Otogenic intracranial inflammations: role of magnetic resonance imaging.

The clinical course of acute otitis media is usually short, and the process terminates because of the host's immune system, the infection-resistant properties of the mucosal linings, and the susceptibility of the major organisms (beta-hemolytic streptococcus or pneumococcus) to penicillin. However, a small proportion (1% to 5%) of untreated or inadequately treated patients may experience complications. Prior to the development of an intracranial complication of otomastoiditis, warning symptoms or signs may be evident; these include severe earache, severe headache, vertigo, chills and fever, and meningeal symptoms and signs. Increasing headache, particularly temporoparietal headache near the affected ear, often indicates an impending intracranial complication. This symptom, often the only indication of an epidural abscess, demands prompt investigation and medical and surgical intervention. In our experience, computed tomography (CT) permits accurate diagnosis of acute coalescent or latent (masked) mastoiditis and its associated complications. However, magnetic resonance imaging (MRI) remains the study of choice to evaluate otogenic intracranial complications. This article demonstrates the important role of MRI in diagnosing various stages of acute otomastoiditis and its associated complications.

Diagnosis of vertebrobasilar insufficiency: time to rethink established dogma?

As isolated symptoms, vertigo, dizziness and imbalance are not regarded by neurologists as reflections of transient ischemia in the vertebrobasilar circulation. The purpose of this retrospective study was to demonstrate that these symptoms can and do occur in isolation. To this end, we analyzed the symptoms, stroke risk factors and diagnostic algorithms in 27 patients with a diagnosis of transient vertebrobasilar ischemia. None of the 27 patients included in the review complained of any associated neurologic symptoms. Against the reference standard of brain imaging, the site of the pathologic lesion was defined in the brainstem/cerebellum with the Torok monothermal caloric test, with a sensitivity greater than 86%. Vestibular decruitment and hyperactive caloric responses were of particular diagnostic value. Thus, we recommend that the neurologic dogma with regard to brainstem cerebellar ischemia be rethought.

Orbital subperiosteal hematoma, cholesterol granuloma, and infection. Evaluation with MR imaging and CT.

Orbital subperiosteal space, a potential space, is an important entity due to its unique anatomy and susceptibility to various pathologic processes. CT scan and MR imaging are important tools in the diagnosis of orbital subperiosteal hematomas, cholesterol granulomas, and infections. MR imaging has emerged as the modality of choice in the evaluation of hematomas and infections of this space due to its multiplanar capability and various imaging sequences giving better information. High-resolution CT scan offers good differentiation in most of these cases. Osseous changes in a cholesterol granuloma is better seen in CT scan, although MR imaging offers better differentiation from epidermoid or dermoid cysts and other subperiosteal process, as well as lacrimal fossa lesions. Subperiosteal abscesses are best evaluated using MR imaging.

Aneurysm clips: magnetic quantification and magnetic resonance imaging safety. Technical note.

Knowledge of the magnetic properties of cerebral aneurysm clips in patients undergoing magnetic resonance (MR) imaging is imperative. The authors quantified in electromagnetic units the magnetic properties of 13 different types of aneurysm clips by using a vibrating sample magnetometer. Their results showed that the magnetic moment of these clips ranged from 0.15 EMU/g to as high as 152.7 EMU/g. Based on these results and tests of the movement of the clips during MR imaging, they conclude that aneurysm clips with a magnetic moment less than 1 EMU/g may be safely used during MR imaging. The quantification of magnetic properties into electromagnetic units by using a vibrating sample magnetometer is a reliable method applicable to any testing field gradient. This method can be used as a standard to measure and label the magnetic properties of aneurysm clips.

MRI artifacts following anterior cervical diskectomy.

BACKGROUND: Magnetic resonance imaging (MRI), despite being an excellent imaging technique in neurosurgical practice, is unfortunately susceptible to numerous artifacts. Some of these artifacts are easily identifiable and do not interfere; however, others are more subtle and can be easily mistaken for false pathology. Postoperative MRI can further complicate the imaging interpretation, by producing another group of artifacts. It is imperative for practicing neurosurgeons, as well as neuroradiologists, to have a clear understanding of these postoperative artifacts. METHODS: We discuss four cases who had been operated for anterior cervical decompression with bony fusion. All the patients had a postoperative MRI of the cervical region that showed a "false compression" of the cervical cord. The normal computed tomography (CT) scan in some cases and the discrepancy with the clinical condition of the patients excluded the diagnosis of compression of the cervical cord. RESULTS: The overall appearance of the postoperative MRI can be very difficult to interpret. The artifact seen following anterior cervical diskectomy is an example of such a situation. We have confirmed that the postoperative MRIs showing artifacts do not indicate cord or root compression; a routine postoperative plain X ray or CT scan of the operated area can also confirm the absence of compression. CONCLUSION: These are examples of cases in which the postoperative MRI had an unexpected metallic artifact that not only caused difficulty in the interpretation of the images but at times suggested a clinical problem when actually there was none. Very thin cut CT scans may not show these artifacts that are picked up by the sensitive MRI study. A proper clinical evaluation and selection of the appropriate MRI techniques and the MRIs can eliminate or at least decrease the incidence of the artifacts. Above all, further education of practicing physicians is needed to avoid false alarms caused by these metallic artifacts.

