Overview of MR imaging modalities

Practical approaches to optimization of the use of gadolinium in MR imaging comprise a range of advances in data-acquisition techniques and pulse sequences that augment tissue contrast and reduce scanning times, increasing throughput and patient comfort. In addition to the effects of magnetic field strengths and manipulation of contrast doses for routine spin-echo (SE) imaging, several approaches are reviewed. These include: fat suppression, which helps to resolve enhancing lesions from tissues with inherently high signal on post-gadolinium T1-weighted imaging; gradient-echo (GRE) and partial radio-frequency (RF) echoplanar techniques, which tend to reduce data acquisition times; MR angiography, which enables elucidation of slow-flow vessels and mass-vessel relationships; and three-dimensional GRE scan displays, which relate lesion location to regional and surface anatomy.

Ocular melanoma

Uveal melanoma is the second most frequent ocular malignancy after metastasis and the most common primary ocular malignant neoplasm in adults. The diagnosis is usually made from clinical examination and ocular ultrasound. CT and MR may be helpful for further evaluation.

Spinal nerve enhancement with Gd-DTPA: MR correlation with the postoperative lumbosacral spine

PURPOSE

To search for a probable source of the recurrent signs and symptoms associated with lumbosacral postsurgical syndrome on intravenous gadolinium-enhanced MR.

METHODS

A retrospective study of 120 patients with recurrent symptomatology following lumbar disk surgery was carried out with spin-echo MR pre- and postenhancement with gadopentetate dimeglumine (0.1 mmol/kg). In addition, 10 asymptomatic subjects were evaluated at least 6 months postoperatively using the same imaging protocol.

RESULTS

21.6% of the symptomatic subjects (N = 26) had enhancement of one or more spinal nerve root. This enhancement was focal or multisegmental, and involved single or multiple nerve roots. The abnormal neural enhancement was associated with otherwise isolated epidural fibrosis in 88.5%, and with herniated nucleus pulposus in the remaining 11.5%. The overall clinical correlation of single root enhancement with a monoradiculopathy and multiroot enhancement with a polyradiculopathy was 95.7%. However, 21.7% of these same cases also showed additional nerve root enhancement that did not have an overt clinical correlation. All of these latter patients were imaged relatively early in the postoperative period (5 days to 8 months). The 10 patients in the asymptomatic group all manifested degrees of postoperative epidural scarring on MR, but no abnormal radicular enhancement or other associated pathology.

CONCLUSION

In the chronic postoperative phase (more than 6 to 8 months), the presence of radicular enhancement on MR imaging in symptomatic individuals, and its absence in asymptomatic subjects, suggests that neural enhancement serves as a marker for active neural pathology that may in certain individuals be related temporally to the signs and symptoms associated with the lumbosacral postsurgical syndrome.

Intracranial meningioma

This case shows many of the imaging features classically associated with meningiomas. The illustrations show common location, shape, and local effects as well as enhancement characteristics. Hyperostosis and bone destruction, a fluid "cleft" surrounding the extraaxial mass, gray-white interface displacement, and secondary intraparenchymal changes are correlated with gross pathology findings. These key features are summarized in Table 1 and the composite anatomic diagram (Fig. 6).

Radiologic-pathologic correlation. Epidermoid tumor of the cerebellopontine angle

This case demonstrated the classic gross pathologic, CT, and MR appearances of epidermoid tumors. The imaging features and differential diagnosis are summarized.

Multiple sclerosis in adolescents: CT and MR findings

The MR and CT findings in 12 adolescents with multiple sclerosis were compared with reported findings in adults. The adolescent group showed a more striking female predominance, more severe disease characteristics, and more frequent infratentorial involvement. Cortical atrophy and abnormal iron accumulation in the basal ganglia were uncommon in the adolescents. Neither group demonstrated a correlation between symptom severity and either extent or location of disease as delineated by MR imaging. MR was more sensitive than CT in detecting demyelinating plaques.

Multiple sclerosis in adolescents: CT and MR findings

The MR and CT findings in 12 adolescents with multiple sclerosis were compared with reported findings in adults. The adolescent group showed a more striking female predominance, more severe disease characteristics, and more frequent infratentorial involvement. Cortical atrophy and abnormal iron accumulation in the basal ganglia were uncommon in the adolescents. Neither group demonstrated a correlation between symptom severity and either extent or location of disease as delineated by MR imaging. MR was more sensitive than CT in detecting demyelinating plaques.

