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The Acute Abdomen

Iím going to talk to you today about radiology in the evaluation of patients who present to the Emergency Room with an acute abdomen. Weíre going to concentrate primarily on plain film evaluation. When I am talking about an acute abdomen, Iím talking to you about those patients that you examine and they have acute tenderness. They have rebound tenderness. Iím going to recommend to you that the place to start with these patients is with a plain film series of the abdomen and weíll talk about some of the films. Ultrasound probably has a role in selected instances and CT scanning is beginning to have a bigger role in the evaluation of patients with an acute abdomen but, unfortunately, those are not always available 24 hours a day at every hospital. Plain films of the abdomen are the place to start in evaluating a patient with an acute abdomen.

When you look at an abdomen film, I want you to remember, please, that you have some very inexpensive tools available to you. You know, when you send a patient to us to evaluate their bowel, we put contrast in and we can do small bowel series and barium enemas and so on and so forth, but when you are looking at a plain film of the abdomen, you also have an inexpensive contrast media there and that is air.

Number one, it's like buying a house. Location is important. If you remember back to the gross lab, the small bowel is fixed with a mesentery and all of the loops of the small bowel are kind of tethered in the mid abdomen. So if the dilated loops of bowel that you are seeing are centrally located.

As opposed to colon, remember that the colon is partially a retroperitoneal structure. It is peripheral in its location. The ascending and descending colons are retroperitoneally fixed and the colon, because itís different than small bowel, has the haustra which are 2-3mm thick.

One thing thatís important to look at when youíre looking at plain films in these patients is to make sure that the technologist gives you a film including the rectum and the sigmoid. Because if you donít see any gas in the rectosigmoid, that should make you think more strongly about the possibility of obstruction. This was a patient that a barium enema was done on to rule out the possibility of a colonic obstruction and you can see that this patient had an annular obstructing lesion in the descending colon, an adenocarcinoma.

Iím going to say just a few words about markedly distended loops of bowel. One of the areas in the bowel that you should be concerned about, particularly when it becomes distended, is the cecum. A rule of thumb to remember is that the cecum should not ever be more than 9-10 cm in diameter. If it is greater than that in diameter, that places the patient at risk of perforation. The thing to remember, too, about a distended cecum is it doesnít matter if the patient is obstructed or not. This could be a patient with a severe ileus, maybe with pneumonia or postoperatively. Once the cecum gets to be about 9-10 cm, there is vascular compromise. So even if that colon is not obstructed, the patient can still perforate. So always be cognizant of the patient whose cecum is this distended and these are the patients that I would refer to the gastroenterologist for decompression or to the surgeons for a cecostomy.

Iím going to show you an example of a couple of very specific bowel obstructions. This is a sigmoid volvulus. You may or may not have seen this before but remember that the sigmoid colon is on a long mesentery and particularly in elderly patients, the colon can twist upon itself. The classic radiographic finding is this U-shaped loop of bowel rising up out of the pelvis. These patients need to be decompressed because the pathophysiology is the same as with a distended cecum. The vascular supply to the colon is compromised and they can become ischemic and perforate.

Hereís another specific example of a distended bowel loop that you should recognize. This is a cecal volvulus. This was a case that one of our residents had on call at an outside hospital. The first thought that the resident had was that that big distended loop of bowel on the mid abdomen was the stomach. So they put down a nasogastric tube and the stomach did not decompress so he then had to start thinking about other things.

Classically when the cecum, which is also on a mesentery and may be on a very long mesentery in some patients, becomes twisted, classically what happens when this cecum twists upon itself, it flaps up into the left upper quadrant mid abdomen. One of the radiographic findings is this distended loop of bowel, kind of kidney-bean shaped, in the mid abdomen to the left upper quadrant. Then look in the right lower quadrant and there is no cecum. So this would be very suspicious for cecal volvulus.

Iím going to talk a little bit about another plain film finding and thatís pneumatosis intestinalis and that is gas in the wall of the bowel. Here we see a patient who was a patient in the intensive care unit at the VA hospital. You see this is a loop of colon. This is the hepatic flexure and you can see there is a lot of fecal material in the colon but there is also this area surrounding that loop of bowel. This is air within the bowel wall or pneumatosis.

Primary pneumatosis is idiopathic, benign. The patients are asymptomatic and it requires no therapy. The problem is there is also pneumatosis which is associated with bowel necrosis that is not benign and does require treatment. So when you see pneumatosis, give some consideration to necrotizing enterocolitis if the patient is a child, vascular compromised if the patient is an adult and mesenteric arterial occlusion in adults with bowel infarction. Itís a very concerning finding when you see pneumatosis on a plain film.

The other thing to remember about pneumatosis, in the patient that I showed you initially, the patient who has chronic obstructive lung disease, those patients can dissect air into their mediastinum and down into the retroperitoneum out into the mesentery. So thatís a patient population who can get benign pneumatosis also. So itís like when you find pneumatosis on a plain film, your antenna should go up and say, "This patient could be potentially very ill" and then you have to correlate all of things that you are finding on the plain film.

Weíre going to switch gears here and talk about another gas collection in the abdomen that can be of clinical significance and that is pneumobilia or air within the bowel ducts. It is a fairly common finding, particularly here at the University where we have so many liver patients. Probably the most common cause of air in the bowel ducts is a sphincterotomy. That could be the patient who has had an ERCP and sphincterotomy or a patient who has gone to the Operating Room for cholecystectomy and stone retrieval. Another possible cause is a patient who has had a biliary enteric anastomosis for some sort of obstructive process.

