Pitfalls: Guts & Mesentery

Pitfalls of the Bowel and Mesentery

The lesions in both of these areas are easy to miss and to mischaracterize. An organized search and knowledge of certain pattern recognitions are key.

Multiplanar reformation, how many times are we gonna say this? It's really important. We all agree it's important, are very helpful.

Small bowel disease is common with some overlap of clinical and imaging features.

I remember in the Pleistocene era when I was in residency and we tried to distinguish among small bowel diseases on a barium small bowel follow through. And it was nearly impossible.

I think some people take the same attitude about CT. I see bowel wall thickening and it could be inflammatory, ischemic, neoplastic, blah, blah, blah. And I'm gonna hopefully give you some keys here that will allow you to offer a more narrow and clinically useful differential diagnosis.

This is the pages of one of my books opened up, Expert Differential Diagnosis, Abdomen. And it shows you the approach that I've tried to take with a couple of hundred common imaging findings, whether it be solid or a cystic renal mass, or in this case, segmental or diffuse small bowel wall thickening.

What I've tried to do in each of these is to list the common and uncommon, some cases, rare etiologies for this, and then to give you some general principles and then to list each of the potential entities along with no more than a few lines of the means to make this recognition as a specific diagnosis or at least narrow it down.

We'll focus in a little bit, and I think we'll get a chance to cover nearly all of these in this presentation.

Approach to Small Bowel Wall Thickening

Technique

The key issues to approach the first of these is technique. You have to give an adequate volume of contrast and you have to give it at an adequate rate.

I know a lot of people, once they move to helical, multi detector row CT scanners said, we can make white blood vessels with giving only 50 or 75 ml a contrast. And that's true enough. All you're trying to do is distinguish blood vessels from other, that may be possible, but for many other indications, you really need to give that full volume of contrast.

You really won't get adequate enhancement of the bowel mucosa or another setting liver mass and so forth without giving an adequate volume and tear contrast.

Our attitude to this is definitely evolving over the years. We used to almost always give positive contrast, medium, either dilute barium or iodine containing solution. But in fact, if you're specifically looking for bowel pathology, and this is counterintuitive, it's actually better to distend the bowel with water or some neutral agent such as Voluma. This accentuates our ability to recognize mucosal enhancement, a mural, mass luminal narrowing, and so forth.

Distribution of the Disease

Alright, the next key approach is the distribution of the disease. Is it focal? In most cases, that's going to be neoplastic or endometriosis as Jen just showed you examples of, or Crohn disease.

Segmental is the most common and therefore the least specific. If it's diffuse, it's not going to be neoplastic, probably not infectious. Think about things like vasculitis shock or portal hypertension.

You want to note whether the colon is or is not involved because that will narrow the differential diagnosis as well.

Bowel Wall Abnormalities

Next key to the approach is don't just say that the wall is thickened, but really try to see which part of the bowel wall is abnormal. Is it the mucosa? Is it the submucosa? Or least commonly is it the cosa?

In many most cases, it's going to be the submucosa, which is thickened. Don't just say it's thick, but really try to zero in on the density or attenuation of that thickened submucosa.

If it's gas density, then you're dealing with pneumatosis. It may be infarction or it may be one of the many benign causes, non ischemic causes of pneumatosis.

Is it fat density? Many of us have had drilled into our head, if you have a fat density thickened submucosa, that's indolent or inflammatory bowel disease in remission. It may be, but it frequently is not. So there are others who are just normal variants, obese patients. And then you can have it as a even acute finding in some patients who are undergoing cytotoxic therapy such as a bone marrow transplant patient.

If the submucosa density is near that of water near zero hounsfield units, it is not neoplastic. So that's a very useful thing to be able to drop off the differential diagnosis. It's going to be infectious, inflammatory or ischemic.

If it's soft tissue density submucosa, it still could be inflammation, but now tumor enters the differential diagnosis. And if it's blood density higher than soft tissue density, greater than 60 hounds field units, that's really pretty specific for hemorrhage.

Fat density submucosa normal variant in diabetics. Those with metabolic syndrome, those on steroid therapy distribution tends to be colon and distal small bowel. And the reason is, that's just take that as a given there following cytotoxic therapy, again, the bone marrow transplant, what you're doing in that situation is wiping out the lymphoid tissue. Lymphoid tissue is also more prevalent in the right side of the colon and the distal small bowel. So once again, the distribution of the fat density tends to follow fat pattern and inactive or chronic inflammatory bowel disease. Ulcerative colitis more often than Crohn's disease can also give you a fat density submucosa.

