或）乳突软组织肿块及膝状神经窝区内质破坏,如肿瘤扩展到中颅窝或肋腺也可一并显示,1例起源于内听道,桥脑小脑角区的面神经瘤,CT,MRI清楚地显示了桥脑小脑角区肿块,内听道扩大,迷路段面神经管扩大,以及扩展到膝状神经窝区的病灶。结论 CT和MRI能准确地描绘面神经瘤的受累情况,CT在显示骨破坏细节方面极佳,而增强MRI对肿瘤本身的显示优于CT。     

Unusual lesions of the cerebellopontine angle: a segmental approach.

Tumors of the cerebellopontine angle (CPA) are frequent; acoustic neuromas and meningiomas represent the great majority of such tumors. However, a large variety of unusual lesions can also be encountered in the CPA. The site of origin is the main factor in making a preoperative diagnosis for an unusual lesion of the CPA. In addition, it is essential to analyze attenuation at computed tomography (CT), signal intensity at magnetic resonance (MR) imaging, enhancement, shape and margins, extent, mass effect, and adjacent bone reaction. CPA masses can primarily arise from the cerebellopontine cistern and other CPA structures (arachnoid cyst, nonacoustic schwannoma, aneurysm, melanoma, miscellaneous meningeal lesions) or from embryologic remnants (epidermoid cyst, dermoid cyst, lipoma). Tumors can also invade the CPA by extension from the petrous bone or skull base (cholesterol granuloma, paraganglioma, chondromatous tumors, chordoma, endolymphatic sac tumor, pituitary adenoma, apex petrositis). Finally, CPA lesions can be secondary to an exophytic brainstem or ventricular tumor (glioma, choroid plexus papilloma, lymphoma, hemangioblastoma, ependymoma, medulloblastoma, dysembryoplastic neuroepithelial tumor). A close association between CT and MR imaging findings is very helpful in establishing the preoperative diagnosis for unusual lesions of the CPA.     

Evaluation of high-resolution CT and MR cisternography in the diagnosis of cerebrospinal fluid fistula.

PURPOSEWe undertook this study to determine the accuracy of MR cisternography and plain high-resolution CT as a noninvasive alternative to CT cisternography in the diagnosis of CSF fistula in patients with clinically suspected CSF rhinorrhea.METHODSForty-five consecutive patients with clinically suspected CSF rhinorrhea were examined prospectively for CSF fistula with MR cisternography and plain high-resolution CT. Twenty-one patients also underwent CT cisternography. The MR imaging technique included 3-mm thin-section T1-weighted coronal sequences and fast spin-echo T2-weighted coronal, axial, and sagittal sequences in the supine position. The plain high-resolution CT study included 3-mm and sometimes 1- to 1.5-mm thin coronal sections in the prone position. Similar sequences were used after injecting nonionic contrast material intrathecally via lumbar puncture for the CT cisternographic study. The plain high-resolution CT and MR cisternographic studies were compared with results of CT cisternography; surgical findings were used as the standard of reference.RESULTSPlain high-resolution CT successfully depicted the presence or absence of CSF fistula in 42 of 45 patients, whereas MR cisternography was correct in 40 patients. MR cisternography or plain high-resolution CT correctly showed the site(s) of CSF fistula leakage in 36 of the 38 cases proved surgically. The combined techniques also correctly indicated the absence of CSF leakage in seven cases, six of which were confirmed at CT cisternography. Both MR cisternography and high-resolution CT failed to definitively locate the CSF fistula in two patients. High-resolution CT was accurate in 93% of patients, whereas MR cisternography was accurate in 89% of patients. The combination of high-resolution CT and MR cisternography was accurate in 96% of patients.CONCLUSIONIn the presence of clinically diagnosed CSF leakage, the combination of MR cisternography and plain high-resolution CT is highly accurate in locating the site and extent of CSF fistula and should be considered a viable noninvasive alternative to CT cisternography.     

MR diagnosis of acoustic neuromas

Two hundred forty-three patients with clinically suspected acoustic neuroma were evaluated radiologically by CT, and in selected cases CT cisternography and/or magnetic resonance imaging. Fifty-one acoustic neuromas were diagnosed and surgically removed; 36 were large tumors with extracanalicular extension and 15 were strictly intracanalicular small tumors. With routine CT (without and with contrast medium) large and enhancing lesions (36 of 51) were visualized, but small intracanalicular tumors (15 lesions) were missed. The latter were visualized by CT cisternography (seven cases) or MR (eight cases). Magnetic resonance, when used with spin-echo technique using both short as well as long sequences for axial and coronal thin slices (5 mm or smaller), demonstrated all the surgically verified lesions.     

