MR evaluation of early myelination patterns in normal and developmentally delayed infants

This study demonstrates the ability of MR imaging to show progression of myelination in 64 infants and young children (ages 4 days to 36 months). T2-weighted spin-echo pulse sequences, frequently used for routine screening of intracranial disease, were used. Gray-white matter differentiation was seen in all patients, and changes occurring with age were documented. Three distinct patterns were seen, and age ranges were established for each pattern in developmentally normal children: (1) infantile (birth-6 months); (2) isointense (8-12 months); and (3) early adult (10 months onward). There was a statistically significant difference between the age ranges of the normal and developmentally delayed children showing all three patterns. These data should be helpful for identifying and following sequentially both infants with clinically suspected developmental delay and those with dysmyelinating or demyelinating disease.     

MR imaging assessment of myelination in the very preterm brain

BACKGROUND AND PURPOSE: MR imaging was performed in very preterm infants by using an MR imager in the neonatal intensive care unit. The aims of this study were to assess the development of myelination in the preterm brain based on MR imaging findings and to compare the ability of T1-weighted conventional spin-echo, inversion recovery fast spin-echo, and T2-weighted fast spin-echo MR imaging to show myelination in these infants. METHODS: MR imaging was performed for 26 preterm infants with a median gestational age of 28 weeks who had normal neurodevelopmental outcomes at 2 years corrected age. RESULTS: Myelin was evident in the gracile and cuneate nuclei and fasciculi, vestibular nuclei, cerebellar vermis, inferior and superior cerebellar peduncles, dentate nucleus, medial longitudinal fasciculus, medial geniculate bodies, subthalamic nuclei, inferior olivary nuclei, ventrolateral nuclei of the thalamus, decussation of the superior cerebellar peduncles, medial lemnisci, lateral lemnisci, and inferior colliculi at < or = 28 weeks gestational age. From this gestational age, myelination was not visualized at any new site until 36 weeks gestational age, when myelin was visualized in the corona radiata, posterior limb of the internal capsule, corticospinal tracts of the precentral and postcentral gyri, and lateral geniculate bodies. T2-weighted fast spin-echo MR imaging showed myelin in gray matter nuclei at an earlier gestational age than did T1-weighted conventional spin-echo or inversion recovery fast spin-echo MR imaging. T1-weighted conventional spin-echo MR imaging showed myelin earlier in some white matter tracts in the preterm brain. CONCLUSION: Myelination was evident in numerous gray and white matter structures in the very preterm brain. A knowledge of myelination milestones will allow delays to be detected at an early stage.     

Kidneys in infants and children: evaluation with MR

Magnetic resonance (MR) imaging was performed in 58 children aged 1 day to 17 years. In 43 patients with suspected renal abnormalities, the results of MR were compared with those obtained by ultrasonography, computed tomography, or excretory urography. The remaining 15 children with no known renal disease were initially imaged to define the appearance on MR images of the normal kidneys according to the child's age. The signal intensity from hilar adipose tissue increased with age; corticomedullary differentiation was best seen in younger children. Compared with other imaging modalities, MR added useful information in evaluating the complications associated with renal failure and in patients with renal neoplasms. The use of MR in children with possible renal disease is limited, and the modality should be used as an adjunct to renal ultrasonography in a carefully selected group of patients.     