I've seen a bunch of cases that have been referred in or I've seen them in some other context. And they'll say, I'm looking at this patient who has kind of a straight looking colon. And the submucosa is fat density, which it truly is. You can see it on multiple sections here. This patient must have ulcerative colitis. I talked to this patient. He has no history of inflammatory bowel disease at all. He has no history of any kind of bowel disease, and this is just fat density. This is just normal variant obesity.

Mucosal Enhancement

Another key to the approach, the degree of mucosal enhancement normal is a hyperdense thin line, similar throughout the various segments of bowel. So there's not one focal segment of bowel that is hyper enhancing.

If there is focal increased enhancement of the mucosa brighter than the other bowel, then it's a sign of acute inflammation. Crohn's would be a typical example of that.

If there's decreased or absent mucosal enhancement in one segment as opposed to some other segment of bowel, then you're dealing with ischemia or infarction.

Effect on the Bowel Lumen

Next key. What is the effect on the bowel lumen? First of all, let me tell you, one of my pet peeves is when one of the residents says to me, I look at a CT scan, the bowel is thick. I have no idea what that means. Do you mean the bowel wall is thick? Do you mean the lumin is dilated?

I really get 'em to zero in on talking about lumen versus wall and then even the three layers of the bowel wall.

The abnormal bowel may have no effect on the lumen. It may have mild narrowing of the lumen, which is the most common, that may be totally obstructed with dilation of the lumen upstream, or there may be abnormal bowel wall and the lumen is dilated. And that's what we refer to as aneurysmal dilation.

I was always taught that that was almost specific for non-Hodgkin's lymphoma of the bowel. But in fact, we see this with melanoma metastases to the bowel, and we also see it in primary GI stromal tumors of the small bowel. They may look identical to lymphoma.

Associated Findings

Next key associated findings look for evidence of prior therapy. So for instance, anastomotic staple lines that you might see in somebody with Crohn's or brachytherapy beads that you might see in somebody who has abnormal small bowel loops in the pelvis, raising an issue of possible radiation therapy or could be a tumor.

Lymphadenopathy is an important associated finding that I'll allude to a number of times. Look for other evidence of tumors such as liver metastases and use the electronic medical record or the telephone.

Particularly if you're dealing with something that might be a life-threatening situation such as ischemia, and often the key to a narrow or a specific differential diagnosis is one key bit of information. I don't expect you to do a complete history and physical or completely review the medical records. A lot of times it's a matter of picking up the phone call or checking the laboratory and seeing whether the patient, for instance, has elevated amylase, lipase if the patient has an elevated lactic acidosis and so forth.

When you're thinking about ischemia, I really never, ever put into a radiology report paragraph impression such and such. Recommend clinical correlation. I can tell you that our clinical colleagues just see that as a cover your ass, cop out. And in most cases, frankly, I think it is, if you, there's a specific element of clinical correlation that you're thinking about, that's what you want to tell them about.

In a case of suspected bowel ischemia, you're looking for significant, usually severe abdominal pain and nausea. You're looking for acidosis, lactic elevated white count, elevated amylase. If you think that the pattern is most likely that of Crohn's disease, you wanna see if there's any clinical or radiographic evidence of prior episodes or chronic or intermittent disease.

But there's often a key question that you can ask of the referring clinician or actually just look up in the medical record as we do many, many times per day.

Specific Diseases

Crohn's Disease

All right, let's go through some specific diseases here. Crohn's disease distribution, segmental with skip areas, submucosa. In the acute flare event, the submucosa is generally water density. Again, in the inactive phase, it may revert to fat density, mucosal enhancement often marked, and the mucosa may be thickened is a good sign, a very specific sign of acute involvement associated findings.

Mesenteric hyperemia in the acute stage, the comb sign that you're familiar with fibro, fatty mesenteric, fat proliferation and mesenteric lymphadenopathy.

If you said to me, I'm looking at a CT scan and I see a patient that has segmental bowel wall thickening, what am I dealing with? That's an unanswerable question. If the patient has this set of findings, you're almost certainly dealing with Crohn's disease.

Here we have a patient who has had recurrent bouts of abdominal pain up to this point, not diagnosed or really even thoroughly evaluated. What do I see? For one thing, this bowel loop sort of stands out by itself because it's surrounded by proliferated, fibro fatty, tissue. The mucosa is both thickened and hyper enhancing. Telling me that there is an acute component to this. The fatty proliferation tells me there is a chronic component to it. And then we have mesenteric hyperemia, we have submucosal edema.

I'm having a little trouble with my hand there pointing. And then there, this is basically acute on chronic Crohn's disease. There's really virtually nothing else that looks like this other than Crohn's disease.

