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00:00Hello everyone, it's Megan from KenHub here and welcome to our tutorial on the retroperitoneum.
00:07The retroperitoneum is the collective term for the structures that are located posterior to
00:12the parietal peritoneum, which we can see here highlighted in green. During this tutorial we'll
00:18be looking at different organs and vessels found in the retroperitoneum and we'll do this by
00:23focusing mainly on the image in front of you, which is an anterior view of the abdominal cavity.
00:29It's good to keep in mind that the structures we're talking about today are also referred to as
00:33retroperitoneal. But before we start looking at the retroperitoneum, let's first have a look at
00:39some structures we can see within the parietal peritoneum. Here in green we see the median
00:45umbilical fold, which is a ridge of the lower parietal peritoneum. If this part of the peritoneum
00:51were to be reflected back into its original anatomical position, the median fold would
00:56run from the umbilicus to the bladder. This fold contains the urecus, a remnant of the allantois,
01:02which is a canal found in the fetus. Another ridge of the parietal peritoneum is the medial
01:08umbilical fold. This is actually a paired structure and there's one found on either side of the body.
01:15As you may have noticed, these folds have a very similar name to the one we just discussed,
01:20so it's very easy to get them mixed up. A good way to remember is that the median umbilical fold is
01:26closer to the median line of the body, whereas the medial umbilical folds have an L in their name,
01:32so are located more laterally. These folds are the remnants of the fetal umbilical arteries,
01:38and can be used as a landmark during laparoscopic surgery for inguinal hernia repairs.
01:43Moving superiorly, we can see another fold of peritoneum here, which is known as the sigmoid
01:50mesocolon. The sigmoid mesocolon is a mesentery, which is a double fold of peritoneum that attaches
01:57parts of the intestines to the posterior abdominal wall. A mesentery that specifically attaches to
02:02parts of the colon is called a mesocolon. Now that I've explained these definitions, you'll
02:08understand that the sigmoid mesocolon functions to attach the sigmoid colon to the posterior abdominal
02:14wall. The mesentery that attaches to the small intestine, the small bowel mesentery, arises from
02:21this structure here, the root of the mesentery. The root of the mesentery runs diagonally from the end
02:27of the duodenum and is about 15cm long in adults. Now let's move on to look at the retroperitoneal
02:34structures, starting with the right kidney. The kidneys are important in maintaining electrolyte
02:40and water balance in the body, as well as having an important role in endocrine function. The right
02:45kidney is located posterior to the parietal peritoneum and is slightly lower than the left
02:50kidney due to its location inferior to the liver. In this illustration on the right, we can see the
02:56diaphragmatic surface of the liver highlighted in green. We'll talk about the significance of this
03:01surface later on in the tutorial. Superior and slightly medial to the right kidney is the right
03:08adrenal gland, which is another retroperitoneal structure. The adrenal glands are also known as
03:14the suprarenal glands, as they are located superior to the kidneys. They are endocrine organs that produce
03:20and secrete hormones and steroids such as adrenaline and cortisol. The next structure we'll look at is the
03:27left kidney, which we can see here highlighted in green. The left kidney is also located posterior
03:34to the parietal peritoneum and is usually larger and located slightly higher than the right kidney.
03:41Supramedial to the left kidney is the left adrenal gland, which is also called the left suprarenal gland.
03:48The left adrenal gland is slightly larger than the right adrenal gland, but they both weigh about 5g.
03:54A significant portion of the diaphragmatic surface of the liver is covered by peritoneum. However,
04:01there's also a portion of this surface which is bare and comes in direct contact with the right hemidiaphragm.
04:08This bare area is an extension of the retroperitoneal space and through it,
04:13pathological processes taking place in this space can spread to the thoracic cavity and vice versa.
04:19We're now going to look at some veins of the retroperitoneum, which are the hepatic veins.
04:25The hepatic veins arise inside the liver's tissues as smaller venules. They remain there for most of
04:31their course and exit to the retroperitoneal space only to merge with the inferior vena cava.