A specific disease process that can cause pneumobilia is gallstone ileus where you have a gallstone which has incited an inflammatory response in the gallbladder and a stone erodes into the small bowel. That stone then can pass through the small bowel, usually until it hits the distal ileum. The distal ileum is too small to let the stone go through and so the patients develop small bowel obstructions.

You can also get pneumobilia in a patient who has severe peptic ulcer disease. If you remember where the duodenum and the common duct are in relation to each other anatomically, if you have a posteriorly perforated duodenal ulcer, you can get air in the bile ducts. Also you could potentially have a patient who had a malignancy of the sphincter of Oddi that was necrotic and led to the formation of the communication between the bile ducts and the gut.

This is a patient who has a gallstone ileus and you see kind of a fluid level here in the right upper quadrant. Thatís air within the bowel ducts that we are looking at right here. Itís important to recognize that tubular gas collection in the right upper quadrant as opposed to portal vein gas which has a grave prognostic significance. When you see portal vein gas, that means that your patient has dead bowel. This is probably the best example of portal vein gas I have ever seen. This is a patient who, unfortunately, had extensive bowel necrosis and we can see all of these tubular structures.

Pneumoperitoneum, I think you guys are all familiar with what it looks like on the upright chest x-ray where you see gas collecting under the right hemidiaphragm. Hereís a little less subtle case where you see the huge collection of gas under the right hemidiaphragm. You are probably all familiar with the appearance on the decubitus film. You look in the right upper quadrant for gas collection up over the liver and underneath the right hemidiaphragm. The important thing to remember is, particularly in female patients, this may be the highest part of the abdominal cavity and so you always want to look. Make sure that the technologist shows you the ileum because that may be the only place that gas will collect.

The thing to remember is this is what you want the decubitus film to look like because all you are interested in is whether or not there is gas and extra elementary air that collects up over the liver. So if the technologists brings you a film that shows you bone and shows you the bowel gas pattern, itís probably not exposed appropriately. You want to tell them to use air technique, more like a chest x-ray, because thatís all youíre looking for is gas. Hereís just a closeup to show you what youíre looking for. Again, this is probably the edge of the liver and this is the right hemidiaphragm.

Hereís a little bit more subtle case of pneumoperitoneum. This is a chest x-ray that was obtained on a patient that was admitted  with abdominal pain. If you look carefully, you can see in the left upper quadrant there is this little triangular collection of gas which you can see right here and that was a pneumoperitoneum. This patient had a perforated gastric ulcer and I think that there was an inflammatory process going on so that the pneumoperitoneum did not assume the configuration that I just showed you as classic. You have to always be kind of suspicious of unusual gas collections and that was just showing a little piece of the underside of the left hemidiaphragm which we should never be able to see.

I talked to you about all of those wonderful films that we would ideally want to obtain and unfortunately not every patient can go through the rigors of getting all of those films. So every once in awhile the best you might be able to do is to get a supine film of the abdomen. So Iím going to tell you a couple of things to look for to help you diagnose pneumoperitoneum on a supine film.

This is the falciform ligament right here which everyone has but we shouldnít be able to see it. The reason we can see it in this patient is because itís got air outlining it so this patient has a huge pneumoperitoneum. Just remember, you donít want to see their falciform ligament.

Hereís another patient who has a pneumoperitoneum and, again, itís a little bit subtle to detect. Weíre looking at whatís called the "double wall" sign and I think I have an enlarged view of this. In the right upper quadrant you can see air in the lumen of the bowel but you can also see the outer wall of the loop of bowel. So the only way you are going to see that is if it is outlined by air. So this patient has a pneumoperitoneum. Thatís the "double wall" sign. The one caveat I would give you about that is if you have a bunch of loops of bowel lying on top of each other, you can sometimes get fooled that you are seeing a double wall sign when you are really just seeing a bunch of loops of bowel superimposed on each other. But thatís a telltale sign of a pneumoperitoneum.

If you find a pneumoperitoneum in your patients who have any evidence of peritonitis, it means that they have a perforated viscus and it means that they go to your surgical colleagues because they need to go to the Operating Room.

The thing to remember is if you somehow have a patient with a pneumoperitoneum and the patient is just "smoking and joking", as we say, and in no pain, remember that there can be benign causes of pneumoperitoneum. Iatrogenic is probably the biggest cause. If the patient was just in the OR a day earlier and had a laparotomy, itís not at all uncommon to see a pneumoperitoneum. The thing to remember about the postoperative pneumoperitoneum is it should go away within seven days. So if you have a patient who is seven or eight days postop who pops up with a pneumoperitoneum and you hadnít seen one previously, then suspect that there may be a complication postoperative or that thereís a perforated viscus.

Some patients can develop spontaneous pneumoperitoneum. That patient I showed you who had the pneumatosis intestinalis, that can perforate and cause extra-elementary air. But that patient is going to be not clinically sick and you can probably just kind of watch and see what happens. There can be gynecologic causes of pneumoperitoneum. I think the classic one is the woman who is just maybe newly pregnant and goes waterskiing and just isnít maybe very good at it and spends a lot of time dragging her bottom end through the water. She can develop a pneumoperitoneum because she has really direct communication between the outside via the fallopian tubes, so just remember that as a possibility. Then there can be intrathoracic causes of pneumoperitoneum. The patient who has bad COPD, remember, I told you can rupture an alveoli and the air can dissect down into the abdomen.

Iím going to say just a couple of words about appendicitis. 20% of patients with appendicitis present with atypical findings. In other words, 80% of the time you donít need radiology to help you make the diagnosis of appendicitis as a clinical diagnosis. Weíll be happy to help you at any time but you donít really need us.