When you look at the coronal reformations, however, look how much more evident the mesenteric lymphadenopathy is Another sign that we typically associate with Crohn's disease. Look how much easier it is to recognize the longitudinal extent and what piece of bowel we're really talking about. Look at the comb sign. Look at the engorged mesenteric vessels. So much more evident on this, this shaded surface display coronal reformation.

So please incorporate that into your routine reading of abdominal pelvic CT scans.

Ischemic Enteritis

Ischemic enteritis distribution segmental may involve the right colon. For instance, somebody who has SMV occlusion or SMA embolization, submucosal density pneumatosis. If it's infarcted, maybe edema, which may be seen in ischemia and you may have bleeding if there's intramural hemorrhage.

Mucosal enhancement is very important. And again, this is something that you're not gonna be able to appreciate if you've given the patient positive oral contrast medium. But using a neutral contrast agent like water or voluma absent foal absent or segmentally absent mucosal enhancement is very worrisome for ischemia.

On the arterial side in the venous occlusion, you may have normal mucosal enhancement or counterintuitively even increased enhancement associated findings. You're gonna closely look at the SMA and SMV, you're gonna look for ascites and you're gonna look for bowel obstruction upstream, particularly in a setting like or bowel obstruction in a setting of a closed loop obstruction, which is often accompanied by bowel ischemia.

By the way, these findings and the whole point of this course really including this lecture, these are all things now that are really important. They've always been important for patient care, but they're starting to find their way into the malpractice courts as well.

I have a case on my desk right now where I'm trying to defend a radiologist, and there are findings on the scan of distended bowel and submucosal edema and so forth and so on at focal ascites and a really subtle finding. I probably shouldn't describe it more in detail, and I think he did a pretty good job of listing a limited differential diagnosis, including mentioning the real diagnosis of ischemia. But he is being sued for not coming down harder on the specific diagnosis of ischemia.

The referring clinician didn't put two and two together, didn't pay close attention to the laboratory findings and so forth. And now they're trying to lay this all on the radiologist as well. You're supposed to make a specific diagnosis, doctor, and I'm seeing this over and over again. And I think that should add another element of stimulation to try to make as specific a diagnosis as possible.

Here's a case of bowel ischemia. The bowel wall was thickened in some areas in a segmental distribution. The mesentary is infiltrated. It's probably a little ascites. And then look carefully at the major blood vessels. Here is a branch of the superior mesenteric artery, the one of the al branches. And here is an engorged and occluded branch of the superior mesenteric vein. There's the superior mesenteric drunk trunk that has a thrombus within it.

So bowel ischemia associated with venous thrombosis. This is an elderly woman who was hypotensive following cardiac cath when she woke up for ischemia or from her surgery, rather anesthesia. She was complaining of severe abdominal pain. They sent her down for a CT scan and she's got ascites and she's got bowel wall thickening. The mucosa is enhancing. Fortunately there's a lot of submucosal edema, there's a little bit of ascites. And I said, I think this woman has ischemic bowel. And they looked at the laboratories and they said, yeah, she does have elements of that. She's starting to look better. And in fact, we did a repeat CT scan a day or two later and this had completely returned to normal.

So I'm sure that this was bowel ischemia, but fortunately it was self correcting after fluid resuscitation and getting her blood pressure back to normal. So I can't necessarily predict what the course of the bowel ischemia is, but it's very important to alert them to it. I have probably seen 10 malpractice cases on this exact topic right here.

So please perk up your ears on this. Radiologist looks at the scan and says, I see dilated small bowel and there's collapsed small bowel downstream paragraph. Impression, mechanical small bowel obstruction. That's true, but not enough because surgeons now are taking a very hands-off approach to most cases of bowel obstruction. They're waiting for them to improve on their own as many of them do.

But if you look at the additional findings here and say, we've got fally dilated bowel, the bowel, the small bowel upstream was actually not particularly dilated. There is infiltration of the mesentery to these specific bowel loops. The mucosa is enhancing poorly. The margins of the bowel are very obliterated here and there's an abnormal pattern of the bowel loops.

If you look again at the coronal and the sagittal reformations, I think you get a little better feel for that balloons on a string appearance that is so characteristic of closed loop bowel obstruction. This is a red flag emergency. You must get on the phone and call the clinician and personally alert them to this finding. This is a life-threatening situation that cannot be just sat on.