04:37In this illustration, we can actually see the three hepatic veins draining into the IVC.
04:42Between the two kidneys is another retroperitoneal structure, the duodenum.
04:48The duodenum has four parts, the superior part, the descending part, the horizontal part and the
04:56ascending part. These are also commonly referred to as the first, second, third and fourth parts of
05:02the duodenum. Most of the duodenum is considered to be retroperitoneal, only the superior part is
05:09intraperitoneal, which means it's contained within the peritoneum.
05:13And in case you were wondering about the structure which can be seen above the first part of the
05:17duodenum, this is the hepatoduodenal ligament. It's not considered a structure of the retroperitoneum,
05:24however it acts as a bridge for vessels and fatty tissue between regions of the retroperitoneal space.
05:32Next, we're going to have a look at a glandular organ, which is the pancreas.
05:36The pancreas also consists of four parts, the head, the neck, the body and the tail.
05:45The first three parts are considered retroperitoneal, as they are covered by
05:49the parietal peritoneum anteriorly. However, like the superior part of the duodenum,
05:55the tail is intraperitoneal and is located within the splenorenal ligament.
06:00The pancreas is considered to be an exocrine gland, secreting enzymes into ducts, which aid in the
06:06process of digestion. It also has an important endocrine function, secreting the hormones insulin
06:13and glucagon, which have an essential role in glucose homeostasis. Superior to the pancreas,
06:20we can see another retroperitoneal structure, which is the abdominal esophagus. This part of the
06:26esophagus, which we can see highlighted in green, is the cardiac orifice, which is the opening between
06:33the esophagus and the stomach. Moving inferiorly, we can see more retroperitoneal structures.
06:40One of these is the ascending colon, which is located on the right-hand side of the abdomen.
06:45The ascending colon is the main portion of the large intestine that's involved with fluid and
06:50electrolyte absorption, along with the transverse colon. In this image, we can see the part of
06:55the abdominal wall that lies posterior to the ascending colon. Medial to the ascending colon,
07:02we can see the right ureter, a thin tube that transports urine from the right kidney to the bladder.
07:09The ureters are about 25 to 30 centimetres in length, and have muscular walls which aid in
07:15the peristalsis of urine. Each ureter crosses over a common iliac artery, at the point where
07:21they bifurcate into an internal and external iliac artery. The other part of the colon that's
07:27retroperitoneal is the descending colon. The descending colon is about 25 centimetres in length,
07:34and is located between the transverse colon and the sigmoid colon.
07:38The anterior part and sides of the descending colon are covered by parietal peritoneum.
07:44As we saw earlier, in this image, we can see the part of the abdominal wall
07:48that lies posterior to the descending colon. Inferomedial to the descending colon,
07:54we can see this structure here, which is the left ureter. Like in the right ureter,
08:00peristaltic contractions in the left ureter aid in the flow of urine from the left kidney to the bladder.
08:07If we take a closer look at the bottom part of this image, we can see the rectum,
08:11which is located between the sigmoid colon and the anus. Only the middle third of the
08:16rectum is considered to be retroperitoneal. There are also many blood vessels that are
08:22part of the retroperitoneum, including the abdominal aorta, which we can see in the middle of this image.
08:28The abdominal aorta begins at the level of T12, where it pierces through the diaphragm,
08:34travelling from the mediastinum of the thorax into the abdomen.
