MR myelography of the spine and MR peripheral nerve imaging

Fluoroscopic, Computed Tomographic, and Magnetic Resonance Myelography

Despite all the advantages of magnetic resonance (MR) imaging, there still exist contraindications or limitations to its use. Thus, MR imaging has not entirely replaced fluoroscopic or computed tomographic (CT) myelography to depict the outline of the spinal cord and its nerve roots after intrathecal injection of contrast medium. The growing recent interest of neuroradiologists to accurately diagnose and treat cerebrospinal fluid leaks has also driven a resurgent need for familiarity with this image-guided procedure. This article reviews the numerous technical and periprocedural aspects of fluoroscopic and CT myelography, and the use of noninvasive MR myelography in certain clinical scenarios.

Brachial Plexus Magnetic Resonance Neurography: Technical Challenges and Solutions

ABSTRACT

Magnetic resonance neurography of the brachial plexus (BP) is challenging owing to its complex anatomy and technical obstacles around this anatomic region. Magnetic resonance techniques to improve image quality center around increasing nerve-to-background contrast ratio and mitigating imaging artifacts. General considerations include unilateral imaging of the BP at 3.0 T, appropriate selection and placement of surface coils, and optimization of pulse sequences. Technical considerations to improve nerve conspicuity include fat, vascular, and respiratory artifact suppression techniques; metal artifact reduction techniques; and 3-dimensional sequences. Specific optimization of these techniques for BP magnetic resonance neurography greatly improves image quality and diagnostic confidence to help guide nonoperative and operative management.

Quantifying cerebrospinal fluid dynamics: A review of human neuroimaging contributions to CSF physiology and neurodegenerative disease

Cerebrospinal fluid (CSF), predominantly produced in the ventricles and circulating throughout the brain and spinal cord, is a key protective mechanism of the central nervous system (CNS). Physical cushioning, nutrient delivery, metabolic waste, including protein clearance, are key functions of the CSF in humans. CSF volume and flow dynamics regulate intracranial pressure and are fundamental to diagnosing disorders including normal pressure hydrocephalus, intracranial hypotension, CSF leaks, and possibly Alzheimer's disease (AD). The ability of CSF to clear normal and pathological proteins, such as amyloid-beta (Aβ), tau, alpha synuclein and others, implicates it production, circulation, and composition, in many neuropathologies. Several neuroimaging modalities have been developed to probe CSF fluid dynamics and better relate CSF volume and flow to anatomy and clinical conditions. Approaches include 2-photon microscopic techniques, MRI (tracer-based, gadolinium contrast, endogenous phase-contrast), and dynamic positron emission tomography (PET) using existing approved radiotracers. Here, we discuss CSF flow neuroimaging, from animal models to recent clinical-research advances, summarizing current endeavors to quantify and map CSF flow with implications towards pathophysiology, new biomarkers, and treatments of neurological diseases.

Imaging of Degenerative and Infectious Conditions of the Spine

: Imaging is important in the evaluation of patients with degenerative disease and infectious processes. There are numerous conditions that can manifest as low back pain (LBP) or neck pain in a patient, and in many cases, the cause may be multifactorial. Clinical history and physical examination are key components in the evaluation of such patients; however, physical examination has variable sensitivity and specificity. Although studies have demonstrated that uncomplicated acute LBP and/or radiculopathy are self-limited conditions that do not warrant any imaging, neuroimaging can provide clear anatomic delineation of potential causes of the patient's clinical presentation. Various professional organizations have recommendations for imaging of LBP, which generally agree that an imaging study is not indicated for patients with uncomplicated LBP or radiculopathy without a red flag (eg, neurological deficit such as major weakness or numbness in lower extremities, bowel or bladder dysfunction, saddle anesthesia, fever, history of cancer, intravenous drug use, immunosuppression, trauma, or worsening symptoms). Different imaging modalities have a complementary role in the diagnosis of pathologies affecting the spine. In this review, we discuss the standard nomenclature for lumbar disk pathology and the utility of various clinical imaging techniques in the evaluation of LBP/neck pain for potential neurosurgical management. The imaging appearance of spinal infections and potential mimics also is reviewed. Finally, we discuss advanced neuroradiological techniques that offer greater microstructural and functional information.

ABBREVIATIONS

ADC, apparent diffusion coefficientDTI, diffusion tensor imagingDWI, diffusion-weighted imagingDOM, diskitis-osteomyelitisLBP, low back painMRM, magnetic resonance myelographySNA, spinal neuroarthropathySPECT, single-positron emission computed tomographySTIR, short tau inversion recovery.