Here's a patient who has findings that we'd all see. We see portal venous gas, we see pneumatosis, we see ascites, we see gas in the veins, draining this segment of small bowel. We actually see hemorrhage between these bowel loops. So yeah, this is Almost certainly bowel infarction, but I have seen many cases of pneumatosis and even some cases of portal venous gas in patients that do not have bowel ischemia or infarction.

So the findings themselves are very worrisome for infarction, but we cannot make the specific diagnosis of infarction with very rare exceptions without knowing what's going on with the patient clinically. And when we call the clinician, say, yeah, this guy looks really sick, and yes, his lactic acid is up and yes, his white count and amylase are up. This is obviously bowel infarction.

You know that because you call the md there are more than 50 causes for pneumatosis And it's not always ischemia. So the diagnosis of ischemia is an imaging clinical and laboratory diagnosis. The clinicians are lousy at diagnosing it on their own and we are not good at diagnosing it on our own. You really need to put the information together.

Medications, particularly steroids and immunosuppression and chemotherapy is a common cause of pneumatosis. You may have pneumatosis upstream from a bowel obstruction that is not related to ischemia. If there's been recent instrumentation or a bowel to bowel anastomosis, you may have pneumatosis. And there are many, many more causes.

Here's a patient photographed at lung windows where the patient has exuberant pneumatosis, but there's no ileus. There's no ascites. The patient actually feels fine. I know that because I called the clinician and we find, she's had a recent bone marrow transplant. Now I've almost never seen bowel ischemia not accompanied by an ileus. And I have never one time I called one of my clinicians, I said, I seem some findings here and I'm really worried about bowel ischemia. And he says, that's interesting Mike, 'cause I'm looking at the patient and she's eating lunch. Patients with bowel ischemia aren't eating lunch. Okay?

So clinical correlation of a specific type is really important.

Shock Bowel

Shock bowel, we've seen this dozens of times. You've seen it if you work in a trauma center distribution, the entire small bowel plus or minus the colon, the submucosa density is edema. Water density, mucosal enhancement is striking. This is sort of a reperfusion finding really.

We often see associated pan peripancreatic and mesenteric edema. We often see other signs of hypotension such as the collapsed cava sign. We may see hemoperitoneum, by the way, you can see this in a patient who has no abdominal injury whatsoever and maybe even no blood loss with brain or spine trauma. So it's not correct to con consider this a sign of shock or hypovolemia. It can be seen in other causes of hypoperfusion.

Here's the 17-year-old boy injured in a motor vehicle crash. He has diffuse thickening of the bowel wall, small bowel submucosal edema, not blood. This is not hematoma. He has intense mucosal enhancement. There's a lot of mesenteric edema. There's the collapsed cava sign, collapsed renal veins. And you don't wanna send this kid to the operating room for a non-therapeutic laparotomy. In fact, that's very dangerous to this kid.

This needs to be recognized as shock bowel, not bowel trauma, not mesenteric trauma. And this will resolve with just recent fluid resuscitation of the patient. In fact, we repeated a CT scan the next morning and it reverted completely to normal portal hypertension.

Portal Hypertension

Portal hypertension backs up pressure within the veins of the mesentery. Hypo protein anemia, which often accompanies the cirrhotic patient, contributes to leaking of fluid out of the vessels into the bowel wall. So we may see this in the stomach, the colon, small bowel submucosal density is as expected that of water or edema. Mucosal enhancement is normal.

How are we gonna make this diagnosis? We're gonna look for associated signs of cirrhosis and portal hypertension, the big three, ascites, splenomegaly, and varice.

So this patient has marked right-sided colon wall thickening. There was some small bowel wall thickening as well. If you showed me only this image, I have no idea what all is going on here. The ascites in this case is probably part of the portal. Hypertension, I recognize the splenomegaly and then I recognize the cirrhosis. We have the widened fissures, the small nodular looking liver and so forth.

So I see this literally almost every day since we have a big transplant program and all the hospitals that I've worked at. Portal, hypertensive pathy or enteropathy is extremely common. It's okay if you wanna say, look, I can't be sure that this patient doesn't have some colitis. But that again, is an easy correlation with any clinical signs of colitis such as diarrhea and so forth. Anyway, this was all just portal. Hypertension, radiation, enteritis distribution, segmentally usually in the pelvis.

Radiation Enteritis

Submucosal density edema in the acute stage. Soft tissue in the chronic phase when fibrosis may replace the muscle and submucosal fat. Mucosal enhancements should be normal in the acute phase of radiation. Enteritis, it may actually be increased. Lumen is usually narrowed if there is a stricture and there may be signs of a small bowel obstruction with dilation of the lumen upstream associated findings, evidence of surgery such as anastomotic staples or clips in the pelvis or brachytherapy beads.

