Evaluation of the extracardiac conduit modification of the Fontan operation for thrombus formation using magnetic resonance imaging.

BACKGROUND: The prevalence of thrombosis after the Fontan procedure depends upon the surgical technique used and the method of detection employed. Current investigations for thrombosis lack sensitivity and specificity or, in the paediatric population, require a general anaesthetic. We undertook a study to examine the feasibility of using magnetic resonance imaging (MRI) to detect thrombosis within the conduit, cardiac chambers and pulmonary arteries after the extracardiac conduit modification of the Fontan procedure. METHODS: Of the 50 children who had undergone this procedure at our institution between 1997 and 2002, 26 were eligible for, and 13 underwent, MRI study. The mean age was 10.2 years (range 8.2-16.8 years, median 9.5 years) and the average time from operation was 63 months (range 29-79 months, median 68 months). The mean age at Fontan operation was 4.9 years (range 2.1-10.5 years). Ten were on low dose aspirin, two were on warfarin and one was not anti-coagulated. In all cases, satisfactory imaging of the venous pathways and pulmonary arteries was obtained and there were no thrombi detected. CONCLUSIONS: We conclude that MRI is a potentially useful tool for the detection of thrombus in patients who have undergone the Fontan operation.

Mid-femur geometry and biomechanical properties in 15- to 18-yr-old female athletes.

PURPOSE: Right-leg mid-femur geometry and biomechanical indices of bone strength were compared among elite cyclists (CYC), runners (RUN), swimmers (SWIM), triathletes (TRI), and controls (C)-10 subjects per group. METHODS: Bone cross-sectional areas (CSA), volumes (Vol), and cross-sectional moments of inertia (CSMI) were assessed by magnetic resonance imaging (MRI), and cortical volumetric bone density (volBMD) was determined as the quotient of DXA-derived bone mineral content (BMC) and MRI-derived cortical bone volume. Bone strength index (BSI) was calculated as the product of cortical volBMD and CSMI. RESULTS: RUN had higher (P < 0.05) size- (femur length and body mass) adjusted (ANCOVA) cortical CSA than C, SWIM, and CYC; and higher size, age, and years of sport-specific training- (YST) adjusted cortical CSA than SWIM and CYC. TRI had higher (P < 0.05) size-adjusted CSA than SWIM. SWIM and CYC had significantly larger (P < 0.05) size-adjusted medullary cavity CSA than RUN and TRI, and the difference between CYC and RUN persisted after additional adjustment for age and YST. RUN had significantly (P < 0.05) greater size-adjusted CSMI and BSI than C, SWIM, and CYC; and higher size, age, and YST-adjusted CSMI and BSI than SWIM and CYC. Mid-femur areal bone mineral density (BMD) was significantly (P < 0.05) higher for RUN compared with CYC only, but there were no other differences among groups for BMC, bone volumes, or volumetric total or cortical BMD. CONCLUSIONS: Running, a weight-bearing exercise, is associated with more favorable geometric and biomechanical characteristics in relation to bone strength, compared with the weight supported activities of swimming and cycling. Differences may reflect skeletal adaptations to the specific mechanical-loading patterns inherent in these sports.

An investigation of neuronal integrity in severe paediatric traumatic brain injury.

Magnetic Resonance Spectroscopy (MRS) and its association with neuropsychological functioning was examined in the chronic injury phase of paediatric traumatic brain injury (TBI). Fifteen children, aged 10-16 years, with severe TBIs were compared with 15 controls, matched for age and gender. The TBI group was found to have significantly lower levels of -acetyl aspartate (NAA) and Choline (Cho) in the right frontal lobe and generally displayed reduced performances on neuropsychological tests. A correlation between metabolites and reaction times was also obtained. Findings indicate a role of proton MRS as a measure of neuronal integrity following severe paediatric TBI and suggest a potential association of MRS with specific neuropsychological impairments.

Effects of single-leg drop-landing exercise from different heights on skeletal adaptations in prepubertal girls: a randomized controlled study.

Few studies have explored osteogenic potential of prepubertal populations. We conducted a 28-week school-based exercise trial of single-leg drop-landing exercise with 42 prepubertal girls (6 to 10 years) randomly assigned to control (C), low-drop (LD) or high-drop (HD) exercise groups. The latter two groups performed single-leg drop-landings (3 sessions/week-1 and 50 landings/session-1) from 14 cm(LD) and 28 cm(HD) using the nondominant leg. Osteogenic responses were assessed using Dual Energy X-ray Absorptiometry (DXA). Single-leg peak ground-reaction impact forces (PGRIF) in a subsample ranged from 2.5 to 4.4 x body-weight (BW). No differences (p > .05) were observed among groups at baseline for age, stature, lean tissue mass (LTM), leisure time physical activity, or average daily calcium intake. After adjusting for covariates of body mass, fat mass and LTM, no differences were found in bone mineral measures or site-specific bone mineral density (BMD) at the hip and lower leg among exercise or control groups. Combining data from both exercise groups failed to produce differences in bone properties when compared with the control group. No changes were apparent for between-leg differences from baseline to posttraining. In contrast to some reports, our findings suggest that strictly controlled unimodal, unidirectional single-leg drop-landing exercises involving low-moderate peak ground-reaction impact forces are not osteogenic in the developing prepubertal female skeleton.