The radiologic assessment of trigeminal neuropathy

The clinical and radiologic records of 76 patients with trigeminal neuropathy and an abnormal imaging study (CT and/or MR) were analyzed retrospectively. The trigeminal nerve (cranial nerve V) was divided into proximal (brainstem, preganglionic, gasserian ganglion, and cavernous sinus) and distal (extracranial V1, V2, and V3) segments. Lesions were organized according to segments and correlated with the type and distribution of clinical symptoms or signs. The purpose of the study was to (1) determine the efficacy of clinical localization of cranial nerve V lesions, (2) compare CT and MR for cranial nerve V imaging, (3) develop an MR protocol for effective cranial nerve V imaging, and (4) construct a differential diagnosis by anatomic segment for lesions of cranial nerve V. Clinical localization was found to be extremely inaccurate. CT was not as sensitive as MR for lesions involving the basal cisterns and skull base and will not detect the most common brainstem lesions (small infarcts and multiple sclerosis plaques). The MR protocol developed does not rely heavily on clinical localization. On the basis of lesions found in this series, a differential diagnosis by segment was developed. Patients with cranial nerve V symptoms should undergo MR imaging according to the protocol provided in this article. CT is not as effective as MR in imaging some cranial nerve V segments. Clinical localization is inaccurate.

Computed tomographic features of nonthyroid extraocular muscle enlargement

While Graves' disease is the most common cause of enlarged extraocular muscles, other disorders may masquerade as dysthyroid orbitopathy. The authors conducted a retrospective analysis of the computed tomographic (CT) scans of 60 patients with nonthyroid enlarged extraocular muscles to establish the differential radiographic features of these disorders. The diseases were classified as primary or local invasion of neoplasm (26%), inflammatory (25%), metastatic tumor (20%), vascular (13%), infection (12%), and acromegaly (3%). The inflammatory cases demonstrated more bilateral involvement (40%) and less involvement of the tendons (47%) than previously appreciated. The relatively high incidence of these features in the inflammatory group is important because both features have been considered pathognomonic for Graves' disease. Primary and metastatic tumors produced a nodular muscle enlargement with sharp borders and frequent bone changes. Certain tumors showed a predilection for certain muscle groups. Vascular cases involved multiple unilateral muscles and usually enlarged the superior ophthalmic vein. Infectious cases usually demonstrated fusiform muscle enlargement with blurred margins, whereas acromegaly caused moderate enlargement of all recti. Although certain diagnosis-specific radiographic patterns are described, no feature is pathognomonic for any disorder.

Efficacy, safety, and tolerability of ioversol in intra-arterial digital subtraction angiography

Twenty-two women and 18 men undergoing intra-arterial digital subtraction angiography were enrolled in an open-label, noncomparative study to assess the efficacy, safety, and patient tolerance of the contrast medium ioversol. The quality of radiographs generated was excellent in 60.0% of the studies, diagnostic in 37.5%, and nondiagnostic in 2.5%. There were no clinically significant drug-related changes in vital signs or laboratory tests among the patients, and no drug-related adverse effects were reported. Heat and pain related to injection of ioversol were graded on a four-point scale, with 0 indicating none and 3 indicating severe. The average scores were 1.3 for heat and 0.1 for pain. In this study, ioversol was a safe and effective contrast medium for angiography and was associated with a low incidence of patient discomfort.

The radiologic assessment of trigeminal neuropathy

The clinical and radiologic records of 76 patients with trigeminal neuropathy and an abnormal imaging study (CT and/or MR) were analyzed retrospectively. The trigeminal nerve (cranial nerve V) was divided into proximal (brainstem, preganglionic, gasserian ganglion, and cavernous sinus) and distal (extracranial V1, V2, and V3) segments. Lesions were organized according to segments and correlated with the type and distribution of clinical symptoms or signs. The purpose of the study was to (1) determine the efficacy of clinical localization of cranial nerve V lesions, (2) compare CT and MR for cranial nerve V imaging, (3) develop an MR protocol for effective cranial nerve V imaging, and (4) construct a differential diagnosis by anatomic segment for lesions of cranial nerve V. Clinical localization was found to be extremely inaccurate. CT was not as sensitive as MR for lesions involving the basal cisterns and skull base and will not detect the most common brainstem lesions (small infarcts and multiple sclerosis plaques). The MR protocol developed does not rely heavily on clinical localization. On the basis of lesions found in this series, a differential diagnosis by segment was developed. Patients with cranial nerve V symptoms should undergo MR imaging according to the protocol provided in this article. CT is not as effective as MR in imaging some cranial nerve V segments. Clinical localization is inaccurate.

