- Email: [email protected]
Plain Film Radiologic Examination of the Abdomen
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Figure 1. A, Extensive small bowel dilatation is present throughout the abdomen. Notice that the valvulae conniventes of the small bowel extend across total diameter of the lumen (arrows). This helps differentiate small bowel from colon dilatation. B, Numerous air fluid levels at different heights are seen in this same patient on the erect film, suggestive of a mechanical small bowel obstruction. C,A string of pearls sign is seen in this patient with high-grade obstruction (arrows). lllustration continued on opposite page
looked to get to the "juicer" part of the film, but commonly are an acute, reversible cause of the patient's problem. After checking catheter position, one should scan the film for abnormal calcification and, at the same time, examine the bony skeleton. Unless one makes a mental check list to search for these, they will be overlooked. Next, the film interpreter should determine the location of abdominal gas collections (intraluminal, extraluminal, and so on), and only then should the bowel gas pattern be analyzed.
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Small Bowel Obstruction. One of the most difficult tasks in evaluation of suspected bowel obstruction is determining whether the distended loops of bowel are colonic or small bowel. The mucosal folds of the small bowel (valvulae conniventes) extend across the total diameter of the small bowel. The colonic haustra cross only approximately one third of the luminal diameter.36Fluid levels at different heights in the same distended bowel loop are very suggestive of mechanical small bowel o b s t r u ~ t i o n(Fig. ~ , ~ ~1 A,B); however, this pattern occasionally is seen in adynamic i l e ~ s . ~ A~ "string , ~ ~of, pearls" ~ ~ sign (linear collection of tiny air bubbles) occasionally is seen in patients with high grade or closed-loop obstruction and almost totally fluid-filled bowel loops (Fig. 1C). The condition represented by the misnomer, gallstone ileus (which really is obstruction of the small bowel by a gallstone), is identified by the triad of small bowel obstruction, recognition of a gallstone (usually lodged in the distal ileum at the ileocecal valve), and air in the biliary tree.17 If the diagnosis of obstruction is uncertain after clinical and plain film radiographic findings have been reviewed, it is safe to give oral barium sulfate if no signs of peritonitis or perforation are present.25It is a common fallacy that barium is unsafe in small bowel obstruction and that water soluble contrast material should be used. This practice is both nondiagnostic and possibly dangerous.24 A mechanical small bowel obstruction is unlikely if contrast reaches the ascending colon within 12 hours. A single contrast barium enema often is very useful in identifying the obstruction site in very distal small bowel obstruction, and in differentiating small bowel from proximal colon obstruction. Colon Obstruction. Proximal and mid large bowel obstructions can be identified readily on AP and decubitus films by the distention of the proximal large bowel with air fluid levels (on the erect film) and distal large bowel. Distinguishing distal large bowel obstruction (LBO) (Fig. 2) from ileus often is very difficult. On supine radiographs, air may be seen in distended large and small bowel loops (if a patent ileocecal valve is present). Large airlfluid levels may be present on upright or decubitus films in both conditions. In these problem cases, right lateral decubitus films often shift gas into the descending colon, and a prone film may help move gas into the r e c t ~ m .If~ air ~ ,still ~ ~is not seen in sigmoid or rectum, a distal large bowel obstruction may be present. If differentiation of these two conditions is still difficult, direct visualization or a barium enema may be helpful. The risks of moving an acutely ill patient out of the ICU and distending his colon with contrast clearly must be weighed against the potential benefit of this examination. Evaluation of an LBO by oral contrast is contraindicated because the barium may solidify in the large bowel as the water is absorbed.15 Barium is the preferred rectal contrast medium, and water soluble contrast should be used only if perforation or anastomotic leak is suspected or if the cecum is greater than 10 cm in diameter.33r35If the cause of obstruction is thought to be diverticulitis or inflammatory bowel disease, CT should be performed rather than a barium examination, which may be contraindicated in these condition^.^,^^
Figure 3. A distended loop of sigmoid colon arises from the pelvis and is pointed towards the left upper quadrant. The dilatation of the colon proximal to this is suggestive of a sigmoid volvulus rather than a cecal volvulus.