Magnetic characteristics of Yasargil aneurysm clips.

BACKGROUND: Metallic bioimplants are subject to great scrutiny in order to ensure that they are totally harmless to patients. Aneurysm clips are no exception to this rule. Considering the number of aneurysm clips used and their potential for injury, they should be evaluated very meticulously. Determining the magnetic characteristics of these clips is an important part of the evaluation process. In this study, a new method for evaluating magnetism is described and the importance of that information is briefly discussed. METHODS: Twenty Yasargil aneurysm clips were analyzed using a vibrating sample magnetometer under 1.5 Tesla. This device is highly sensitive, and is capable of measuring the magnetism of small objects. RESULTS: Our measurements showed magnetism of the aneurysm clips ranged from 0.0334-0.1369 electromagnetic units (emu). CONCLUSIONS: Magnetometer measurements and real life tests under magnetic resonance imaging (MRI) have shown that these clips have a very low magnetism and are safe to use in 1.5 Tesla MRI scanners. This study also proves that the vibrating sample magnetometer is a useful device for analyzing the magnetism of aneurysm clips, and their emu values can be used as another industry standard in the production line to increase the safety of these clips.

Encephalopathy in AIDS patients: evaluation with MR imaging.

The presence and extent of encephalopathy were evaluated in 47 patients with AIDS or AIDS-related complex (ARC) by the use of MR imaging. Twenty-nine (62%) of the patients showed some form of white matter disease, exhibited as high signal intensity on T2-weighted images. Focal white matter lesions were seen in 23 (49%) of the patients, while a diffuse white matter process was observed in six patients (13%). Of the 29 patients who had white matter disease on MR scans, 17 (36%) had a suggestion of white matter involvement on an initial CT study. Meanwhile, 12 (26%) of the patients had a normal CT scan on the initial examination. MR findings showed predominant disease in the subinsular and peritrigonal white matter areas. Marked cerebral atrophy was observed in 17 (36%) of 47 patients, cerebellar atrophy in 18 (38%), and brainstem atrophy in seven patients (15%). Pathologic findings showed that toxoplasmosis was present in eight patients (17%), and primary CNS lymphoma was present in three patients (6%). Cryptococcal meningitis was noted in two (4%) of the patients at autopsy, and Mycobacterium tuberculosis was seen in one (2%) of the patients at autopsy. MR imaging has been shown to be a valuable technique for the detection of encephalopathy in AIDS patients.

Imaging studies in patients with central vestibular disorders.

MR is the radiologic examination of choice when a patient's symptoms indicate the presence of some retrolabyrinthine pathology. CT dynamic studies now permit both heart and brain assessment for poor blood circulation problems of the hindbrain.

Potential use of in vivo proton spectroscopy for head and neck lesions.

Early experience with in vivo MRS has shown its potential for obtaining biochemical information, thus enhancing the diagnostic sensitivity of MRI studies. Further work on combined MRI and in vivo MRS is needed, with the goal of characterization and abnormal conditions according to their spectral patterns and for identification of tumor markers. We presented in this communication our preliminary results. It seems that the resonance from melanin can be used as a marker for melanotic tumors.

Central auditory and vestibular pathology.

MR is the radiologic examination of choice when a patient's symptoms indicate the presence of some retrolabyrinthine pathology. CT dynamic studies now permit both heart and brain assessment for poor blood circulation problems of the hindbrain.

MR of the normal and abnormal internal auditory canal.

MR performed with thin, contiguous sections has replaced CT for the study of the cerebellopontine angle and for diagnosis of acoustic neuromas. In our experience large acoustic neuromas are well seen in all pulse sequences. Tumors with small extracanalicular components are seen in the T1- and spin-density-weighted sequences whereas purely intracanalicular lesions are often visualized only in the T1-weighted images. Small acoustic neuromas producing thickening of the nerve are easily recognizable in narrow internal auditory canals but may be missed in large canals because of partial volume averaging. Since further enhancement of the signal intensity of tumors can be obtained by IV injection of paramagnetic agents, we foresee the use of such agents in the near future in the diagnosis of acoustic neuromas.

