Females follow a more "compact" early human brain development model than males. A case-control study of preterm neonates

The pattern of sexual differentiation of the human brain is not well understood, particularly at the early stages of development when intense growth and multiple maturational phenomena overlap and interrelate. A case-control study of 20 preterm males and females matched for age was conducted. Three-dimensional images were acquired with 3 T MRI. The cerebral volume and the cortical folding area (FA), defined as the surface area of the interface between cortical gray and white matter, were compared between males and females. Females had smaller cerebra than males even after removing the influence of overall size differences between the subjects. The cortical FA increased in relation to volume by a power of 4/3 in both groups. Females had larger cortical FA compared with males with similar cerebral volumes. The study provides in vivo evidence of sexually dimorphic early human brain development. The relatively more "compact" female model may well relate to sex differences in neural circuitry and cognitive domains.

Magnetic Resonance Imaging of Cells Overexpressing MagA, an Endogenous Contrast Agent for Live Cell Imaging

Molecular imaging with magnetic resonance imaging (MRI) may benefit from the ferrimagnetic properties of magnetosomes, membrane-enclosed iron biominerals whose formation in magnetotactic bacteria is encoded by multiple genes. One such gene is MagA, a putative iron transporter. We have examined expression of MagA in mouse neuroblastoma N2A cells and characterized their response to iron loading and cellular imaging by MRI. MagA expression augmented both Prussian blue staining and the elemental iron content of N2A cells, without altering cell proliferation, in cultures grown in the presence of iron supplements. Despite evidence for iron incorporation in both MagA and a variant, MagAE137V, only MagA expression produced intracellular contrast detectable by MRI at 11 Tesla. We used this stable expression system to model a new sequence for cellular imaging with MRI, using the difference between gradient and spin echo images to distinguish cells from artifacts in the field of view. Our results show that MagA activity in mammalian cells responds to iron supplementation and functions as a contrast agent that can be deactivated by a single point mutation. We conclude that MagA is a candidate MRI reporter gene that can exploit more fully the superior resolution of MRI in noninvasive medical imaging.

Magnetic resonance imaging of cells overexpressing MagA, an endogenous contrast agent for live cell imaging

Molecular imaging with magnetic resonance imaging (MRI) may benefit from the ferrimagnetic properties of magnetosomes, membrane-enclosed iron biominerals whose formation in magnetotactic bacteria is encoded by multiple genes. One such gene is MagA, a putative iron transporter. We have examined expression of MagA in mouse neuroblastoma N2A cells and characterized their response to iron loading and cellular imaging by MRI. MagA expression augmented both Prussian blue staining and the elemental iron content of N2A cells, without altering cell proliferation, in cultures grown in the presence of iron supplements. Despite evidence for iron incorporation in both MagA and a variant, MagAE137V, only MagA expression produced intracellular contrast detectable by MRI at 11 Tesla. We used this stable expression system to model a new sequence for cellular imaging with MRI, using the difference between gradient and spin echo images to distinguish cells from artifacts in the field of view. Our results show that MagA activity in mammalian cells responds to iron supplementation and functions as a contrast agent that can be deactivated by a single point mutation. We conclude that MagA is a candidate MRI reporter gene that can exploit more fully the superior resolution of MRI in noninvasive medical imaging.

Muscle metabolism and acid-base status during exercise in forearm work-related myalgia measured with31P-MRS

