Keith A. Cauley

Correlation of Apparent Diffusion Coefficient With Ki-67 Proliferation Index in Grading Meningioma

OBJECTIVE A noninvasive method to predict aggressiveness of high-grade meningiomas would be desirable because it would help anticipate tumor recurrence and improve tumor management and the treatment outcomes. The Ki-67 protein is a marker of tumor proliferation, and apparent diffusion coefficient (ADC) is related to tumor cellularity. Therefore, we sought to determine whether there is a statistically significant correlation between ADC and Ki-67 values in meningiomas and whether ADC values can differentiate various meningioma subtypes. MATERIALS AND METHODS MRI examinations and histopathology of 68 surgically treated meningiomas were retrospectively reviewed. Mean ADC values were derived from diffusion imaging. Correlation coefficients were calculated for mean ADC and Ki-67 proliferation index values using linear regression. An independent unpaired Student t test was used to compare the ADC and Ki-67 proliferation index values from low-grade and more aggressive meningiomas. RESULTS A statistically significant inverse correlation was found between ADC and Ki-67 proliferation index for low-grade and aggressive meningiomas (r(2) = -0.33, p = 0.0039). ADC values (± SD) of low-grade meningiomas (0.84 ± 0.14 × 10(-3) mm(2)/s) and aggressive (atypical or anaplastic) meningiomas (0.75 ± 0.03 × 10(-3) mm(2)/s) were significantly different (p = 0.0495). Using an ADC cutoff value of 0.70 × 10(-3) mm(2)/s, the sensitivity for diagnosing aggressive meningiomas was 29%, specificity was 94%, positive predictive value was 67%, and negative predictive value was 75%. CONCLUSION ADC values correlate inversely with Ki-67 proliferation index and help differentiate low-grade from aggressive meningiomas.

Diffusion-Tensor Imaging of Small Nerve Bundles: Cranial Nerves, Peripheral Nerves, Distal Spinal Cord, and Lumbar Nerve Roots— Clinical Applications

OBJECTIVE The purpose of this article is to review recent advances in diffusion-tensor imaging (DTI) and tractography of the cranial and peripheral nerves. CONCLUSION Advances in MR data acquisition and postprocessing methods are permitting high-resolution DTI of the cranial and peripheral nerves in the clinical setting. DTI offers information beyond routine clinical MRI, and DTI findings have implications for the diagnosis and treatment of nerve disease.

Magnetic resonance diffusion tensor imaging and tractography of intracranial cavernous malformations: preliminary observations and characterization of the hemosiderin rim

OBJECT Cavernous malformations (CMs) can cause symptoms that appear out of proportion to the lesion size, leading one to hypothesize that they may have an effect on adjacent white matter that is not fully explained by local mass effect. The goal of this study was to investigate the diffusion tensor (DT) properties of CMs, the hemosiderin rim, and normal-appearing adjacent white matter. METHODS Eighteen cavernous malformations were characterized using standard MR imaging sequences as well as 6-direction DT imaging with single-shot echo planar-gradient echo imaging at 3 tesla. RESULTS Diffusion tensor imaging demonstrated that CMs have a characteristic signature on DT imaging, with low fractional anisotropy (FA) and high mean diffusivity centrally within the lesion. The hemosiderin rim had a high FA value relative to the central lesion or adjacent white matter. Tractography revealed that tracts neatly deviate around CMs. Tracts were typically seen to pass through the hemosiderin rim. CONCLUSIONS The hemosiderin rim of CMs was intimately associated with white matter tracts that were deviated by the central lesion. These findings are consistent with histopathological reports that the hemosiderin rim is composed of blood breakdown products deposited in viable white matter.

Improved image quality and detection of small cerebral infarctions with diffusion-tensor trace imaging.

OBJECTIVE The purpose of this study was to test a hypothesis that routinely performed diffusion-tensor trace imaging is of sufficient image quality and sensitivity for infarct detection to safely and routinely replace standard diffusion-weighted imaging (DWI) in the clinical setting. MATERIALS AND METHODS Both routine DWI and 15-direction diffusion-tensor imaging (DTI) with parallel acquisition technique were obtained on all brain MRI studies from a single 1.5-T MRI scanner at a tertiary care referral center over a 1-year period, permitting direct comparison of the two different diffusion studies on the same patients (2537 studies, 365 infarct-positive studies). A subset of images was assessed for image quality and quantitatively for ability to detect brain infarctions. The total set of positive studies was reviewed qualitatively for ability to detect small cerebral infarctions. RESULTS Fifteen-direction isotropic DWI (DTI trace images) with parallel acquisition technique resulted in consistently higher image quality with less distortion and higher image detail than routine DWI. Small infarcts were better seen, and in 12 cases, infarcts could only be seen on 15-direction isotropic diffusion-weighted images. The additional scanning time required for 15-direction isotropic DWI did not result in significantly increased motion-related reduction in image quality compared with standard DWI. CONCLUSION Diffusion-tensor trace images obtained with parallel acquisition technique are of improved image quality and improved sensitivity for detection of small cerebral infarctions relative to standard DWI. If such DTI data are acquired, routine DWI can be omitted.

