The central neurons system and its overlying bones are subject to a variety of malformations and developmental diseases. The defect described in the question stem is a cranial encephalocele, in which brain herniates through a defect in the skull bones. The most common site for such a herniation is the occipital bone. Small defects in the occipital bone can be treated surgically, but large defects are very problematic, paicularly if significant herniation has occurred, since the brain becomes very vulnerable to trauma and infection. Meningocele is the term used when the meninges, but not the brain or spinal cord, herniate through a defect in the bony cranium or spinal column. Myelocele is the term used when the spinal cord herniates through a defect in the spinal column. Spina bifida refers to veebral defects through which the spinal cord or meninges may herniate. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 16. Fetal Imaging. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.