 In this video, we'll be covering another hyalotopic, neural tube defects. It's important to have a good understanding of these defects because they incorporate both embryology and neuroanatomy. They're heavily tested on step one. The spectrum of neural tube defects exists due to a failure of a process called nerulation, which happens in the third and fourth weeks of fetal development. There's a few key steps of central nervous system development that are key to understand when studying neural tube defects. As you may recall from studying neuroembryology, the central nervous system begins forming when the notochord, which you see here, indices the formation of the neural plate. The neural plate then undergoes a conformational change to form the neural fold, which you can see here. The neural fold eventually undergoes a further conformational change to become the neural tube, like you see here. An error in any step of this process from formation of the neural plate to the neural fold to the neural tube can lead to a neural tube defect. There are five different varieties of neural tube defects that you need to know for step one. They range in severity from relatively benign to very serious, some requiring surgery and often resulting in lifelong disability. We start with spina bifida occulta. Spina bifida occulta is caused by a failure of the caudal aspect of the neural tube to close completely. As you can see in this sample image, there's a defect in the lower spine, but the spinal cord is still contained within the spinal canal. There's no herniation of the contents. Questions describing spina bifida occulta will often also describe a tuft of hair on the lower back at the level of the spina bifida. Spina bifida occulta is the most common type of neural tube defect, and you should always suspect it if you get a question about a child who has a tuft of hair on their lower back. The next neural tube defect we'll discuss is a meningocial. As you'll see here, this defect is similar to spina bifida occulta in that there's a defect in the spine, but this time there's a herniation of some of the contents out of the defect. It's important to note that only the meningiolayer of the spinal cord has herniated, but none of the tissue of the spinal cord of the occulta equina or any nerves have actually come out of the defect. This is in contrast to something called a myeloma meningocial. A myeloma meningocial is similar to a meningocial, but now you can see that we have some neural tissue. In the case of this image here, some of the spinal nerves from the occulta equina present inside that herniated pocket. This is a very serious condition and can lead to lifelong disability in these patients. In spina bifida occulta, meningocial, and myeloma meningocial, the defect is at least covered by a layer of the meninges or skin. This is important to note as we talk about something called myeloskesis. A myeloskesis is similar to a myeloma meningocial, but it lacks any kind of skin or meningiol covering over the herniated nervous tissue. So in the case of myeloskesis, the escaped contents of the spinal cord are open to the environment without any kind of tissue covering. This again is a very serious condition. Finally, we have perhaps the worst of all the neural tube defects, anencephaly. Anencephaly, as opposed to the other neural tube defects we've discussed earlier, happens at the rostral end of the neural tube or closer to the brain. These cases are quite dramatic and typically result in a fetus that's missing a significant portion of its skull and cerebral cortex. Anencephaly, unfortunately, is not compatible with life. Now, there's a few other things we need to know about neural tube defects. For example, what are some of the risk factors for developing a neural tube defect? The primary risk factor for developing a neural tube defect is a low maternal folate level. Maternal diabetes is also associated, but the main one you want to remember is low maternal folate. This is part of the reason for the US Preventative Service Task Force recommendation that all women of childbearing age take a daily supplement containing folic acid. As we just mentioned, this critical period of neural development happens in the third and fourth weeks, so it's possible that a woman may not even realize she's pregnant at this time. Thus, it's a recommendation that women of childbearing age be replete with folate, especially if they plan to become pregnant. Now, how are neural tube defects diagnosed? In women with regular prenatal care, these defects are often picked up during pregnancy via ultrasound images of the growing fetus. Additionally, a maternal serum alpha-feta protein level can indicate that a neural tube defect might be present, but the loan is not diagnostic. This has been a quick review of neural tube defects and should give you all the information you need to get these questions right when they come up on your board exams. I would encourage you to be familiar not only with the description of these various neural tube defects, but also how they look in photos. You'll often get questions that ask you to identify these defects based on a picture of a patient, and you may even get a second or third order question that asks you to link the details of the neural tube defect to the actual neuroembryology. Thanks again for tuning in. We hope you found this video useful. Be sure to leave us some comments on other topics you'd like to see videos on.