J. Van Goethem

Tuberculosis of the central nervous system: overview of neuroradiological findings

Abstract. This article presents the range of manifestations of tuberculosis (TB) of the craniospinal axis. Central nervous system (CNS) infection with Mycobacterium tuberculosis occurs either in a diffuse form as basal exudative leptomeningitis or in a localized form as tuberculoma, abscess, or cerebritis. In addition to an extensive review of computed tomography and magnetic resonance features, the pathogenesis and the relevant clinical setting are discussed. Modern imaging is a cornerstone in the early diagnosis of CNS tuberculosis and may prevent unnecessary morbidity and mortality. Contrast-enhanced MR imaging is generally considered as the modality of choice in the detection and assessment of CNS tuberculosis.

Imaging findings in diffuse axonal injury after closed head trauma

Abstract. Even in patients with closed head trauma, brain parenchyma can be severely injured due to disruption of axonal fibers by shearing forces during acceleration, deceleration, and rotation of the head. In this article we review the spectrum of imaging findings in patients with diffuse axonal injuries (DAI) after closed head trauma. Knowledge of the location and imaging characteristics of DAI is important to radiologists for detection and diagnosis. Common locations of DAI include: cerebral hemispheric gray-white matter interface and subcortical white matter, body and splenium of corpus callosum, basal ganglia, dorsolateral aspect of brainstem, and cerebellum. In the acute phase, CT may show punctate hemorrhages. The true extent of brain involvement is better appreciated with MR imaging, because both hemorrhagic and non-hemorrhagic lesions (gliotic scars) can be detected. The MR appearance of DAI lesions depends on several factors, including age of injury, presence of hemorrhage or blood-breakdown products (e. g., hemosiderin), and type of sequence used. Technical aspects in MR imaging of these patients are discussed. Non-hemorrhagic lesions can be detected with fluid attenuated inversion recovery (FLAIR), proton-density-, or T2-weighted images, whereas gradient echo sequences with long TE increase the visibility of old hemorrhagic lesions.

Intracranial hemorrhage: principles of CT and MRI interpretation

Abstract. Accurate diagnosis of intracranial hemorrhage represents a frequent challenge for the practicing radiologist. The purpose of this article is to provide the reader with a synoptic overview of the imaging characteristics of intracranial hemorrhage, using text, tables, and figures to illustrate time-dependent changes. We examine the underlying physical, biological, and biochemical factors of evolving hematoma and correlate them with the aspect on cross-sectional imaging techniques. On CT scanning, the appearance of intracranial blood is determined by density changes which occur over time, reflecting clot formation, clot retraction, clot lysis and, eventually, tissue loss. However, MRI has become the technique of choice for assessing the age of an intracranial hemorrhage. On MRI the signal intensity of intracranial hemorrhage is much more complex and is influenced by multiple variables including: (a) age, location, and size of the lesion; (b) technical factors (e.g., sequence type and parameters, field strength); and (c) biological factors (e.g., pO2, arterial vs venous origin, tissue pH, protein concentration, presence of a blood-brain barrier, condition of the patient). We discuss the intrinsic magnetic properties of sequential hemoglobin degradation products. The differences in evolution between extra- and intracerebral hemorrhages are addressed and illustrated.

Review article: MRI of the postoperative lumbar spine.

Imaging assessment of the lumbosacral spine following surgery is complex and depends upon several factors, including the anatomy of the patient, the surgical procedure and the disease process for which it was performed, the age of the patient, the biomechanical condition of the underlying cortical and cancellous bone, intervertebral disc and musculoligamentous tissues, the time since surgery procedure and the duration and nature of the postsurgical syndrome. Depending upon these factors, one or a combination of complementary imaging modalities may be required to demonstrate any clinically relevant abnormality, to assist the surgeon in deciding if repeat surgery is necessary, its nature and at which vertebral level(s) it should be directed. This review stresses the important role of MRI following lumbar discectomy, intervertebral fusion and/or instrumentation in achieving the most beneficial and timely outcome in the patient presenting with an acute, subacute or chronic failed back surgery syndrome.

Distribution and incidence of degenerative spine changes in patients with a lumbo-sacral transitional vertebra

The purpose of this prospective study was to determine the overall incidence and distribution of lumbo-sacral degenerative changes (i.e. disc protrusion or extrusion, facet degeneration, disc degeneration, nerve root canal stenosis and spinal stenosis) in patients with and without a lumbo-sacral transitional vertebra (LSTV). The study population consisted of 350 sequential patients with low back pain and/or sciatica, referred for medical imaging. In all cases CT scans of the lumbosacral region were obtained. In 53 subjects (15%) an LSTV was found. There was no difference in overall incidence of degenerative spine changes between the two groups. We did find, however, a different distribution pattern of degenerative changes between patients with and those without an LSTV Disc protrusion and/or extrusion occurred more often at the level suprajacent to the LSTV than at the same level in patients without LSTV (45.3% vs 30.3%). This was also the case for disc degeneration (52.8% vs 28%), facet degeneration (60.4% vs 42.6%) and nerve root canal stenosis (52.8% vs 27.9%). For spinal canal stenosis there was no statistically significant difference between the two categories. In conclusion, our findings indicate that an LSTV does not in itself constitute a risk factor for degenerative spine changes, but when degeneration occurs, it is more likely to be found at the disc level above the LSTV.

