Video: Neurovasculature of the female perineum

Hey everyone! This is Nicole from Kenhub, and welcome to our tutorial on the neurovasculature of the female perineum. So, in this tutorial, we're going to be looking at this inferior view of the female pelvis with the skin and some organs cut away and that means our pubic symphysis which is our reference point for the anterior part of the pelvis is up here and the sacrum which is our marker for the posterior part of the body is down here.

In this image, we can also see some muscles which are not part of the perineum just here as well as some of the arteries that supply the perineum and some muscles that are, of course, related to this area and we'll have a look at some of those arteries a little bit later.

So as you can see in this image, the female perineum is an anatomical diamond-shaped region which is located below the pelvic floor and between the thighs. It's bounded anteriorly by the pubic symphysis which we mentioned before and posteriorly by the coccyx which is the little bit of bone that is inferior to the sacrum and anterolaterally, it's bounded by the ischiopubic rami and posterolaterally, we can see that the perineum is bounded by the sacrotuberous ligaments which we can see dotted in blue. And as you can see, they run from the ischial tuberosity to the sacrum.

The female perineum can also be divided into two parts – an anterior urogenital triangle and a posterior anal triangle. Let's have a quick talk through what's in the anterior urogenital triangle first.

So, in the anterior urogenital triangle, we can see that there is a mons pubis which is a fatty mound of tissue that sits over the pubic bones. There's also the labia majora which are two folds of adipose tissue which surrounds the labia minora. We have the labia minora which are two folds of inner skin that surrounds the vagina. We have the clitoris which is the female erectile body and the vaginal orifice which is the opening into the vagina and we also have the urethral orifice which is the orifice through which urine exits.

Moving now to the posterior anal triangle, we can see that the posterior anal triangle contains the anus which is the opening of the rectum, the external anal sphincter which is a sphincter of muscle which surrounds the anus, and the ischioanal fossa which is this horseshoe region just here. And throughout this tutorial, we're going to be talking about the arteries, the veins and the nerves of the female perineum. So, let's begin, and let's of course begin by talking about the arteries of the female perineum.

So, as you might be able to guess already, the role of the arteries is to supply oxygen-rich blood to the structures within the female perineum. And today, we're going to be looking at five arteries that supply this area, the main one being the internal pudendal artery which is the main artery of the perineum. And we're also going to be looking at four of its branches – the inferior rectal artery, the perineal artery, the artery of the vestibular bulb and the deep artery of the clitoris.

Let's begin by talking about the internal pudendal artery which is highlighted in green. And the internal pudendal artery is the terminal branch of the anterior division of the internal iliac artery, and we can see the internal iliac artery more clearly on this posterior view of the rectal and pelvic arteries within the pelvis, of course, with the muscles and the vertebral spine and many organs cut away. And in this image, you can see a little bit more clearly how it enters the perineum through the greatest sciatic foramen and curves around the sacrospinous ligament.

Once it enters the perineum through the lesser sciatic foramen, it travels within a canal with the internal pudendal vein and the internal pudendal nerve and this canal is known as the pudendal canal. And, in this image, you can see the pudendal canal dotted out in blue with the internal pudendal vein and the pudendal nerve traveling along with it. And this canal is pretty important to know as it's within this canal that the internal pudendal artery gives off many branches which supply the structures in the perineum and we'll talk about some of these arteries a little bit more over the next few slides.

So the first branch of the internal pudendal artery I want to talk about is the inferior rectal artery which you can now see highlighted in green and it arises just after the internal pudendal artery enters through the lesser sciatic foramen and as you can see in the image, it arises within the pudendal canal.

Now, let's move back to our inferior view of the female perineum. And we can see the inferior rectal artery arising from the inferior pudendal artery in blue as it passes through the lesser sciatic foramen and, as you can see, the inferior rectal artery divides into two or three main branches which run anteromedially through the ischioanal fossa. In order to show you the supply, we're just going to bring in one more image for this particular artery because I have this coronal section of the rectum and anus, the rectum being up here in blue and the anus being down here in blue – and this is just to give you a little bit of an idea of what it supplies. And so the inferior rectal artery supplies the inferior part of the anal canal below the pectinate line which is this line visible just here within the anus that separates the superior and inferior parts of the anal canal.

The next artery that branches off the internal pudendal artery is the perineal artery which is now seen highlighted in green and it arises from the anterior part of the posterior anal triangle. It runs medially towards the midline of the perineum and supplies the transverse perineal muscles, the perineal body and the posterior part of the labia.

