Posterior Midbody Research Articles

Abnormal Development of the Corpus Callosum in Autism Spectrum Disorder: An MRI Study.

Altered size in the corpus callosum (CC) has been reported in individuals with autism spectrum disorder (ASD), but few studies have investigated younger children. Moreover, knowledge about the age-related changes in CC size in individuals with ASD is limited. Our objective was to investigate the age-related size of the CC and compare them with age-matched healthy controls between the ages of 2 and 18 years. Structural-weighted images were acquired in 97 male patients diagnosed with ASD; published data were used for the control group. The CC was segmented into 7 distinct subregions (rostrum, genu, rostral body, anterior midbody, posterior midbody, isthmus, and splenium) as per Witelson's technique using ITK-SNAP software. We calculated both the total length and volume of the CC as well as the length and height of its 7 subregions. The length of the CC measures was studied as both continuous and categorical forms. For the continuous form, Pearson's correlation was used, while categorical forms were based on age ranges reflecting brain expansion during early postnatal years. Differences in CC measures between adjacent age groups in individuals with ASD were assessed using a Student t-test. Mean and standard deviation scores were compared between ASD and control groups using the Welch t-test. Age showed a moderate positive association with the total length of the CC (r = 0.43; Padj = 0.003) among individuals with ASD. Among the subregions, a positive association was observed only in the anterior midbody of the CC (r = 0.41; Padj = 0.01). No association was found between the age and the height of individual subregions or with the total volume of the CC. In comparison with healthy controls, individuals with ASD exhibited shorter lengths and heights of the genu and splenium of the CC across wide age ranges. Overall, our results highlight a distinct abnormal developmental trajectory of CC in ASD, particularly in the genu and splenium structures, potentially reflecting underlying pathophysiological mechanisms that warrant further investigation.

Prenatal ultrasound reassessment of the corpus callosum based on cortical connectivity information

IntroductionRoutine prenatal ultrasound assessment of the corpus callosum (CC) does not reflect information on fibrous connections. The primary purpose was to construct detailed reference ranges of quantitative characteristics of the foetal CC based on cortical connectivity information. Secondary goals were to examine for sex differences and assess the validity of the measurement technique for cases with CC dysplasia.Material and methodsPregnant women referred to a tertiary centre for sonographic examination were recruited to undergo a detailed foetal scan from 19 to 40 weeks. The foetal CC was divided into 5 distinct segments using the Hofer & Frahm classification technique. The thickness of each segment and the overall length of the CC were measured. Additionally, a segmental evaluation was conducted on partial agenesis of the CC. The inter- and intraobserver variability were assessed by interclass correlation coefficients. Regression analysis was used to determine the association between the biological measurements and gestational age.ResultsA total of 852 foetuses (403 males and 449 females) were included in the final analysis. Intra- and interobserver reliability coefficients ranged from 0.86 to 0.98 and 0.84 to 0.97, respectively. Reference ranges were established for the thickness and length of its segments. We observed that the biometric measurements of the foetal CC showed a curvilinear increase with gestational age. There was a statistically significant sex effect for the CC. At the average gestation age 29.6 weeks, the genu, anterior midbody, posterior midbody, and isthmus of male foetuses were 0.06280 mm, 0.04435 mm, 0.01731 mm, and 0.01556 mm, respectively, thicker than those of female foetuses, whereas the splenium of the female foetus was 0.06583 mm thicker than the male foetus.ConclusionsThe study uncovers distinct patterns of thickness and length growth in the foetal CC and establishes precise reference ranges. These findings can aid in evaluating normal brain development and conducting comprehensive assessments of CC abnormalities.

Abnormal microstructure of corpus callosum in children with primary nocturnal enuresis: a DTI study.