In this study, we examined muscle metabolic and acid-base status during incremental wrist extension exercise in the forearm of individuals with work-related myalgia (WRM). Eighteen women employed in full-time occupations involving repetitive forearm labor were recruited in this cross-sectional study. Nine of these women were diagnosed with WRM, while the other nine had no previous WRM history and were used as age-matched controls (Con). Phosphorus-31 magnetic resonance spectroscopy (31P-MRS) was used to noninvasively monitor the intracellular concentrations of phosphocreatine ([PCr]) and inorganic phosphate ([Pi]) as well as intracellular pH (pHi) status during exercise in WRM and Con. We observed a 38% decreased work capacity in WRM compared with Con [0.18 W (SD 0.03) vs. 0.28 W (SD 0.10); P = 0.007]. Piecewise linear regression of the incremental exercise data revealed that the onset of a faster decrease in pHi(i.e., the pH threshold, pHT) and the onset of a faster increase in log([Pi]/[PCr]) (i.e., the phosphorylation threshold, PT) occurred at a 14% relatively lower power output in WRM [pHT: 45.2% (SD 5.3) vs. 59.0% (SD 4.6), P < 0.001; PT: 44.8% (SD 4.3) vs. 57.8% (SD 3.1), P < 0.001; % of peak power output, Con vs. WRM, respectively]. Monoexponential modeling of the kinetics of [PCr] and pHirecovery following exercise demonstrated a slower ( P = 0.005) time constant (τ) for [PCr] in WRM [113 s (SD 25)] vs. Con [77 s (SD 23)] and a slower ( P = 0.007) τ for pHiin WRM [370 s (SD 178)] vs. Con [179 s (SD 52)]. In conclusion, our results suggest that WRM is associated with an increased reliance on nonoxidative metabolism. Possible mechanisms include a reduction in local muscle blood flow and perfusion, an increased ATP cost of force production, or both.

Changes in cerebral oxygen consumption and high-energy phosphates during early recovery in hypoxic-ischemic piglets: a combined near-infrared and magnetic resonance spectroscopy study

Near-infrared spectroscopy (NIRS) offers the ability to assess brain function at the bedside of critically ill neonates. Our group previously demonstrated a persistent reduction in the cerebral metabolic rate of oxygen (CMRO(2)) after hypoxia-ischemia (HI) in newborn piglets. The purpose of this current study was to determine the causes of this reduction by combining NIRS with magnetic resonance spectroscopy (MRS) to measure high-energy metabolites and diffusion-weighted imaging to measure cellular edema. Nine piglets were exposed to 30 min of HI and nine piglets served as controls. Proton and phosphorous MRS spectra, apparent diffusion coefficient (ADC) maps, and CMRO(2) measurements were collected periodically before and for 5.5 h after HI. A significant decrease in CMRO(2) (26 +/- 7%) was observed after HI. Incomplete recovery of nucleotide triphosphate concentration (8 +/- 3% <controls) and reduced ADC (16 +/- 5%) suggested mitochondrial dysfunction. However, CMRO(2) did not correlate with any metabolite concentration during the last 3 h of the recovery period, and no significant changes were found in phosphocreatine and lactate levels. Therefore, the CMRO(2) decrease is likely a combination of impaired mitochondrial function and reduced energy demands during the acute phase, which has been previously observed in the mature brain.

The effect of forearm posture on wrist flexion in computer workers with chronic upper extremity musculoskeletal disorders

Background

Occupational computer use has been associated with upper extremity musculoskeletal disorders (UEMSDs), but the etiology and pathophysiology of some of these disorders are poorly understood. Various theories attribute the symptoms to biomechanical and/or psychosocial stressors. The results of several clinical studies suggest that elevated antagonist muscle tension may be a biomechanical stress factor. Affected computer users often exhibit limited wrist range of motion, particularly wrist flexion, which has been attributed to increased extensor muscle tension, rather than to pain symptoms. Recreational or domestic activities requiring extremes of wrist flexion may produce injurious stress on the wrist joint and muscles, the symptoms of which are then exacerbated by computer use. As these activities may involve a variety of forearm postures, we examined whether changes in forearm posture have an effect on pain reports during wrist flexion, or whether pain would have a limiting effect on flexion angle.

Methods

We measured maximum active wrist flexion using a goniometer with the forearm supported in the prone, neutral, and supine postures. Data was obtained from 5 subjects with UEMSDs attributed to computer use and from 13 control subjects.

Results

The UEMSD group exhibited significantly restricted wrist flexion compared to the control group in both wrists at all forearm postures with the exception of the non-dominant wrist with the forearm prone. In both groups, maximum active wrist flexion decreased at the supine forearm posture compared to the prone posture. No UEMSD subjects reported an increase in pain symptoms during testing.

