[Music] so when i think about things i like to make things as simple as possible um and so when you think about spinal dysrapism there's all kinds of categories and different ways of thinking about things in terms of embryology and subsequent management presentation cell lines things like that but i like to think of these in a very simple way in two categories so open or what you might have known as spina bifida aperta and then there's closed which is spina bifida occulta okay so i think about these things as open and closed and if you think about that from a surgical standpoint it makes things very simple for you so this is a more complicated table but it's kind of been broken down in a way that we look at open and closed so we're going to start off by talking about open spinal dysrapism and the most commonly seen open neural tube defect or open spinal disrupt uh dysrafism topic is myelomeningocele and that makes up 98 percent of open spinal dysrafism cases that we see other ones include a myeloma myelocell a hemi myelomeningocele and a hemi myelocyle i'll tell you the bottom three i have never encountered in clinical practice or in training closed spinal dysravism will go through these categories a bit later on but i want to spend a majority of our time today talking about myelomeningocele so when we talk about normal embryology of the spine the most important process that we talk about is neuralation which is really fancy for development of the brain and the spinal cord when you talk about closure of the open neural tube it typically happens first in the upper cervical region and then it extends down to l1 l2 and then it comes back ross rostrally towards the nasion these these kind of slides here show you that the general uh embryology of this area where you have a flat neural plate that's surrounded by ectoderm and as this process happens that neural plate folds and that ectoderm comes into a position that's superficial or superior and the third plate shows a normal neural tube that's completely closed surrounded by neural crest cells more superficially and then the ectoderm on top of that now primary neurallation describes the the term for the spinal cord uh formation all the way to the lower lumbar level and abnormalities and primary neurolation lead to myelomeningocele formation lipomyelomeninx formation intraspinal dermoid and epidermoid cysts and split chord malformations all of which i'll talk about later so don't get hung up on the terms too much these typically this process of primary neurolation typically occurs at days 18 to 28 of development the caudal most aspect again below the lower lumbar level undergoes what's called secondary neurolation and that happens between days 28 and 48 of development and this typically is two processes known as canalization and subsequent regression so when we talk about canalization of the spine this is really this caudal cell mass and it forms the distal spinal segments as well as the nerves that encompass and go with these segments of the spinal cord when we talk about regression we talk about involution of partial a partial aspect of this caudal cell mass which involutes and it forms the phylum terminale which is really the distal aspect of the spinal cord and it doesn't routinely have function in it so after the phylum terminalis is formed the vertebral canal actually grows faster than the neural tube and so oftentimes a routine question for fourth year medical students and interns is well at what age does the conus medullaris ascend to its anatomic position and typically this happens at about three months so at birth the tip or the bottom of the conus typically occurs at between l2 and l3 can be as low as l3 l4 and at 3 months of age again as that vertebral column grows but the neural tube is not growing as quickly that changes to its position at l1 l2 which typically stays at for the rest of their life and so that's a common thing to recognize especially as you work up neural tube defects and spinal dysravism uh to see if there's tethering of the spinal cord because you want to look at the location of the conus hey everyone ryan rad here from neurosurgery training.org if you like that video subscribe and donate to keep our content available for medical students across the world