Primary nocturnal enuresis (PNE) is a common childhood disorder with abnormal sleep or arousal. The corpus callosum (CC) continues to develop into adulthood and plays an important role in sleep arousal. This study aimed to evaluate the microstructure of the CC in children with PNE. Diffusion tensor imaging (DTI) indices were extracted throughout the CC and its seven subregions were compared between the children with PNE and healthy children (HC). The correlation between abnormal DTI indices of the CC and cognitive condition was also tested. Compared to HC, decreased fiber number (NF) (F = 8.492, PFDR = 0.032) and fractional anisotropy (FA) value (F = 8.442, PFDR = 0.040) were found in the posterior midbody of the CC, increased RD was found in the posterior midbody (F = 6.888, PFDR = 0.040) and isthmus (F = 7.967, PFDR = 0.040) in children with PNE. The reduction of FA value was more obvious in boys than girls with PNE. In children with PNE, there was a significant positive correlation between the NF of the posterior midbody and full IQ (r = 0.322, P = 0.025) and between the FA value and the general knowledge memory (r = 0.293, P = 0.043). This study provides imaging evidence for abnormalities in the microstructure of the CC in children with PNE, especially in male PNE, which might affect the children's cognitive performance.

Aberrant interhemispheric structural and functional connectivity within whole brain in schizophrenia

ObjectiveSchizophrenia is a serious mental disorder whose etiology remains unclear. Although numerous studies have analyzed the abnormal gray matter functional activity and whole-brain anatomical changes in schizophrenia, fMRI signal fluctuations from white matter have usually been ignored and rarely reported in the literature. MethodsWe employed 45 schizophrenia subjects and 75 healthy controls (HCs) from a publicly available fMRI dataset. By combining the voxel-mirrored homotopic connectivity (VMHC) measure and fiber tracking method, we investigated the interhemispheric functional and structural connectivity within whole brain in schizophrenia. ResultsCompared to HCs, patients with schizophrenia exhibited significantly reduced VMHC in the bilateral middle occipital gyrus, precentral gyrus, postcentral gyrus and corpus callosum. Fiber tracking results showed the changes in structural connectivity for the bilateral precentral gyrus, and the bilateral corpus callosum, and the fiber bundles connecting bilateral precentral gyrus and connecting the bilateral corpus callosum passed through the posterior midbody, isthmus and splenium of mid-sagittal corpus callosum, which closely related to the interhemispheric integration of visual and auditory information. More importantly, we observed a negative correlation between averaged VMHC values in the postcentral gyrus and SAPS scores, and a positive correlation between the fractional anisotropy of fiber bundle connecting the bilateral precentral gyrus and Matrix Reasoning scores in schizophrenia. ConclusionOur findings provide a novel perspective of white matter functional images on understanding abnormal interhemispheric visual and auditory information transfer in schizophrenia.

Widening the clinical, radiological and genetic spectrum of autosomal recessive ataxia of Charlevoix-Saguenay in Indian patients.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS), classically presenting as a triad of early-onset cerebellar ataxia, lower extremity spasticity and peripheral neuropathy, is caused by mutations in SACS gene which encodes the protein sacsin. To provide new insight into the occurrence of SACS mutations in South India. Patients with three cardinal features of ARSACS-peripheral neuropathy, cerebellar ataxia, and pyramidal tract signs were included. Nine patients were clinically identified and genetically evaluated. Mutation screening of SACS by targeted sequencing of 40 recessive ataxia genes panel by next-generation sequencing was conducted. Additional investigations included magnetic resonance imaging (MRI), fundoscopy, optical coherence tomography (OCT) and nerve conduction studies (NCS). Functional disability was assessed by the Spinocerebellar Degeneration Functional Score. Two hundred and fifteen cerebellar ataxia patients were screened, and 9 patients with cerebellar ataxia with spasticity, peripheral neuropathy and MRI brain characteristics, consistent with a clinical diagnosis of ARSACS were identified, of which 7 patients were identified to have mutation in the SACS gene and are detailed hereafter. Age of presentation ranged from 20 to 55years (29.8 ± 11.9) with a mean disease duration of 12.7years (SD-7.65, range 5-22years). All except one had onset of symptoms in the form of an ataxic gait noticed before 20years of age. Additional features were subnormal intelligence (4/7), slow and hypometric saccades (1/7), seizures (1/7), kyphoscoliosis (1/7) and dysmorphic facies (1/7). SDFS was 3 in 5/7 patients signifying moderate disability with independent ambulation. MRI showed cerebellar atrophy with predominant atrophy of the superior vermis (7/7), horizontal linear T2 hypointensities in the pons(7/7), hyperintensities where lateral pons merges with the middle cerebellar peduncle (MCP) (7/7) well seen in fluid-attenuated inversion recovery (FLAIR) images, thickening of MCP (3/7), symmetric lateral thalamic hyperintensities (6/7), posterior fossa arachnoid cyst (4/7),thinning of posterior mid-body of corpus callosum (7/7), marginal mineralisation of the basal ganglia (7/7), bilateral parietal atrophy (7/7) and thinning of corticospinal tract on diffusion tensor imaging (DTI) (7/7). We identified pathogenic homozygous frameshift mutations in the SACS gene in six patients (including two siblings), while one patient had a heterozygous pathogenic deletion. This is the largest series of genetically confirmed ARSACS patients from India highlighting the clinical, ophthalmological, imaging and genetic features of this cohort.