Conclusion

The UEMSD group exhibited reduced wrist flexion compared to controls that did not appear to be pain related. A supine forearm posture reduced wrist flexion in both groups, but the reduction was approximately 100% greater in the UEMSD group. The effect of a supine forearm posture on wrist flexion is consistent with known biomechanical changes in the distal extensor carpi ulnaris tendon that occur with forearm supination. We infer from these results that wrist extensor muscle passive tension may be elevated in UEMSD subjects compared to controls, particularly in the extensor carpi ulnaris muscle. Measuring wrist flexion at the supine forearm posture may highlight flexion restrictions that are not otherwise apparent.

Phenolic acid content and composition in leaves and roots of common commercial sweetpotato (Ipomea batatas L.) cultivars in the United States

Phenolic acids in commercially important sweet potato cultivars grown in the United States were analyzed using reversed-phase high-performance liquid chromatography (HPLC). Caffeic acid, chlorogenic acid, 4,5-di-O-caffeoylquinic acid, 3,5-di-O-caffeoylquinic acid, and 3,4-di-O-caffeoylquinic acid were well separated with an isocratic elution in less than 25 min compared to about 120 min for analyzing and re-equilibrating the column with a gradient method. The isocratic elution order of these caffeoylquinic acid derivatives was confirmed by LC-MS/MS. Chlorogenic acid was the highest in root tissues, while 3,5-di-O-caffeoylquinic acid and/or 4,5-di-O-caffeoylquinic acid were predominant in the leaves. Steam cooking resulted in statistically nonsignificant increases in the concentration of total phenolics and all the individual phenolic acids identified. Sweetpotato leaves had the highest phenolic acid content followed by the peel, whole root, and flesh tissues. However, there was no significant difference in the total phenolic content and antioxidant activity between purees made from the whole and peeled sweet potatoes.

Optimization of 3D MP-RAGE for neonatal brain imaging at 3.0 T

Three-dimensional (3D) magnetic resonance imaging (MRI) has shown great potential for studying the impact of prematurity and pathology on brain development. We have investigated the potential of optimized T1-weighted 3D magnetization-prepared rapid gradient-echo imaging (MP-RAGE) for obtaining contrast between white matter (WM) and gray matter (GM) in neonates at 3 T. Using numerical simulations, we predicted that the inversion time (TI) for obtaining strongest contrast at 3 T is approximately 2 s for neonates, whereas for adults, this value is approximately 1.3 s. The optimal neonatal TI value was found to be insensitive to reasonable variations of the assumed T1 relaxation times. The maximum theoretical contrast for neonates was found to be approximately one third of that for adults. Using the optimized TI values, MP-RAGE images were obtained from seven neonates and seven adults at 3 T, and the contrast-to-noise ratio (CNR) was measured for WM versus five GM regions. Compared to adults, neonates exhibited lower CNR between cortical GM and WM and showed a different pattern of regional variation in CNR. These results emphasize the importance of sequence optimization specifically for neonates and demonstrate the challenge in obtaining strong contrast in neonatal brain with T1-weighted 3D imaging.

Apparent diffusion coefficient pseudonormalization time in neonatal hypoxic-ischemic encephalopathy

The apparent diffusion coefficient changes with time after hypoxic-ischemic brain injury. In this study, we quantitatively examined the relationship between the apparent diffusion coefficient and postnatal age for neonates with hypoxic-ischemic encephalopathy and poor outcome, and determined the postnatal age at which these values cannot be distinguished from those of neonates without hypoxic-ischemic encephalopathy (pseudonormalization time). Diffusion-weighted brain images were obtained from clinical scans of term neonates with hypoxic-ischemic encephalopathy and poor outcome (12 neonates, 23 scans) and from control subjects (30 neonates, 31 scans). The correlation between apparent diffusion coefficient and postnatal age was investigated for several brain regions. Pseudonormalization times were determined (1) from the intersection of the regression lines for the hypoxic-ischemic encephalopathy and control groups, as well as (2) from intrasubject apparent diffusion coefficient changes between two scans within a small subgroup. Pseudonormalization times from the regression ranged from 8.3 +/- 1.9 days to 10.1 +/- 2.1 days. Slightly (approximately 1 day) longer values were obtained from the intrasubject analysis. The results suggest that, although abnormally decreased apparent diffusion coefficient values may be evident from approximately 2 days to almost 1 week of postnatal age, abnormally elevated values may not be apparent until late in the second week of life.