Identification of the nervus intermedius using 3T MR imaging

BACKGROUND AND PURPOSE:Improved MR imaging at higher field strengths enables more detailed imaging of cranial nerves. The aim of this study was to assess the identifiability of the NI in the CPA and IAC by using high-resolution 3T MR imaging.MATERIALS AND METHODS:Twenty-seven healthy volunteers (13 men and 14 women; mean age, 33 years) underwent 3T MR imaging of the CPA. The section thicknesses of the CISS sequence was 0.4 mm (TR, 12.18 ms; TE, 6.09 ms) using a 12-channel head coil. Evaluation was performed by using MPR mode. Image quality and identifiability of the NI were rated independently by 2 observers according to predefined criteria on an ordinal scale. Interobserver agreement was assessed by κ statistics.RESULTS:Fifty-four NIs were evaluated. Both observers were able to identify the NI in nearly 60% of cases. It was possible to indentify at least 1 NI in 70% of all volunteers in the CPA and/or IAC. Image quality ratings showed a substantial agreement (κ = 0.65) and identifiability ratings an almost perfect (κ = 0.83) agreement.CONCLUSIONS:Careful evaluation of all nervous and vascular structures in the CPA and IAC at high-resolution 3T MR imaging allows reliable depiction of the NI.

The NI contains sensory and parasympathetic fibers that innervate the parotid, submandibular, submental, and minor palatine and pharyngeal salivary glands as well as the lacrimal glands. The NI is also responsible for the sensation of taste in the anterior two-thirds of the tongue. The NI originates at the brain stem between the facial nerve and the vestibulocochlear nerve in the lateral medullopontine sulcus.¹ In its further course, the NI accompanies the facial nerve or the vestibulocochlear nerve. In the latter case, it crosses over to the facial nerve at the level of the internal auditory meatus. Anatomic studies² revealed multiple variations of the NI in the CPA and IAC, both in its origin and course.Until now, depiction of the NI by imaging was not possible by using either CT or MR imaging at 1.5T.³ One major advantage of high-field MR imaging (ie, at 3T) is an increased SNR. This higher SNR results in better spatial resolution.⁴ Data on a possible improvement of imaging of the CPA at 3T, in particular the NI,⁵ are limited. Consequently, this study investigated the hypothesis that imaging the NI in the CPA and IAC is possible by using 3T MR imaging.     

Diagnosis of epidermoid cysts by metrizamide CT cisternography

Summary The authors describe three cases of intracranial epidermoid cysts specifically diagnosed by metrizamide CT cisternography. In CT cisternography of epidermoid cysts, metrizamide enters deep in the tumor clefts and depicts the lobulated margin of the tumor. We consider these findings are specific for this tumor and similar to the findings reported previously in pneumoencephalography or positive contrast cisternography.     

Imaging of cerebellopontine angle lesions: an update. Part 2: intra-axial lesions,skull base lesions that may invade the CPA region,and non-enhancing extra-axial lesions

Computed tomography (CT) and magnetic resonance (MR) imaging reliably demonstrate typical features of vestibular schwannomas or meningiomas in the vast majority of mass lesions responsible for cerebellopontine angle (CPA) syndrome. However, a large variety of unusual lesions can also be encountered in the CPA. Covering the entire spectrum of lesions potentially found in the CPA, these articles explain the pertinent neuroimaging features that radiologists need to know to make clinically relevant diagnoses in these cases, including data from diffusion- and perfusion-weighted imaging or MR spectroscopy, when available. A diagnostic algorithm based on the lesion’s site of origin, shape and margins, density, signal intensity and contrast material uptake is also proposed. Non-enhancing extra-axial CPA masses are cystic (epidermoid cyst, arachnoid cyst, neurenteric cyst) or contain fat (dermoid cyst, lipoma). Tumours can also extend into the CPA by extension from the skull base (paraganglioma, chondromatous tumours, chordoma, cholesterol granuloma, endolymphatic sac tumour). Finally, brain stem or ventricular tumours can present with a significant exophytic component in the CPA that may be difficult to differentiate from an extra-axial lesion (lymphoma, hemangioblastoma, choroid plexus papilloma, ependymoma, glioma, medulloblastoma, dysembryoplastic neuroepithelial tumour).     

Computed tomographic diagnosis of suprasellar masses by intrathecal enhancement.

Ten suspected suprasellar mass lesions were evaluated by CT cisternography (CTC). In each case the cisterns could be defined. Suprasellar mass lesions were found in six. Precise assessment of the anterior, lateral, posterior, and superior extent, made by metrizamide CTC, was verified at surgery. In two masses the intravenously enhanced scan was not diagnostic, while a lesion was visualized by intrathecal (metrizamide) CT. The major diagnostic entity was an enlarged third ventricle. When a chiasmic lesion is suspected and the conventional scan is negative, metrizamide CTC is the examination of choice.     

