Magnetic resonance imaging virtual endoscopy of the labyrinth

OBJECTIVE: To explore the feasibility of applying virtual endoscopic (VE) techniques to examine the normal anatomy of the labyrinth using magnetic resonance imaging (MRI) data. STUDY DESIGN: Feasibility study using data from a normal subject. MATERIALS AND METHODS: MRI data was acquired in a single normal subject using a three-dimensional (3D) CISS (Constructive Interference in the Steady State) sequence. Perspective volume rendering (PVR) techniques were used to produce virtual endoscopic visualization of the fluid filled structures of the inner ear. RESULTS: The reconstructive algorithms enabled generation of a "fly-through" simulation of the labyrinth. The cochlea, the oval window, the vestibule, the common crus, and the semicircular canals were successfully visualized. CONCLUSIONS: Virtual endoscopic techniques were successfully applied to MRI data enabling a 3D virtual display of the internal anatomy of the normal labyrinth.     

Intraoperative magnetic resonance imaging

Intraoperative magnetic resonance imaging is a widely accepted method for resection control of glial tumors. Increasingly, it is also used during the resection of skull base tumors. Several studies have independently demonstrated an increase in the extent of resection in these tumors with improved prognosis for the patients. Technical innovations combined with the easier operation of this imaging modality have led to its widespread implementation. The development of digital image processing has also brought other modalities such as ultrasound and computed tomography to the focus of skull base surgery.     

High-resolution three-dimensional magnetic resonance imaging of the vestibular labyrinth in patients with atypical and intractable benign positional vertigo

Benign paroxysmal positional vertigo (BPPV) is a most common cause of dizziness and usually a self-limited disease, although a small percentage of patients suffer from a permanent form and do not respond to any treatment. This persistent form of BPPV is thought to have a different underlying pathophysiology than the generally accepted canalolithiasis theory. We investigated 5 patients who did not respond to physical treatment, presented with an atypical concomitant nystagmus or both with high-resolution three-dimensional magnetic resonance imaging of the inner ear. This method provides an excellent imaging of the inner ear fluid spaces. In all 5 patients, we found structural changes such as fractures or filling defects in the semicircular canals which we did not find in control groups. One patient clinically presented with the symptoms of a 'heavy cupula'. Whereas crosssections through the ampullary region and the adjoining utricle showed no abnormalities, there were significant structural changes in the semicircular canals, which are able to provide an explanation for the symptoms of a heavy cupula.     

Fundamentals of magnetic resonance imaging

Recent advances in diagnostic imaging have accounted in part for the early detection of space occupying lesions in and around the temporal bone. To appreciate fully the modality of nuclear magnetic resonance imaging, the physician must understand the limitations and potential applications for this newest of radiologic studies. This update introduces the otologist to the language and principles of magnetic resonance imaging scanning.     

Cortical sensorimotor control in vocalization: a functional magnetic resonance imaging study

Background: Verbal communication is a human feature and volitional vocalization is its basis. However, little is known regarding the cortical areas involved in human vocalization. Methods: Therefore, functional magnetic resonance imaging at 3 Tesla was performed in 16 healthy adults to evaluate brain activations related to voice production. The main experiments included tasks involving motor control of laryngeal muscles with and without intonation. In addition, reference mappings of the sensorimotor hand area and the auditory cortices were performed. Results: Related to vocalization, in addition to activation of the most lateral aspect of the primary sensorimotor cortex close to the Sylvian fissure (M1c), we found activations medially (M1a) and laterally (M1b) of the well‐known sensorimotor hand area. Moreover, the supplementary motor area and the anterior cingulate cortex were activated. Conclusions: Although M1a could be ascribed to motor control of breathing, M1b has been associated with laryngeal motor control. Consequently, even though M1c represents a laryngeal sensorimotor area, its exclusiveness as suggested previously could not be confirmed. Activations in the supplementary motor area and anterior cingulate cortex were ascribed to “vocal‐motor planning.” The present data provide the basis for further functional magnetic resonance imaging studies in patients with neurological laryngeal disorders.     

High-resolution magnetic resonance imaging of the human temporal bone.