The cecum may twist along an elongated mesentery, or a redundant sigmoid colon may twist upon itself and simulate a severe ileus. In postoperative patients, ileus and lax abdominal musculature may allow the cecum to dilate and twisL3 In one studv. almost 50% of cecal volvulae initially were missed by the radiologist.' Classically, the mobile, distended cecum is twisted in an oblique axis in the left u m e r auadrant with no distal bowel distention.18 Cecal volvulus should be reduced by endoscopy rather than barium enema. In sigmoid volvulus, the radiographic findings usually show a greatly distended bowel loop arising from the pelvis into the upper abdomen, forming an upside down U18 with marked distention of proximal colon (Fig. 3). A barium enema usually can reduce sigmoid volvulus, although endoscopy or rectal tube placement at the bedside may be preferred in the ICU. i ,
I 1
I
Colitis
After the presence of obstruction has been excluded and it is determined that all the air collections on the radiograph are in the bowel lumen, the mucosal contour and wall thickness should be evaluated. The normal bowel wall should be less than 2 mm in thi~kness.'~ If the wall is thickened or if there are nodular densities instead of smooth mucosa, colitis may be present. If the small bowel is affected, regional enteritis may be the cause; in the large bowel, however, it is difficult to discriminate between Crohn's colitis, ulcerative colitis, and pseu-
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283
domembranous Furthermore, plain film findings usually are seen only in very severe presentations of these diseases. To see whether inflammatory bowel disease may be present, one plain film hint is to check the sacroiliac joints because the arthritis associated with these entities may include bilaterally symmetrical sacroiliitis and appear very similar to ankylosing spondylitis.16 If further investigation of the bowel is necessary, then a computed tomographic (CT) scan should be obtained instead of a barium enema. Wall thickening often is present in ischemic bowel as well as in many inflammatory conditions and is demonstrated well on CT. In addition, barium enema often is nondiagnostic for conditions other than obstruction in the very ill ICU patient. Toxic Megacolon
Toxic megacolon, acute dilatation of a segment of large bowel, in a severely ill patient, may be associated with ulcerative colitis, Crohn's disease, or amebic and pseudomembranous c o l i t i ~The . ~ transverse colon is the segment most commonly involved. Mucosal irregularity, fold thickening, and pseudopolyposis usually are seen on the abdominal radiograph. Enemas and colonoscopy may perforate the thin, friable bowel wall if performed on these patients. Acute Mesenteric Ischemia
Many signs of bowel gas patterns have been associated with mesenteric ischemia. These include thumbprinting (Fig. 4) (submucosal edema), splenic flexure cut-off sign, and edematous bowel mucosa. These signs, unfortunately, are seen only rarely and are non~pecific.'~,~~ The most common radiographic sign seen in ischemia is marked small bowel dilatation, mimicking Extraluminal Air
Before the plain film of the abdomen is examined for bowel gas pattern, the interpreter should make certain that all the visible air is in the bowel lumen. Extraluminal air may be present free in the peritoneal or extraperitoneal space, or loculated in an abscess cavity. Extraluminal air also may be present in the solid organs, venous system, or bowel wall. Pneumoperitoneum
Pneumoperitoneum usually is caused by perforation of a hollow viscus by trauma or recent surgery.' Air may reach the peritoneal cavity . . from pneumoretroperitoneum, vneumothorax, or pneumomediastin ~ m . ~ ~If ,free * intraperitoneal air is identified on the radiograph, a careful examination of the chest radiograph is indicated, particularly in the ventilated ICU patient, who is susceptible to barotrauma. Although
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ROSZLER
Figure 4. Diffuse thumbprinting of the transverse colon because of subrnucosal edema (arrows). This is most often seen in patients with ischemia.
many radiographic signs of pneumoperitoneum have been described on the supine radiograph ("double wall sign," visualization of the falciform ligament, and air under anterior leaflet of diaphragm) (Figs. 5, 6), they usually are detected only when large amounts of free air are present.2It therefore is mandatory to obtain a left lateral decubitus or erect film in all patients in whom free air is suspected (Fig. 7). Pneumoretroperitoneum
Pneumoretroperitoneum may be caused by direct trauma or rupture of an ulcer or diverticulum, or may occur postoperatively.2 In the ICU, it may be due to barotrauma with development of a pneumomediastinum
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Figure 5. Both sides of the bowel wall are visualized on this examination (arrow). This is due to a large amount of free air that demonstrates the outer wall of the bowel.
and inferior dissection of gas into the retroperitoneal space (Fig. 8). Gas in the retroperitoneal space is differentiated from intraperitoneal gas in that it does not move upon changing patient position and it may outline psoas muscle fiber^.^ Abscess Cavity
Unless an abscess cavity contains air, it cannot be seen directly on plain films. When air is present, the cavity may present as an airlfluid collection in an unusual location (i.e., not the stomach) or small gas bubbles not in the bowel lumen.28Usually only the largest abscesses are detected on plain film prospectively, however, and if an abscess is thought to be present, a CT scan should be obtained (Figs. 9, 10).
Two types of pneumatosis coli have been identified. The discrete cystic form, which usually is "benign," may be due to chronic obstruc-
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ROSZLER
Figure 6. The arrows demonstrate a radiolucent crescent of air under the anterior leaflet of the diaphragm. This is one of the most sensitive signs of intraperitoneal air on supine plain film.
Figure 7. An erect lateral film shows a small amount of air underneath the anterior leaflet of the diaphragm (white arrow) outlining the liver margin (black arrow).
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287
tive pulmonary disease or idiopathic causes. The linear form often is due to ischemia and necrosis of the bowel all^^,^^,^^ (Fig. 11A,B). There may be some overlap in appearance and causes of intramural bowel wall gas collections. If linear intramural air is identified, the right upper quadrant of the radiograph should be inspected for air in the portal veins.