Imaging of cerebellopontine angle lesions: an update. Part 1: enhancing extra-axial lesions

Computed tomography (CT) and magnetic resonance (MR) imaging reliably demonstrate typical features of vestibular schwannomas or meningiomas in the vast majority of mass lesions in the cerebellopontine angle (CPA). However, a large variety of unusual lesions can also be encountered in the CPA. Covering the entire spectrum of lesions potentially found in the CPA, these articles explain the pertinent neuroimaging features that radiologists need to know to make clinically relevant diagnoses in these cases, including data from diffusion and perfusion-weighted imaging or MR spectroscopy, when available. A diagnostic algorithm based on the lesion’s site of origin, shape and margins, density, signal intensity and contrast material uptake is also proposed. Part 1 describes the different enhancing extra-axial CPA masses primarily arising from the cerebellopontine cistern and its contents, including vestibular and non-vestibular schwannomas, meningioma, metastasis, aneurysm, tuberculosis and other miscellaneous meningeal lesions.     

Metrizamide cisternography and computed tomography for the investigation of pituitary lesions

Summary Metrizamide cisternography and computed tomography (CT) have been performed on 22 patients suspected of having pituitary or suprasellar lesions, using a low dose of metrizamide. These patients would otherwise have been subjected to air encephalography. The technique is described and the results are presented. The lesions demonstrated included empty sellae and suprasellar extensions of pituitary tumours. We also identified those patients in whom there was no suprasellar extension of a pituitary tumour. The diagnostic information required was obtained in all cases by a combination of the two techniques and air encephalography was avoided in all but one case. The side effects were mild and no serious complications were encountered. We consider this combination of methods to be very useful for the investigation of pituitary lesions.     

CSF flow studies of intracranial cysts and cyst-like lesions achieved using reversed fast imaging with steady-state precession MR sequences

BACKGROUND AND PURPOSE: Differentiating between intracranial cysts or cyst-like structures and communicating or noncommunicating cysts is often not possible with cranial CT or nonfunctional MR imaging. We evaluated a retrospective ECG-gated fast imaging with steady-state precession (PSIF) MR sequence with optional cine mode to differentiate cystic masses from enlarged CSF spaces and to determine the accuracy of detecting communication between cysts and neighboring CSF spaces. METHODS: Fourteen patients with intracranial cystic masses underwent CSF flow studies with an ungated and a retrospective ECG-gated cine-mode PSIF sequence in addition to spin-echo imaging. Findings were evaluated retrospectively by using a five-point rating scale and without knowledge of clinical or other imaging findings. Results were compared with intraoperative findings or with results of intrathecal contrast studies. RESULTS: Eighteen arachnoid cysts and one enlarged cisterna magna were diagnosed. Improved differentiation between cysts and enlarged CSF spaces was obtained with cine-mode PSIF imaging in six lesions (six patients). Increased diagnostic certainty as to communication between cysts and CSF spaces was obtained in 18 cysts (13 patients). Diagnoses were verified by membranectomy in five lesions, by CT cisternography in five lesions, and indirectly by shunting in one cystic lesion. In one case, MR diagnosis was not confirmed by CT cisternography. CONCLUSION: Cine-mode MR imaging with a retrospective ECG-gated flow-sensitive PSIF sequence contributed to the certainty of communication between arachnoid cysts and neighboring CSF spaces with an accuracy of 90%, using surgical findings or intrathecal contrast studies as reference. Differentiation between intracranial cysts and enlargement of CSF spaces and other cystic masses was improved in 25% of cases.     

MR imaging of syringomyelia and hydromyelia

The relative effectiveness of plain computed tomography (CT), metrizamide CT, conventional myelography, and magnetic resonance (MR) imaging was compared for the examination of cystic spinal cord lesions. Intramedullary cavities in 18 patients were demonstrated by MR imaging: cavities were uncomplicated in 13 patients, associated with spinal tumors in two, and studied after occipital craniectomy for treatment of Chiari malformation and syringomyelia in two. Cavities were shown by MR imaging in all enlarged spinal cords, but a cavity was shown in only one of four small cords. The rostral limits of the cavities were demonstrated better than were the caudal extensions. Ventricular communication was not demonstrated. Chiari malformation was shown only in cavities that did not involve the medulla. Syringes associated with tumor were indistinguishable from uncomplicated cavities, but the tumor had abnormal signal on long spin-echo sequences in two cases. Cystic cord tumor (one case) had an inhomogeneous appearance. Caudal displacement of the cerebellar hemisphere through the surgical defect associated with compression of the fourth ventricle was shown in two cases after posterior fossa craniectomy. Thirteen patients were studied with metrizamide CT also. MR imaging proved to be as accurate as metrizamide CT in the diagnosis of intramedullary cavities that result in spinal cord enlargement, but it was less sensitive in detecting cavities within normal-sized or diminished spinal cords. It had the advantage that tumor tissue could be distinguished from associated syrinx cavities by differences in signal characteristics; and cerebellar ectopia was evaluated easily on sagittal MR views.