Benefits of Meniscal Repair in Selected Patients Aged 60 Years and Older.

Background:Little is known about the benefits and outcomes of meniscal repair in patients older than 60 years.Purpose:To (1) report the clinical and radiographic outcomes of meniscal repair in patients aged ≥60 years and compare them with matched patients who underwent meniscectomy and (2) identify procedural failures.Study Design:Cohort study; Level of evidence, 2.Methods:We included 32 knees in 32 patients aged ≥60 years (20 female, 12 male; mean age, 64.5 ± 4.6 years) who underwent meniscal repair surgery at a single medical institution between 2010 and 2020. Patients were matched according to age, sex, body mass index, and meniscal tear type with a comparison cohort who underwent meniscectomy (n = 49 patients [49 knees]; 32 female, 17 male). For all patients, demographic information, clinical history, physical examination findings, treatment details, and radiographic images were reviewed and analyzed. At final follow-up (mean, 42.2 months; range, 13-128 months), patients completed the 2000 International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, Knee injury and Osteoarthritis Outcome Score (KOOS), and Lysholm score. Clinical failure was defined as revision surgery and/or progression to total knee arthroplasty (TKA). A matched-pairs t test was used to analyze differences between the 2 treatment groups, and Kaplan-Meier analysis was used to determine the rates of knee osteoarthritis and progression to TKA.Results:The majority of patients had a medial meniscal tear (72.8%), whereas the lateral meniscus was torn in 27.2% of cases. Most tears were located in the meniscal root (56.8%), followed by the posterior horn (34.6%) and midbody (8.6%). At final follow-up, all outcome scores were higher in the repair group compared with the meniscectomy group (IKDC, 78.9 ± 13.4 vs 56.0 ± 15.4; KOOS, 86.6 ± 11.9 vs 61.7 ± 16.2; Lysholm, 88.3 ± 13.3 vs 68.7 ± 15.2, respectively; P < .001 for all). Clinical failure was observed in 22% of patients in the repair group.Conclusion:All clinical outcome scores were higher in the meniscal repair group compared with the matched meniscectomy group at final follow-up. The clinical failure rate of the repair group was 22%. These findings support meniscal repair in selected patients aged ≥60 years.

Impact of chronic exposure to legacy environmental contaminants on the corpus callosum microstructure: A diffusion MRI study of Inuit adolescents