Efficacy of motion artifact reduction in neonatal DW segmented EPI at 3 T using phase correction by numerical optimization and segment data swapping

Segmented echoplanar imaging (EPI) is a potentially valuable acquisition method for neonatal diffusion-weighted imaging (DWI) due to the lower acoustic noise levels as well as reduced blurring and distortion associated with it, as compared with single-shot EPI. Reduced acoustic noise may be important for the safety of neonates. However, little information regarding the efficacy of segmented EPI motion correction schemes is available for the neonatal population. We quantitatively assessed the efficacy of a postprocessing technique for motion artifact reduction involving phase correction by nonlinear optimization, alone and in combination with a novel method of utilizing a second data set (referred to as segment data swapping). These methods were applied to three-directional eight-segment echoplanar DW images obtained from 13 sedated neonates and to nine-directional DW images from 3 unsedated neonates. For comparison, the efficacy of the nonlinear optimization method was also evaluated in four adults. Motion correction efficacy was quantified using the motion artifact-to-signal ratio (ASR). The median, 70th percentile and 90th percentile ASR values obtained from neonatal three-directional DWI using nonlinear optimization alone were 2.8%, 4.6% and 9.6%, respectively. Efficacy improved (P<.005), particularly in dealing with the images most difficult to correct, when the phase correction by numerical optimization was combined with segment data swapping (median ASR=1.9%, 70th percentile ASR=2.7%, 90th percentile ASR=4.3%). Similar results were obtained for nine-directional diffusion tensor imaging. Nonlinear optimization alone applied to adult images showed significantly (P<.001) lower ASR values (median ASR=0.9%, 70th percentile ASR=2.1%, 90th percentile ASR=4.1%), demonstrating the greater challenge in DWI of neonates with segmented EPI. In conclusion, phase correction by nonlinear optimization provides effective motion correction for neonatal DW eight-segment EPI, especially when used in conjunction with segment data swapping.

Effects of hyperventilation on phosphocreatine kinetics and muscle deoxygenation during moderate-intensity plantar flexion exercise

The effects of controlled voluntary hyperventilation (Hyp) on phosphocreatine (PCr) kinetics and muscle deoxygenation were examined during moderate-intensity plantar flexion exercise. Male subjects ( n = 7) performed trials consisting of 20-min rest, 6-min exercise, and 10-min recovery in control [Con; end-tidal Pco2(PetCO2) ∼ 33 mmHg] and Hyp (PetCO2∼17 mmHg) conditions. Phosphorus-31 magnetic resonance and near-infrared spectroscopy were used simultaneously to monitor intramuscular acid-base status, high-energy phosphates, and muscle oxygenation. Resting intracellular hydrogen ion concentration ([H+]i) was lower ( P < 0.05) in Hyp [90 nM (SD 3)] than Con [96 nM (SD 4)]; however, at end exercise, [H+]iwas greater ( P < 0.05) in Hyp [128 nM (SD 19)] than Con [120 nM (SD 17)]. At rest, [PCr] was not different between Con [36 mM (SD 2)] and Hyp [36 mM (SD 1)]. The time constant (τ) of PCr breakdown during transition from rest to exercise was greater ( P < 0.05) in Hyp [39 s (SD 22)] than Con [32 s (SD 22)], and the PCr amplitude was greater ( P < 0.05) in Hyp [26% (SD 4)] than Con [22% (SD 6)]. The deoxyhemoglobin and/or deoxymyoglobin (HHb) τ was similar between Hyp [13 s (SD 8)] and Con [10 s (SD 3)]; however, the amplitude was increased ( P < 0.05) in Hyp [40 arbitrary units (au) (SD 23)] compared with Con [26 au (SD 17)]. In conclusion, our results indicate that Hyp-induced hypocapnia enhanced substrate-level phosphorylation during moderate-intensity exercise. In addition, the increased amplitude of the HHb response suggests a reduced local muscle perfusion in Hyp compared with Con.