Figure 8. A, An unusual air collection can be seen in the mid-abdomen which is air in the retroperitoneal space. B, Tension pneumothorax and pneumomediastinum that extended inferiorly into the retroperitoneum causing air in the retroperitonealspace in Figure 8A. Notice 1, "8
cavity.
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Figure 9. On this erect film, the nasogastric tube is in the stomach (open arrow). The two smaller arrows demonstrate an air fluid collection of the subphrenic space representing a subphrenic abscess. Generally, free intraperitoneal air does not contain an air fluid level.
Portal Vein Gas Gas in the portal veins in the adult is an ominous sign that usually signifies bowel infarction (Fig. 12A) and impending death.34Gas may enter the portal veins directly from the bowel lumen via the necrotic bowel wall or may be caused by gas producing organisms.'' Gas in the portal veins is seen in a more peripheral location over the liver and in smaller channels than gas in the biliary tree (which is a relatively benign condition). Gas in the Biliary Tree Gas in the biliary tree usually is secondary to postoperative procedures (bowel anastomosis or sphincterotomy), erosion of a gallstone
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Figure 11. A, There is air present in the bowel wall (arrow). This is linear pneumatosis intestinalis and is associated with bowel wall infarction. B, There is air present throughout the sigmoid colon wall in this patient who has infarcted his sigmoid colon. The patient expired shortly after.
Emphysematous Cystitis
In contrast to emphysematous gyelonephritis, air in the wall of the bladder is not a surgical emergency and can be treated with antibiotic agents (Fig. 14). The condition is seen in diabetic and immunocompromised patients with bladder infection^.^^ The air in the bladder lumen should be differentiated from air in the bladder seen after bladder catheterization.
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Figure 12. A, Air is present in the main portal vein (arrows) in the portal venous system. The peripheral location of the gas differentiatesthis from gas in the biliary tree. 6,Air can be seen In me olllary tree. Notlce tne central locatlon ot the air and that it does not extend into the periphery. This is usually a relatively benign condition.
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Figure 13. There is air present in the collecting system of the kidney on the left (arrows). There also is present some air in the periphery of the kidney representing emphysematous pyelonephritis.
Figure 14. There is air present in the bladder wall (arrows) that is emphysematous cystitis. This is a relatively benign condition and may be treated with antibiotics.
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Calcifications
In addition to checking the radiograph for position of catheters, bowel gas pattern, and location of all gas collections, one should look for abnormal calcifications in both the abdomen and pelvis. Phleboliths
Phleboliths or calcifications in the pelvic veins are the most commonly identified calcification in the pelvis, and are seen in almost 50% of people in their fifth decade of life.8These calcifications usually have an interior lucency and are multiple. It is important not to confuse these completely incidental type calcifications with a stone in a ureter or an appendicolith. They tend to be differentiated from calculi by both their radiolucent center and their typical location, inferior to the ischial spines. Appendicolith
A calcification in the lumen of the appendix is the most important plain film finding of acute appendicitis (Fig. 15). It is seen in fewer than 15% of patients but, when present, is indicative of acute appendicitis, often with perforation.3r5These stones usually are larger, denser, and higher in the abdomen than phleboliths, which usually are below the ischial spines and in the distribution of the major pelvic vessels. The diagnosis of appendicitis also is aided by focal right lower quadrant ileus and a soft tissue mass. Calcifications in the Genitourinary Tract
Calcifications may be found in the kidneys, ureters, or bladder. Nephrocalcinosis is calcification in the renal parenchyma, and usually is due to systemic disease, such as hyperparathyroidism, other hypercalcernic states, renal tubular acidosis, and medullary sponge kidney. These often are bilateral and symmetrical. Nephrolithiasis is stones in the collecting system and may be caused by nephrocalcinosis, but usually is due to other metabolic diseases. The calculi may be small (opaque or lucent), or large and opaque (staghorn).l8 Ultrasonography is the preferred method of evaluating whether calculi are obstructive or whether associated renal inflammatory disease exists. Stones in the pelvic ureters may simulate a phlebolith in appearance, but often are irregular in shape and do not have a radiolucent center. If hydronephrosis is thought to be present, ultrasonography should be the initial modality of choice because it is portable, noninvasive, inexpensive, and directlv images the kidneys. There i s -RnnrnximAte 10%false-negative rate for acute renal obstruction on renal ultrasonography due to minimal early hydronephrosis. For acute obstruction, therefore, intravenous urography may be preferred.
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Figure 15. A laminated calcification (arrows) can be seen overlying the right sacroiliac joint. This is a large calcified appendicolith in a patient with appendicitis. Also noted is residual oral medication.
Calcifications in the Biliary Tree and Pancreas Only 20% of gallstones calcify13, but if seen, they are a very important clue to gallbladder pathology. Their location can be confirmed by ultrasonography. Intraductal calculi in the pancreas usually are associated with alcoholic pancreatitis27 and may provide important clinical information in very ill patients. Vascular Calcifications The amount of calcification in vascular disease varies. When the aortic wall calcifies, however, a very important clue is present on the plain radiograph. In patients who suddenly become hypotensive, a careful search of the plain film should be made for an aortic aneurysm.