Disorders of histogenesis: the neurocutaneous syndromes

MRI is uniquely suited to demonstration of the wide array of brain abnormalities in the neurocutaneous syndromes, due to its ability to provide previously unattainable neuroanatomic information on T1-weighted images and its extreme sensitivity to changes in water content of brain structures on T2-weighted images. It therefore is assisting physicians in better understanding the full expression of these heritable disorders, such as the extent of optic pathway involvement in optic nerve glioma, the presence of hamartomas in TS, and abnormal myelination in Sturge-Weber syndrome. It may in the future have a role in genetic counseling in TS. CT provides complimentary information to MRI in the evaluation of intracranial pathology in the neurocutaneous syndromes. Bone abnormalities and abnormal states of calcification may at times still be better evaluated by CT. Additionally, CT is a less expensive means of following existent abnormalities over time.

Normal and diseased acoustic pathway: evaluation with MR imaging

To evaluate the use of magnetic resonance (MR) imaging in the assessment of the normal and diseased acoustic pathway, 176 patients with sensorineural hearing loss (SNHL) underwent MR imaging. In 65 patients an abnormality was detected at MR; in 50 of the 65, the abnormality was believed to be definitely or possibly responsible for the SNHL. In 47% of cases, the cochlea (3%) or vestibulocochlear nerve (44%) was involved by primary lesions. Computed tomography (CT) was performed, in addition to MR, in 25 patients in whom an abnormality was seen at MR; in 18 (72%), MR was believed to be superior to CT for lesion display. A review of 30 normal MR images of the cerebellopontine angle and brain disclosed that the cochlea was directly imaged in all cases with the use of short or long repetition times (TRs). The vestibulocochlear nerve was directly seen in 77% of cases with the use of short TR imaging. In conclusion, MR imaging delineates the acoustic pathway more clearly than does CT and is recommended for the examination of abnormalities in this region.

CT/MR spectrum of far lateral and anterior lumbosacral disk herniations

Forty-eight patients had 50 extraforaminal disk herniations (EFDHs) demonstrated on CT and/or MR by (1) presence of disk density or disk signal material lateral to the neural foramen, (2) displacement or obliteration of paravertebral fat, and (3) nerve root or ganglion compression or displacement. Forty-one of 50 EFDHs had a coexisting intraforaminal component; nine of 50 had an isolated far lateral herniated nucleus pulposus. EFDHs typically occurred in the absence of a coexisting intraspinal disk herniation. Migratory fragments were seen in 50% of all cases and were at or cephalad to the interspace of origin in all cases. Forty-six percent of EFDHs were at L2-L3 or L3-L4, although the most commonly affected level was L4-L5 (38%). EFDHs, which were often overlooked (15/50 scans reviewed), are an important preventable cause of failed intraspinal diskectomy. EFDHs can be readily identified on both CT and MR if appropriate scans are obtained from L2 through S1 and if the neural foramina and paravertebral spaces are carefully examined.

Non-Hodgkin's lymphoma of the head and neck: CT evaluation of nodal and extranodal sites

Forty-five patients with non-Hodgkin's lymphoma (NHL) of the extracranial head and neck who had undergone CT as part of their evaluation were reviewed to assess the impact of CT on clinical management. The sites of tumor deposition were subdivided by location: I, nodal; II, extranodal, lymphatic (Waldeyer's ring); and III, extranodal, extralymphatic (orbit, sinonasal, deep facial spaces, mandible, salivary gland, skin, and larynx). The CT appearance of NHL in each of the three locations was analyzed for characteristic CT signatures. Nodal NHL was suspected when CT showed multiple, large, homogeneous lymph nodes, often in unusual nodal chains of the head and neck. Extranodal, lymphatic NHL of Waldeyer's ring was indistinguishable from squamous cell carcinoma of this area unless synchronous tumor deposit in an extranodal, extralymphatic location was also present. When NHL was in nodes and/or Waldeyer's ring, CT-derived information was of limited clinical value since treatment was unfocused (chemotherapy and/or large-field radiotherapy). The CT appearances of extranodal, extralymphatic NHL was generally not distinguishable from other malignancies of these areas. However, CT-derived information regarding deep-tissue tumor size and extent was critical to planning the radiotherapy ports.

Vagal neuropathy: evaluation with CT and MR imaging

The vagus nerve, as a result of its protracted course from the brain stem to the abdomen, can present a difficult imaging problem when it is compromised by a clinically occult lesion. The clinical and radiologic records of 48 patients with suspected vagus nerve dysfunction were reviewed to derive an efficient and effective approach to imaging this patient population. An imaging algorithm is proposed in which vagal neuropathies are divided both clinically and radiologically into proximal and distal categories. Proximal vagal lesions are part of a cranial neuropathy complex and have associated oropharyngeal signs and symptoms (e.g., abnormal gag reflex, uvular deviation). Distal vagal lesions occur as an isolated paralysis of the vagus nerve with no symptoms or signs referable to the oropharynx. Either computed tomography (CT) or magnetic resonance imaging can be used to diagnose proximal or distal lesions. However, CT will be insensitive in the detection of the more cephalic proximal lesions, especially those in the brain stem, basal cisterns, and skull base.