Terminal zones of myelination: MR evaluation of children aged 20-40 months

BACKGROUND AND PURPOSE: MR imaging is the method of choice for assessment in vivo of the development of myelination of the human central nervous system. During the first months of life, the myelination process follows well-defined steps, whereas little information exists about the later phases of myelination. To improve our understanding of this aspect and to identify the specific sites involved in the process of myelination in its terminal phase, we evaluated normal MR brain studies in children aged 20-40 months. METHODS: We retrospectively evaluated 85 MR brain studies of 81 children aged 20-40 months who were without diseases potentially affecting white matter. The MR studies were performed with a 1.5-T system, with T2-weighted spin-echo and turbo spin-echo sequences. Subjective analysis of the signal intensity of the white matter was made in four areas: subcortical frontal, temporal, and parietal lobes and peritrigonal region. Extension of myelination was graded on an ordinal scale; 0 indicated the absence of myelin, and the maximum value indicated complete myelination. RESULTS: A persistent T2 hyperintensity of the subcortical areas was noted after 20 months of age. With advancing age, a progressive increase in the grade of myelination was noted in these regions, and at about 40 months of age myelination was complete. However, in most of our patients aged 20 months, myelination in the peritrigonal areas appeared complete. CONCLUSION: The only area that can still exhibit a persistent T2 hyperintensity on MR images at about 2 years of age is considered to be the peritrigonal region: the so-called terminal zone. At this age in our patients, however, a persistent T2 hyperintensity was noted in the frontotemporal subcortical regions. In these areas, the myelination appeared complete at 36-40 months of age. The so-called terminal zones were the subcortical areas rather than the peritrigonal area, and complete myelination took place by about age 3 years.     

Cerebral maturation in premature infants: quantitative assessment using MR imaging

BACKGROUND AND PURPOSE: The assessment of whether brain development is at an appropriate level for age has become an integral part of clinical MR reporting, although few studies have quantitatively defined the developmental changes occurring in premature infants. We have developed a simple scoring system to assess four parameters of cerebral maturation--myelination, cortical folding, glial cell migration, and germinal matrix distribution--to determine the total maturation score (TMS). The aim of this study was to validate this scoring system in a large population of preterm infants across a range of gestational ages. METHODS: A retrospective analysis was conducted of MR images acquired over a 3-year period with an identical imaging protocol. Infants born more than 14 days before the imaging examination and those with a clinical or radiologic history suggestive of neuroabnormality were excluded from the study. The TMS was derived by consensus. Interobserver agreement was evaluated by using the Bland-Altman plot. RESULTS: Images from 134 infants (23-41 weeks' gestational age) were evaluated. The TMS was significantly related to the postmenstrual age of the infant, with the mean TMS for each age group increasing with advancing postmenstrual age. Interobserver agreement was found to be high (mean difference in score = 0.07, SD = 0.56). CONCLUSION: This scoring system provides a standardized method for assessing cerebral maturation in the premature infant. The TMS is easy to calculate from standard MR images, is reproducible, and can help detect changes occurring within a postnatal age of a few weeks.     

Pelvic abnormalities in children: assessment with MR imaging

Multiplanar images of 62 pelvic lesions in 58 children and adolescents (aged 7 months to 19 years; mean, 10.6 years) were obtained with 0.3-T magnetic resonance (MR) imaging. Lesions were divided into three categories: congenital anomalies, cystic lesions and fluid collections, and neoplasms. MR demonstrated lesions well in all categories. Midline lesions were best imaged sagittally, and lesions of paired structures, axially. The coronal plane was useful in evaluating the superoinferior extent of lesions and in defining the extent of lymphadenopathy. T1-weighted sequences were sufficient to depict most congenital and cystic lesions. T2-weighted sequences were useful in demonstrating the extent of neoplasms and the position of ectopic gonads. Ultrasonography (US) was also performed in 45 cases. MR and US delineated lesions equally well in 25 cases (55.5%), MR was superior in 19 (42.4%), and US was superior in one (2.2%). Computed tomography (CT) was performed in 13 cases. MR and CT delineated lesions equally well in eight cases (61.5%), MR was superior in four (30.8%), and CT was superior in one (7.7%).     