Exposure to environmental contaminants is an important public health concern for the Inuit population of northern Québec, who have been exposed to mercury (Hg), polychlorinated biphenyls (PCBs) and lead (Pb). During the last 25 years, the Nunavik Child Development Study (NCDS) birth cohort has reported adverse associations between these exposures and brain function outcomes. In the current study, we aimed to determine whether contaminant exposure is associated with alterations of the corpus callosum (CC), which plays an important role in various cognitive, motor and sensory function processes. Magnetic resonance imaging (MRI) was administered to 89 NCDS participants (mean age ± SD = 18.4 ± 1.2). Diffusion-weighted imaging was assessed to characterize the microstructure of the CC white matter in 7 structurally and functionally distinct regions of interest (ROIs) using a tractography-based segmentation approach. The following metrics were computed: fiber tract density, fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD). Multiple linear regression models adjusted for sex, age, current alcohol/drug use and fish nutrients (omega-3 fatty acids and selenium) were conducted to assess the association between diffusion-weighted imaging metrics and Hg, PCB 153 and Pb concentrations obtained at birth in the cord blood and postnatally (mean values from blood samples at 11 and 18 years of age). Exposures were not associated with fiber tract density. Nor were significant associations found with cord and postnatal blood Pb concentrations for FA. However, pre- and postnatal Hg and PCB concentrations were significantly associated with higher FA of several regions of the CC, namely anterior midbody, posterior midbody, isthmus, and splenium, with the most pronounced effects observed in the splenium. FA results were mainly associated with lower RD. This study shows that exposure to Hg and PCB 153 alters the posterior microstructure of the CC, providing neuroimaging evidence of how developmental exposure to environmental chemicals can impair brain function and behavior in late adolescence.

Aberrant callosal morphology in ex-smokers.

Cigarette smoking is associated with widespread structural alterations in both brain hemispheres as well as of the corpus callosum (i.e., the brain's main interhemispheric white matter pathway). While similar hemispheric alterations have also been reported in ex-smokers, no study has yet examined the corpus callosum in ex-smokers. We compared callosal morphology in a sample of 107 ex-smokers (57 males/50 females) and 193 non-smokers (73 males/120 females), aged between 42 and 97 years. More specifically, we measured the total callosal area as well as seven callosal subregions using the Witelson parcellation scheme. At uncorrected levels, we detected significantly smaller callosal areas in ex-smokers than in non-smokers within the posterior midbody, genu, and isthmus (albeit the latter only on a trend level). When applying corrections for multiple comparisons, only the effect within the posterior midbody remained significant. Our findings suggest a weaker interhemispheric connectivity in ex-smokers compared to non-smokers, specifically between frontal and temporal areas.

Brain dysmorphologies associated with Alzheimer disease in Down syndrome

Down syndrome (DS) is a genetic disorder occurring in 1 out of every 700 to 1,000 live births caused by trisomy of chromosome 21. The overexpression of the Amyloid Precursor Protein (APP) gene located on this chromosome leads to an early onset and rapid accumulation of ß‐amyloid (Aß) in the brain that invariably results in Alzheimer Disease (AD) in people with DS. Therefore, AD, the most common form of dementia, is currently one of the most relevant medical issues in people with DS. In this study, we assessed brain morphological patterns to quantify dysmorphologies associated with AD in Down syndrome.Brain shape and size analyses were performed using Geometric Morphometrics in a sample of 243 adults, including 153 euploid healthy controls (EU) and 90 individuals with DS at different stages of dementia: asymptomatic DS with no signs of AD‐related cognitive impairment (N=58), individuals with DS and prodromal AD (N=21) and individuals diagnosed with AD dementia (N=11). A set of 38 3D brain landmarks representing the overall shape of the brain and internal brain structures (ventricles, corpus callosum, cerebellum and pons) were located on magnetic resonance images of the head.Results showed a significant separation between EU and DS populations based on both global and local brain shape and size analyses. Individuals with DS displayed a smaller cerebellum, a protruding posterior midbody in the corpus callosum, a frontally projected brain and expanded ventricles. Significant brain shape differences were detected in individuals diagnosed with AD, which mainly affected the shape of enlarged brain ventricles. Remarkably, individuals at advanced stages of the disease displayed more severe dysmorphologies as compared to those individuals at prodromal stages and individuals with no signs of dementia, confirming a phenotypic continuum associated with the severity of dementia that highlights the impact of this neurodegenerative disorder in brain morphology.

Prenatal antidepressant exposure and sex differences in neonatal corpus callosum microstructure.