Trauma of the spine and spinal cord: imaging strategies

Traumatic injuries of the spine and spinal cord are common and potentially devastating lesions. We present a comprehensive overview of the classification of vertebral fractures, based on morphology (e.g., wedge, (bi)concave, or crush fractures) or on the mechanism of injury (flexion-compression, axial compression, flexion-distraction, or rotational fracture-dislocation lesions). The merits and limitations of different imaging techniques are discussed, including plain X-ray films, multi-detector computed tomography (MDCT), and magnetic resonance imaging (MRI) for the detection. There is growing evidence that state-of-the-art imaging techniques provide answers to some of the key questions in the management of patients with spine and spinal cord trauma: is the fracture stable or unstable? Is the fracture recent or old? Is the fracture benign or malignant? In summary, we show that high-quality radiological investigations are essential in the diagnosis and management of patients with spinal trauma.

Magnetic resonance imaging of localized giant cell tumour of the tendon sheath (MRI of localized GCTTS)

Abstract The objective of this study was to evaluate the appearance of localized giant cell tumour of the tendon sheath (GCTTS) on unenhanced and Gd-enhanced MR images. MR images of 13 histologically proven cases of localized GCTTS were evaluated for mean size, location, homogeneity and signal intensity (SI) on both T1- and T2-weighted images, and enhancement pattern. All lesions except 1 affected young adults. On T1- and T2-weighted images, lesions showed predominantly low SI equal to or slightly higher than skeletal muscle. On Gd-enhanced T1-weighted images, strong homogeneous enhancement was seen. These findings reflect the underlying histological composition of the lesion; haemosiderin deposition in xanthoma cells, shortening T2-relaxation time, and abundant collagenous proliferation are responsible for low SI on T1- and T2-weighted images. Strong homogeneous enhancement originates from numerous proliferative capillaries in the collagenous stroma. We conclude that these characteristic MR features, together with clinical information, are a valuable diagnostic tool in offering a correct preoperative diagnosis.

MRI after successful lumbar discectomy

Our aim was to establish the normal range of MRI findings after successful lumbar discectomy. We prospectively examined 34 consecutive patients with an excellent clinical outcome by MRI 6 weeks and 6 months after surgery. All examinations included sagittal and axial spin-echo (SE) T1-weighted images before and after intravenous gadolinium-DTPA and fast SE T2-weighted images. Contrast enhancement along the surgical tract was seen in all patients 6 weeks and 6 months after surgery. After 6 months minimal or no mass effect on the dural sac by epidural scar was seen. In 20% of patients there was recurrent disc herniation, with mass effect. Enhancing nerve roots were seen in 20% of patients 6 weeks postoperatively, and half of these were associated with recurrent disc herniation at the same side. None of these patients still showed nerve root enhancement 6 months after surgery. Postoperative MRI studies must be interpreted with great care since the features described in the failed back surgery syndrome are also found, to some extent, in asymptomatic postoperative patients.

Magnetic Resonance Imaging of the Brain

Magnetic resonance imaging (MRI) examinations of the brain can be performed with several coil types, depending on the design of the MRI unit and the information required. Traditionally, MRI examinations of the brain are performed with quadrature (i.e., circularly polarized) head coils. These volume coils are closely shaped around the head of the patient and usually present a so-called “bird-cage” configuration. Many coils are split in half, for easier patient access and positioning. Recently, phased-array head coils have become the standard of practice for state-of-the-art high-resolution MRI of the brain. Phased-array head coils contain multiple small coil elements, which are arranged in an integrated design which surrounds the head (e.g., 8-, 12- or even 32-channel head coils). Data from the individual coils are integrated by special software to compensate for the nonuniform distribution of the signal-to-noise ratio (SNR) between the peripheral and central parts of the brain. The major advantage of a multichannel, phased-array head coil is that it allows the application of parallel acquisition techniques (PAT), which can be used to speed up MRI. The concept is to reduce the number of phase-encoding steps by switching a field gradient for each phase-encoding step. Skipping, for example, every second phase-encoding line accelerates the acquisition speed by a factor of two. This is called the acceleration or PAT factor. The trade-off for this increased imaging speed is a decrease in SNR. Image reconstruction with PAT techniques is more complicated, and several algorithms have been described, depending on whether image reconstruction takes place before (SMASH, GRAPPA (generalized autocalibrating partially parallel acquisition)) or after (SENSE) Fourier transform of the image data.

The value of MRI in the diagnosis of postoperative spondylodiscitis

Abstract We evaluated the role of MRI in the diagnosis of postoperative spondylodiscitis. Spondylodiscitis is a serious complication of surgery, and the diagnosis frequently depends on a combination of clinical, laboratory and imaging findings. We compared the MRI findings in six patients with biopsy- or surgery-proven spondylodiscitis with those in 38 asymptomatic postoperative patients. Contrast enhancement and signal changes in the intervertebral disc or the vertebral endplates are not specific for spondylodiscitis, being also seen in the asymptomatic patients. However, absence of Modic type 1 changes, of contrast enhancement of the disc or of enhancing paravertebral soft tissues suggests that the patient does not have spondylodiscitis. MRI appears more useful for exclusion than for confirmation of postoperative spondylodiscitis.