Developmental delay in children: assessment with proton MR spectroscopy

BACKGROUND AND PURPOSE: The cause of developmental delay frequently is unknown, and clinicians and families can be frustrated by the lack of neuroimaging correlation especially when considering therapeutic options and long-term prognosis. We sought to determine if proton MR spectroscopy can depict abnormalities in patients with developmental delay who have structurally normal brain MR images. METHODS: Children with developmental delay who were older than 2 years (mean age, 5.0 years; range, 3.0-10.0 years) and those aged 2 years or younger (mean age, 1.5 years; range, 0.5-2.0 years) and age-matched control subjects for each patient group underwent brain MR imaging and proton MR spectroscopy. A point-resolved spectroscopy sequence (2000/144 [TR/TE]) was used. Voxels (8 cm(3)) were placed in the subcortical white matter of the frontal and parieto-occipital lobes bilaterally. N-acetylaspartate (NAA)/creatine (Cr) and choline (Cho)/Cr ratios were assessed. RESULTS: All patients had normal brain MR images. In children with developmental delay who were aged 2 years or younger, no statistically significant differences were detected in the NAA/Cr or Cho/Cr ratios compared with those of the control subjects. In children with developmental delay who were older than 2 years, decreases in the NAA/Cr ratio were observed in frontal (P <.001) and parieto-occipital (P <.017) subcortical white matter, and elevations in the Cho/Cr ratio were detected in the frontal (P <.24) and parieto-occipital (P <.002) subcortical white matter compared with age-matched control subjects. CONCLUSIONS: In children with developmental delay who are older than 2 years, proton MR spectroscopy depicted abnormalities in the NAA/Cr and Cho/Cr ratios. Proton MR spectroscopy should be performed as part of the neuroimaging evaluation of developmental delay. Further studies will be needed to determine if abnormalities detected with proton MR spectroscopy can be used as a diagnostic tool and neuroimaging marker to assess long-term functional outcome.     

MR of the cerebral operculum: abnormal opercular formation in infants and children.

PURPOSETo evaluate abnormalities of the cerebral operculum in infants and children and to propose the embryogenic basis of abnormal opercular formation as determined from MR imaging findings.METHODSEighty-six infants and children who had abnormally wide interopercular distances and/or distorted opercular topography seen on MR images were studied retrospectively. Clinically, patients presented with tonal abnormalities, macrocephaly, microcephaly, seizures, developmental delay, cerebral palsy, or facial dysmorphism. The abnormal opercula were compared with developing opercula at different stages of gestation.RESULTSAmong the 86 infants and children, two categories of opercular abnormalities were identified: an underdeveloped operculum (n = 64) and a malformed operculum (n = 22). The malformed operculum was further classified into three subtypes: nonformation of the operculum with lissencephaly (n = 1, 1%), abnormal opercular formation with pachygyria (n = 11, 13%), and nonformation or abnormal formation of the operculum without pachygyria or lissencephaly (n = 10, 12%). Two subtypes of the underdeveloped operculum were identified: an open operculum without a normal insula (n = 6, 7%) and an open operculum with a normal insula (n = 58, 67%). The five subtypes of abnormal opercular configuration showed a range of maturity that was comparable to the developing operculum at different ages.CONCLUSIONOpercular anomalies appear to follow sequentially predetermined normal steps in development. Arrest in opercular development or malformation may occur after an initial insult. MR imaging is the method of choice by which to identify these abnormalities.     

Postoperative complications in otospongiosis: usefulness of MR imaging.

BACKGROUND AND PURPOSE: Sensorineural hearing loss (SNHL) is a rare complication of stapes surgery that may arise for many reasons. Usually, the pathogenesis of SNHL can be established by clinical and CT examinations. The purpose of this study was to evaluate the utility of MR imaging when CT findings are normal or not contributive. METHODS: Eleven patients with SNHL (in some instances, associated with vertigo) after stapedectomy, in whom CT showed no well-defined cause, were examined by MR imaging. RESULTS: MR studies established the additional findings of reparative intravestibular granuloma (n = 2), intralabyrinthine hemorrhage (n = 1), and bacterial labyrinthitis (n = 1). In five cases, MR findings were similar to CT findings. In two cases, CT and MR results were normal. Revision surgery was performed in five patients and confirmed the MR findings in each case. CONCLUSION: If CT is not contributive as to the origin of SNHL and vertigo occurring after stapes surgery, then MR imaging may be helpful in these patients.     

