An acardiac twin with advanced development of the brain: a histologic and volumetric study

We describe a rare case of an acardiac twin (acardius anceps) with advanced brain development. Complete serial sections of the brain were made for microscopic observation and volumetric analysis. The cerebral surface showed unusual gyri and sulci with absence of the right olfactory bulb. Cortical lamination was almost normal, except for the insula where polymicrogyria and leptomeningeal neuroglial heterotopia were seen. The latter was also observed in the basal forebrain. Partial agenesis of the corpus callosum was noted with a very thick left cingulate gyrus. The anterior commissure did not cross the midline. Subcortical structures including basal ganglia, diencephalon, and brainstem/cerebellum appeared grossly normal, but hypo- or dysplasic changes were observed in some regions. The ventricles were enlarged and the left internal carotid artery was absent. In addition, porencephalic foci were located in the right temporal and parietal lobes. On comparative volumetry, the total brain was normal, but brain structures showed variable volumetric changes, with higher volume in the ventricles, diencephalon, and archi-/paleopallium, and lower volume in the periventricular germinal layer, basal ganglia, cerebral cortex, and brainstem/cerebellum. These observations showed that brain development can proceed nearly normally in acardia if blood flow is relatively preserved.