Which type of neural tube defect is visible outside the body?

Myelomeningocele is a type of neural tube defect that is characterized by the herniation of the spinal cord and its protective covering (the meninges) through a defect in the bony encasement of the spinal column. This defect leads to a notable protrusion that is visible outside the body, distinguishing it from other types of neural tube defects.

In myelomeningocele, the spinal cord is not only exposed but also often contains nerve tissue, which can lead to significant disability and complications. The visible sac contains both the meninges and the neural elements, making this condition evident upon physical examination.

In contrast, spina bifida occulta is a mild form of spina bifida where there is an incomplete closure of the spine, but it does not result in any external protrusion, making it not visible from the outside. Meningocele involves the protrusion of the meninges without neural tissue involvement, which can also result in a visible sac, though less frequently compared to myelomeningocele. Myeloschisis is a more severe defect where the spinal cord is completely open and exposed, but it does not typically present as a defined sac that is visible externally.