Prenatal exposure to selective serotonin reuptake inhibitor (SSRI) antidepressants may influence white matter (WM) development, as previous studies report widespread microstructural alterations and reduced interhemispheric connectivity in SSRI-exposed infants. In rodents, perinatal SSRIs had sex-specific disruptions in corpus callosum (CC) axon architecture and connectivity; yet it is unknown whether SSRI-related brain outcomes in humans are sex specific. In this study, the neonate CC was selected as a region-of-interest to investigate whether prenatal SSRI exposure has sex-specific effects on early WM microstructure. On postnatal day 7, diffusion tensor imaging was used to assess WM microstructure in SSRI-exposed (n=24; 12 male) and nonexposed (n=48; 28 male) term-born neonates. Fractional anisotropy was extracted from CC voxels and a multivariate discriminant analysis was used to identify latent patterns differing between neonates grouped by SSRI-exposure and sex. Analysis revealed localized variations in CC fractional anisotropy that significantly discriminated neonate groups and correctly predicted group membership with an 82% accuracy. Such effects were identified across three dimensions, representing sex differences in SSRI-exposed neonates (genu, splenium), SSRI-related effects independent of sex (genu-to-rostral body), and sex differences in nonexposed neonates (isthmus-splenium, posterior midbody). Our findings suggest that CC microstructure may have a sex-specific, localized, developmental sensitivity to prenatal SSRI exposure.

Improvement in callosal disconnection syndrome with recovery of callosal connectivity

ABSTRACT Recent advancements in radiological techniques have enabled the observation of the topographic distribution of the human corpus callosum. However, its functional connectivity remains to be elucidated. The symptoms of callosal disconnection syndrome (CDS) can potentially reveal the functional connections between the cerebral hemispheres. Herein, we report a patient with CDS, whose callosal lesion was restricted to the posterior midbody, isthmus, and an anterior part of the dorsal splenium. A 53-year-old right-handed woman demonstrated CDS following cerebral infarction associated with subarachnoid hemorrhage. She exhibited CDS including ideomotor apraxia, and tactile anomia with the left hand, cross-replication of hand postures, cross-localization of the fingers, and constructional impairment with the right hand. Six months after onset, the left-handed ideomotor apraxia on imitation improved, but that to command did not, which indicated the difference in the nature of the transcallosal connections between ideomotor apraxia on imitation and ideomotor apraxia to command. Longitudinal CDS observation and corpus callosum tractography will prove useful in expanding our understanding of the nature of the organization of interhemispheric information transference.

Morphological alterations of the corpus callosum in antipsychotic-naive first-episode schizophrenia before and 1-year after treatment

ObjectiveThe corpus callosum (CC) is known to be altered in patients with schizophrenia. However, its morphologic characteristics are less well studied in treatment-naive first-episode schizophrenia patients, as is the effect of antipsychotic treatment on this structure. MethodsT-1 weighted MRI scans were obtained from 160 antipsychotic-naïve first-episode schizophrenia patients (AN-FES) and 155 healthy controls (HCs) before treatment initiation. Among the patients, forty-four were available for follow-up studies after one year of antipsychotic treatment, and were divided into good-outcome (n = 31) and poor-outcome subgroups (n = 13) based on whether there was a 50% reduction in Positive and Negative Symptom Scale (PANSS) total scores from baseline. A computer algorithm was applied to automatically identify the mid-sagittal plane (MSP) and obtain morphological measurement parameters of the CC. ResultsCompared with HCs, AN-FES patients showed a significant reduction of thickness in the posterior midbody of the CC. This deficit was correlated with severity of negative symptoms. After one year of antipsychotic treatment, there was no significant change in CC morphological measurements in schizophrenia patients, nor was there a significant difference of CC morphological measurements between good-outcome and poor-outcome subgroups at baseline or at 1-year follow-up. ConclusionThickness of the posterior midbody of the CC is reduced in the early course of schizophrenia before treatment. This alteration was not affected by antipsychotic treatment and was unrelated to treatment outcome at 1-year.

