Imaging of the cervical spine.

The emergence of multiplanar spiral computed tomography and high-resolution magnetic resonance imaging has resulted in the ability to see cervical spine anatomy and pathologic conditions in detail. Appropriately chosen and performed, these imaging studies can provide an anatomic basis for a clinical diagnosis and a therapeutic plan. In the evaluation of cervical spondylosis, magnetic resonance imaging is more commonly performed than computed tomography because of its superior depiction of soft tissue anatomy, including intervertebral discs and spinal cord disease. However, computed tomography still has a role, particularly in the assessment of osseous neural foraminal stenosis. In cervical spine trauma, routine radiography remains the procedure of choice. Computed tomography is performed in patients who have abnormal plain radiographs or in patients in whom there is a strong clinical suspicion of fracture with inconclusive radiographs. In the neurologically compromised patient, magnetic resonance imaging is useful in the diagnosis of cord and nerve root injury. Magnetic resonance imaging is the most sensitive and specific imaging study in the assessment of spinal infection, including osteomyelitis, discitis, and epidural abscess. Magnetic resonance imaging has also supplanted all other imaging methods in the evaluation of primary and secondary tumors of the spinal cord and spinal column. Despite the precise depiction of cervical spine anatomy provided by these imaging methods, the role of the clinician in determining the true cause of a patient's symptoms is in no way diminished. The presence of an imaging study abnormality does not automatically imply causality.

The phylogenetic distribution of a transposable dioxygenase from the Niagara River watershed.

Horizontal gene transfer in the Bacteria has been demonstrated to occur under natural conditions. The ecological impact of gene transfer events depends on the new genetic material being expressed in recipient organisms, and on natural selection processes operating on these recipients. The phylogenetic distribution of cbaAB genes for chlorobenzoate 3,4-(4,5)-dioxygenase, which are carried within Tn5271 on the IncP beta plasmid pBRC60, was investigated using isolates from freshwater microcosms and from the Niagara River watershed. The latter included isolates from surface water, groundwater and bioremediation reactor samples. The cbaAB genes have become integrated, through interspecific transfer, primarily into species of the beta Proteobacteria (44/48 isolates). Only four isolates, identified as Pseudomonas fluorescens (3/48) and Xanthomonas maltophilia (1/48), belonged to the gamma Proteobacteria, despite the observation that pBRC60 was capable of mobilizing these genes into a wide range of beta and gamma Proteobacteria in the laboratory. The natural host range correlated with the distribution of the meta-ring-fission pathway for metabolism of protocatechuates formed when the cbaAB genes were expressed (45/48 isolates). We proposed the hypothesis that natural selection has favoured recipients that successfully integrate the activity of the transferred dioxygenase with the conserved meta ring-fission pathway. The hypothesis was tested by transferring a plasmid construct containing the cbaAB genes into type strains representative of the beta and gamma Proteobacteria. The concept of applying mobile catabolic genes to probe the phylogenetic distribution of compatible degradative pathways is discussed.

MRI of normal brain maturation.

The unprecedented gray/white differentiation obtained with magnetic resonance imaging (MRI) has created a unique opportunity to trace the normal process of myelination. Fifty-nine children referred for evaluation of a nonneurologic problem or a nonspecific neurologic complaint were studied with MRI using spin-echo technique. Children ranged in age from term (40 weeks intrauterine) to 16 years. Scans were reviewed for quantitative and qualitative changes with age. T1 and T2 relaxation times were measured for 13 regions of interest in 37 children. With increasing age a sharp decrease in both T1 and T2 values, most pronounced during the first year of life, was seen. The prolonged relaxation times in the newborn infant correspond to the known high water content of the neonatal brain; the subsequent decline corresponds to the decrease in water content and increase in myelination observed in autopsy studies of infants. Qualitative changes in the MRI appearance of the brain with age using a spin-echo sequence (2 sec repetition time) demonstrated that the process of myelination was most rapid during the first 2-3 years of life. Myelination appeared to occur earliest in the posterior fossa, with the middle cerebellar peduncle identifiable at only 3 months. By the age of 1 year, all major white matter tracts including the corpus callosum, subcortical white matter, and the internal capsule were well defined. However, due to subtle changes in appearance, the refined configuration of the adult brain was not attained until early adolescence.