Prior exercise delays the onset of acidosis during incremental exercise

The effects of prior moderate- and prior heavy-intensity exercise on the subsequent metabolic response to incremental exercise were examined. Healthy, young adult subjects (n = 8) performed three randomized plantar-flexion exercise tests: 1) an incremental exercise test (approximately 0.6 W/min) to volitional fatigue (Ramp); 2) Ramp preceded by 6 min of moderate-intensity, constant-load exercise below the intracellular pH threshold (pHT; Mod-Ramp); and 3) Ramp preceded by 6 min of heavy-intensity, constant-load exercise above pHT (Hvy-Ramp); the constant-load and incremental exercise periods were separated by 6 min of rest. (31)P-magnetic resonance spectroscopy was used to continuously monitor intracellular pH, phosphocreatine concentration ([PCr]), and inorganic phosphate concentration ([P(i)]). No differences in exercise performance or the metabolic response to exercise were observed between Ramp and Mod-Ramp. However, compared with Ramp, a 14% (SD 10) increase (P < 0.01) in peak power output (PPO) was observed in Hvy-Ramp. The improved exercise performance in Hvy-Ramp was accompanied by a delayed (P = 0.01) onset of intracellular acidosis [Hvy-Ramp 60.4% PPO (SD 11.7) vs. Ramp 45.8% PPO (SD 9.4)] and a delayed (P < 0.01) onset of rapid increases in [P(i)]/[PCr] [Hvy-Ramp 61.5% PPO (SD 12.0) vs. Ramp 45.1% PPO (SD 9.1)]. In conclusion, prior heavy-intensity exercise delayed the onset of intracellular acidosis and enhanced exercise performance during a subsequent incremental exercise test.

Changes in tissue water content measured with multiple-frequency bioimpedance and metabolism measured with 31P-MRS during progressive forearm exercise

Multiple-frequency bioimpedance analysis (MFBIA) has been used to determine the cellular water composition in the human body. It is noninvasive and has demonstrated good correlations with other invasive measures of tissue water. However, the ability of this method to study transient changes in tissue water in specific muscle groups has not been explored. In this study, MFBIA was used to assess changes in forearm intracellular water (ICW), extracellular water (ECW), and total water (TW) in seven healthy volunteers during and after a progressive wrist flexion exercise protocol. In an identical trial, (31)P magnetic resonance spectroscopy ((31)P-MRS) was used to assess changes in intracellular pH and phosphocreatine (PCr). At the completion of exercise, forearm ICW increased 12.6% (SD 0.07, P = 0.003), TW increased 10.1% (SD 0.06, P = 0.005), and no significant changes were recorded for ECW. A significant correlation was found between the changes in intracellular pH and changes in ICW during exercise (r = -0.84, P = 0.018). With the use of regression analysis, average changes in P(i), PCr, and pH were found to predict changes in ICW (R(2) = 0.98, P = 0.005). In conclusion, MFBIA was sensitive enough to measure transient changes in the exercising forearm muscle. The changes seen were consistent with the hypothesis that intracellular acidification and PCr hydrolysis are important mediators of cellular osmolality and therefore may be responsible for the increased volume of water in the intracellular space that is often recorded after short-term high-intensity exercise.