So again, if you first look at this, you're gonna see the ascites. You're gonna see the thickened wall of the small bowel. You're gonna hopefully note that it's a submucosal edema. But then you might say, what else do I have going on here? What do I have that would enable me to narrow the differential diagnosis?

Well, I see that the patient's had a midline abdominal surgery. Maybe I go to the workstation that sits right next to our view boxes and see, she's had endometrial surgery. The distribution in this case are pelvic bowel loops that are in the radiation therapy field. There's actually a bit of mu mucosal hyper enhancement in these affected bowel loops. And then we have the associated ascites. We do have some dilation of the bowel upstream because there was some narrowed segments with narrowed lumen. And we also can note the surgical absence of the uterus and ovaries.

So what's the clinical correlation here? The history and imaging evidence of cancer and radiation therapy. And of course the coronal imaging helps to better define the real distribution of the disease. The segments down here with a narrowed lumen and bowel wall thick or yes bowel wall thickening and the segments upstream that are dilated because of the luminal narrowing from the radiation and neuritis.

Opportunistic Infections

Opportunistic infections such as CMV cytomegalovirus or TB distribution is generally segmental submucosal density water to soft tissue mucosal enhancement may be decreased in the setting of CMV, which can cause ischemia actually, or it may be normal to even increase associated findings. Other signs of opportunistic infections. Lymphadenopathy which may have a characteristic low density center with enhancing periphery, so-called caius necrosis of lymph nodes that are pretty characteristic of tuberculosis.

What's the clinical correlation? I think Ali showed you actually a case of this history of AIDS or transplantation or leukemia. He showed you some third world immigrants who had abdominal tuberculosis. So something to think about. Certainly not common, but a possible diagnosis.

This is a 31-year-old woman who's had a lung transplant and we see long segment of bowel wall thickening, submucosal edema. There probably is some involvement of the proximal colon as well. And now could this be some other opportunistic? I can't tell which opportunistic infection this is. In the setting of a bone marrow transplant, would I be able to distinguish this from graft versus host? No, but what's the clinical correlation? Endoscopic biopsy, they can make a diagnosis very quickly once we tell them the narrow differential diagnosis of what's going on.

Vasculitis

Vasculitis is interesting, uncommon but not rare. Distribution is segmental. Submucosa is gonna be edema gas only if there's gone on to infection or well we wouldn't have immunosuppress. Sometimes yes, we will have from immunosuppression, you may get pneumatosis blood. For instance, patients with hens shown line perra, I've seen hemorrhage in the bowel wall.

The mucosal enhancement may be normal to increase. And then what are some associated findings? Look at involvement of other organs. Many patients with vasculitis such as arteritis, Noosa, have segmental ischemic injuries to the kidneys and other organs. And you may even be sharp enough to pick up aneurysms or occlusions of mid to large vessels depending on which particular type of vasculitis it is.

So this is a 21-year-old woman with severe abdominal pain. And again, I could tell them, yes, there's bowel wall thickening and give them a differential diagnosis. That's 15 things long. But if we also note that she's got sort of a striated nephro here, many of you think of pyelonephritis for striated neph and that's certainly a common cause. But ischemic, particularly ischemia due to vasculitis is another cause of that.

This is with those two findings. We called them and said, young person with this set of findings, think vasculitis. And this was proven to be rheumatoid arthritis. What did they do for clinical correlation? They checked serum markers such as rheumatoid factor and so forth, just more of the segmental involvement in her.

Angioedema

Here's a diagnosis I've had the chance to make a number of times that is angioedema either on the hereditary or drug induced variety distribution is segmental submucosal. Thickening is that of edema. Mucosal enhancement will be normal associated mesentary edema and ascites. And this will be a very scary looking abdomen. So I'll give you a little anecdote about that in a minute.

History here is key prior similar episodes for both the hereditary or patients who have been on ace inhibitors for some time and of course eliciting a history of this. And they will often have other symptoms of emus tissues such as laryngeal edema.

I actually saw a spate of these in a short period of time. Some years ago it was just about to write it up. And then I looked in the literature and there are dozens of articles about this in the cardiology literature. Believe me, your cardiologist know about this, but radiologists often don't, and radiologists may actually send them off in a wild goose chase looking for other things.

This is a case I'm very proud. One of our residents made this diagnosis on call second year resident at night had heard some version of this talk and this patient comes in, elderly man, and he's got abdominal pain. And the resident noted the segmental distribution of the submucosal edema normal bowel wall. I think I see a, do I see a uterus down there that would be embarrassing if this is supposed to be a elderly man. Anyway, I'll think about that.

