Can MR Imaging Diagnose Adult-Onset Alexander Disease?

BACKGROUND AND PURPOSE: In recent years, the discovery that mutations in the glial fibrillary acidic protein gene (GFAP) were responsible for Alexander disease (AD) brought recognition of adult cases. The purpose of this study was to demonstrate that MR imaging allows identification of cases of AD with adult onset (AOAD), which are remarkably different from infantile cases.MATERIALS AND METHODS: In this retrospective study, brain and spinal cord MR imaging studies of 11 patients with AOAD (7 men, 4 women; age range, 26–64 years; mean age, 43.6 years), all but 1 genetically confirmed, were reviewed. Diffusion and spectroscopic investigations were available in 6 patients each.RESULTS: Atrophy and changes in signal intensity in the medulla oblongata and upper cervical spinal cord were present in 11 of 11 cases and were the diagnostic features of AOAD. Minimal to moderate supratentorial periventricular abnormalities were seen in 8 patients but were absent in the 3 oldest patients. In these patients, postcontrast enhancement was also absent. Mean diffusivity was not altered except in abnormal white matter (WM). Increase in myo-inositol (mIns) was also restricted to abnormal periventricular WM.CONCLUSIONS: Awareness of the MR pattern described allows an effective selection of the patients who need genetic investigations for the GFAP gene. This MR pattern even led to identification of asymptomatic cases and should be regarded as highly characteristic of AOAD.

Up to a few years ago, Alexander disease (AD) was known as a rare, genetically determined leukoencephalopathy affecting infants and children, characterized by macrocephaly, seizures, spasticity, and retarded psychomotor development, and leading to death in 2 months to 7 years.¹ The diagnostic MR imaging features established by van der Knaap et al² consisted of extensive white matter (WM) increased signal intensity on T2-weighted images, mainly in the frontal regions; a rim of periventricular T2 hypointensity; involvement of the basal ganglia, thalami, and brain stem; and postcontrast enhancement in the periventricular regions and scattered areas of the brain stem. These features allowed the diagnosis without biopsy, which was performed in the search for Rosenthal fibers, the histologic hallmark of the disease.^2,3Milder forms with spastic paraparesis, ataxia, or lower brain stem signs and juvenile (2–12 years of age) or adult onset (≥13 years) had been diagnosed as AD at postmortem examination because of the presence of Rosenthal fibers.⁴ After 2001, the discovery that mutations in the glial fibrillary acidic protein gene (GFAP) were responsible for the disease^5,6 allowed recognition during life of juvenile or adult forms^1,7–20 that have an MR imaging pattern remarkably different from that observed in children, with predominant focal involvement of the lower brain stem.In the last 4 years, on the basis of the MR imaging findings, we suggested the diagnosis of adult-onset AD (AOAD) in 11 patients, all but one genetically confirmed, and were struck by the constant involvement of the medulla oblongata and upper spinal cord. Therefore, we have analyzed retrospectively the imaging studies to verify the reliability of MR in making the diagnosis. The results of the genetic studies are also briefly reported.     

Colloid Cysts of the Third Ventricle: Are MR Imaging Patterns Predictive of Difficulty with Percutaneous Treatment?

BACKGROUND AND PURPOSE: Colloid cysts of the third ventricle are rare benign brain tumors. The purpose of this study was to correlate their patterns on MR images with the probability of success of percutaneous treatment. METHODS: Nineteen patients underwent endoscopic treatment for colloid cysts of the third ventricle. The cases were divided into two groups based on difficulty of the aspiration procedure. We reviewed CT scans and MR images and divided cysts into groups based on their signal intensity on the MR images and their density on CT scans. Intensity and density were correlated with difficulty of aspiration during the endoscopic procedure. RESULTS: The aspiration procedure was difficult in 63% of the cases. Eighty-nine percent of hyperdense cysts on unenhanced axial CT scans were categorized as difficult, and 75% of hypodense cysts were categorized as easy. On T2-weighted MR sequences, 100% of low-signal cyst contents were difficult and nearly 63% of high-signal lesions were easy. There was a significant correlation between the T2-weighted sequences and the CT scans regarding the difficulty of the aspiration procedure. CONCLUSION: T2-weighted MR sequences are useful for predicting difficulty of aspiration during stereotactic or endoscopic procedures. A T2-weighted low-signal cyst is correlated with high-viscosity intracystic contents.     

