A developmental structural anomaly of the stalk-like part of the brain that comprises the midbrain (aka mesencephalon), the pons (aka pons Varolii), and the medulla oblongata, and connects the cerebral hemispheres with the cervical spinal cord. The phenotype is Brainstem dysplasia (HP_0002508). Also known as: Brainstem hypoplasia/dysplasia, Malformation of brainstem structures.