Resistive Index Variability in Anterior Cerebral Artery Measurements During Daily Transcranial Duplex Sonography: A Predictor of Cerebrovascular Complications in Infants Undergoing Extracorporeal Membrane Oxygenation?

OBJECTIVES: The purpose of this study was to determine the value of resistive index (RI) variability in predicting cerebrovascular complications during extracorporeal membrane oxygenation (ECMO). METHODS: This retrospective study included 36 infants treated by ECMO. The RI was measured on daily transfontanellar duplex sonography, obtained first without fontanel compression and then after gentle compression with the transducer. The age at ECMO cannulation, sex, gestational age at birth, method of delivery, indication, and type and duration of ECMO were recorded. RESULTS: There was a statistically significant difference in RI variability in infants who developed cerebrovascular complications as opposed to those who did not (P = .002). Resistive index variability of 10% or greater on any day was associated with an increased risk for cerebrovascular complications (P = .0482; χ2 = 3.9). Variability in the first 5 days was significantly higher than on following days (P < .0001). The age at ECMO cannulation showed a significant difference, with mean ± SD values of 1.1 ± 0.9 days in the complications group and 2.7 ± 2.2 days in the no-complications group (P = .043). CONCLUSIONS: Resistive index variability of 10% or greater on any day had a statistically significant risk of cerebrovascular complication development. Extracorporeal membrane oxygenation cannulation at younger than 3 days conferred an increased risk of cerebrovascular complications.

Acute Brain Imaging in Children: Can MRI Replace CT as a Screening Tool?

BACKGROUND AND PURPOSE: To determine if axial T2-weighted imaging can serve as screening tool for pediatric brain imaging. METHODS: We retrospectively evaluated consecutive brain magnetic resonance imaging (MRI) data of 161 children (74 girls) with a mean age of 7.44 ± 5.71 years. Standard of reference was the final report of neuroradiology attendings. Three readers with different levels of experience were blinded for clinical diagnoses and study indications. First, readers studied only the axial T2-weighted screening sequence. Second, they studied all available anatomical and functional MRI sequences as performed per standard protocol for each clinical indication. The readings were classified as normal or abnormal. Sensitivity and specificity were measured. RESULTS: Axial T2 screening yielded a sensitivity of 77-88% and a specificity of 92%. The full studies/data sets had a sensitivity of 89-95% and a specificity of 86-93%. Nineteen of 167 studies were acquired for acute and 148 of 167 studies for nonacute clinical indication. Twenty-five false-negative diagnoses paneled in three groups were made by all readers together. Readers misread four of 19 studies with acute and 21 of 148 studies with nonacute clinical indication. Four of 21 misread studies with nonacute indications harbored unexpected findings needing management. CONCLUSIONS: Axial T2 screening can detect pediatric brain abnormalities with high sensitivity and specificity and can possibly replace CT as screening tool if the reading physician is aware of possible limitations/pitfalls. The level of experience influences sensitivity and specificity. Adding diffusion-weighted imaging and susceptibility-weighted imaging to a 3-dimensional T2-weighted sequence would most likely further increase sensitivity and specificity.

The Role of ADC-Based Thermometry in Measuring Brain Intraventricular Temperature in Children.