Meningovascular syphilis: CT and MR findings.

The radiologic findings in three cases of meningovascular syphilis are presented. Angiography demonstrated varying degrees of narrowing and ectasia of the supraclinoid carotid, basilar, and proximal anterior and middle cerebral arteries, as well as distal branches. Computed tomography (CT) showed multifocal infarction with variable enhancement. Similarly, in the one case studied with magnetic resonance (MR), several regions of high signal intensity on T2-weighted sequences were found, which were compatible with foci of ischemia. Although the radiologic findings are nonspecific, the diagnosis of meningovascular syphilis should be considered in patients with vasculitis of uncertain etiology.

MR imaging of calcified intracranial lesions.

Fifty calcified intracranial lesions diagnosed with computed tomography (CT) were evaluated with magnetic resonance (MR) using a spin-echo sequence. MR images demonstrated 41 of 50 lesions seen as calcified on CT scans, among them 29 of 30 cerebral neoplasms and all ten arteriovenous malformations. The presence of calcification was suspected prospectively in about 60% of calcified lesions but was also suspected in 45% of uncalcified lesions (reviewed as control cases). No fine calcifications and only 25% of punctate calcifications were disclosed on MR images. In the nine lesions undetected by MR, calcification was the only abnormal CT finding. The findings of calcification on MR images were nonspecific, ranging from signal void or signal dampening on all sequences to no alteration of signal intensity. The most common finding of calcification was a focus of signal diminution, rather than signal void, as commonly reported.

Magnetic resonance imaging of primary intracranial tumors: a review.

The experience in magnetic resonance (MR) imaging of primary intracranial neoplasia at University of California, San Francisco is reviewed. Seventy patients have been evaluated by MR and computerized tomography (CT). MR scans were performed using a multi-slice spin echo technique with a long pulse repetition time (TR = 2000 msec), and long echo sampling delay (TE = 56 msec). This method was most sensitive in differentiating normal gray and white matter and in detecting both cerebral edema and abnormal tissue with prolonged T2 characteristics. More sensitive to slight alterations in normal tissue, MR may detect a focal lesion in cases in which CT shows only mass effect. Moreover, MR may demonstrate more thoroughly the extent of tumor infiltration and broaden the characterization of abnormal tissue. Posterior fossa and brainstem anatomy are invariably better depicted by MR. The major limitations of MR include its inability to detect foci of tumor calcification, demonstrate the severity of bone destruction, or reliably distinguish tumor nidus from surrounding edema.

High-resolution CT of temporal bone trauma.

Computed tomographic (CT) findings in 18 patients with temporal bone trauma were reviewed. Eight patients suffered longitudinal fractures of the petrous bone, which were associated with ossicular dislocation in two patients. Transverse fractures were detected in six patients, with a contralateral mastoid fracture in one patient. In four patients, the fractures were restricted to the mastoid region. Of the 14 patients in whom adequate neurologic evaluation was available, seven had a permanent facial nerve or hearing deficit while five suffered at least a transient neurologic deficit related to the temporal bone trauma. Routine head CT (10 mm sections) demonstrated only eight of 19 petrous bone injuries. Clues to such injury included opacification of the mastoid air cells (10 patients), sphenoid sinus (11 patients), external canal and middle ear air space (10 patients), and local pneumocephalus (five patients). Evidence of brain trauma or extraaxial hematoma was seen in 12 patients. In 13 cases, high-resolution CT was also performed, demonstrating temporal bone injuries in all. This latter technique allows rapid and detailed evaluation of temporal bone trauma. Reports of radiographic evaluation of temporal bone trauma tend to deal with a somewhat skewed population, selected on the basis of clinical symptomatology. In a major trauma center equipped with high-resolution CT, it was found that temporal bone fractures may be seen incidentally, or in patients in whom symptomatology related to temporal fracture is obscured by much more serious neurologic compromise.