Undecussated superior cerebellar peduncles and absence of the dorsal transverse pontine fibers: a new axonal guidance disorder?

Midbrain, Pons, and Medulla: Anatomy and Syndromes

The anatomy of the brainstem is complex. It contains numerous cranial nerve nuclei and is traversed by multiple tracts between the brain and spinal cord. Improved MRI resolution now allows the radiologist to identify a higher level of anatomic detail, but an understanding of functional anatomy is crucial for correct interpretation of disease. Brainstem syndromes are most commonly due to occlusion of the posterior circulation or mass effect from intrinsic space-occupying lesions. These syndromes can have subtle imaging findings that may be missed by a radiologist unfamiliar with the anatomy or typical manifesting features. This article presents the developmental anatomy of the brainstem and discusses associated pathologic syndromes. Congenital and acquired syndromes are described and correlated with anatomic locations at imaging, with diagrams to provide a reference to aid in radiologic interpretation. ^©RSNA, 2019.

Variability of Ponto-cerebellar Fibers by Diffusion Tensor Imaging in Diverse Brain Malformations

To describe pontine axonal anomalies across diverse brain malformations. Institutional review board-approved review of magnetic resonance imaging (MRI) and genetic testing of 31 children with brain malformations and abnormal pons by diffusion tensor imaging. Anomalous dorsal pontocerebellar tracts were seen in mid-hindbrain anomalies and in diffuse malformations of cortical development including lissencephaly, gyral disorganization with dysplastic basal ganglia, presumed congenital fibrosis of extraocular muscles type 3, and in callosal agenesis without malformations of cortical development. Heterotopic and hypoplastic corticospinal tracts were seen in callosal agenesis and in focal malformations of cortical development. There were no patterns by chromosomal microarray analysis in the non-lissencephalic brains. In lissencephaly, there was no relationship between severity, deletion size, or appearance of the pontocerebellar tract. Pontine axonal anomalies may relate to defects in precerebellar neuronal migration, chemotactic signaling of the pontine neurons, and/or corticospinal tract pathfinding and collateral branching not detectable with routine genetic testing.

Biallelic mutations in human DCC cause developmental split-brain syndrome

Motor, sensory, and integrative activities of the brain are coordinated by a series of midline-bridging neuronal commissures whose development is tightly regulated. Here we report a new human syndrome in which these commissures are widely disrupted, thus causing clinical manifestations of horizontal gaze palsy, scoliosis, and intellectual disability. Affected individuals were found to possess biallelic loss-of-function mutations in the gene encoding the axon-guidance receptor 'deleted in colorectal carcinoma' (DCC), which has been implicated in congenital mirror movements when it is mutated in the heterozygous state but whose biallelic loss-of-function human phenotype has not been reported. Structural MRI and diffusion tractography demonstrated broad disorganization of white-matter tracts throughout the human central nervous system (CNS), including loss of all commissural tracts at multiple levels of the neuraxis. Combined with data from animal models, these findings show that DCC is a master regulator of midline crossing and development of white-matter projections throughout the human CNS.