BACKGROUND AND PURPOSE: To determine the feasibility of apparent diffusion coefficient (ADC)-based thermometry to assess intraventricular temperature in children. METHODS: ADC maps were generated from diffusion tensor imaging data, which were acquired with diffusion gradients along 20 noncollinear directions using a b-value of 1000 s/mm(2) . The intraventricular temperature was calculated based on intraventricular ADC values and the mode method as previously reported. The calculated intraventricular temperature was validated with an estimated brain temperature based on temporal artery temperature measurements. We included 120 children in this study (49 females, 71 males, mean age 6.63 years), 15 consecutive children for each of the following age groups: 0-1, 1-2, 2-4, 4-6, 6-8, 8-10, 10-14, and 14-18 years. Forty-three children had a normal brain MRI and 77 children had an abnormal brain scan. Polynomial fitting to the temperature distribution and subsequent calculation of mode values was performed. A correlation coefficient and a coefficient of determination were calculated between ADC calculated temperatures and estimated brain temperatures. Linear regression analysis was performed to investigate the two temperature measures. RESULTS: ADC-based intraventricular temperatures ranged between 31.5 and 39.6 °C, although estimated brain temperatures ranged between 36.3 and 38.1 °C. The difference between the temperatures is larger for children with more than 8,000 voxels within the lateral ventricles compared to children with less than 8,000 voxels. The correlation coefficient between ADC-based temperatures and the estimated brain temperatures is .1, the respective R(2) is .01 indicating that 1% of the changes in estimated brain temperatures are attributable to corresponding changes in ADC-based temperature measurements (P = .275). CONCLUSIONS: ADC-based thermometry has limited application in the pediatric population mainly due to a small ventricular size.

Pediatric skull fracture diagnosis: should 3D CT reconstructions be added as routine imaging?

OBJECT: The authors compared the efficacy of combining 2D+3D CT reconstructions with standard 2D CT images in the diagnosis of linear skull fractures in children with head trauma. METHODS: This was a retrospective evaluation of consecutive head CT studies of children presenting with head trauma. Two experienced pediatric neuroradiologists in consensus created the standard of reference. Three readers independently evaluated the 2D CT images alone and then in combination with the 3D reconstructions for the diagnosis of linear skull fractures. Sensitivity and specificity in the diagnosis of linear skull fractures utilizing 2D and 2D+3D CT in combination were measured for children less than 2 years of age and for all children for analysis by the 3 readers. RESULTS: Included in the study were 250 consecutive CT studies of 250 patients (167 boys and 83 girls). The mean age of the children was 7.82 years (range 4 days to 17.4 years). 2D+3D CT combined had a higher sensitivity and specificity (83.9% and 97.1%, respectively) compared with 2D alone (78.2% and 92.8%, respectively) with statistical significance for specificity (p < 0.05) in children less than 2 years of age. 2D+3D CT combined had a higher sensitivity and specificity (81.3% and 90.5%, respectively) compared with 2D alone (74.5% and 89.1%, respectively) with statistical significance for sensitivity (p < 0.05) in all children. CONCLUSIONS: In this study, 2D+3D CT in combination showed increased sensitivity in the diagnosis of linear skull fractures in all children and increased specificity in children less than 2 years of age. In children less than 2 years of age, added confidence in the interpretation of fractures by distinguishing them from sutures may have a significant implication in the setting of nonaccidental trauma. Furthermore, 3D CT is available at no added cost, scan time, or radiation exposure, providing trainees and clinicians with limited experience an additional valuable tool for routine imaging of pediatric head trauma.

Neuroimaging findings in pediatric cerebral sinovenous thrombosis.

PURPOSE: Pediatric cerebral sinovenous thrombosis (CSVT) is a potentially life-threatening condition which is usually diagnosed by MRI. We analyzed the signal changes of the thrombus over time and the role of diffusion-weighted/tensor imaging (DWI/DTI) in the diagnosis of CSVT. METHODS: Clinical histories were reviewed for risk factors for CSVT, neurologic manifestation, and interval from onset of symptoms related to CSVT to the neuroimaging diagnosis. MRI studies were retrospectively evaluated for the appearance of thrombi on T1- and T2-weighted, fluid-attenuated inversion recovery (FLAIR), DWI/DTI, susceptibility-weighted imaging (SWI), and magnetic resonance venography (MRV) images. RESULTS: Thirty-three children with CSVT were included in this study. Seventy-seven thrombi were found. Seventy-four thrombi could be identified on T1- or T2-weighted images (96 %), 72 thrombi were seen on DWI/DTI (94 %) and 68 on FLAIR (88 %). DWI showed restricted diffusion in 29 thrombi (40 %). Thrombi older than 1 day were more likely to have a T1-hyperintense signal (p = 0.002). No additional correlation between signal intensity and age of the thrombi was found. Intraparenchymal changes secondary to CSVT were seen in 11 children. CONCLUSION: MR sequences individually are not sensitive enough to provide the diagnosis. DWI/DTI does not provide complementary diagnostic value. Approximation of the age of the thrombus is difficult because of poor correlation between signal intensity and age of the thrombi.