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SUMMARY
In conclusion, when evaluating the abdominal plain film of the ICU patient, one should follow this mental checklist: 1. Are the catheters in satisfactory position? 2. What is the bowel gas pattern? 3. Is all the air in the bowel lumen? 4. Are there any abnormal calcifications?
References 1. Anderson JR, Mills JOM: Cecal volvulus: A frequently missed diagnosis? Clin Radiol 35:65-69, 1985 2. Baker SR: Main film radiology of the peritoneal and retroperitoneal spaces. In the Abdominal Plain Film. Norwalk, CT, Appleton & Lange, 1990, pp 72-91 3. Baker SR: Plain film radiology of the intestines and appendix. In the Abdominal Plain Film. Norwalk, CT, Appleton & Lange, 1990, pp 178-231 4. Bliznak J, Ramsey J: Emphysematous pyelonephritis. Clin Radiol 23:61-64, 1977 5. Brady BM, Carroll DS: The significance of the calcified appendiceal enterolith. Radiology 68:648-655, 1957 6. Cho HL, Morehouse HT, Allerman DD, et al: Sigmoid diverticulitis: diagnostic role of CT. Comparison with barium enema studies. Radiology 5:29%315, 1980 7. Christensen EE, Landay MR: Visible muscle of the diaphragm: Sign of extraperitoneal air. AJR 135:521-523, 1980 8. Culligan JM: Phleboliths. J Urol l5:175-188, 1926 9. Frimann-Dahl J: Special pathological findings. In Roentgen Examinations in Acute Abdominal Diseases, ed 3. Springfield, IL, Charles C Thomas, 1974, pp 88-131 10. Eisenberg RL: Gas in the biliary system (pancreaticobiliaryreflux). In Gastrointestinal Radiology: A Pattern Approach, ed 1. Philadelphia, JB Lippincott, 1983, pp 868-875 11. Eisenberg RL: Gas in the portal veins. In Gastrointestinal Radiology: A Pattern Approach, ed 1. Philadelphia, JB Lippincott, 1983, pp 876-880 12. Eisenberg RL: Gas in the bowel wall (pneumatosis intestinalis). In Gastrointestinal Radiology: A Pattern Approach, ed 1. Philadelphia, JB Lippincott, 1983, pp 89&932 13. Eisenberg RL: Fistulas involving the small or large bowel. In Gastrointestinal Radiology: A Pattern Approach, ed 1. Philadelphia, JB Lippincott, 1983, pp 970-975 14. Elkin M: Radiology of Urinary Systems, ed 1. Boston, Little Brown, 1980, pp 590-646 15. Gelfaud DW: Complications of gastrointestinal radiologic procedures. I. Complications of routine fluoroscopic studies. Gastrointestinal Radiol 5:293-315, 1980 16. Greenfield GB: Radiology of Bone Disease, ed 3. Philadelphia, JB Lippincott, 1980, pp 749-753 17. Harris JH Jr, Harris WH: Abdomen. In The Radiology of Emergency Medicine, ed 2. Baltimore, Williams & Wilkins, 1981, pp 430-442 18. Jones B, Braver BM: Essentials of Gastrointestinal Radiology, ed 3. Philadelphia, WB Saunders, 1982, pp 4%72 19. Keyting WS, McCaver RR, Ravack JG, et al: Pneumatosis Intestinalis: A new concept. Radiology 76:73>741, 1961 20. Kleinman PK, Brill PW, Whalen JP: Anterior pathway for transdiaphragmatic extension of pneumoperitoneum. AJR 131:271-275, 1978 21. Lowman RM, Davis C: Evaluation of cecal size in imuending.perforation of the cecum. Surg ~ ~ n e c Obstet oi 105:711-718, 1956
".