Dual X-ray absorptiometry model for characterizing water in the human forearm using multiple frequency bioimpedance analysis

The purpose of this study was to develop a method for measuring intracellular (ICW) and extracellular water (ECW) in the human forearm using multiple frequency bioimpedance analysis (MFBIA). The approach was (i) to measure whole-body and forearm fat-free mass using dual X-ray absorptiometry (DXA); (ii) to use these measurements to estimate the fat-free mass (FFM) resistivity in both the forearm and in the whole body; and (iii) to use the ratio of these FFM resistivities to estimate the resistivity in the ICW and ECW compartments of the forearm. To first demonstrate the accuracy of the DXA software in differentiating lean body mass from fat and bone within a volume of tissue, ex-vivo bovine muscle tissue samples (n = 3) were used to approximate the physical properties of the human forearm. It was found that although the human whole-body software overestimates FFM, it was slightly underestimated by the small animal software. Using this technique, DXA measures of FFM were obtained from human volunteers (n = 11; age = 20 ± 5 years; height = 170 ± 12 cm; mass = 64 ± 16 kg). These measures were used in conjunction with MFBIA measures of impedance of the whole body and of the forearm to determine the resistivities of the ICW and ECW compartments of the forearm, namely 375.8 ± 25.2 Ωcm and 55.6 ± 3.7 Ωcm, respectively. These were used in MFBIA equations to calculate the ICW, ECW, and total arm water (TAW) volumes of the human forearm. The calculated TAW and the ECW (± SD) volume fraction (667.29 ± 200.15 mL and 0.169 ± 0.039 mL, respectively) were in agreement with literature values. MFBIA results were compared with those obtained using nuclear magnetic resonance relaxometry (NMRR). MFBIA was performed on 15 subjects before and after an intense maximal handgrip exercise to estimate changes in water volume in muscle. Following exercise, the total and intracellular water of the forearm increased on average by 8% ± 3% and 10% ± 4% (mean ± SD), respectively. In 5 healthy volunteers, MFBIA and NMRR were performed before and after a similar exercise of the forearm muscle. The changes with exercise of intracellular and total arm water volumes as measured by MFBIA were estimated. The percent increases in total water were found to be 9.4% ± 4.2% and 9.4% ± 2.6% and in intracellular water were found to be 10.6% ± 4.6% and 12.0% ± 2.8% (mean ± SD) for NMRR and MFBIA, respectively. The results show that the exercise-induced changes in ICW and TAW determined with the MFBIA model are consistent with those observed with NMRR and radiotracer literature.

Cross-relaxation bottleneck in water–lysozyme proton magnetization exchange

The proton spin-lattice relaxation parameters in natural and deuterated lysozyme solutions have been measured as a function of temperature (0-50 degrees C). The variation of the apparent magnitudes of the water proton magnetizations in the solutions with temperature indicates that magnetic coupling mixes protein and water proton magnetizations. The results are consistent with an exchange cross-relaxation model (Hills, B. P., Mol Phys 1992, 76, 489-508) in which the cross-relaxation acts between the labile and nonlabile protons, rather than between water and protein protons. Although this cross-relaxation pathway clearly affects the observed magnetization fractions in this protein solution, its influence on the relaxation rates is less apparent.

Characteristics of a MR-compatible ankle exercise ergometer for a 3.0 T head-only MR scanner

An exercise ergometer, for isometric or dynamic contraction of both dorsiflexion and/or plantarflexion exercise, was designed and constructed for a 3.0 T head-only MR scanner. The principal features of this MR-compatible ergometer include electronic devices for quantification of force (during isometric exercise) and angular displacement (during dynamic exercise), without any significant losses to external motions or frictions. The ergometer was also made to be adjustable for subject leg length and was designed for suspension within the bore of the magnet to eliminate transmission of force and vibration to the MR scanner. A description of the design and construction, as well as the important technical features, is presented herein.

Neonatal Brain: Regional Variability of in Vivo MR Imaging Relaxation Rates at 3.0 T—Initial Experience

PURPOSE

To retrospectively investigate regional in vivo magnetic resonance (MR) imaging transverse and longitudinal relaxation rates at 3.0 T in neonatal brain, the relationship between these rates, and their potential use for gray matter (GM) versus white matter (WM) tissue discrimination.