Serendipity in the diagnosis of pheochromocytoma.

OBJECTIVES: Pheochromocytomas are increasingly being discovered incidentally on imaging studies performed without clinical suspicion of the existence of an adrenal lesion. We aimed to determine the rate of diagnosis of adrenal pheochromocytoma as an incidental finding during a recent 7-year period. METHODS: We obtained the Department of Pathology database to study all the patients at our institution with newly diagnosed pheochromocytomas in the 7-year period from 2005 to 2011 to determine the clinical presentation and the means of diagnosis. RESULTS: In 40 (70.2%) of the 57 patients, an adrenal pheochromocytoma was detected in an imaging study performed without suspicion of an adrenal lesion. There were 13 chest computed tomography studies-8 to evaluate for possible pulmonary emboli. Other indications included abdominal pain or discomfort (n = 8), trauma (n = 3), abnormal liver function tests (n = 3), suspect renal artery stenosis (n = 3), hematuria (n = 2), colitis (n = 2), and 4 miscellaneous indications. DISCUSSION: Our study documents that the commonest current means of initial detection of pheochromocytoma is by serendipitous discovery. In 16 of our 40 patients with serendipitously discovered pheochromocytomas, there were no clinical symptoms of pheochromocytoma; these were true incidentalomas. More than two thirds of the new cases of pheochromocytoma were detected by serendipity (found during studies not performed to evaluate for pheochromocytoma), approximately one third were true incidentalomas (pheochromocytomas in patients without symptoms). CONCLUSIONS: In a 7-year period at a single institution, 40 patients, 70% of new cases of surgically proven pheochromocytoma, were initially detected by serendipity. Sixteen patients, 40% of those incidentally discovered represented true examples of "incidentalomas."

MDCT of adrenal masses: Can dual-phase enhancement patterns be used to differentiate adenoma and pheochromocytoma?

OBJECTIVE: The purpose of this study was to compare enhancement of adrenal adenomas and pheochromocytomas during dual-phase (arterial and venous phases) CT performed with currently used MDCT protocols with the goal of defining enhancement patterns predictive of pathologic findings. MATERIALS AND METHODS: Pathologically proven pheochromocytomas were retrospectively compared with adrenal adenomas. Inclusion criteria for adenomas, collected by searching the radiology database, were confirmatory adrenal CT (unenhanced with or without washout) and absence of clinical indicators of pheochromocytoma. A fellowship-trained attending radiologist blinded to the pathologic diagnosis reviewed existing images from dual-phase IV contrast-enhanced CT examinations to measure enhancement of adrenal lesions and characterize the appearance (homogeneous versus heterogeneous). Student t test analysis was performed to compare arterial and venous phase enhancement levels. RESULTS: The findings in 39 patients with 41 adenomas were compared with those in 10 patients with 12 pheochromocytomas. Mean arterial and venous enhancement of adenomas at 37 HU (-6 to 85 HU) and 60 HU (16-133 HU) was significantly lower than that of pheochromocytomas at 104 HU (42-190 HU) and 119 HU (61-195 HU) (p < 0.001). No adenoma was more than 85-HU enhancing in the arterial phase, and 58% of pheochromocytomas were more than 110-HU enhancing. Most adenomas (85%) were more enhancing in the venous phase. No adenoma was more enhancing in the arterial phase, but 25% (3/12) of pheochromocytomas were. Most (58%) pheochromocytomas were heterogeneous in appearance, compared with 22% of adenomas. CONCLUSION: For indeterminate adrenal masses identified at dual-phase IV contrast-enhanced CT, higher enhancement during the arterial phase, arterial phase enhancement levels greater than 110 HU, and lesion heterogeneity should prompt consideration of pheochromocytoma.

Pulmonary artery measurements in pulmonary hypertension: the role of computed tomography.