Moving on now to talk about the artery of the vestibular bulb. Once the internal pudendal artery enters the anterior urogenital triangle, it gives off an artery known as the artery of the vestibular bulb. And like the perineal artery, the artery of the vestibular bulb travels medially towards the midline of the perineum. Now in order to show you the supply, I'm just going to bring in another image which is a coronal section of the female pelvis, and in this image, you can see the uterus, the vagina and the vaginal vestibule down the bottom and over here, you can see the vestibular bulbs which are masses of erectile tissue highlighted in green. And the vestibular bulbs are equivalent to the bulb of the penis. The artery of the vestibular bulb also supplies the erectile tissue of the vagina.

The final branch that I want to talk about today that we can see here is the deep artery of the clitoris which is considered to be one of two terminal branches of the internal pudendal artery. And as you can see, it runs anteromedially within the anterior urogenital triangle to supply the corpus cavernosum of the clitoris which in turn makes up one half of the crus or hood of the clitoris.

I just want to make this image a little bit larger so we can see some of these structures a bit more clearly. So in this zoom, you can see the glans clitoris highlighted in blue up here and the corpus cavernosum up here forming the hood of the clitoris before running deep to the ischiocavernosus muscle where they become the crus or the legs of the clitoris.

Now that we're finished talking about the arteries of the female perineum, let's talk about the veins of the female perineum. So, the veins of the female perineum have a very similar distribution to the arteries that we just looked at, and there are five of these and these include the deep veins of the clitoris, the vein of the vestibular bulb, the perineal veins and the inferior rectal veins, and all of these drain into the internal pudendal vein. Let's begin, of course, with our deep veins of the clitoris.

So the deep veins of the clitoris usually have two veins – one on either side – and they drain the corpora cavernosa of the clitoris. And as we mentioned before, the two corpora cavernosa form the crura or the hood of the clitoris. The deep veins of the clitoris travel posterolaterally in the anterior urogenital triangle and these drain into the internal pudendal vein.

Next, let's have a look at the vein of the vestibular bulb and like its name suggests, it drains the vestibular bulb which you can see in this image just here in blue beneath the bulbospongiosus muscle as well as the erectile tissue of the vagina. Like the deep vein of the clitoris, the vein of the vestibular bulb also courses posterolaterally in the anterior urogenital triangle before draining into the internal pudendal vein.

The perineal veins which we can now see on this slide drain blood from the transverse perineal muscles, the perineal body and the posterior labia and the perineal veins course laterally through the anterior urogenital triangle to drain into the internal pudendal vein.

Next on our list are the inferior rectal veins which we can see here highlighted in green, and the inferior rectal veins which are also known as the inferior hemorrhoidal veins drain blood from the inferior part of the rectum before coursing laterally within the posterior anal triangle, and they drain into the internal pudendal vein just before it exits the perineum. And as we've already mentioned, all of the four veins we just discussed drain into the internal pudendal vein which is this vein now seen highlighted in green.

And in females, the internal pudendal vein is essentially a continuation of the deep veins of the clitoris which, if you remember, are these veins highlighted just here in blue and it then courses posteriorly within the pudendal canal with the internal pudendal artery and the pudendal nerve before it exits the perineum via the lesser sciatic foramen. And in this image, we can also see that the internal pudendal vein drains into the internal iliac vein.

Let's move on now to talk about the nerves of the female perineum and there are six groups of nerves that we're going to be looking at in our tutorial today starting with the pudendal nerve, the inferior rectal nerve, the dorsal nerve of the clitoris, the perineal nerve, the posterior labial nerves and also the anococcygeal nerves. And these nerves are all responsible for the sensory and motor innervation to structures which are part of the female perineum.

Let's, of course, begin with the pudendal nerve. And this nerve is derived from the sacral plexus which consists of the sacral nerves S2 to S4. It enters the perineal region via the lesser sciatic foramen – and over here you can see the lesser sciatic foramen in blue. It then travels within the pudendal canal with the internal pudendal artery and vein before dividing into multiple branches, and the pudendal nerve also contains both motor and sensory fibers.

Let's now talk about the inferior rectal nerves which are the first branches of the pudendal nerve, and these are also sometimes called the inferior anal nerves. And these nerves branch off the pudendal nerve within the pudendal canal and then run medially towards the midline over the ischioanal fossa. The inferior rectal nerves provide motor innervation to the external anal sphincter which you can see over here again and sensory innervation to the skin of the anal canal inferior to the pectinate line. In addition, these nerves sometimes provide sensory innervation to the lower part of the vagina and in this coronal section of the vagina, you can see the lower part of the vagina that is innervated highlighted in blue.