Um, so anyway, it looks like it could be one of the many causes of segmental bowel edema, bowel inflammation. He had noted that the patient was a cardiac patient. He called up the ED and asked if the guy was on ACE inhibitors and if he had had previous episodes like this. Yeah, in fact, he had, so he made a specific diagnosis of ace inhibitor induced angioedema of the small bowel. And I've personally seen at least six cases identical to this.

But when you first look at it, elderly person with this finding, you're thinking of bowel ischemia. So you absolutely need that clinical correlation.

Small Bowel Carcinoma

Small bowel carcinoma, not segmental or diffuse, but focal. In fact, anytime you see a focal abnormality of the bowel wall, you want to be thinking about neoplasm. Submucosa, soft tissue density, inflammatory ischemic infectious are usually more edema or water density mucosa absent because the primary carcinomas arising from the mucosa and carcinomas are not hypervascular lesions associated luminal narrowing or obstruction in primary small bowel carcinomas. And then of course you're gonna look for evidence of metastases.

I think this is kind of a subtle finding made easier when you blow it up and put an arrow on it here. But there was dilation of the proximal small bowel and then some kinda lump here. I think it's more evident when you look at the coronal reformations. There's actually a classic apple core lesion of the jejunum that's causing soft tissue density, thickening of the wall, narrowing of the lumen partial obstruction. And once again, the mesenteric lymphadenopathy is much more evident on coronal reformations.

Anytime you see mesenteric adenopathy near a focal mass in the bowel wall, small bowel or colon, I want you to think about a primary carcinoma that's almost always gonna turn out to be the diagnosis. And in this case, picking up the phone and calling them. They said, would it make a difference that the patient had a history of celiac disease? And I said, celiac disease alone is not going to cause this. This could be a carcinoma or a lymphoma, both of which are more common in spr, but lymphoma generally does not cause bowel obstruction.

So this was what it should have been, which is a primary small bowel carcinoma, correctly diagnosed preoperatively. This patient has a middle-aged woman with a history of hereditary non polyposis colon cancer, but she doesn't have a colon cancer. She has a soft tissue density mass in small bowel, again, sort of an apple core lesion with mesenteric lymphadenopathy. It's a focal soft tissue density lesion Because of the mesenteric infiltration. Gives evidence of a larger mass effect. But this was a primary small bowel carcinoma in this setting.

Here's the axial images, The mass, again, soft tissue density, submucosa, not emus. Lymphoma really looks different. Metastasis can look just like carcinoma. Lymphoma looks different than primary bowel carcinoma 'cause lymphomas tend to be, well, they may be multifocal and they tend not to obstruct the bowel lumen. Lymphomas are soft as opposed to carcinomas, which are very securous. It again, though either will give you soft tissue density in the bowel wall. If you, you may see.

And I'm gonna show you a case of a patient who has a malignant carcinoid tumor. And there are bowel segments that are emus. I don't want you to get confused here. The edema, the emus bowel wall segments don't have the cancer in them, but they, or the ones that are, have occlusion or narrowing of their blood vessels. So those segments with the emus wall are secondarily involved, but not by cancer itself.

Metastasis

What are the associated findings? Well, obviously if there's a known or primary malignancy, such as a melanoma, other metastases such as liver aneurysmal, dilation of the lumen, again, is something that we see in melanoma, non-Hodgkin's lymphoma and gist. And then you are gonna look for signs of bowel obstruction and interoception.

In patients with melanoma in the mesentery or bowel wall, they will often lead to interoceptions. So here's a patient who has a abrupt well dilation of the stomach and do edem. There's nasogastric tube to decompress the stomach, and then the bowel wall becomes abruptly thickened as it goes from second to third Duodenum, the lumen is essentially obliterated. There's some surrounding infiltration soft tissue density of the surrounding fat.

This could absolutely be a primary duodenal carcinoma. Turns out on surgery to be metastatic from this woman's known breast cancer. But either way, this is going to be cancer.

Here's a patient with lymphoma. We have coronal, which helps to I think show the mesenteric lymphadenopathy once again. And also the multifocal distribution of the disease. You're gonna correlate, of course the axial as well as the coronal images. So multifocal soft tissue density submucosa in spite of these big masses, there's no evidence of bowel obstruction, essentially. Never see that in carcinoma. And what are the symptoms in this case? Well, they probably know the patient has lymphoma, but maybe not. Maybe this is a new presentation and we'd ask about night sweats, fever, weight loss. The typical B symptoms that we see in patients with lymphoma Here are metastases to the bowel. And in this case, it is mostly the cirr rosa that is involved.