-
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-
-
l
r
a
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s
p
o
r
r
i
=
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mediastinum: clinical imvlications. Arch Intern Med 64:913, 1939 23. Miller RE: The technical approach to the acute abdomen. Semin Roentgen01 8:267-279, 1973
24. Mindelzun RE, McCort JJ: Radiology: Acute abdomen. In Margulis AR, Burhenne HJ (eds): Alimentary Tract Radiology. St Louis, CV Mosby, 1983, pp 397434 25. Nelson SW, Christoforides AJ: The use of barium sulfate suspensions in the study of suspected mechanical obstruction of the small intestine. AJR 101:367-378, 1967 26. Rice RP: Plain abdominal film roentgenographic diagnosis of ulcerative diseases of the colon. AJR 104:544550, 1968 27. Ring EJ, Eaton SB, Ferrucci JT, et al: Differential diagnosis of pancreatic calcifications. AJR 117:446-452, 1973 28. Sands WW: Extraluminal localized gas vesicles: An aid in the diagnosis of abdominal abscesses from plain roentgenograms. AJR 74:195-203, 1955 29. Schwartz S, Boley SJ, Robinson K, et al: Roentgenologic features of vascular disorders. Radiol Clin North Am 2:71-87, 1964 30. Schwartz SS: The differential diagnosis of intestinal obstruction. Semin Roentgen01 8:323-338, 1973 31. Scott JR, Miller WT, Urso M, et al: Acute mesenteric infarction. AJR 113:269-279,1971 32. Shaffer HA Jr: Small bowel diseases: Diagnosis using radiographic pattern analysis. Curr Probl Diagn Radiol 13(3):1-71, 1984 33. Shaffer HA Jr: Perforation and obstruction of the gastrointestinal tract. Radiol Clin North Am 30(2):405-426, 1992 34. Sister PB: Gas in the portal venous system. Radiology 77:103-107, 1961 35. Skucas J, Spataro RF: Colon. In Radiology of the Acute Abdomen, ed 1. New York, Churchill Livingstone, 1986, pp 181-248 36. Skucas J, Spataro RF: Small bowel. In Radiology of the Acute Abdomen, ed 1. New York, Churchill Livingstone, 1986, pp 135-180 37. Skucas J, Spataro RF: Bladder, prostate, and urethra. In Radiology of the Acute Abdomen, ed 1. New York, Churchill Livingstone, 1986, pp 625-626 38. Stanley RJ, Nelson GL, Tedesco FJ, et al: Plain film findings in severe pseudomembraneous colitis. Radiology 118:7-11, 1976 39. Tomchk FS, Wittenberg J, Ottinger LW, et al: The roentgenographic spectrum of bowel infarction. Radiology 96:249-260, 1970
Address reprint requests to Myer H. Roszler, MD Department of Radiology Detroit Receiving Hospital 4201 St. Antoine-3L-8 Detroit, MI 48201
ROSZLER
Figure 1. A, Extensive small bowel dilatation is present throughout the abdomen. Notice that the valvulae conniventes of the small bowel extend across total diameter of the lumen (arrows). This helps differentiate small bowel from colon dilatation. B, Numerous air fluid levels at different heights are seen in this same patient on the erect film, suggestive of a mechanical small bowel obstruction. C,A string of pearls sign is seen in this patient with high-grade obstruction (arrows). lllustration continued on opposite page
looked to get to the "juicer" part of the film, but commonly are an acute, reversible cause of the patient's problem. After checking catheter position, one should scan the film for abnormal calcification and, at the same time, examine the bony skeleton. Unless one makes a mental check list to search for these, they will be overlooked. Next, the film interpreter should determine the location of abdominal gas collections (intraluminal, extraluminal, and so on), and only then should the bowel gas pattern be analyzed.
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Small Bowel Obstruction. One of the most difficult tasks in evaluation of suspected bowel obstruction is determining whether the distended loops of bowel are colonic or small bowel. The mucosal folds of the small bowel (valvulae conniventes) extend across the total diameter of the small bowel. The colonic haustra cross only approximately one third of the luminal diameter.36Fluid levels at different heights in the same distended bowel loop are very suggestive of mechanical small bowel o b s t r u ~ t i o n(Fig. ~ , ~ ~1 A,B); however, this pattern occasionally is seen in adynamic i l e ~ s . ~ A~ "string , ~ ~of, pearls" ~ ~ sign (linear collection of tiny air bubbles) occasionally is seen in patients with high grade or closed-loop obstruction and almost totally fluid-filled bowel loops (Fig. 1C). The condition represented by the misnomer, gallstone ileus (which really is obstruction of the small bowel by a gallstone), is identified by the triad of small bowel obstruction, recognition of a gallstone (usually lodged in the distal ileum at the ileocecal valve), and air in the biliary tree.17 If the diagnosis of obstruction is uncertain after clinical and plain film radiographic findings have been reviewed, it is safe to give oral barium sulfate if no signs of peritonitis or perforation are present.25It is a common fallacy that barium is unsafe in small bowel obstruction and that water soluble contrast material should be used. This practice is both nondiagnostic and possibly dangerous.24 A mechanical small bowel obstruction is unlikely if contrast reaches the ascending colon within 12 hours. A single contrast barium enema often is very useful in identifying the obstruction site in very distal small bowel obstruction, and in differentiating small bowel from proximal colon obstruction. Colon Obstruction. Proximal and mid large bowel obstructions can be identified readily on AP and decubitus films by the distention of the proximal large bowel with air fluid levels (on the erect film) and distal large bowel. Distinguishing distal large bowel obstruction (LBO) (Fig. 2) from ileus often is very difficult. On supine radiographs, air may be seen in distended large and small bowel loops (if a patent ileocecal valve is present). Large airlfluid levels may be present on upright or decubitus films in both conditions. In these problem cases, right lateral decubitus films often shift gas into the descending colon, and a prone film may help move gas into the r e c t ~ m .If~ air ~ ,still ~ ~is not seen in sigmoid or rectum, a distal large bowel obstruction may be present. If differentiation of these two conditions is still difficult, direct visualization or a barium enema may be helpful. The risks of moving an acutely ill patient out of the ICU and distending his colon with contrast clearly must be weighed against the potential benefit of this examination. Evaluation of an LBO by oral contrast is contraindicated because the barium may solidify in the large bowel as the water is absorbed.15 Barium is the preferred rectal contrast medium, and water soluble contrast should be used only if perforation or anastomotic leak is suspected or if the cecum is greater than 10 cm in diameter.33r35If the cause of obstruction is thought to be diverticulitis or inflammatory bowel disease, CT should be performed rather than a barium examination, which may be contraindicated in these condition^.^,^^
Figure 3. A distended loop of sigmoid colon arises from the pelvis and is pointed towards the left upper quadrant. The dilatation of the colon proximal to this is suggestive of a sigmoid volvulus rather than a cecal volvulus.