Effect of magnetic resonance myelography on the target volume in craniospinal irradiation in children

AIMS

To examine the potential role of magnetic resonance myelography (MRM) in defining the clinical target volume for the spinal field in craniospinal irradiation in children.

MATERIALS AND METHODS

Of the 42 patients for whom magnetic resonance imaging (MRI) of the spine was carried out, 12 patients had MRM. The width of the cerebrospinal fluid (CSF) with any lateral extension at different levels was measured from the coronal MRM. The clinical target volume was defined using MRM and the conformal field surface area was compared with the direct conventional field. The inferior border of the thecal sac was determined from MRI spine of 42 patients.

RESULTS

Coronal MRM showed variation in the width of the CSF at different levels. The maximum width was 2.9 cm (level of C2). In the same case, the width of the CSF at the level of D8 was 1.7 cm. The mean surface area of the conventional field that covered the CSF was 190.6 cm(2), as compared with 150.5 cm(2) using conformal field, with an 18.5% reduction in the irradiated surface area. The thecal sac ended at S2 in 40.4% of the patients, whereas it ended above and below this level in 28.6 and 31%, respectively.

CONCLUSIONS

Implementation of coronal MRM during the treatment planning will improve target definition and lead to a more conformal field. Planning systems with the ability to fuse MRM with reconstructed coronal computed tomography are highly desirable. The use of MRI is highly recommended to individualise the lower border of the spinal field in craniospinal irradiation.

Occult cervical (C1-2) dural tear causing bilateral recurrent subdural hematomas and repaired with cervical epidural blood patch

The authors report the case of a 56-year-old previously healthy man who presented with a 4-month history of postural headache accompanied by nausea and vomiting. The results of initial imaging studies of the brain were normal. Repeated MR imaging demonstrated bilateral subdural hematomas which were drained and reaccumulated over a period of time. Spinal myelography revealed a cerebrospinal fluid leak at the C1-2 level. A cervical epidural blood patch, with repeated injections of 10 ml autologous blood at the site of the leak, dramatically improved the headache within 24 hours and eliminated the recurrent subdural hematomas. The results of follow-up computed tomography of the brain at 1, 4, 8, and 16 weeks were normal, and at 1-year follow-up the patient was completely free of symptoms and working.

Neurography of the spinal nerve roots by diffusion tensor scanning applying motion-probing gradients in six directions

PURPOSE

Diffusion-weighted (DW) magnetic resonance (MR) imaging of the nerve roots and peripheral nerves has been reported. We applied a sequence similar to brain diffusion tensor (DT) tractography to such a technique and assessed its feasibility.

METHODS

On a 1.5-T MR system, we acquired DW images in the axial plane using a single-shot echo-planar short tau inversion-recovery (STIR)-based sequence. Motion-probing gradients (MPGs) were applied in 6 directions with a b-value of 500 s/mm(2). For postprocessing, we performed maximum-intensity projection to reconstruct the images. We obtained cervical spine images from 3 volunteers and 8 patients and thoracolumbar spine images from 3 volunteers and 6 patients. On the source images of the cervical spine obtained from the volunteers, we compared the signal-to-noise ratios (SNRs) of the neural structures between images obtained applying MPG in 6 directions and in 3 directions. We visually assessed the nerve roots and proximal portions of the contiguous peripheral nerves in the images from volunteers and patients.

RESULTS

The SNRs were significantly superior in the images obtained with the application of MPGs in 6 directions to those obtained with the application of MPGs in 3 directions (P<0.01). Visual assessment demonstrated the nerve roots as well as the nerve ganglia and the contiguous peripheral nerves up to 3 cm or more from the respective neural foramina in each subject. Image distortion was minimal.

CONCLUSIONS

Our technique provides neurographic images of the nerve roots and proximal portions of the contiguous peripheral nerves, and images obtained using our sequence applying MPGs in 6 directions are superior to those obtained in 3 directions.

Sciatic nerve palsy after primary total hip arthroplasty: a new perspective

More than half of sciatic nerve palsies after primary total hip arthroplasties are unexplained. In 2 such cases, magnetic resonance imaging localized compressive injury between the ischial tuberosity and femoral insertion of the gluteus maximus. After these cases, we hypothesized that during limb positioning, the sciatic nerve is compressed by the gluteus maximus tendon. We present the magnetic resonance imaging findings from these 2 cases and compare the number of sciatic nerve palsies in patients with release of the gluteus maximus tendon to patients without release during primary total hip arthroplasty. There were no cases of sciatic nerve palsy when the gluteus maximus was released, compared with 3 cases in the control group.