Dynamic computed tomography and its application to ophthalmology.

In this review of 31 patients, dynamic CT is discussed as a valuable tool in the study of the dynamics of blood flow in patients with unexplained visual problems that may be related to ischemic optic neuropathy. Dynamic CT scans are obtained by rapid-sequence CT imaging during and following a rapid bolus injection of intravenous contrast medium. It demonstrates the initial passage of contrast material through the area of interest, thus giving a true picture of the degree of vascularity and the dynamics of blood flow.

Paraorbital tumors and tumor-like conditions: role of CT and MRI.

Tumors and tumor-like conditions of the paraorbital tissues that affect the eye usually require CT or MR imaging for complete evaluation. This article provides an overview of the wide variety of pathologic conditions to be considered when a paraorbital tumor is discovered or suspected. Some of the CT and MR imaging features of these disorders that aid in the differential diagnosis are reviewed.

Rapid dynamic CT scanning to distinguish schizophrenic from normal subjects.

Rapid dynamic computerized axial tomography (CT) density-time curves were used to detect abnormal brain regions in groups of controls and DSM-III diagnosed schizophrenics. Density-time curves were designated as plateau curves if, following a bolus injection of contrast material, they exhibited a plateau from the peak value rather than a decrease. Five of the 10 schizophrenics versus none of the 11 controls were found to possess two or more plateau curves. The physiological basis for the plateau curves is not known, but an increase in blood-brain-barrier permeability could be involved.

CT in the evaluation of the orbit and the bony interorbital distance.

The distance between the orbits and their individual dimensions are important in the diagnosis of craniofacial anomalies. Most observers rely on standard radiographs for measuring the bony interorbital distance. Tomography of the skull base and orbital computed tomography (CT) can also be used. This article describes the normal range of the bony interorbital distance and other useful orbital linear and angular measurements as determined from a series of CT scans of the orbits in 400 adults who had CT for other purposes. The normal interorbital distance measured at the posterior border of the frontal processes of the maxilla on nonrotated scans, in the plane of the optic nerve, ranges from 2.29 to 3.21 cm (average, 2.67 cm) in men and 2.29 to 3.20 cm (average, 2.56 cm) in women. The widest interorbital distance lies behind the posterior poles of the globes. This ranges from 3.16 to 4.10 cm (average, 3.37 cm) in men and 2.93 to 3.67 cm (average, 3.20 cm) in women.

CT densitometry of the cochlear capsule in otosclerosis.

Cochlear otosclerosis can be recognized in most cases by high-definition axial and coronal CT images. However, routine technique does not allow a quantitative measurement of the changes. Reported here is a study of cochlear CT densitometry. The densitometric profile of the cochlear capsule was obtained in 10 ears with normal hearing and 50 ears in 27 patients with known clinical otosclerosis and progressive mixed-type hearing loss. Patients with hearing loss had decreased absorption of as much as 60% in comparison to the normal range. In 42 ears with abnormal densitometric profiles, the changes were visibly apparent on the CT images, whereas in eight others, the densitometric profile alone demonstrated decreased absorption.

Diagnostic potential of CT in neurotological disorders.

The reliability of a neurotological evaluation in differentiating labyrinthine (end organ) lesions from retrolabyrinthine lesions has been well established. The purpose of this communication is to determine the diagnostic potential of computed tomography (CT) in patients suspected of having retrolabyrinthine lesions on the basis of their neurotological evaluations. Our study indicates that the validity of central vestibular and audiometric signs can be best substantiated with CT. The anatomy of neurovascular bundles within the internal auditory canal and cerebellopontine cistern can be readily visualized and identified by CT pneumocisternomeatography. By obtaining appropriate thin CT sections not only can very small lesions be identified but their anatomic locations can also be accurately established. CT pneumocisternomeatography is the method of choice to diagnose an intracanalicular acoustic neuroma. An unusually large vascular loop of the internal auditory canal may be responsible for sensorineural hearing loss and tinnitus in some patients.

Multidirectional and computerized tomography of the vestibular aqueduct in Meniere's disease.

Multidirectional and computerized tomography have been used for the radiographic assessment of the vestibular aqueduct in Meniere's disease. The results of studies performed by us and/or other authors indicate that there is a statistically significant difference in the size of the vestibular aqueduct between the Meniere's and control groups (in Meniere's disease the vestibular aqueduct is often narrowed or obliterated); and that periaqueductal pneumatization is often decreased or absent in ears affected by Meniere's disease. Recent histological studies performed on temporal bones of patients with Meniere's disease have confirmed these radiographic observations.