The cecum may twist along an elongated mesentery, or a redundant sigmoid colon may twist upon itself and simulate a severe ileus. In postoperative patients, ileus and lax abdominal musculature may allow the cecum to dilate and twisL3 In one studv. almost 50% of cecal volvulae initially were missed by the radiologist.' Classically, the mobile, distended cecum is twisted in an oblique axis in the left u m e r auadrant with no distal bowel distention.18 Cecal volvulus should be reduced by endoscopy rather than barium enema. In sigmoid volvulus, the radiographic findings usually show a greatly distended bowel loop arising from the pelvis into the upper abdomen, forming an upside down U18 with marked distention of proximal colon (Fig. 3). A barium enema usually can reduce sigmoid volvulus, although endoscopy or rectal tube placement at the bedside may be preferred in the ICU. i ,
I 1
I
Colitis
After the presence of obstruction has been excluded and it is determined that all the air collections on the radiograph are in the bowel lumen, the mucosal contour and wall thickness should be evaluated. The normal bowel wall should be less than 2 mm in thi~kness.'~ If the wall is thickened or if there are nodular densities instead of smooth mucosa, colitis may be present. If the small bowel is affected, regional enteritis may be the cause; in the large bowel, however, it is difficult to discriminate between Crohn's colitis, ulcerative colitis, and pseu-
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283
domembranous Furthermore, plain film findings usually are seen only in very severe presentations of these diseases. To see whether inflammatory bowel disease may be present, one plain film hint is to check the sacroiliac joints because the arthritis associated with these entities may include bilaterally symmetrical sacroiliitis and appear very similar to ankylosing spondylitis.16 If further investigation of the bowel is necessary, then a computed tomographic (CT) scan should be obtained instead of a barium enema. Wall thickening often is present in ischemic bowel as well as in many inflammatory conditions and is demonstrated well on CT. In addition, barium enema often is nondiagnostic for conditions other than obstruction in the very ill ICU patient. Toxic Megacolon
Toxic megacolon, acute dilatation of a segment of large bowel, in a severely ill patient, may be associated with ulcerative colitis, Crohn's disease, or amebic and pseudomembranous c o l i t i ~The . ~ transverse colon is the segment most commonly involved. Mucosal irregularity, fold thickening, and pseudopolyposis usually are seen on the abdominal radiograph. Enemas and colonoscopy may perforate the thin, friable bowel wall if performed on these patients. Acute Mesenteric Ischemia
Many signs of bowel gas patterns have been associated with mesenteric ischemia. These include thumbprinting (Fig. 4) (submucosal edema), splenic flexure cut-off sign, and edematous bowel mucosa. These signs, unfortunately, are seen only rarely and are non~pecific.'~,~~ The most common radiographic sign seen in ischemia is marked small bowel dilatation, mimicking Extraluminal Air
Before the plain film of the abdomen is examined for bowel gas pattern, the interpreter should make certain that all the visible air is in the bowel lumen. Extraluminal air may be present free in the peritoneal or extraperitoneal space, or loculated in an abscess cavity. Extraluminal air also may be present in the solid organs, venous system, or bowel wall. Pneumoperitoneum
Pneumoperitoneum usually is caused by perforation of a hollow viscus by trauma or recent surgery.' Air may reach the peritoneal cavity . . from pneumoretroperitoneum, vneumothorax, or pneumomediastin ~ m . ~ ~If ,free * intraperitoneal air is identified on the radiograph, a careful examination of the chest radiograph is indicated, particularly in the ventilated ICU patient, who is susceptible to barotrauma. Although
284
ROSZLER
Figure 4. Diffuse thumbprinting of the transverse colon because of subrnucosal edema (arrows). This is most often seen in patients with ischemia.
many radiographic signs of pneumoperitoneum have been described on the supine radiograph ("double wall sign," visualization of the falciform ligament, and air under anterior leaflet of diaphragm) (Figs. 5, 6), they usually are detected only when large amounts of free air are present.2It therefore is mandatory to obtain a left lateral decubitus or erect film in all patients in whom free air is suspected (Fig. 7). Pneumoretroperitoneum
Pneumoretroperitoneum may be caused by direct trauma or rupture of an ulcer or diverticulum, or may occur postoperatively.2 In the ICU, it may be due to barotrauma with development of a pneumomediastinum
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Figure 5. Both sides of the bowel wall are visualized on this examination (arrow). This is due to a large amount of free air that demonstrates the outer wall of the bowel.