A magnetic resonance imaging (MRI) system (Hitachi, Naka, Japan) with a superconductive magnet running at 2.11 T was used to obtain 2-mm-thick slices of fixed, decalcified and celloidin-embedded human temporal bone. The temporal bone was then sectioned and stained for routine histological evaluation. Both the MR images and the histological sections were in the mid-modiolar slice plane, and comparable images and sections were analyzed to confirm the identity of the inner-ear structures visualized on the MR images. The cochlear duct, scala tympani, scala vestibuli and basement membrane of all three cochlear turns were clearly imaged on MRI. In addition, the vestibule and three semicircular ducts were also clearly seen. This study raises the possibility of some day using MRI for the diagnosis of inner-ear diseases.     

Fat obliteration in paranasal sinuses: a comparative magnetic resonance imaging and histopathologic study

OBJECTIVES: To assess postoperative changes after fat tissue obliteration of the paranasal sinuses with the use of magnetic resonance imaging (MRI) and correlate the findings with correspondent histology. STUDY DESIGN: By using an animal model with fat obliteration of the maxillary paranasal sinus. METHODS: We correlated postoperative changes of the fatty tissues by means of histopathologic analysis and MRI. The study group included 15 rabbits undergoing autologous fat tissue obliteration of their maxillary paranasal sinus. After 1 month (n = 5), 3 months (n = 5), and 6 months (n = 5), both MRI and histopathologic evaluations of the fatty tissue status were performed. Contrast enhanced MRI was used to identify vital fat tissue. Subsequently, MRI findings were compared with a correspondent histologic status and proliferative factors such as angio- and osteogenesis and presence of abundant granulocytes, macrophages, and giant cells. RESULTS: After a period of 6 months, the obliteration sites in all animals showed vital fat tissues, whereas at 1 month after surgery, vital fat tissue was rarely observed. The microscopic appearance of the obliteration tissue after 1 month was characterized by fat tissue necrosis and distinct tissue reactions including blood vessel dilatation, abundant macrophages, granulocytes, and lymphocytes. MRI after 1 month showed a clear contrast enhancement because of the hyperemia and inflammation reaction. CONCLUSION: Fat tissue transplants used for obliteration of paranasal sinuses are almost completely degraded after transplantation and replaced by vital fat tissue over a period of at least 6 months. Contrast enhanced MRI is a well-suited technique for follow-up imaging and assessing the transplant vascularization and tissue remodeling status.     

Functional magnetic resonance imaging: contemporary and future use

PURPOSE OF REVIEW: Functional magnetic resonance imaging is a relatively new neuroimaging technique that is being used in both research and clinical applications. Increasing work has been done to elucidate the auditory cortex. RECENT FINDINGS: Current studies focus on enhancing the sensitivity of functional magnetic resonance imaging in studying the auditory cortex and subcortical pathways in response to tonal stimulation, to evaluate the integrity of the auditory cortex before cochlear implantation, and as a screening tool for hearing impairment in the young child. SUMMARY: Recent work has been encouraging: silent functional magnetic resonance imaging techniques allow for better evaluation of the auditory cortex with less confounding scanner noises. Functional magnetic resonance imaging can be safely and reproducibly performed in hearing-impaired children and in the preoperative evaluation of candidates for cochlear implantation.     

Vertigo: analysis by magnetic resonance imaging and angiography

The relationship of vascular disease of the vertebrobasilar artery system to isolated vertigo was examined by magnetic resonance imaging and angiography. Eighty-nine individuals complaining of vertigo were evaluated by standard otoneurologic investigations, and the data were correlated with the vascular patterns of the cervical region and posterior fossa. The age distribution extended from the fourth decade to the ninth decade; the peak occurrence was observed in the eighth. Approximately 85% of the group experienced numerous episodes of vestibular dysfunction from months to years before examination; the remaining segment was examined following the first episode due to severity or persistence of symptoms. The criteria for vascular abnormality proposed by the authors are based upon comparison with previous normal findings. Approximately 52% of the cohort demonstrated abnormal configurations or evidence of diminished flow within the vertebrobasilar artery system. Of this segment, a vertebral artery was most frequently abnormal, in 76%; the basilar artery was judged pathological in 32%, and combined disease of several arteries was evident in 20%.     