Control of drop attacks with selective posterior callosotomy: Anatomical and prognostic data

ObjectiveIn a previous proof of concept study, selective posterior callosotomy achieved similar degree of control of drop attacks as total callosotomy, while sparing prefrontal interconnectivity. The present study aims to confirm this finding in a larger cohort and to provide anatomical and prognostic data. MethodsFifty-one patients with refractory drop attacks had selective posterior callosotomy and prospective follow up for a mean of 6.4 years. Twenty-seven patients had post-operative magnetic resonance imaging (MRI) and 18 had tractography (DTI) of remaining callosal fibers. Pre and postoperative falls were quantified and correlated with demographic, clinical and imaging data. ResultsMean monthly frequency of drop attacks had a 95 % reduction, from 297 before to 16 after the procedure. Forty- one patients (80 %) had either complete or greater than 90 % control of the epileptic falls. Age and duration of epilepsy at surgery correlated with outcome (p values, respectively, 0.042 and 0.005). Mean index of callosal section along the posterior-to-anterior axis was 53.5 %. Extending the posterior section anterior to the midbody of the corpus callosum did not correlate with seizure control (p 0.91), providing fibers interconnecting the primary motor (M1) and caudal supplementary motor areas (SMA) were sectioned. Only one patient had a notable surgical complication which resolved in two days. ConclusionsThis level III cohort study with objective outcome assessment confirms that selective posterior callosotomy is safe and effective to control epileptic falls. Younger patients with smaller duration of epilepsy have better results. A posterior section contemplating the splenium, isthmus and posterior half of the body (posterior midbody) seems sufficient to achieve complete or almost complete control of drop attacks.

Evaluation of Ideal Extent of Corpus Callosotomy Based on the Location of Intracallosal Motor Fibers

The corpus callosotomy (CCT) has been reported as an effective procedure to alleviate drop attacks. However, the extent of CCT remains debatable. Classical studies suggest that motor fibers traverse mainly through the anterior half of the corpus callosum (CC), although recent diffusion tensor imaging studies described that motor fibers crossed the CC in a more posterior location, emphasizing the posterior midbody and the isthmus. Cortical and subcortical structures were examined in 30 hemispheres prepared for white matter fiber dissection. Dissections were carried out under surgical magnification to trace fibers originating from the primary motor cortex and their course through the CC. The distance of the most anterior and posterior motor fibers to the tip of the genu were measured, and the extent of CCT enabling disconnection of all motor fibers was calculated. Motor fibers coursed through the posterior half of the CC in the majority of hemispheres, mainly locating in posterior midbody and the isthmus. Callosal fibers should be interrupted to an average of 61% ± 0.07% point of the CC to reach the anterior limit of motor fibers and to an average of 69% ± 0.07% point to include posterior limit of motor fibers. Motor fibers were extending until the posterior one third of the CC in 22 specimens. Anterior-half CCT did not include all motor fibers in any specimen. Anterior two thirds CCT disrupted all motor fibers in one fourth of the cases. Our findings suggest that an ideal CCT should extend to the posterior midbody and isthmus of the CC.

Statistical shape analysis of corpus callosum in restless leg syndrome

ABSTRACT Objectives In this study we aimed to investigate corpus callosum shape differences between restless leg syndrome patients and healthy controls, and to determine whether disease severity and duration are indicators for corpus callosum deformation in RLS patients. Methods This study was conducted using the magnetic resonance imaging scans of 33 restless leg syndrome patients and 33 control subjects. Landmarks were marked on the digital images and callosal landmark coordinate data were used to assess shape difference by performing Generalized Procrustes analysis. The shape deformation from controls to the patients was evaluated performing the Thin Plate Spline approach. Results There was a statistically significant shape difference between the groups. Highest deformation was determined at the posterior midbody of the corpus callosum. Growth curve analyses showed that with the increase in disease duration and severity, the CC size decreased. Discussion The present study demonstrated callosal shape differences in restless leg syndrome using a landmark-based geometric morphometric approach, considering the topographic distribution of corpus callosum for the first time.