and inferior dissection of gas into the retroperitoneal space (Fig. 8). Gas in the retroperitoneal space is differentiated from intraperitoneal gas in that it does not move upon changing patient position and it may outline psoas muscle fiber^.^ Abscess Cavity
Unless an abscess cavity contains air, it cannot be seen directly on plain films. When air is present, the cavity may present as an airlfluid collection in an unusual location (i.e., not the stomach) or small gas bubbles not in the bowel lumen.28Usually only the largest abscesses are detected on plain film prospectively, however, and if an abscess is thought to be present, a CT scan should be obtained (Figs. 9, 10).
Two types of pneumatosis coli have been identified. The discrete cystic form, which usually is "benign," may be due to chronic obstruc-
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ROSZLER
Figure 6. The arrows demonstrate a radiolucent crescent of air under the anterior leaflet of the diaphragm. This is one of the most sensitive signs of intraperitoneal air on supine plain film.
Figure 7. An erect lateral film shows a small amount of air underneath the anterior leaflet of the diaphragm (white arrow) outlining the liver margin (black arrow).
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tive pulmonary disease or idiopathic causes. The linear form often is due to ischemia and necrosis of the bowel all^^,^^,^^ (Fig. 11A,B). There may be some overlap in appearance and causes of intramural bowel wall gas collections. If linear intramural air is identified, the right upper quadrant of the radiograph should be inspected for air in the portal veins.
Figure 8. A, An unusual air collection can be seen in the mid-abdomen which is air in the retroperitoneal space. B, Tension pneumothorax and pneumomediastinum that extended inferiorly into the retroperitoneum causing air in the retroperitonealspace in Figure 8A. Notice 1, "8
cavity.
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Figure 9. On this erect film, the nasogastric tube is in the stomach (open arrow). The two smaller arrows demonstrate an air fluid collection of the subphrenic space representing a subphrenic abscess. Generally, free intraperitoneal air does not contain an air fluid level.
Portal Vein Gas Gas in the portal veins in the adult is an ominous sign that usually signifies bowel infarction (Fig. 12A) and impending death.34Gas may enter the portal veins directly from the bowel lumen via the necrotic bowel wall or may be caused by gas producing organisms.'' Gas in the portal veins is seen in a more peripheral location over the liver and in smaller channels than gas in the biliary tree (which is a relatively benign condition). Gas in the Biliary Tree Gas in the biliary tree usually is secondary to postoperative procedures (bowel anastomosis or sphincterotomy), erosion of a gallstone
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Figure 11. A, There is air present in the bowel wall (arrow). This is linear pneumatosis intestinalis and is associated with bowel wall infarction. B, There is air present throughout the sigmoid colon wall in this patient who has infarcted his sigmoid colon. The patient expired shortly after.
Emphysematous Cystitis
In contrast to emphysematous gyelonephritis, air in the wall of the bladder is not a surgical emergency and can be treated with antibiotic agents (Fig. 14). The condition is seen in diabetic and immunocompromised patients with bladder infection^.^^ The air in the bladder lumen should be differentiated from air in the bladder seen after bladder catheterization.
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Figure 12. A, Air is present in the main portal vein (arrows) in the portal venous system. The peripheral location of the gas differentiatesthis from gas in the biliary tree. 6,Air can be seen In me olllary tree. Notlce tne central locatlon ot the air and that it does not extend into the periphery. This is usually a relatively benign condition.
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Figure 13. There is air present in the collecting system of the kidney on the left (arrows). There also is present some air in the periphery of the kidney representing emphysematous pyelonephritis.
Figure 14. There is air present in the bladder wall (arrows) that is emphysematous cystitis. This is a relatively benign condition and may be treated with antibiotics.