Cranial bone marrow in children: assessment of normal development with MR imaging

Magnetic resonance images of cranial bone marrow in 238 patients (246 examinations) less than 25 years old were reviewed to establish normal age-related standards. Bone marrow in the clivus and calvaria had uniformly low signal intensity (grade 1) on T1-weighted images in most infants less than 1 year old. The number of patients with grade 1 marrow decreased rapidly in early childhood, while the number of patients with marrow of low and high signal intensity (grade 2) and uniformly high signal intensity (grade 3) gradually increased with age. A grade 1 marrow was no longer observed in either the clivus or calvaria after age 7. Most patients had a grade 3 marrow by age 15. Because bone marrow in certain pathologic conditions has decreased signal on T1-weighted images and therefore resembles grade 1 or 2 appearances of normal marrow in children, these results may be useful for differentiating normal and abnormal bone marrow signal intensities in infants and children.     

The changing MR imaging appearance of polymicrogyria: a consequence of myelination

BACKGROUND AND PURPOSE: During the review of MR studies of multiple patients with polymicrogyria (PMG), it was noted that the patterns of cortical abnormality differed significantly among affected patients. In particular, the cortex appeared very thin in some patients, but was thick in others. The purpose of the present study was to attempt to clarify the cause of the different imaging appearances. METHODS: T1- and T2-weighted images obtained in 17 patients (age range, 3 days to 43 years) with PMG diagnosed on the basis of imaging characteristics were retrospectively reviewed. One patient was examined four times over a period of 21 months. Particular attention was paid to the thickness and signal intensity of the cortex and underlying white matter and how these features varied with maturation of the cortex and white matter. RESULTS: T2-weighted images revealed two patterns of PMG. Pattern 1 showed small, fine, and undulating cortex with normal thickness (3-4 mm) in seven patients, all younger than 12 months; and pattern 2, a bumpy cortex that appeared abnormally thick (6-8 mm) and had an irregular cortical-white matter junction in seven patients older than 18 months. Both patterns were observed in four patients between 15 months and 2 years of age (ie, pattern 1 in the anterior frontal region and pattern 2 in the posterior frontal, parietal, or perisylvian regions). A layer of T2 prolongation (2-3 mm) was recognized between pattern 1 PMG and underlying myelinated white matter in four patients 11 months to 2 years of age. T1-weighted images showed either poor differentiation of the cortex and underlying white matter or pattern 2. Serial MR imaging in one patient depicted longitudinal changes of the PMG from pattern 1 to pattern 2. CONCLUSION: These findings suggest that the two appearances (thin and thick) of the cortex seen in PMG likely represent the same process, with the apparent difference being the result of myelination in subcortical and intracortical fibers that cause a change of the appearance and apparent thickness of PMG on T2-weighted images.     

Early assessment of brain maturation by MR imaging segmentation in neonates and premature infants