Cochlear implant candidates: assessment with CT and MR imaging

Eighty-seven patients with severe to profound hearing loss were evaluated for possible placement of a multichannel cochlear implant hearing device. After initial clinical screening, 42 patients underwent computed tomographic (CT) examination. Five of these patients were also examined with magnetic resonance (MR) imaging. Twenty-two patients received implants. CT of the middle and inner ear was normal in 24 patients (57.1%) and showed labyrinthine ossification in 12 (28.6%), cochlear or fenestral otosclerosis (or both) in four (9.5%), and congenital cochlear malformation in two (4.8%). The information provided by CT was used to (a) exclude patients in whom multichannel cochlear implantation would most likely be unsuccessful (owing to obliterative labyrinthine ossification, or congenital cochlear malformation, severe cochlear, or fenestral otosclerosis), (b) help select the best ear for implantation, and (c) provide a preoperative picture of normal variants and avoidable surgical pitfalls. MR experience is limited but assessment of the size of the cochlear nerve and the membranous labyrinth is possible with this modality and may provide additional information in the evaluation of these patients.

Ranulas and their mimics: CT evaluation

The spectrum of computed tomographic (CT) findings in ten patients with pathologically proved simple and diving ranulas is reviewed. These retention cysts originate within the sublingual space from obstruction of the sublingual or minor salivary glands; when they enlarge, the cysts herniate to involve the submandibular and inferior parapharyngeal spaces (the so-called diving or plunging ranula). CT findings in 38 additional patients with a variety of cystic lesions in the floor of the mouth are contrasted with findings in cases of ranulas. The relevant anatomy is reviewed. This experience indicates that a unilocular, cystic mass emanating from the sublingual space and extending into the adjacent submandibular and/or inferior parapharyngeal spaces can be considered a diving ranula in virtually all cases. A unilocular, cystic mass entirely within the sublingual space can be considered a simple ranula in most instances, although absolute distinction between a simple ranula and an epidermoid cyst cannot be made radiographically.

CT patterns of facet fracture dislocations in the thoracolumbar region

Thoracolumbar facets are not as commonly dislocated as are those of the cervical spine. It is, however, crucial to make an early and accurate diagnosis of thoracolumbar facet dislocation since the injury may be unstable and require reduction and internal fixation. This paper presents three major CT patterns of thoracolumbar facet fracture dislocation. The first represents anterior subluxation of the vertebral body with anteriorly locked facets. The second is a lateral vertebral body subluxation with laterally locked facets. The third is an acute kyphosis with little vertebral body subluxation but superiorly dislocated facets. Since the vertebral body subluxation may be missed on axial CT images, these facet-dislocation patterns should be recognized by identifying the paired superior and inferior facets and establishing their congruency. Identification of the facets is accomplished by their orientation with respect to the vertebral body (superior facets are directed posteromedially and inferior facets are directed anterolaterally) as well as by the shape of the articular surface (superior facet articular surface is concave, inferior facet articular surface is flat or convex).

Radiographic evaluation of brachial plexopathy

Neurologic signs and symptoms of brachial plexopathy may be subtle or confusing, making clinical localization of disease along the length of the brachial plexus difficult. To determine the most direct radiographic approach to diagnosing and anatomically delineating the cause of brachial plexopathy, we reviewed the clinical and radiographic records of 43 patients presenting with signs and symptoms referable to the brachial plexus who received CT and/or myelography as part of their radiographic evaluation. The study population was divided into two groups, those with and those without trauma. Significant deficiencies were detected in the radiographic evaluation of the nontraumatic group, with 35% of these patients having an incomplete or inappropriate CT examination that failed to visualize the full extent of the brachial plexus. In four patients, this led to a significant (greater than 6 months) delay in diagnosis. It was concluded that trauma patients presenting with brachial plexus symptoms should have cervical myelography first, rather than CT. Patients without a history of trauma should be classified on the basis of clinical findings as having central (cord, epidural space, neural foramen) or peripheral (retroclavicular space, axillary apex) disease. If the abnormality is central, myelography should be the first technique used; if peripheral disease is present, CT should be the first study. If the disease extends beyond the confines of the anatomic compartment suggested clinically, the other technique should be used for further evaluation. CT scan protocols for brachial plexus evaluation should employ bolus/drip contrast enhancement to distinguish vascular structures from masses.(ABSTRACT TRUNCATED AT 250 WORDS)