08:38If we take a closer look at the abdominal aorta, we can see that it bifurcates into a
08:43left common iliac artery and a right common iliac artery. This bifurcation occurs at the
08:49level of the fourth lumbar vertebra. So branching from the abdominal aorta, we can see the right common
08:56iliac artery. The right common iliac artery is about 5cm long and is located medial to the inferior
09:03vena cava. It's crossed by the right ureter, where it bifurcates into the external and internal iliac
09:11arteries. In the next illustration, we can see the right external iliac artery highlighted in green,
09:18but the internal iliac artery is not visible. The external iliac arteries are considered to be
09:24the principal arteries of the lower limb, whereas the internal iliac arteries are the main arteries
09:29of the pelvis. Corresponding to the right common iliac artery, we have the left common iliac artery,
09:36which is about 1cm shorter than its counterpart. At the level of the sacroiliac joint, the left common
09:43iliac artery bifurcates into external and internal iliac arteries. In the lower part of our image,
09:50we can see the left external iliac artery. Like the abdominal aorta and its branches that we've looked
09:56at so far, the left external iliac artery is covered by parietal peritoneum. This helps separate
10:03it from the sigmoid colon and parts of the small intestine anteriorly. In the upper right hand part of
10:10our image, we can see the splenic artery highlighted in green. It's a branch of the celiac artery,
10:16which is the first branch of the abdominal aorta. The splenic artery provides the main blood supply
10:22to the spleen, which is an important organ involved in our immune function. Please note that in this
10:28illustration, we can't actually see the spleen, but we can see where it would normally be located
10:33within the peritoneum. Despite the fact that the spleen is considered an intraperitoneal organ,
10:39most of the splenic artery is retroperitoneal. Another vessel that arises from the abdominal aorta
10:46is the superior mesenteric artery, which arises about 1cm inferior to the celiac artery.
10:53We can see this artery within the root of the mesentery, located next to the superior mesenteric
10:59vein. The superior mesenteric artery gives off many branches that supply both the small and large
11:05intestines. It branches off the abdominal aorta in the retroperitoneal space behind the pancreas.
11:12It then becomes intraperitoneal as it courses superficially to the duodenum to enter the area
11:18of the mesentery. To the right of the superior mesenteric artery is the superior mesenteric vein,
11:26which is located within the root of the mesentery. This vein drains blood from the small intestine,
11:31the cecum, the ascending colon and the transverse colon. It enters the retroperitoneal space after
11:38it courses through the root of the mesentery, as it dives beneath the pancreas.
11:44Another branch of the abdominal aorta is the inferior mesenteric artery,
11:48which we can see branching off to the left. It arises below the duodenum,
11:53and about 3-4 cm above the bifurcation of the aorta. Branching off from the left of the inferior
12:00mesenteric artery, we can see this vessel here, the left colic artery. Like the rest of the vessels
12:07we've looked at, it's retroperitoneal, or located posterior to the parietal peritoneum. It gives off
12:14many small branches that supply the transverse and descending colon.
12:18To the right of the abdominal aorta, we can also see this vessel here, which is the inferior vena cava.
12:26The inferior vena cava is formed by the common iliac veins and is also covered by peritoneum.
12:32It travels superiorly to the heart, coursing deep beneath the duodenum and the pancreas.
12:38Structures that are part of the retroperitoneum are important to know in abdominal surgery,
12:43and of course may come up in exams. A tip to remember the main retroperitoneal structures
12:49is to remember the mnemonic SADPUCKER.
12:52S stands for the suprarenal glands. A stands for the abdominal aorta and the inferior vena cava,
12:58as well as their branches. D stands for duodenum, P for pancreas, U for ureters, and C for colon,
13:06specifically the ascending and descending parts. K stands for kidneys, E stands for esophagus,
13:14and R stands for the middle third of the rectum.
13:18To finish off this tutorial, we'll go over some clinical notes in relation to the retroperitoneum.
13:23Hematomas can occur within the retroperitoneum, and these are often caused by major pellet fractures,
13:29ruptures of arterial aneurysms, or severe pancreatitis. Retroperitoneal hematomas,
13:36also referred to as a retroperitoneal haemorrhage, present with abdominal pain and haematuria,
13:42and may lead to hypovolemic shock. Blood seeps into the retroperitoneal fat,
13:47and can even form bruises visible on the skin of the flanks. This bruising is a clinical sign commonly
13:54known as the grey Turner's sign. A CT scan is the investigation of choice, and treatment
14:00involves non-surgical and surgical approaches, depending on the severity of the injury.
14:06So that brings us to the end of our tutorial on the retroperitoneum.
14:10I hope you enjoyed it, and thank you for listening.
14:24I hope you enjoyed it.
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