The effects of large neutral amino acid supplements in PKU: an MRS and neuropsychological study.

OBJECTIVE: To determine the effects of large neutral amino acid (LNAA) supplements on brain and plasma phenylalanine (Phe) levels and other metabolites in early treated subjects with classical phenylketonuria (PKU), and to investigate the relationship between these metabolites and neuropsychological performance. METHODS: This was a prospective, double blind, cross over study consisting of four two-week phases with a 4 week washout period. Sixteen subjects (7 males), with classical PKU were recruited into the study and completed all 4 phases. Each phase consisted of either the LNAA supplement or placebo, and either the patient's usual medical product or not. Subjects were instructed to follow their usual Phe restricted diet, maintain energy intake and complete a 3-day food record during each phase. At the end of each phase, brain Phe and other metabolites were measured by proton magnetic resonance spectroscopy (MRS), and plasma amino acids quantified. A detailed neuropsychological assessment was performed on the same day as the MRS and plasma collection. RESULTS: There was no correlation between plasma and brain Phe, but few of the plasma Phe readings were over 1200 micromol/L. Plasma Phe decreased with LNAA supplementation when patients were not taking their medical formula. LNAA supplementation had a specific impact on executive functions particularly in verbal generativity and cognitive flexibility. Measures of attention were better on medical product, with or without LNAA supplements. CONCLUSIONS: LNAA supplementation was associated with a trend to a lowering of plasma Phe levels. LNAA supplementation had a specific impact on executive functions particularly in verbal generativity and flexibility. For individuals already complying with diet and PKU medical product, additional supplementation with LNAA is of limited value. LNAA supplementation may be of benefit to those unable to comply with PKU medical product by reducing plasma Phe, perhaps by competing with Phe at the level of transport across the gut.

Enlarged temporal lobes in Turner syndrome: an X-chromosome effect?

Gender differences in brain morphology have previously been reported in the temporal lobe and an 'X-chromosome dosage effect' has been described in Turner syndrome (45,X). To examine this further, we investigated temporal lobe morphology, metabolism and function in nine children with non-mosaic Turner syndrome using magnetic resonance imaging, (1)H magnetic resonance spectroscopy and neuropsychological testing and compared outcomes with results from nine age-matched control girls (46,XX). Turner subjects were found to have significantly larger superior temporal lobes (P = 0.004) and middle temporal lobes (P = 0.047) than controls. The size of the temporal lobe was found to correlate negatively with temporal lobe choline-containing compounds suggesting that increased temporal lobe size is associated with larger cells and/or decreased dendrites. This suggests a developmental failure to prune neurons. The degree of enlargement correlates negatively with functional performance on temporal-lobe associated tasks, suggesting that the enlargement may be a compensatory mechanism, or possibly causative in the case of semantic fluency performance. These temporal lobe abnormalities are discussed with reference to genes which are absent in Turner syndrome and to hormonal differences between Turner syndrome subjects and 46,XX controls.

Familial, anthropometric, and metabolic associations of intramyocellular lipid levels in prepubertal males.

The cause of skeletal muscle insulin resistance is unclear, but high levels of intramyocellular lipids are often present in affected individuals. We aimed to establish the metabolic, familial, and anthropometric associations of intramyocellular lipid in a pediatric population. We studied 41 boys aged 6.9-9.9 y and 23 of their mothers by proton magnetic resonance spectroscopy. We related muscle lipid levels to important factors that define an increased risk of developing insulin resistance in adult life. There were significant associations between the boys' intramyocellular lipid and their waist circumference (r = 0.42, p = 0.007), body mass index SD score (r = 0.32, p = 0.04), weight SD score (r = 0.32, p = 0.04), glucose:insulin ratio (r= -0.59, p = 0.04), maternal log fasting insulin levels (r = 0.44, p = 0.04), maternal body mass index (r = 0.46, p = 0.03), and maternal intramyocellular lipid (r = 0.62, p = 0.003). In the 41 boys, waist circumference explained 19% of the variance in the boys' intramyocellular lipid. Maternal intramyocellular lipid explained 39% of the variance in the boys' intramyocellular lipid in the sub-group of 23 boys. Intramyocellular lipid levels have both metabolic and anthropometric associations in childhood. Before puberty, children develop or inherit muscle metabolic characteristics that are associated both with insulin resistance and risk factors for the development of insulin resistance syndrome in adult life.