Regional callosal integrity and bilaterality of limb weakness in amyotrophic lateral sclerosis

Background and Objectives: The corpus callosum is a site of pathological involvement in the neurodegenerative disorder amyotrophic lateral sclerosis (ALS). The corpus callosum shows widespread cortical connectivity topographically distributed along its length. Initial limb weakness in ALS is typically unilateral, becoming bilateral with disease progression. The precise anatomical substrate for this spread is uncertain. The present study investigated sub-regional variations in corpus callosum integrity in ALS, and whether these reflect a relationship with the development of unilateral or bilateral limb weakness. Methods: Sporadic ALS patients were categorized into unilateral (n = 14) or bilateral (n = 25) limb weakness at the time of assessment and underwent diffusion tensor imaging. Probabilistic bundle-specific tracking was carried out using MRtrix and TractSeg to parcellate the corpus callosum into seven anatomical segments (rostrum; genu; rostral body; anterior midbody; posterior midbody; isthmus; splenium). White matter tract integrity was assessed in all segments and compared with MRI data acquired from 25 healthy controls. Results: In the combined patient group, the most prominent differences in diffusivity metrics were in the rostral body, posterior midbody and isthmus of the corpus callosum (p < 0.04). Loss of corpus callosum integrity was most prominent in the sub-group with unilateral limb weakness at the time of scanning (p < 0.05). Conclusions: Corpus callosum involvement in ALS is detectable across multiple segments, in keeping with a widespread cortical distribution of pathology. The association of unilateral limb weakness with greater loss of corpus callosum integrity informs connectivity-based hypotheses of symptom propagation in ALS.

Meniscal Injury Does Not Significantly Affect the Dimensions of the Intact Meniscus in the Opposite Compartment of the Knee.

Background:Meniscal allograft transplant requires precise matching of the size of the allograft with the dimensions of the recipient knee. Estimation of contralateral meniscal size on magnetic resonance imaging (MRI) has been considered the ideal method to measure menisci before transplant. We questioned whether a contralateral intact meniscus with meniscal injury in the opposite compartment could be used as a reference to determine allograft size. Our question was derived from knowledge of meniscal injury influencing structures of the opposite compartment of the knee, including the meniscus.Purpose:To compare meniscal dimensions between intact meniscus with meniscal injury in the opposite compartment and normal meniscus with a normal opposite compartment.Study Design:Cross-sectional study; Level of evidence, 3.Methods:This observational, cross-sectional study was performed between 2016 and 2017. The control group consisted of 200 knees with normal medial and lateral menisci. The medial intact group consisted of 150 cases of medial intact meniscus with injured lateral meniscus, and the lateral intact group consisted of 150 cases of lateral intact meniscus with injured medial meniscus. All patients were male. Mean age, height, and weight did not differ among groups. We investigated meniscal dimensions on MRI, including anteroposterior and mediolateral lengths, distance between the anterior and posterior horns (AHPH distance), and widths and heights of the anterior and posterior horns and midbody.Results:Most medial meniscal dimensions were similar between the control and medial intact groups, but the AHPH distance was smaller in the medial intact group (P < .001). Likewise, most lateral meniscal dimensions were similar between the control and lateral intact groups, but the AHPH distance was smaller in the lateral intact group (P < .001).Conclusion:Most dimensions of the intact meniscus with meniscal injury in the opposite compartment were similar to those of the normal meniscus with normal opposite compartment. Measuring the dimensions of the contralateral intact meniscus with meniscal injury in the opposite compartment on MRI can be an appropriate method to determine meniscal allograft size.

Myelin Water Imaging and Transcranial Magnetic Stimulation Suggest Structure-Function Relationships in Multiple Sclerosis

Demyelination can be assessed structurally by magnetic resonance imaging and functionally with transcranial magnetic stimulation. Here we combined these techniques to investigate demyelination of the corpus callosum in multiple sclerosis. Our objective was to determine if corpus callosal demyelination impacts transcallosal inhibition (TCI). TCI is a brief suppression of voluntary activity in the primary motor cortex elicited by stimulation of the homologous region of the contralateral hemisphere, which is assumed to be transmitted via the corpus callosum. Magnetic resonance imaging and transcranial magnetic stimulation were performed in 26 participants with MS and 10 controls. Myelin water fraction (MWF) was measured in five regions of the corpus callosum and compared with the onset latency, duration, and depth of TCI as measured by electromyography at the forearm. Callosal MWF was greatest posteriorly compared to other regions of the corpus callosum. Lower MWF in MS compared to controls was more pronounced in the posterior corpus callosum. MS participants had a prolonged TCI duration (p=0.016), which correlated with EDSS (p=0.020) and disease duration (p=0.045). In MS, TCI depth correlated negatively with the MWF of the posterior callosal midbody (p=0.039), a region thought to mediate TCI transmission. In summary, TCI duration was increased in MS and demyelination of the posterior corpus callosum midbody was associated with measurable functional changes. This work demonstrates the potential for combining magnetic resonance imaging and transcranial magnetic stimulation with electromyography to draw insights about structure-function relationships in MS pathophysiology.