There is some submucosal edema in segments of bowel that are not primarily, this is not a cancer of this bowel, but rather there's a lot of cancer in the mesentery here and on the surface of the bowel leading to the bowel wall thickening. So veins and lymphatics are occluded by the metastases from this woman's ovarian cancer and that led to the small bowel wall edema.

Carcinoid

Carcinoid, what's the distribution? The great majority of the cases are in the ileum more than the jejunum. Submucosa soft tissue density for the primary tumor, tumor edema for other segments of affected small bowel. You will see hyper enhancement of the primary tumor. The primary tumor is often less evident than the mesenteric metastases, which is interesting. And they often have calcifications in the mesenteric mass.

What are associated findings? The desmoplastic effect on adjacent bowel loops and liver metastases, which are often hypervascular and only or best seen on the arterial phase of imaging.

Here's a patient who has a hypervascular mass that narrow, oops, narrows the lumen of this segment of ileum. There are hypervascular masses, which I will show you in the liver. And the peritoneum and the mesentery and the mass in this case narrows the lumen as primary bowel wall tumors often do. Here are peritoneal metastases in Morrison's pouch and another one on the surface of the liver. This is actually not probably in the liver itself, but rather intraperitoneal. Same patient. We have mesenteric uh, metastasis here. There's a desmoplastic uh, effect on the mesentary primary GI stromal tumors distribution focal, almost always solitary, often large.

GI Stromal Tumors

The most common sites are stomach then duodenum, then small bowel, then colon submucosal, soft tissue density. It may areas of hyper enhancement and central necrosis. The mucosa is not involved. This is by definition a mass arising from the V wall. The lumen may be narrowed or normal or even ironically aneurysm dilated, but it rarely causes obstruction. And you may see associated liver metastases.

Here is a pri or here's a mass in the duodenum and is not causing bowel obstruction. Portions of it are very vascular, while other portions of it are quite necrotic looking, but there's no bowel obstruction. So it'd be a very bad appearance for a primary duodenal carcinoma. They're not hypervascular nor necrotic. And carcinomas would presume would more often obstruct the lumen.

Look at it in multiple planes, you get a little better feeling of the exophytic nature of this mass. If you saw this arising from the stomach, I think most of you would feel quite comfortable calling this a gi stromal tumor. Well it is, but just happens to be arising from the duodenum bowel wall hematoma.

Bowel Wall Hematoma

We're getting into the last of the density changes in the bowel wall. This is really the only one that will cause mural thickening of greater than soft tissue density. The lumen will be squeezed, narrowed. Other associated findings may be signs of trauma, history of instrumentation or anticoagulation.

Here's a young child that was injured in blunt trauma. This is the lumen of the du second duodenum and or its mucosa. And there's mark narrow lumens, tremendous thickening of the wall crossing. Over the third duodenum. There's a little bit of hemoperitoneum and this is a intramural hematoma of the duodenum from blunt trauma.

This was a follow-up upper GI series. Seven days later you still see the mass effect in the second and third duodenum that is narrowing the lumen. And that's a fairly specific diagnosis.

Summary

In summary, before we go on to the questions, I would really like you to try to provide a specific or very narrow differential diagnosis for cases of bowel wall thickening or abnormal small bowel.

The keys are proper technique, prefer water as the oral contrast medium. You need a good bolus of IV contrast you need to view in multiple planes. Look at and characterize specifically the density of the submucosa air density you're dealing with. Pneumatosis fat density can't be acute disease. Water density equals edema, not neoplasm. Soft tissue density could be any etiology, but a focal soft tissue density luminal narrowing process in the bowel is probably tumor. And finally, higher than soft tissue density is going to be an intramural hematoma.

Look at the distribution. Focal is worrisome for tumor. Segmental is the most common and non-specific. Diffuse is probably going to be some systemic process. Hypotension, hypo protein, anemia, portal hypertension and so forth.

Mucosal enhancement absent worry about ischemia, normal nonspecific, increased active inflammation associated findings as previously discussed and illustrated. Don't end your report with a blanket. Recommend clinical correlation. If you're worried about ischemia or some specific etiology, bring that to their attention. Often a quick phone call to the referring MD or a glance at the medical records will lead to a specific diagnosis.

Questions and Cases

Sam, question number one. 78-year-old man comes in with early satiety and epigastric discomfort. I'm testing your short-term memory recall right now. I'm starting off with a softball here. So what do you like for your diagnosis here? There's a duodenal lesion mass effect. Is this carcinoma or Crohn's disease or gi stromal tumor or lymphoma?

