Transcallosal connectivity and cortical rhythms: findings in children with spina bifida

Magnetoencephalography and normal pressure hydrocephalus: A case report

A 82-year-old male experiencing headaches, dementia, urinary incontinence and gait instability was diagnosed with normal pressure hydrocephalus (NPH) and underwent a resting state magnetoencephalography (MEG) examination. MEG data were recorded in a magnetically shielded room with a whole-head 122 channel biomagnetometer. Following MEG, a ventriculoperitoneal (VP) shunt was placed in his head and greatly improved his symptomatology. Spontaneous MEG recordings revealed lower magnetic fields at frontal and frontotemporal regions compared to central and posterior regions. This finding correlated well with the significant ventricular distention, and specifically the enlargement of the frontal horns of the lateral ventricles, observed in presurgical CT. The regional pattern of MEG signal decrease in NPH seems to be quite different from that encountered in brain atrophy. In the latter case, a more generalized distribution of low magnetic fields is observed, possibly reflecting the high sensitivity of MEG to activity originating in sulci. Acquired data suggest that MEG may be able to differentiate between NPH and brain atrophy. Furthermore, MEG could potentially constitute a non-invasive, non-imaging tool, useful in the selection of patients with NPH to undergo shunt surgery. The findings of this study warrant further research in patient groups before firm conclusions can be drawn.

Structure, integrity, and function of the hypoplastic corpus callosum in spina bifida myelomeningocele

Although there are many studies of people with complete or partial hypogenesis of the corpus callosum (CC), little is understood about the hypoplastic CC in which all structures are present but thinned. Spina bifida myelomeningocele (SBM) is a model organism for such studies because many have either a hypogenetic or hypoplastic CC. We used diffusion tensor tractography (DTT) to evaluate the hypoplastic CC in SBM and its relation to interhemispheric functions and intelligence quotient (IQ). Participants were individuals with SBM and an intact or hypoplastic CC (n=28), who were compared to a typically developing comparison group (n=32). Total and regional DTT volume and integrity measures (fractional anisotropy, axial diffusivity, and radial diffusivity) of the CC were related to measures of intelligence (IQ), bimanual motor functioning, and dichotic auditory performance. As predicted, DTT showed variations in volume and integrity that were maximized in the entire CC and the posterior CC. IQ correlated with entire CC volume, anterior and posterior regional CC volumes, and also with measures of integrity. Bimanual motor functioning correlated with the anterior and posterior volumes of the CC but not with any integrity measures. Axial diffusivity in the posterior CC was negatively correlated with right ear dichotic listening performance. The hypoplastic CC is not macrostructurally or microstructurally intact in SBM, even when it appears radiologically intact. Both volume and integrity of the posterior regions were related to reductions in IQ and to interhemispheric processing. These findings may transfer to other disorders characterized by a hypoplastic CC.

Differential vulnerability of white matter structures to experimental infantile hydrocephalus detected by diffusion tensor imaging

PURPOSE

The differential vulnerability of white matter (WM) to acute and chronic infantile hydrocephalus and the related effects of early and late reservoir treatment are unknown, but diffusion tensor imaging (DTI) could provide this information. Thus, we characterized WM integrity using DTI in a clinically relevant model.

METHODS

Obstructive hydrocephalus was induced in 2-week-old felines by intracisternal kaolin injection. Ventricular reservoirs were placed 1 (early) or 2 (late) weeks post-kaolin and tapped frequently based solely on neurological deficit. Hydrocephalic and age-matched control animals were sacrificed 12 weeks postreservoir. WM integrity was evaluated in the optic system, corpus callosum, and internal capsule prereservoir and every 3 weeks using DTI. Analyses were grouped as acute (<6 weeks) or chronic (≥6 weeks).

RESULTS

In the corpus callosum during acute stages, fractional anisotropy (FA) decreased significantly with early and late reservoir placement (p = 0.0008 and 0.0008, respectively), and diffusivity increased significantly in early (axial, radial, and mean diffusivity, p = 0.0026, 0.0012, and 0.0002, respectively) and late (radial and mean diffusivity, p = 0.01 and 0.0038, respectively) groups. Chronically, the corpus callosum was thinned and not detectable by DTI. FA was significantly lower in the optic chiasm and tracts (p = 0.0496 and 0.0052, respectively) with late but not early reservoir placement. In the internal capsule, FA in both reservoir groups increased significantly with age (p < 0.05) but diffusivity remained unchanged.

CONCLUSIONS

All hydrocephalic animals treated with intermittent ventricular reservoir tapping demonstrated progressive ventriculomegaly. Both reservoir groups demonstrated WM integrity loss, with the CC the most vulnerable and the optic system the most resilient.

Interhemispheric effective and functional cortical connectivity signatures of spina bifida are consistent with callosal anomaly

The impact of the posterior callosal anomalies associated with spina bifida on interhemispheric cortical connectivity is studied using a method for estimating cortical multivariable autoregressive models from scalp magnetoencephalography data. Interhemispheric effective and functional connectivity, measured using conditional Granger causality and coherence, respectively, is determined for the anterior and posterior cortical regions in a population of five spina bifida and five control subjects during a resting eyes-closed state. The estimated connectivity is shown to be consistent over the randomly selected subsets of the data for each subject. The posterior interhemispheric effective and functional connectivity and cortical power are significantly lower in the spina bifida group, a result that is consistent with posterior callosal anomalies. The anterior interhemispheric effective and functional connectivity are elevated in the spina bifida group, a result that may reflect compensatory mechanisms. In contrast, the intrahemispheric effective connectivity is comparable in the two groups. The differences between the spina bifida and control groups are most significant in the θ and α bands.

Brain mechanisms for reading and language processing in spina bifida meningomyelocele: a combined magnetic source- and structural magnetic resonance imaging study

OBJECTIVE

The development of the ability to process spoken and written language depends upon a network of left hemisphere temporal, parietal, and frontal regions. The present study explored features of brain organization in children with spina bifida meningomyelocele (SBM) and shunted hydrocephalus, who commonly present with precocious development of word reading skills and preservation of vocabulary and grammar skills.

METHOD

Eight children with SBM were compared with 15 IQ and reading-level matched, typically developing controls on MRI-based morphometric and Magnetic Source Imaging-derived neurophysiological profiles.

RESULTS

Children with SBM showed reduced magnetic activity in left inferior parietal regions during spoken word recognition and pseudoword reading tasks. We also noted reduced surface area/volume in inferior parietal and posterior temporal regions in SBM and increased gray matter volumes in left middle frontal regions and gyral complexity in left posterior temporal and inferior parietal regions.

CONCLUSIONS

A complex pattern of changes in cortical morphology and activation may serve as evidence for structural and functional brain reorganization ensuring preservation of language and decoding abilities in children with SBM.