PURPOSE: We evaluated the impact of premature extrauterine life on brain maturation. PATIENTS AND METHODS: Twelve neonates underwent MR imaging at 40 (39.64 +/- 0.98) weeks (full term). Fifteen premature infants underwent 2 MR imaging examinations, after birth (preterm at birth) and at 40 weeks (41.03 +/- 1.33) (preterm at term). A 3D MR imaging technique was used to measure brain volumes compared with intracranial volume: total brain volume, cortical gray matter, myelinated white matter, unmyelinated white matter, basal ganglia (BG), and CSF. RESULTS: The average absolute volume of intracranial volume (269.8 mL +/- 36.5), total brain volume (246.5 +/- 32.3), cortical gray matter (85.53 mL +/- 22.23), unmyelinated white matter (142.4 mL +/-14.98), and myelinated white matter (6.099 mL +/-1.82) for preterm at birth was significantly lower compared with that for the preterm at term: the average global volume of intracranial volume (431.7 +/- 69.98), total brain volume (391 +/- 66,1), cortical gray matter (179 mL +/- 41.54), unmyelinated white matter (185.3 mL +/- 30.8), and myelinated white matter (10.66 mL +/- 3.05). It was also lower compared with that of full-term infants: intracranial volume (427.4 mL +/- 53.84), total brain volume (394 +/- 49.22), cortical gray matter (181.4 +/- 29.27), unmyelinated white matter (183.4 +/- 27.37), and myelinated white matter (10.72 +/- 4.63). The relative volume of cortical gray matter (30.62 +/- 5.13) and of unmyelinated white matter (53.15 +/- 4.8) for preterm at birth was significantly different compared with the relative volume of cortical gray matter (41.05 +/- 5.44) and of unmyelinated white matter (43.22 +/- 5.11) for the preterm at term. Premature infants had similar brain tissue volumes at 40 weeks to full-term infants. CONCLUSION: MR segmentation techniques demonstrate that cortical neonatal maturation in moderately premature infants at term and term-born infants was similar.     

MR imaging of the abdomen and pelvis in infants, children, and adolescents

Recent developments in magnetic resonance (MR) imaging have profoundly changed the investigation of abdominal and pelvic disease in pediatrics. Motion reduction techniques, such periodically rotated overlapping parallel lines with enhanced reconstruction, or PROPELLER, have resulted in reliable imaging with quiet breathing. Faster imaging sequences minimize artifact and allow for more efficient studies. Diffusion-weighted imaging has become increasingly important in the evaluation of neoplastic disease, depicting disease with increased cellularity and helping to differentiate benign from malignant masses. MR enterography helps visualize intra- and extraluminal bowel pathologic conditions. MR cholangiopancreatography can depict congenital and acquired causes of pancreatic and biliary abnormalities. MR urography is an effective technique for a one-stop-shop evaluation of structural urinary tract abnormality and renal function. Three-dimensional acquisitions allow volumetric display of structures from multiple angles. Specialized techniques allow quantification of iron and fat in the viscera in children with hemolytic anemia and obesity, respectively. This article covers current techniques and strategies to perform and optimize MR imaging of the abdomen and pelvis in infants, children, and adolescents and describes important practical applications.     

Accelerated myelination in early Sturge-Weber syndrome demonstrated by MR imaging

Magnetic resonance imaging of the brain in two infants with Sturge-Weber syndrome has demonstrated a pattern of accelerated myelination in the abnormal cerebral hemisphere. The extent of myelination was most apparent on the T1-weighted inversion recovery sequence while the T2-weighted images demonstrated concomitant changes in hydration of the brain. We propose an explanation for this finding based on cerebral ischemia underlying the leptomeningeal angioma.     

The usefulness of MR imaging in the diagnosis of dysembryoplastic neuroepithelial tumor in children: a study of 14 cases

BACKGROUND AND PURPOSE: Dysembryoplastic neuroepithelial tumors (DNTs) are benign lesions affecting children and are associated with epilepsy. The goal of our study was to better characterize the clinical-radiologic-pathologic spectrum of DNTs (complex and simple forms only) in a series of 14 children. METHODS: Clinical, neuroradiologic, and pathologic features of all cases were retrospectively studied. RESULTS: Eleven cases of complex and three cases of simple DNTs were identified. Mean follow-up was 87 months, and no recurrence was recorded except for one case of simple DNT. We found that some neuroradiologic features may be helpful to support the diagnosis of DNT: presence of "septations," triangular pattern of distribution, and absence of contrast enhancement. CONCLUSION: The evidence of the specific glioneuronal element is found by pathologic examination, but the typical neuroradiologic aspect of DNT suggests this diagnosis preoperatively. Radiologic examination may be helpful for the diagnosis of DNT when pathologic findings are inconclusive.