Diffusion-tensor imaging derived metrics of the corpus callosum in children with neurofibromatosis type I.

OBJECTIVE MR morphometric studies have suggested that structural brain abnormalities including corpus callosum enlargement may, in part, explain cognitive deficits in children with neurofibromatosis type 1 (NF-1). Diffusion tensor imaging (DTI) metrics of the corpus callosum in adults with NF-1 have recently been reported, but such studies in children with NF-1 are needed. The purpose of this study was to quantify the DTI metrics at 3 T of different regions of the corpus callosum in children with NF-1. SUBJECTS AND METHODS DTI metrics from seven consecutively identified patients with NF-1 (6 boys and 1 girl; age range, 3-17 years; average age, 7.0 years) were compared with 11 age- and sex-matched control subjects (10 boys and one girl; age range, 3-17 years; average age, 7.1 years) at 3 T. Fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity were calculated in different sections of the corpus callosum as well as whole-brain mean diffusivity. RESULTS Comparing children with NF-1 to control subjects, there were statistically significant decreases in fractional anisotropy in the genu, anterior body, and isthmus of the corpus callosum and significant increases in radial diffusivity in the genu and anterior body. Whole-brain mean diffusivity histograms revealed significant increases in whole-brain mean diffusivity in children with NF-1. CONCLUSION Children with NF-1 have abnormal DTI metrics, particularly in the genu, and elevated whole-brain mean diffusivity. NF-1-related microstructural abnormalities of the corpus callosum are detectable in childhood and likely persist through myelination maturation.

Fluoroscopically Guided Lumbar Puncture

OBJECTIVE The objective of this article is to detail the indications, techniques, risks, and benefits of fluoroscopically guided lumbar puncture (LP). CONCLUSION Familiarity with the details of fluoroscopically guided LP can aid in the work flow, increase the success rate, and minimize the complications of the procedure.

Axial Diffusivity of the Corona Radiata Correlated With Ventricular Size in Adult Hydrocephalus

OBJECTIVE Hydrocephalus causes changes in the diffusion-tensor properties of periventricular white matter. Understanding the nature of these changes may aid in the diagnosis and treatment planning of this relatively common neurologic condition. Because ventricular size is a common measure of the severity of hydrocephalus, we hypothesized that a quantitative correlation could be made between the ventricular size and diffusion-tensor changes in the periventricular corona radiata. In this article, we investigated this relationship in adult patients with hydrocephalus and in healthy adult subjects. MATERIALS AND METHODS Diffusion-tensor imaging metrics of the corona radiata were correlated with ventricular size in 14 adult patients with acute hydrocephalus, 16 patients with long-standing hydrocephalus, and 48 consecutive healthy adult subjects. Regression analysis was performed to investigate the relationship between ventricular size and the diffusion-tensor metrics of the corona radiata. Subject age was analyzed as a covariable. RESULTS There is a linear correlation between fractional anisotropy of the corona radiata and ventricular size in acute hydrocephalus (r = 0.784, p < 0.001), with positive correlation with axial diffusivity (r = 0.636, p = 0.014) and negative correlation with radial diffusivity (r = 0.668, p = 0.009). In healthy subjects, axial diffusion in the periventricular corona radiata is more strongly correlated with ventricular size than with patient age (r = 0.466, p < 0.001, compared with r = 0.058, p = 0.269). CONCLUSION Axial diffusivity of the corona radiata is linearly correlated with ventricular size in healthy adults and in patients with hydrocephalus. Radial diffusivity of the corona radiata decreases linearly with ventricular size in acute hydrocephalus but is not significantly correlated with ventricular size in healthy subjects or in patients with long-standing hydrocephalus.

MR imaging of acute cervical spinal ligamentous and soft tissue trauma

The increasing availability of magnetic resonance imaging (MRI) and the high sensitivity of MRI for soft tissue injury are resulting in the increased use of MRI for the evaluation of acute trauma. As cervical spine injury can have a devastating consequence, MRI is being more commonly used to evaluate cervical spine injury in the acute setting, necessitating emergent interpretation by the on-call radiologist. Unless one is formally trained in a trauma center, the MRI findings of soft tissue and ligamentous cervical spine injury may not be fully appreciated. The goal of this pictorial review is to familiarize the reader with some of the more common soft tissue, vascular, and ligamentous injuries seen on MRI of the cervical spine in the emergent setting.

Vestibular Schwannoma, Radiosurgery and Hydrocephalus

Hydrocephalus is an uncommon and controversial complication of radiosurgery for vestibular schwannoma (VS). The controversy arises as hydrocephalus can also be associated with untreated vestibular schwannoma. Nevertheless, retrospective review of radiosurgical cases suggest that in a minority of cases of treated vestibular schwannomas, radiosurgery appears to cause or significantly accelerate subsequent hydrocephalus. This chapter discusses the evidence for this claim, and reviews the frequency of this complication, correlating variables, predisposing factors, proposed mechanisms, and patient management options.