Imaging of the spine: Where do we stand?

The number of patients presenting with spine-related problems has globally increased, with an enormous growing demand for the use of medical imaging to address this problem. The last three decades witnessed great leaps for diagnostic imaging modalities, including those exploited for imaging the spine. These developments improved our diagnostic capabilities in different spinal pathologies, especially with multi-detector computed tomography and magnetic resonance imaging, via both hardware and software improvisations. Nowadays, imaging may depict subtle spinal instability caused by various osseous and ligamentous failures, and could elucidate dynamic instabilities. Consequently, recent diagnostic modalities can discern clinically relevant spinal canal stenosis. Likewise, improvement in diagnostic imaging capabilities revolutionized our understanding of spinal degenerative diseases via quantitative biomarkers rather than mere subjective perspectives. Furthermore, prognostication of spinal cord injury has become feasible, and this is expected to be translated into better effective patient tailoring to management plans with better clinical outcomes. Meanwhile, our confidence in diagnosing spinal infections and assessing the different spinal instrumentation has greatly improved over the past few last decades. Overall, revolutions in diagnostic imaging over the past few decades have upgraded spinal imaging from simple subjective and qualitative indices into a more sophisticated yet precise era of objective metrics via deploying quantitative imaging biomarkers.     

4D Flow MR Imaging of the Left Atrium: What is Non-physiological Blood Flow in the Cardiac System?

Most cardiac diseases cause a non-physiological blood flow pattern known as turbulence around the heart and great vessels, which further worsen the disease itself. However, there is no consensus on how blood flow can be defined in disease conditions. Especially, in the left atrium, the fact that vortex flow already exists makes this debate more complicated. 3D time-resolved phase-contrast (4D flow) MRI is expected to be able to capture blood flow patterns from multiple aspects, such as blood flow velocity, stasis, and vortex quantification. Previous studies have confirmed that physiological vortex flow is predominantly induced by the higher-volume flow from the superior left pulmonary vein. In atrial fibrillation, 4D flow MRI reveals a non-physiological blood flow pattern, which information may add value to well-established clinical risk factors. Currently, the research target of LA analysis has also widened to lung surgeons, pulmonary vein stump thrombosis after left upper lobectomy. 4D flow MRI is expected to be utilized for many more variable diseases that are currently unimaginable.     

Can MR imaging challenge the commonly accepted theory of the pathogenesis of solitary enchondroma of long bone?

Objective

It has been widely postulated that enchondromas arise from cartilage remnants that have been displaced from the growth plate into the metaphysis. However, this theory remains unproven. Based on the common occurrence of enchondromas on routine knee MR imaging (2.9?%), one would expect to find displaced cartilage in the metaphysis of skeletally immature individuals on routine knee MR examinations if the above theory was to be supported.

Materials and methods

The electronic databases of a specialist orthopedic hospital and children’s hospital were searched for skeletally immature patients who underwent MR imaging of the knee for a variety of indications. Individuals with Ollier disease or hereditary multiple exostoses were excluded. The MR images were subsequently reviewed by a musculoskeletal radiologist for evidence of displaced cartilage into the metaphysis.

Results

We reviewed 240 MR examinations of the knee that were performed in 209 patients. There were 125 MR studies in male and 115 MR examinations in female patients (age range: 5?months–16?years; median age: 13?years). In 97.1?%, the growth plates around the knee demonstrated a regular appearance. Seven cases (2.9?%) in six patients showed cartilage extension from the growth plate into the metaphysis, which remained in continuity with the growth plate. There were no cases of displaced cartilage into the metaphysis on MRI.