The next branch of the pudendal nerve that we're going to be looking at is the dorsal nerve of the clitoris. And this nerve is one of two terminal branches of the pudendal nerve and it's a long nerve that runs alongside the ischial ramus which you can see just here and it provides sensory innervation to the corpus cavernosum of the clitoris.

The other terminal branch of the pudendal nerve seen here highlighted in green is the perineal nerve, and it's the larger of the two nerves – the other one being as if you may recall, the dorsal nerve of the clitoris – and it courses in an anteromedial direction before it gives off muscular branches which provide motor innervation to the superficial and deep perineal muscles which you can see here in blue and the deep perineal muscles arise from the ischial ramus and insert with the superficial transverse perineal muscle onto the perineal body, the bulbospongiosus muscle, the ischiocavernosus, the urethral sphincter and the anterior parts of the external anal sphincter and the levator ani.

The perineal nerve also gives off branches to the labia which are known as the posterior labial nerves, and there are usually two posterior labial nerves which travel medially to provide sensory innervation to the skin of the labia majora.

The final nerves that we're going to be looking at in this tutorial are the anococcygeal nerves, and the anococcygeal nerves originate from the coccygeal plexus which is formed by the ventral rami of S4 and S5, and these nerves pierce the sacrotuberous ligament and provides sensory innervation to the skin above the coccyx.

So now that we're finished talking about the arteries, veins and the nerves of the female perineum, let's briefly talk about some clinical notes. And the main thing I want to discuss in our clinical notes section is the pudendal nerve block. So, a pudendal nerve block can be used as analgesia during labor when a spinal or epidural anesthetic is not available and as pudendal nerve provides sensory innervation to the perineum, blocking it with local anesthetic will result in analgesia to the perineum. So, we usually use lignocaine, otherwise known as lidocaine, and that's usually the local anesthetic of choice and that's usually injected transvaginally. And when this is administered, it's administered in the area where the pudendal nerve enters the perineum before it sends off multiple branches.

So now we're finished talking about the clinical notes, let's talk through our summary.

So, today, we, of course, looked at the arteries of the female perineum which included the internal pudendal artery which is one of the main arteries that supplies the female perineum and that gives off four branches which includes the inferior rectal artery which is the first branch of the internal pudendal artery and supplies the inferior anal canal. We also covered the perineal artery which runs medially to supply the transverse perineal muscles, the perineal body and the posterior part of the labia. The third branch we talked about was the artery of the vestibular bulb which also runs medially to supply the vestibular bulb and the erectile tissue of the clitoris. And the last branch we talked about was the deep artery of the clitoris which is one of the terminal branches of the internal pudendal artery, and it supplies the corpus cavernosum of the clitoris.

We also looked at the veins of the perineum which included the deep veins of the clitoris which drain the corpus cavernosum of the clitoris and the vein of the vestibular bulb which drains the vestibular bulb and the erectile tissues of the vagina, the perineal veins which drain blood from the posterior labia, the perineal body and the transverse perineal muscles; the inferior rectal veins also known as the inferior hemorrhoidal veins which drain blood from the inferior part of the rectum, and all of these veins drain into the internal pudendal vein which courses posteriorly within the pudendal canal before exiting the perineum via the lesser sciatic foramen and draining into the internal iliac vein.

And, finally, we talked about the nerves of the perineum which included the pudendal nerve which is derived from the pudendal plexus and travels within the pudendal canal within the internal pudendal artery and vein and then we looked at three of its branches which included the inferior rectal/anal nerves which branch off the pudendal nerve within the pudendal canal. And these nerves provide motor innervation to the external anal sphincter as well as sensory innervation to the skin of the anal canal.

We talked about the dorsal nerve of the clitoris which is one of the terminal branches of the pudendal nerve that provides innervation to the corpus cavernosum of the clitoris, and we looked at the perineal nerve which is the other terminal branch of the pudendal nerve and it gives off muscular branches that provide innervation to the muscles of the perineum, urethral sphincter and the external anal sphincter. And we then covered the posterior labial nerves which are branches of the perineal nerve that provides sensory innervation to the skin of the labia majora and lastly we discussed the anococcygeal nerves which originate from the coccygeal plexus and innervate the skin above the coccyx.

And that brings us to the end of our tutorial today. Thanks for watching!