Periorbita: computed tomography and magnetic resonance imaging findings

PURPOSE: The periorbita has been regarded as the critical structure in decision of exenteration in the patients with paranasal (PNS) malignancies. The purpose of this study is to present the CT and MRI findings of the periorbita with PNS malignancies. MATERIALS AND METHODS: Ten patients with PNS cancers were chosen for this study. PNS CT and MRI scans were performed on all patients. The imaging findings were reviewed retrospectively by consensus of two neuroradiologists. Assessment of the defect of the orbital bone and invasion of the orbital fat was made by CT and MRI. The signal intensity (SI), thickness, enhancement, and correlation with the orbital bone of the periorbita were analyzed on MRI. The intraoperative and pathologic reports were used as the gold standard for orbital invasion. RESULTS: In patients with bone defects, it was impossible to differentiate the periorbita from the mass on CT. The periorbita showed hypointensity on T2-weighted images compared with the SI of mass. On Gd-enhanced T1-weighted images, the periorbita showed less enhancement than the mass in nine patients. Six patients showed two hypointense layers (the outer bony wall and the inner periorbita) between the mass and orbital fat on T2-weighted images. The thickness of the periorbita was 0.79-1.4 millimeter. Orbital invasion was more conspicuous on T2-weighted coronal images than on the CT images. CONCLUSIONS: MRI was more conspicuous for detecting orbital invasion than CT. The mass beyond the thickened periorbita on T2-weighted images was considered to be a positive finding of orbital invasion.     

High-resolution magnetic resonance imaging of human cochlea

OBJECTIVES: High-resolution MRI (MRI) of human inner ear structures provides several advantages over other imaging modalities. High-resolution visualization of inner ear ultrastructure in a noninvasive manner may provide important information about inner ear disease that is not obtainable in other ways. The study was performed to demonstrate the capabilities of MRI at high resolution on the human cochlea, vestibular structures, and facial nerve. Comparative analyses of MRI anatomy with that seen on histological dissection were made. The aim of the study was to define the anatomy of human cadaveric cochlea using a 9.4-Tesla magnetic resonance scanner, currently the most powerful magnetic resonance magnet available. STUDY DESIGN: Experimental pilot study of cadaveric human cochleae. METHODS: Serial scanning using a 9.4-Tesla magnetic resonance imager on normal preserved and fresh cadaveric inner ears was performed in different planes. RESULTS: The images revealed detailed anatomy of the modiolus, utricle, saccule, semicircular canals, and facial nerve. Specifically, identifiable structures within the cochlea included the osseous spiral lamina, Reissner's membrane, membranous spiral lamina, spiral ligament, and others. CONCLUSIONS: Data established through the acquisition of images from cadaver cochlea, facial nerve, and vestibular complex provide a foundation for developing steps for testing temporal bones and, eventually, patients with Meniere's disease and other inner ear disease. The present ongoing project will provide information on baseline images of the inner ear using high-resolution MRI.     

Applications of magnetic resonance imaging in otology

Magnetic resonance (MR) has been employed for the study of patients with peripheral and retrolabyrinthine otologic pathology. Its usefulness has been compared with that of computed tomography (CT). CT remains at present the best study for the assessment of patients with conductive hearing loss and sensorineural hearing loss or vestibular disorders of the peripheral type. However, MR is the study of choice of retrolabyrinthine pathology occurring in the internal auditory canals, cerebellopontine cisterns, and brainstem.     

Lingual thyroid: the diagnostic value of magnetic resonance imaging

Lingual thyroid is an uncommon developmental aberration of embryogenesis. It may present as a mid-line, non-tender, painless, reddish appearing swelling in the throat. Magnetic resonance imaging (MRI) is a relatively new diagnostic method for this condition. Two cases of lingual thyroid are reviewed with their MRI's and surgical results.     

Clinical features of sudden hearing loss associated with a high signal in the labyrinth on unenhanced T1-weighted magnetic resonance imaging

We report on five patients with high signals in the labyrinth on unenhanced magnetic resonance imaging who developed sudden hearing loss and vertigo. Weissman et al. (1992) suggested the possibility that such high signals were caused by hemorrhage. We assessed these patients using audiograms, caloric tests, and auditory brainstem responses to investigate the possibility of inner ear hemorrhage. Most of the patients were found to have severe and irreversible impairment of both cochlear and vestibular function. These findings were consistent with the hypothesis that their symptoms were caused by inner ear hemorrhage. Received: 3 November 1999 / Accepted: 20 January 2000