Scoping Review of the Prenatal Diagnosis of Agenesis of the Corpus Callosum.

OBJECTIVE: To map and summarize the literature related to the prenatal diagnosis of agenesis of the corpus callosum (ACC) to inform nursing practice. DATA SOURCES: We searched MEDLINE, CINAHL, PyscINFO, and Academic Search Complete with the use of strings of curated terms to cover the broad ACC nomenclature. Documents were published in English between 2009 and June 1, 2020. We also hand searched the reference lists of included documents. STUDY SELECTION: We screened 582 abstracts and retrieved the full texts of primary research articles, reviews, discussion papers, and peer-reviewed book chapters if the abstracts specifically mentioned ACC and the prenatal period. We excluded case reports, conference and poster abstracts, papers on broader anomalies, and animal studies. We reviewed 84 full-text documents and identified 61 for inclusion. DATA EXTRACTION: We charted the data through an iterative process under headings for location, article type, study design, participant age, ACC type, recruitment, method, tools/assessments, results, key recommendations, gestational age at diagnosis, termination of pregnancy rate, the definition of isolated ACC, and our notes of critique of the document. DATA SYNTHESIS: We constructed a narrative synthesis from thematically arranged data. In the included documents, ACC was diagnosed between 17 and 38 weeks gestation and was frequently described as heterogeneous because of different causes, presentations, and outcomes. Whether the ACC was isolated as the only anomaly or present with other anomalies was considered the key factor for prenatal counseling. However, the definition of isolated ACC was inconsistent. CONCLUSION: The inconsistent nomenclature and definitions of an isolated presentation of ACC increase the ambiguity in the prenatal diagnosis and must be considered when the outcome and diagnostic efficacy studies are interpreted. There is an absence of research on parents' experiences of prenatal diagnoses of ACC to inform holistic nursing interventions and the provision of psychosocial support.

The Contribution of the Corpus Callosum to Language Lateralization.

The development of hemispheric lateralization for language is poorly understood. In one hypothesis, early asymmetric gene expression assigns language to the left hemisphere. In an alternate view, language is represented a priori in both hemispheres and lateralization emerges via cross-hemispheric communication through the corpus callosum. To address this second hypothesis, we capitalized on the high temporal and spatial resolution of magnetoencephalographic imaging to measure cortical activity during language processing, speech preparation, and speech execution in 25 participants with agenesis of the corpus callosum (AgCC) and 21 matched neurotypical individuals. In contrast to strongly lateralized left hemisphere activations for language in neurotypical controls, participants with complete or partial AgCC exhibited bilateral hemispheric activations in both auditory or visually driven language tasks, with complete AgCC participants showing significantly more right hemisphere activations than controls or than individuals with partial AgCC. In AgCC individuals, language laterality positively correlated with verbal IQ. These findings suggest that the corpus callosum helps to drive language lateralization. SIGNIFICANCE STATEMENT: The role that corpus callosum development has on the hemispheric specialization of language is poorly understood. Here, we used magnetoencephalographic imaging during linguistic tests (verb generation, picture naming) to test for hemispheric dominance in patients with agenesis of the corpus callosum (AgCC) and found reduced laterality (i.e., greater likelihood of bilaterality or right hemisphere dominance) in this cohort compared with controls, especially in patients with complete agenesis. Laterality was positively correlated with behavioral measures of verbal intelligence. These findings provide support for the hypothesis that the callosum aids in functional specialization throughout neural development and that the loss of this mechanism correlates with impairments in verbal performance.

Diverticulum of the third ventricle and absence of the interthalamic adhesion in a dog.

A 10-month-old male Pomeranian dog was examined for neurological abnormalities consistent with diffuse forebrain and cerebellar disease. Based on ultrasound and magnetic resonance imaging (MRI) a diagnosis of diverticulum of the third ventricle, partial agenesis of the corpus callosum, and absence of the interthalamic adhesion was made. As conservative treatment was unsuccessful, a ventriculoperitoneal shunt was placed.