High-resolution imaging of distinct human corpus callosum microstructure and topography of structural connectivity to cortices at high field.

Characterization of the microstructural properties and topography of the human corpus callosum (CC) is key to understanding interhemispheric neural communication and brain function. In this work, we tested the hypothesis that high-resolution T1 relaxometry at high field has adequate sensitivity and specificity for characterizing microstructural properties of the human CC, and elucidating the structural connectivity of the callosal fibers to the cortices of origin. The high-resolution parametric T1 images acquired from healthy subjects (N = 16) at 7T clearly showed a consistent T1 distribution among individuals with substantial variation along the human CC axis, which is highly similar to the spatial patterns of myelin density and myelinated axon size based on the histology study. Compared to the anterior part of the CC, the posterior midbody and splenium had significantly higher T1 values. In conjunction with T1-based classification method, the splenial T1 values were decoded more reliably compared to a conventional partitioning method, showing a much higher T1 value in the inferior splenium than in the middle/superior splenium. Moreover, the T1 profile of the callosal subdivision represented the topology of the fiber connectivity to the projected cortical regions: the fibers in the posterior midbody and inferior splenium with a higher T1 (inferring a larger axon size) were mainly connected to motor-sensory and visual cortical areas, respectively; in contrast, the fibers in the anterior/posterior CC with a lower T1 (inferring a smaller axon size) were primarily connected to the frontal/parietal-temporal areas. These findings indicate that high-resolution T1 relaxometry imaging could provide a complementary and robust neuroimaging tool, useful for exploring the complex tissue properties and topographic organization of the human corpus callosum.

Diffusion tensor imaging reveals microstructural alterations in corpus callosum and associated transcallosal fiber tracts in adult macaques with neonatal hippocampal lesions.

To investigate the effects of neonatal hippocampal lesions on the microstructural integrity of the corpus callosum (CC) in adulthood, macaque monkeys (n = 5) with neonatal bilateral neurotoxic hippocampal lesion (Neo-Hibo) and sham-operated controls (Neo-C, n = 5) were scanned using magnetic resonance diffusion tensor imaging (DTI) technique at 8-10 years old. CC was segmented into seven regionsgrouped into anterior CC (rostrum, genu, rostral body and anterior midbody) and posterior CC (posterior midbody, isthmus and splenium) for data analysis. Associated transcallosal fiber tracts were delineated using probabilistic tractography and evaluated with tract-based spatial statistics (TBSS). Neo-Hibo lesions resulted in significant increased diffusivity indices (mean, axial and radial diffusivity) in CC posterior segments. Also, significant decreased fractional anisotropy (FA) and increased diffusivity indices were seen in the associated transcallosal fiber tracts proximal to motor, posterior parietal and retrosplenial cortices. In Neo-Hibo animals, increased mean diffusivity (MD) in posterior midbody negatively correlated with reduction of CC surface areaand the magnitude of their memory impairments was significantly correlated with FA in transcallosal fiber tracts across splenium. Although no microstructural changes were observed in CC anterior segments, changes in FA values and diffusivity indices were observed in the white matter fibers of the ventromedial prefrontal cortex. Thus, Neo-H lesions resulted in enduring degradation in transcallosal fibers proximal to parietal and retrosplenial cortices, and hemispheric connections through posterior CC. The findings may provide complementary information for understanding the neural substrate of behavioral and cognitive deficits observed in patients with early insult to the hippocampus.