Alright, short-term memory is intact. That's good. That was your Alzheimer's test for today. So this is a very characteristic GI stromal tumor. Again, stomach and duodenum are more most common. Look for hypervascular, mass intramural often exophytic often with areas of necrosis. It rarely obstructs. It may in fact even cause aneurysmal dilation of the lumen.

All right, 78-year-old man comes in with cardiac disease and he has had repeated episodes of severe abdominal pain and nausea. Is this angio neurotic edema, Crohn's disease, bowel ischemia or lymphoma answers please. Oops. All right. They all look alike, don't they? They actually do. Oh, how did you, how did what happened there? I'm going in the opposite direction here.

This is like those teachers that are getting paid by how well their students do on the tests. And they're worried that they're not gonna get a pay raise if their students do badly. So, you know, they, they're actually getting out erasers and changing their kids' answers. This was not my motivation. This is just my elderly fingers misbehaving here. All right.

65-year-old man, abdominal pain and melon and history of prosthetic valves, which I was able to pick up on the scout film of the lower chest and abdomen. And he's got bowel wall thickening here because it looks pretty normal to me and it's really a very focal process here. So what do we like for the diagnosis here? Hematoma. So al hematoma focal or segmental wall thickening greater than soft tissue density associated findings? None. Although I have seen some cases where there are other signs of a coagulopathic hemorrhage.

So if you see like a retroperitoneal bleed with a hematocrit effect patient, it's always a coagulopathic hemorrhage. That's a different lecture, but a good one. And when I called him this guy had an INR of seven. So that's the clinical correlation we need here.

28-year-old woman. This is a good one. 28-year-old woman with abdominal pain and persistent UTI urinary tract infection. I'll let you look at that. And then I'm gonna show you some reformatted images. So we're drawing your attention down here. I probably didn't need your attention drawn. All right. There's the coronal reformatted images And, And a couple of sagittal images. Alright, I'll keep my hands off the mouse here. What's the diagnosis? Carcinoma, lymphoma, Crohn's or infectious enteritis. DD All right.

So we got mostly Crohn's, which is good. Infectious enteritis would be a reasonable consideration. But can I go back here? Let me point out a couple of other things. So yes, there is luminal narrowing, probably some mucosal hyper enhancement, some schmutz in the mesentery here. There's dilation of the bowel upstream. So we know there's an element of bowel obstruction. There's a fistula from the small bowel to the bladder, which I would've found impossible to diagnose on the axial sections, particularly once I showed to you. This is actually focal thickening of the bladder wall.

But the real money shot, I think is these sagittal reformations where you can see a track going from the Foley thickened bladder wall to the affected segment of small bowel. So acute infectious enteritis just isn't gonna do this. This has to be a chronic indolent process. And we know that Crohn's really likes to form fistulas and sinus tracts.

So we were able to say, look, this is almost certainly Crohn's. There is an vesical fistula. And that was very good information for the management of this patient. And here's a nice article for you that there for your reading enjoyment.

Okay, I think the last of the Sam question is 39-year-old man. They didn't volunteer any bowel symptoms. This was found on a scan performed for other reasons. And what do we think is going on? That is the colon, by the way that the arrows are on. Here's coronal reformations with more arrows, drawing your attention to the affected segment of bowel. I think you can see that the mucosa is enhancing. And then there's some thickening of the wall here of different density.

So what do we think is going on here? Normal variant quiescent, inflammatory bowel disease, colitis, or colon cancer. Answers, please. Yeah, normal variant. Now it could, could it be inflammatory bowel disease? Yes, but I think once again, in the absence, I mean, there's really no for shortening of the colon. There's no other associated findings.

What I would probably say in this case is this is most likely just a normal variant, particularly given the fact that this patient's quite obese. If you're going to say, I think that this guy has ulcerative colitis or Crohn's disease, I'd be very concerned about that because you don't wanna label people as having chronic illnesses, particularly something like Crohn's. Again, making insurers and patients and their doctors nervous.

If you wanted to say something like unless there is a history of inflammatory bowel disease, this is most likely going to be a normal variant, that would be fine. But to otherwise say, this finding of fat density is associated with inflammatory bowel disease, that alone would be a bad thing to do. Patients would suffer undue anxiety as a result of that.

So I hope this review has been a good review for you and help you in an area of differential diagnosis. That approach by the way to using decision support tools, I think is a really important one. Not trying to promote my own of that. There are many sources of decision support, but using something to narrow the differential diagnosis and making a clinically more useful report, I think is a critically important thing, a goal for us to have as radiologist.

Thanks for your attention.