Functional neuroimaging to characterize visual system development in children with retinoblastoma

Pediatric abusive head trauma: visual outcomes, evoked potentials, diffusion tensor imaging, and relationships to retinal hemorrhages

PURPOSE

Function and anatomy of the visual system were evaluated in children with abusive head trauma (AHT). The relationships between retinal hemorrhages at presentation were examined with outcome measures.

METHODS

Retrospective review of data in children with AHT for 1) visual acuity at last follow-up, 2) visual evoked potentials (VEP) after recovery, 3) diffusion metrics of white matter tracts and grey matter within the occipital lobe on diffusion tensor imaging (DTI), and 4) patterns of retinal hemorrhages at presentation. Visual acuity was converted into logarithm of minimum angle of resolution (logMAR) after correction for age. VEPs were also scored by objective signal-to-noise ratio (SNR).

RESULTS

Of 202 AHT victims reviewed, 45 met inclusion criteria. Median logMAR was reduced to 0.8 (approximately 20/125 Snellen equivalent), with 27% having no measurable vision. Thirty-two percent of subjects had no detectable VEP signal. VEPs were significantly reduced in subjects initially presenting with traumatic retinoschisis or hemorrhages involving the macula (p < 0.01). DTI tract volumes were decreased in AHT subjects compared to controls (p < 0.001). DTI metrics were most affected in AHT victims showing macular abnormalities on follow-up ocular examination. However, DTI metrics were not correlated with visual acuity or VEPS. There was large inter-subject variability within each grouping.

DISCUSSION

Mechanisms causing traumatic retinoschisis, or traumatic abnormalities of the macula, are associated with significant long-term visual pathway dysfunction. AHT associated abnormalities of the macula, and visual cortical pathways were more fully captured by VEPs than visual acuity or DTI metrics.

Cerebral Visual Impairment Characterized by Abnormal Visual Orienting Behavior With Preserved Visual Cortical Activation

Purpose

Children with cerebral visual impairment (CVI) often have abnormal visual orienting behaviors due to impaired or damaged visual cortex. Alternatively, visual-cortical function is intact but visual information is not transformed downstream into an appropriate oculomotor output (visuomotor dysfunction). We examined visual, anatomic, and oculomotor assessments to distinguish visuomotor dysfunction from CVI associated with severely reduced visual-cortical response.

Methods

We reviewed the medical records from children with CVI having abnormal visual orienting behaviors, normal ocular examinations, and born near term. Relevant data were visual evoked potentials (VEPs), Teller card acuity, eye movements recorded by video-oculography (VOG), and neuroimaging (magnetic resonance imaging [MRI]) including diffusion tensor imaging (DTI) tractography.

Results

Thirty subjects had visuomotor dysfunction based on a normal VEP; of these 33% had a normal MRI and 67% had white matter abnormalities associated with metabolic disease and/or decreased volume of brain parenchyma. VOG recordings showed smooth pursuit gains were uniformly reduced and saccades were dysmetric but followed the main sequence. Ten subjects had severe CVI based on VEPs at noise levels; visual acuities and MRI findings overlapped those of the visuomotor dysfunction group. Developmental delay, seizures, microcephaly, and hypotonia were common across all groups. All subjects with an abnormal conventional MRI had abnormal metrics on DTI tractography from the occipital lobe.

Conclusions

A subset of patients with CVI have abnormal visual orienting behaviors despite a normal VEP (visuomotor dysfunction). A majority have abnormal white matter metrics on tractography suggesting a downstream defect in sensorimotor transformation. Clinically, visuomotor dysfunction is indistinguishable from severe CVI.