PURPOSE: We studied the relationship between pulmonary artery diameter (PAD) as measured on computed tomography (CT) and pulmonary artery pressure (PAP) with the specific goal of assessing the reliability of various measurements on high-resolution chest CT as predictors of pulmonary hypertension (PH). MATERIALS AND METHODS: In a preliminary study we determined the method of measuring the main PAD (mPAD) that best correlated with PAP. Using this approach we measured mPAD on CT and correlated the data with PAP obtained from right heart catheterization in 298 patients with known PH and in 102 controls. Various metrics were analyzed for their specificity and sensitivity as screening measurements for PH. RESULTS: The mean PAD and mPAD/ascending aorta diameter (AAD) ratio were found to have the highest correlation with PAP (r=0.51 and 0.53, respectively; P<0.001). A threshold of mPAD>29.5 mm was found to be 70.8% sensitive and 79.4% specific for PH, and an mPAD threshold >31.5 mm had a sensitivity and specificity of 52.0% and 90.2%, respectively. An mPAD/AAD ratio >1 was found to be 70.8% sensitive and 76.5% specific for PH. There was no significant correlation between mPAD and body surface area or age (r=0.04 and 0.07, respectively). A strong statistically significant difference (P<0.0001) was found between mPAD and mPAD/AAD ratio between controls and the PH group. CONCLUSION: mPAD and mPAD/AAD ratio may be used to detect PH in patients of any age or with any body surface area.

Isolated celiac and superior mesenteric artery dissection identified with MDCT: imaging findings and clinical course.

OBJECTIVE: Isolated celiac or superior mesenteric artery (SMA) dissection is a rare entity in the absence of aortic dissection. Our objective was to detail imaging and clinical course of celiac and or SMA dissections. METHODS: We conducted a retrospective search from 2004 to 2010 using "celiac and/or SMA dissection" keywords. Analysis of medical record and imaging at diagnosis and follow-up was performed. Dissections for any reason without aortic dissection were included. RESULTS: Twenty-four celiac and 18 SMA dissections were detected in 38 patients. One third of the dissections diagnosed with interactive multiplanar reconstruction/maximum intensity projection (MIP)/3-dimensional (3D) rendering were missed on standard imaging planes. No patients had bowel ischemia or died. Eighty-four percent of the patients were observed, 2 patients received anticoagulation, 2 patients received surgical repair, and 3 patients received stenting. Twenty-three of 25 cases treated with observation exhibited no change or improvement/resolution (2/25) with 20.9-month mean follow-up. CONCLUSION: Most isolated celiac and SMA dissections were asymptomatic/incidental, supporting observation and surveillance with intervention reserved for vascular compromise. Interactive multiplanar reconstruction/maximum intensity projection/3D rendering can increase diagnostic sensitivity.

Abundance of correctly folded RNA motifs in sequence space, calculated on computational grids.

Although functional RNA molecules are known to be biased in overall composition, the effects of background composition on the probability of finding a particular active site by chance has received little attention. The probability of finding a particular motif has important implications both for understanding the distribution of functional RNAs in ancient and modern organisms with varying genome compositions and for tuning SELEX pools to optimize the chance of finding specific functions. Here we develop a new method for calculating the probability of finding a modular motif containing base-paired regions, and use a computational grid to fold several hundred million random RNA sequences containing the core elements of the isoleucine aptamer and the hammerhead ribozyme to estimate the probability that a sequence containing these structural elements will fold correctly when isolated from background sequences of different compositions. We find that the two motifs are most likely to be found in distinct regions of compositional space, and that the regions of greatest abundance are influenced by the probability of finding the conserved bases, finding the flanking helices, and folding, in that order of importance. Additionally, we can refine our estimates of the number of random sequences required for a 50% probability of finding an example of each site in unbiased random pools of length 100 to 4.1 x 10(9) for the isoleucine aptamer and 1.6 x 10(10) for the hammerhead ribozyme. These figures are consistent with the facile recovery of these motifs from SELEX experiments.