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Calcifications
In addition to checking the radiograph for position of catheters, bowel gas pattern, and location of all gas collections, one should look for abnormal calcifications in both the abdomen and pelvis. Phleboliths
Phleboliths or calcifications in the pelvic veins are the most commonly identified calcification in the pelvis, and are seen in almost 50% of people in their fifth decade of life.8These calcifications usually have an interior lucency and are multiple. It is important not to confuse these completely incidental type calcifications with a stone in a ureter or an appendicolith. They tend to be differentiated from calculi by both their radiolucent center and their typical location, inferior to the ischial spines. Appendicolith
A calcification in the lumen of the appendix is the most important plain film finding of acute appendicitis (Fig. 15). It is seen in fewer than 15% of patients but, when present, is indicative of acute appendicitis, often with perforation.3r5These stones usually are larger, denser, and higher in the abdomen than phleboliths, which usually are below the ischial spines and in the distribution of the major pelvic vessels. The diagnosis of appendicitis also is aided by focal right lower quadrant ileus and a soft tissue mass. Calcifications in the Genitourinary Tract
Calcifications may be found in the kidneys, ureters, or bladder. Nephrocalcinosis is calcification in the renal parenchyma, and usually is due to systemic disease, such as hyperparathyroidism, other hypercalcernic states, renal tubular acidosis, and medullary sponge kidney. These often are bilateral and symmetrical. Nephrolithiasis is stones in the collecting system and may be caused by nephrocalcinosis, but usually is due to other metabolic diseases. The calculi may be small (opaque or lucent), or large and opaque (staghorn).l8 Ultrasonography is the preferred method of evaluating whether calculi are obstructive or whether associated renal inflammatory disease exists. Stones in the pelvic ureters may simulate a phlebolith in appearance, but often are irregular in shape and do not have a radiolucent center. If hydronephrosis is thought to be present, ultrasonography should be the initial modality of choice because it is portable, noninvasive, inexpensive, and directlv images the kidneys. There i s -RnnrnximAte 10%false-negative rate for acute renal obstruction on renal ultrasonography due to minimal early hydronephrosis. For acute obstruction, therefore, intravenous urography may be preferred.
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Figure 15. A laminated calcification (arrows) can be seen overlying the right sacroiliac joint. This is a large calcified appendicolith in a patient with appendicitis. Also noted is residual oral medication.
Calcifications in the Biliary Tree and Pancreas Only 20% of gallstones calcify13, but if seen, they are a very important clue to gallbladder pathology. Their location can be confirmed by ultrasonography. Intraductal calculi in the pancreas usually are associated with alcoholic pancreatitis27 and may provide important clinical information in very ill patients. Vascular Calcifications The amount of calcification in vascular disease varies. When the aortic wall calcifies, however, a very important clue is present on the plain radiograph. In patients who suddenly become hypotensive, a careful search of the plain film should be made for an aortic aneurysm.
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SUMMARY
In conclusion, when evaluating the abdominal plain film of the ICU patient, one should follow this mental checklist: 1. Are the catheters in satisfactory position? 2. What is the bowel gas pattern? 3. Is all the air in the bowel lumen? 4. Are there any abnormal calcifications?
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mediastinum: clinical imvlications. Arch Intern Med 64:913, 1939 23. Miller RE: The technical approach to the acute abdomen. Semin Roentgen01 8:267-279, 1973
24. Mindelzun RE, McCort JJ: Radiology: Acute abdomen. In Margulis AR, Burhenne HJ (eds): Alimentary Tract Radiology. St Louis, CV Mosby, 1983, pp 397434 25. Nelson SW, Christoforides AJ: The use of barium sulfate suspensions in the study of suspected mechanical obstruction of the small intestine. AJR 101:367-378, 1967 26. Rice RP: Plain abdominal film roentgenographic diagnosis of ulcerative diseases of the colon. AJR 104:544550, 1968 27. Ring EJ, Eaton SB, Ferrucci JT, et al: Differential diagnosis of pancreatic calcifications. AJR 117:446-452, 1973 28. Sands WW: Extraluminal localized gas vesicles: An aid in the diagnosis of abdominal abscesses from plain roentgenograms. AJR 74:195-203, 1955 29. Schwartz S, Boley SJ, Robinson K, et al: Roentgenologic features of vascular disorders. Radiol Clin North Am 2:71-87, 1964 30. Schwartz SS: The differential diagnosis of intestinal obstruction. Semin Roentgen01 8:323-338, 1973 31. Scott JR, Miller WT, Urso M, et al: Acute mesenteric infarction. AJR 113:269-279,1971 32. Shaffer HA Jr: Small bowel diseases: Diagnosis using radiographic pattern analysis. Curr Probl Diagn Radiol 13(3):1-71, 1984 33. Shaffer HA Jr: Perforation and obstruction of the gastrointestinal tract. Radiol Clin North Am 30(2):405-426, 1992 34. Sister PB: Gas in the portal venous system. Radiology 77:103-107, 1961 35. Skucas J, Spataro RF: Colon. In Radiology of the Acute Abdomen, ed 1. New York, Churchill Livingstone, 1986, pp 181-248 36. Skucas J, Spataro RF: Small bowel. In Radiology of the Acute Abdomen, ed 1. New York, Churchill Livingstone, 1986, pp 135-180 37. Skucas J, Spataro RF: Bladder, prostate, and urethra. In Radiology of the Acute Abdomen, ed 1. New York, Churchill Livingstone, 1986, pp 625-626 38. Stanley RJ, Nelson GL, Tedesco FJ, et al: Plain film findings in severe pseudomembraneous colitis. Radiology 118:7-11, 1976 39. Tomchk FS, Wittenberg J, Ottinger LW, et al: The roentgenographic spectrum of bowel infarction. Radiology 96:249-260, 1970
Address reprint requests to Myer H. Roszler, MD Department of Radiology Detroit Receiving Hospital 4201 St. Antoine-3L-8 Detroit, MI 48201