More than meets the eye: Longitudinal visual system neurodevelopment in very preterm children and anophthalmia

Anophthalmia, characterized by the absence of an eye(s), is a rare major birth defect with a relatively unexplored neuroanatomy. Longitudinal comparison of white matter development in an anophthalmic (AC) very preterm (VPT) child with both binocular VPT and full-term (FT) children provides unique insights into early neurodevelopment of the visual system. VPT-born neonates (<32wks gestational age), including the infant with unilateral anophthalmia, underwent neuroimaging every two years from birth until 8 years. DTI images (N = 168) of the optic radiation (OR) and a control track, the posterior limb of the internal capsule (PLIC), were analysed. The diameter of the optic nerves (ON) were analysed using T1-weighted images. Significant group differences in FA and AD were found bilaterally in the OR and PLIC. This extends the literature on altered white matter development in VPT children, being the first longitudinal study showing stable group differences across the 4, 6 and 8 year timepoints. AC showed greater deficits in FA and AD bilaterally, but recovered towards VPT group means from 4 to 8 years-of-age. Complete lack of binocular input would be responsible for these early deficits; compensatory mechanisms may facilitate structural improvement over time. AC's ON exhibited significant atrophy ipsilateral to the anophthalmic eye. Functionally, AC displayed normal visual acuity and form perception, but naso-temporal bias in motion perception. Following these groups and AC longitudinally enabled novel understanding of the joint influence of monocular vision and VPT birth on neurodevelopment.

Altered white matter structure in the visual system following early monocular enucleation

Partial visual deprivation from early monocular enucleation (the surgical removal of one eye within the first few years of life) results in a number of long-term morphological adaptations in adult cortical and subcortical visual, auditory, and multisensory brain regions. In this study, we investigated whether early monocular enucleation also results in the altered development of white matter structure. Diffusion tensor imaging and probabilistic tractography were performed to assess potential differences in visual system white matter in adult participants who had undergone early monocular enucleation compared to binocularly intact controls. To examine the microstructural properties of these tracts, mean diffusion parameters including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were extracted bilaterally. Asymmetries opposite to those observed in controls were found for FA, MD, and RD in the optic radiations, the projections from primary visual cortex (V1) to the lateral geniculate nucleus (LGN), and the interhemispheric V1 projections of early monocular enucleation participants. Early monocular enucleation was also associated with significantly lower FA bidirectionally in the interhemispheric V1 projections. These differences were consistently greater for the tracts contralateral to the enucleated eye, and are consistent with the asymmetric LGN volumes and optic tract diameters previously demonstrated in this group of participants. Overall, these results indicate that early monocular enucleation has long-term effects on white matter structure in the visual pathway that results in reduced fiber organization in tracts contralateral to the enucleated eye. Hum Brain Mapp 39:133-144, 2018. © 2017 Wiley Periodicals, Inc.

Reorganization of Visual Callosal Connections Following Alterations of Retinal Input and Brain Damage

Vision is a very important sensory modality in humans. Visual disorders are numerous and arising from diverse and complex causes. Deficits in visual function are highly disabling from a social point of view and in addition cause a considerable economic burden. For all these reasons there is an intense effort by the scientific community to gather knowledge on visual deficit mechanisms and to find possible new strategies for recovery and treatment. In this review, we focus on an important and sometimes neglected player of the visual function, the corpus callosum (CC). The CC is the major white matter structure in the brain and is involved in information processing between the two hemispheres. In particular, visual callosal connections interconnect homologous areas of visual cortices, binding together the two halves of the visual field. This interhemispheric communication plays a significant role in visual cortical output. Here, we will first review the essential literature on the physiology of the callosal connections in normal vision. The available data support the view that the callosum contributes to both excitation and inhibition to the target hemisphere, with a dynamic adaptation to the strength of the incoming visual input. Next, we will focus on data showing how callosal connections may sense visual alterations and respond to the classical paradigm for the study of visual plasticity, i.e., monocular deprivation (MD). This is a prototypical example of a model for the study of callosal plasticity in pathological conditions (e.g., strabismus and amblyopia) characterized by unbalanced input from the two eyes. We will also discuss the findings of callosal alterations in blind subjects. Noteworthy, we will discuss data showing that inter-hemispheric transfer mediates recovery of visual responsiveness following cortical damage. Finally, we will provide an overview of how callosal projections dysfunction could contribute to pathologies such as neglect and occipital epilepsy. A particular focus will be on reviewing noninvasive brain stimulation techniques and optogenetic approaches that allow to selectively manipulate callosal function and to probe its involvement in cortical processing and plasticity. Overall, the data indicate that experience can potently impact on transcallosal connectivity, and that the callosum itself is crucial for plasticity and recovery in various disorders of the visual pathway.