Conclusions

Our study challenges the widely believed theory that enchondromas arise from displaced growth plate remnants.     

Science to Practice: Can MR imaging replace liver biopsy for the diagnosis of early fibrosis?

A method that could be used to accurately assess portal venous pressure would be valuable when diagnosing portal hypertension, evaluating patient prognosis, and monitoring the progress of therapy. Baik et al have suggested that a qualitative noninvasive Doppler US parameter can be used to monitor therapy of portal hypertension. Further clinical investigation is needed to confirm these results and to determine whether hepatic venous Doppler waveform tracings can be used to monitor patient response to therapy. Ongoing research suggests that microbubble contrast agents may enable a more quantitative noninvasive estimate of intravascular pressures with US.     

Liver diffusion-weighted MR imaging: the tower of Babel?

There is a growing amount of literature regarding diffusion-weighted imaging (DWI) of the liver. The apparent diffusion coefficient (ADC) was introduced in 1986 and is used extensively in studies. However, methods for calculating ADC vary considerably and the value of the ADC strongly depends on the b values chosen for its calculation. Indeed, the ADC incorporates the effects of both diffusion and perfusion, which can vary independently. Since signal attenuation as a function of b follows a bi-exponential pattern, other diffusion/perfusion coefficients can be calculated using DWI, and these may provide more meaningful measurements than the ADC. The absence of standardization for both the terminology and the methodology in DWI of the liver makes it difficult for readers to understand the technique used and strongly limits comparisons between studies. Here, we review the main principles of DWI of the liver, the limits of the ADC, and the exciting capabilities of multi-parametric DWI. We also insisted on the need for a common language for DWI of the liver.     

Can Initial 18F-FDG PET-CT Imaging Give Information on Metastasis in Patients with Primary Renal Cell Carcinoma?

Purpose

The aim of this study was to investigate the relationship between the maximum standardized uptake values (SUVmax) of primary renal cancers with and without metastatic lesions, if any. We also studied the relationship between the size of primary renal cancers and their SUVmax, and tried to find a clinical value of ¹⁸F-FDG PET-CT for the initial evaluation of renal cell carcinoma (RCC).

Methods

The cases of 23 patients, 16 men and 7 women, who underwent PET-CT examination before operation were retrospectively reviewed. We measured the SUVmax of the primary renal cancers and those of any existing metastatic lesions, and the size of the primary renal cancers. We compared the SUVmax of primary RCCs with metastases and those without metastases, SUVmax of primary RCC and those of metastases, and studied the correlation between the size and SUVmax of primary RCCs.

Results

The SUVmax of primary RCC of the 16 patients without metastasis ranged from 1.1 to 5.6 with a median value of 2.6. Those of the patients with metastasis ranged from 2.9 to 7.6 with a median of 5.0. The size of the all 23 primary renal cancers ranged from 1.7 cm to 13.5 cm, with a median of 4.5 cm, and their SUVmax ranged from 1.1 to 7.6, with a median of 2.9. There was a statistically significant difference between the SUVmax of the primary RCC with metastasis (5.3 ± 1.7) and those without metastasis (2.9 ± 1.0). There was a moderate positive correlation between the sizes and SUVmax of all 23 primary RCCs. However, there was no statistically significant correlation between the sizes and SUVmax of primary RCCs with metastatic lesions and the same for RCCs without metastasis. The cutoff value of SUVmax for predicting extra-renal lesion was 4.4 and that for size was 5.8 cm according to the receiver operating characteristic curves.

Conclusions

Those who have primary RCC with high SUVmax are suggested to have a likelihood of metastasis. Also, there was a moderate trend of increasing value of SUVmax of primary RCC as their size increases. Physicians should beware of missing extra-renal lesions elsewhere.