MATERIALS AND METHODS

Informed parental consent for performance of imaging procedures was obtained in each infant. Informed consent for retrospective image analysis was not required; ethics approval was obtained from institutional review board. At 3.0 T, R1 and R2 were measured in brain regions (frontal WM, posterior WM, periventricular WM, frontal GM, posterior GM, basal ganglia, and thalamus) in 13 infants with suspected neurologic abnormality (two term, 11 preterm). Maps of R1 and R2 were acquired with T1 by multiple readout pulses and segmented spin-echo echo-planar imaging sequences, respectively. Accuracy of R1 and R2 map acquisition methods was tested in phantoms by comparing them with inversion-recovery and spin-echo sequences, respectively. Statistical analysis included linear regression analysis to determine relationship between R1 and R2 and Wilcoxon signed rank test to investigate the potential for discrimination between GM and WM.

RESULTS

In phantoms, R1 values measured with T1 by multiple readout pulses sequence were 3%-8% lower than those measured with inversion recovery sequence, and R2 values measured with segmented echo-planar sequence were 1%-8% lower than those measured with spin-echo sequence. A strong correlation of 0.944 (P < .001) between R1 and R2 in neonatal brain was observed. For R2, relative differences between GM and WM were larger than were those for R1 (z = -2.366, P < .05). For frontal GM and frontal WM, (R2(GM) - R2(WM))/R2(WM) yielded 0.8 +/- 0.2 (mean +/- standard deviation) and (R1(GM) - R1(WM))/R1(WM) yielded 0.3 +/- 0.09.

CONCLUSION

Results at 3.0 T indicate that R1 decreases with increasing field strength, while R2 values are similar to those reported at lower field strengths. For neonates, R2 image contrast may be more advantageous than R1 image contrast for differentiation between GM and WM.

Uncomplicated intraventricular hemorrhage is followed by reduced cortical volume at near-term age

BACKGROUND

Intraventricular hemorrhage (IVH) is the most common brain injury among premature infants. Neonates with IVH are at greater risk of impaired neurodevelopmental outcomes, compared with those without IVH. IVH causes destruction of the germinal matrix and glial precursor cells, with possible effects on cortical development.

OBJECTIVE

To investigate cortical development after uncomplicated IVH (with no parenchymal involvement and no posthemorrhagic hydrocephalus). We hypothesized that uncomplicated IVH would be followed by reduced cortical volume among premature infants at near-term age.

METHODS

A prospective cohort study was conducted, with preset selection criteria. Infants with small-for-gestational age birth weight, congenital abnormalities or brain malformations, metabolic disorders, recurrent sepsis, or necrotizing enterocolitis were excluded. Also, infants with posthemorrhagic hydrocephalus, parenchymal involvement of hemorrhage, cystic periventricular leukomalacia, or persistent ventriculomegaly were excluded, on the basis of routine serial ultrasonographic assessments. Three-dimensional images were acquired for 23 infants at near-term age, with 3-T magnetic resonance imaging and a magnetization-prepared rapid gradient echo sequence. Image analysis and segmentation of the cerebrum in different tissue types were based on signal contrast and anatomic localization. The cortical gray matter (CGM), subcortical gray matter, white matter, and intraventricular cerebrospinal fluid volumes of 12 infants with uncomplicated IVH were compared with those of 11 infants without IVH, using multivariate analysis of variance.

RESULTS

The multivariate analysis of variance for the regional brain volumes in the 2 groups indicated significance (Wilks' lambda = 0.546). The CGM volume was significantly reduced in the IVH group (no-IVH group: 122 +/- 12.9 mL; IVH group: 102 +/- 14.6 mL; F = 13.218). This finding remained significant after testing for possible confounding factors and adjustment for size differences between the infants (F = 9.415). There was no difference in the volumes of subcortical gray matter, white matter, and cerebrospinal fluid.

CONCLUSIONS

This is the first study to document impaired cortical development after uncomplicated IVH. The impairment was demonstrated by a 16% reduction in cerebral CGM volume at near-term age. The finding supports concerns regarding possible glial precursor cell loss after germinal matrix IVH, but its clinical significance is still unclear. The alteration in brain development demonstrated in this report supports closer neurodevelopmental follow-up monitoring of preterm infants with uncomplicated IVH.