Spatiotemporal Patterns of Tumor Occurrence in Children with Intraocular Retinoblastoma

PURPOSE

To accurately map the retinal area covered by tumor in a prospectively enrolled cohort of children diagnosed with retinoblastoma.

METHODS

Orbital MRI in 106 consecutive retinoblastoma patients (44 bilateral) was analyzed. For MRI-visible tumors, the polar angle and angle of eccentricity of points defining tumor perimeter on the retina were determined by triangulation from images in three orthogonal planes. The centroid of the mapped area was calculated to approximate tumor origin, and the location and cumulative tumor burden were analyzed in relation to mutation type (germline vs. somatic), tumor area, and patient age at diagnosis. Location of small tumors undetected by MRI was approximated with fundoscopic images.

RESULTS

Mapping was successful for 129 tumors in 91 eyes from 67 patients (39 bilateral, 43 germline mutation). Cumulative tumor burden was highest within the macula and posterior pole and was asymmetrically higher within the inferonasal periphery. Tumor incidence was lowest in the superotemporal periphery. Tumor location varied with age at diagnosis in a complex pattern. Tumor location was concentrated in the macula and superonasal periphery in patients <5.6 months, in the inferotemporal quadrant of the posterior pole in patients 5.6-8.8 months, in the inferonasal quadrant in patients 8.8-13.2 months, and in the nasal and superotemporal periphery in patients >13.2 months. The distribution of MRI-invisible tumors was consistent with the asymmetry of mapped tumors.

CONCLUSIONS

MRI-based mapping revealed a previously unrecognized pattern of retinoblastoma localization that evolves with age at diagnosis. The structured spatiotemporal distribution of tumors may provide valuable clues about cellular or molecular events associated with tumorigenesis in the developing retina.

Cognitive function and social attainment in adult survivors of retinoblastoma: a report from the St. Jude Lifetime Cohort Study

BACKGROUND

Retinoblastoma has a 5-year survival rate exceeding 95%, yet little is known about long-term functional outcomes for these patients.

METHODS

Sixty-nine adult survivors of retinoblastoma (mean age, 33 years; mean years post-diagnosis, 31) who had enrolled in the St. Jude Lifetime Cohort Study completed clinical cognitive evaluations and questionnaires assessing adult social attainment. Scores on all cognitive measures were converted to z-scores (M = 0, SD = 1) using age-adjusted normative data. Multivariable linear regression analyses, adjusted for age at diagnosis and disease laterality, were used to examine associations between disease and treatment exposures and cognitive outcomes.

RESULTS

Retinoblastoma survivors performed within normative expectations across most cognitive domains. In multivariable models, adjusted for disease laterality, survivors diagnosed at ≤1 year of age performed significantly better on measures of short-term verbal memory (β = 0.87, P<.01), long-term verbal memory (β = 0.66, P = .02), verbal learning (β = 0.67, P = .02), and verbal reasoning abilities (β = 0.79, P<.01) compared with survivors diagnosed at >1 year of age. In multivariable models, restricted to bilateral survivors and adjusted for age at diagnosis, whole brain radiation exposure was significantly associated with poorer performance on tasks of short-term verbal memory (β = -0.003, P = .03) and long-term verbal memory (β = -0.003, P = .01). Reported social attainment was consistent with adult developmental expectations.

CONCLUSIONS

Adult survivors of retinoblastoma demonstrate few cognitive or social attainment deficits decades following diagnosis and treatment. Findings suggest the potential for neural reorganization following early insult to the visual system as well as vulnerability of the developing brain to low dose radiation exposure. Early intervention and rehabilitation will be important for these patients.

Increased cortical surface area and gyrification following long-term survival from early monocular enucleation

Purpose

Retinoblastoma is typically diagnosed before 5 years of age and is often treated by enucleation (surgical removal) of the cancerous eye. Here, we sought to characterize morphological changes of the cortex following long-term survival from early monocular enucleation.

Methods

Nine adults with early right-eye enucleation (≤48 months of age) due to retinoblastoma were compared to 18 binocularly intact controls. Surface area, cortical thickness, and gyrification estimates were obtained from T₁ weighted images and group differences were examined.

Results

Early monocular enucleation was associated with increased surface area and/or gyrification in visual (i.e., V1, inferior temporal), auditory (i.e., supramarginal), and multisensory (i.e., superior temporal, inferior parietal, superior parietal) cortices compared with controls. Visual cortex increases were restricted to the right hemisphere contralateral to the remaining eye, consistent with previous subcortical data showing asymmetrical lateral geniculate nucleus volume following early monocular enucleation.

Conclusions

Altered morphological development of visual, auditory, and multisensory regions occurs subsequent to long-time survival from early eye loss.

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Cortical morphology in early monocular enucleation was assessed.

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Enucleation resulted in increased surface area and gyrification of the cortex.

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Visual cortex increases were exhibited contralateral to the remaining eye.

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Non-visual cortex increases in surface area and gyrification were also found.

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Altered cortical development occurs following early monocular enucleation.

In vivo evaluation of optic nerve development in non-human primates by using diffusion tensor imaging

Developmental abnormalities of optic nerve are the leading cause of child blindness. The goal of this study was to use diffusion tensor imaging (DTI) to characterize the optic nerve development of non-human primates during the normal maturation from birth to adulthood. Forty healthy rhesus monkeys aged from 2 weeks to 6 years old were scanned with a clinical 3T scanner. It was demonstrated that the DTI parameters followed an exponential pattern during optic nerve maturation. The time constants of mean diffusivity (MD), fractional anisotropy (FA), axial diffusivity (λ∥) and radial diffusivity (λ⊥) were 16, 14, 18 and 15 months in rhesus monkeys, respectively. Significant decrease in RD was observed firstly at 12 months after birth (p<0.05). No significant differences were observed between the left and right optic nerves in any age group. The in vivo imaging results reveal the normal evolution patterns of DTI parameters during optic nerve maturation in primates. The data might be used as a reference in the examination of optic nerve developmental abnormalities or injury in children or preclinical studies.

Altered anterior visual system development following early monocular enucleation

PURPOSE

Retinoblastoma is a rare eye cancer that generally occurs before 5 years of age and often results in enucleation (surgical removal) of the cancerous eye. In the present study, we sought to determine the consequences of early monocular enucleation on the morphological development of the anterior visual pathway including the optic chiasm and lateral geniculate nucleus.

METHODS

A group of adults who had one eye enucleated early in life due to retinoblastoma was compared to binocularly intact controls. Although structural changes have previously been reported in late enucleation, we also collected data from one late enucleated participant to compare to our early enucleated participants. Measurements of the optic nerves, optic chiasm, optic tracts and lateral geniculate nuclei were evaluated from T1 weighted and proton density weighted images collected from each participant.

RESULTS

The early monocular enucleation group exhibited overall degeneration of the anterior visual system compared to controls. Surprisingly, however, optic tract diameter and geniculate volume decreases were less severe contralateral to the remaining eye. Consistent with previous research, the late enucleated participant showed no asymmetry and significantly larger volume decreases in both geniculate nuclei compared to controls.

CONCLUSIONS

The novel finding of an asymmetry in morphology of the anterior visual system following long-term survival from early monocular enucleation indicates altered postnatal visual development. Possible mechanisms behind this altered development include recruitment of deafferented cells by crossing nasal fibres and/or geniculate cell retention via feedback from primary visual cortex. These data highlight the importance of balanced binocular input during postnatal maturation for typical anterior visual system morphology.

Emerging structure-function relations in the developing face processing system

To evaluate emerging structure-function relations in a neural circuit that mediates complex behavior, we investigated age-related differences among cortical regions that support face recognition behavior and the fiber tracts through which they transmit and receive signals using functional neuroimaging and diffusion tensor imaging. In a large sample of human participants (aged 6-23 years), we derived the microstructural and volumetric properties of the inferior longitudinal fasciculus (ILF), the inferior fronto-occipital fasciculus, and control tracts, using independently defined anatomical markers. We also determined the functional characteristics of core face- and place-selective regions that are distributed along the trajectory of the pathways of interest. We observed disproportionately large age-related differences in the volume, fractional anisotropy, and mean and radial, but not axial, diffusivities of the ILF. Critically, these differences in the structural properties of the ILF were tightly and specifically linked with an age-related increase in the size of a key face-selective functional region, the fusiform face area. This dynamic association between emerging structural and functional architecture in the developing brain may provide important clues about the mechanisms by which neural circuits become organized and optimized in the human cortex.

Diagnostic image quality of gadolinium-enhanced T1-weighted MRI with and without fat saturation in children with retinoblastoma

BACKGROUND

Gadolinium-enhanced T1-weighted MRI without fat saturation has been recommended for assessment of retinoblastoma.

OBJECTIVE

The purpose of this study was to compare diagnostic image quality without and with fat saturation following gadolinium administration.

MATERIALS AND METHODS

High-resolution gadolinium-enhanced T1-weighted sequences with and without fat saturation performed in children with subsequently histopathologically confirmed retinoblastoma were included. Image analysis (image quality [1 = poor, 2 = moderate, 3 = good], anatomical detail depiction, tumour extension) was performed by two neuroradiologists in consensus. Enhancement was scored and measured. Signal- and contrast-to-noise ratios were calculated. Image-assessed tumour invasiveness was compared to histopathological findings. Paired sample t-test was used for statistical analysis.

RESULTS

Thirty-six children (mean age, 19.0 ± 16.8 [SD] months) were included. Image quality and anatomical detail depiction were significantly better without fat saturation (P < 0.001). Tumour enhancement was rated higher with fat saturation (P < 0.001). Fat saturation improved detection of (post-)laminar optic nerve infiltration. Detection of choroidal invasion was improved without fat saturation. Combining both sequences was best in the assessment of tumour extension (sensitivity/specificity for (post-)laminar optic nerve infiltration, 75.0%/100.0%, and for choroidal invasion, 87.5%/85.7%).

CONCLUSION

Combined T1-weighted spin-echo imaging with and without fat saturation improved the image quality for assessment of invasiveness of retinoblastoma.

Functional magnetic resonance imaging of the visual cortex performed in children under sedation to assist in presurgical planning

OBJECT

Advances in brain imaging have allowed for more sophisticated mapping of crucial neural structures. Functional MRI (fMRI) measures local changes in blood oxygenation associated with changes in neural activity and is useful in mapping cortical activation. Applications of this imaging modality have generally been restricted to cooperative patients; however, fMRI has proven successful in localizing the motor cortex for neurosurgical planning in uncooperative children under sedation. The authors demonstrate that the use of fMRI to localize the visual cortex in sedated children can be safely and effectively performed, allowing for more accurate presurgical planning to spare visual structures.

METHODS

Between 2007 and 2009, 11 children (age range 1-11 years) underwent fMRI for neurosurgical planning while under sedation. Blood oxygen level-dependent fMRI was performed to detect visual cortex activation during stimulation through closed eyelids. Visual stimulation was presented in block design with periods of flashing light alternated with darkness.

RESULTS

Functional MRI was successful in identifying visual cortex in each of the 11 children tested. There were no complications with propofol sedation or the fMRI. All children suffered from epilepsy, 5 had brain tumors, and 1 had tuberous sclerosis. After fMRI was performed, 6 patients underwent surgery. Frameless stereotactic guidance was synchronized with fMRI data to design an approach to spare visual structures during resection. There were no cases where a false negative led to unexpected visual field deficits or other side effects of surgery. In 2 cases, the fMRI results demonstrated that the tracts were already disrupted: in one case from a prior tumor operation and in another from dysplasia.

CONCLUSIONS

Functional MRI for evaluation of visual pathways can be safely and reproducibly performed in young or uncooperative children under light sedation. Identification of primary visual cortex aids in presurgical planning to avoid vision loss in appropriately selected patients.