Imaging Acute Abdomen (Part 1)


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Discussion about role, indications and limitations of imaging in patients presenting with acute abdomen. Appropriateness criteria are also included.

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Imaging Acute Abdomen (Part 1)

  1. 1. Imaging Acute Abdomen Part 1: General Concepts Rathachai Kaewlai, M.D. Updated: May 2009 1
  2. 2. Overview Role, indications and limitations of each imaging modality: radiography, US, CT, MR imaging, scintigraphy Appropriateness criteria 2
  3. 3. Acute Abdomen: A Clinical Challenge “Severe abdominal pain develops over a period of hours” Common chief complaints: In USA, stomach and abdominal pain ranked first in patient presentation to emergency departments Difficult diagnosis: Broad differentials Nonspecific history and clinical examination Nonspecific lab tests 3
  4. 4. Acute Abdomen: A Clinical Challenge Require all resources to reach accurate diagnosis, timely management and proper disposition 4
  5. 5. Conventional Radiography Often the first imaging evaluation “Acute abdominal series” Upright chest to evaluate for pneumonia, subdiaphragmatic pneumoperitoneum Upright and supine abdomen Decubitus view of abdomen if upright radiograph not possible To detect small pneumoperitoneum The patient must be in decubitus position for several minutes before radiograph taken to allow relocation of pneumoperitoneum to perihepatic space 5
  6. 6. Conventional Radiography Helpful for the detection of: Pneumoperitoneum Bowel obstruction Pneumonia mimicking abdominal pain Suspected emphysematous pyelonephritis or emphysematous cholecystitis on ultrasound 6
  7. 7. diaphragm diaphragm liver Large pneumoperitoneum: supine chest radiograph in a 70-year-old man shows a large amount of pneumoperitoneum under the dome of the diaphragm bilaterally. The patient had perforated stomach following biopsy. 7
  8. 8. Small bowel obstruction: Supine and upright abdominal radiographs show disproportionate dilatation of small bowel (SB) with a relatively small amount of colonic gas (C). There are air-fluid levels (arrows) with different height in the same small bowel loops. Small bowel obstruction due to adhesion 8
  9. 9. Conventional Radiography Pitfalls/Limitations Poor sensitivity to detect several causes of acute abdomen including appendicitis, cholecystitis and diverticulitis Poor sensitivity to detect small pneumoperitoneum and free fluid Low interobserver agreement on the diagnosis of bowel obstruction (particularly with low-grade small bowel obstruction) 9
  10. 10. free air Small pneumoperitoneum not detected on chest radiograph: Axial CT image of the upper abdomen shows small dots of extraluminal air in the omentum (long arrow) and gastrohepatic ligament (short arrows) in a 54-year- old man who had perforated gastric ulcer. 10
  11. 11. SB SB “Pseudo” small bowel obstruction on radiography: Supine abdominal radiograph shows multiple loops of dilated small bowel (SB) with paucity of colonic gas. Coronal CT image of the abdomen performed on the same day does not show evidence of bowel obstruction. 11
  12. 12. Ultrasound Right upper quadrant (RUQ) ultrasound Renal ultrasound Abdominal ultrasound Limited ultrasound 12
  13. 13. RUQ Ultrasound Evaluation of biliary tree (i.e. liver, intrahepatic biliary duct, common bile duct and gallbladder), pancreas, right kidney Indications Right upper quadrant pain attributed to hepatobiliary tract Imaging of choice to evaluate acute cholecystitis Intra/extrahepatic biliary duct dilatation Right hydronephrosis, calculi 13
  14. 14. gallstone Acute cholecystitis: Sagittal ultrasound image of a 63-year-old man presenting with right upper quadrant pain shows an impacted gallstone in the gallbladder neck and a positive sonographic’s Murphy sign. Surgically and pathologically proven acute cholecystitis. 14
  15. 15. A B “double duct” dilated CBD Biliary ductal dilatation: (A) Transverse grey-scale ultrasound image of the liver shows a “double-duct” sign (between arrows). They represent a dilated intrahepatic duct and a portal vein branch. In a normal subject, a portal vein is the only structures in portal triads visualized in the periphery of the liver. (B) The color Doppler image of the same patient shows a dilated common bile duct anterior to the main portal vein. Obstructive biliary system due to pancreatic head cancer. 15
  16. 16. RUQ Ultrasound: Limitations (1) Recent meal (within 4-6 hours) will contract gallbladder, therefore: Limiting evaluation for gallstones May lead to ‘false-positive’ thickening of gallbladder wall Recent morphine will contract gallbladder and mask the presence of sonographic Murphy’s sign 16
  17. 17. RUQ Ultrasound: Limitations (2) Limited evaluation in patients with Obesity (poor ultrasound beam penetration) Fatty liver (obscuring liver pathology) Significant bowel gas (obscuring pancreas) Low sensitivity to detect CBD stones (CBD often cannot be visualized in its entirety) 17
  18. 18. liver gallbladder Severe fatty liver: Transverse ultrasound image of the liver shows marked attenuation of the liver echo due to the presence of fatty change. Internal structures of the liver (i.e. hepatic veins, portal veins, bile ducts) cannot be visualized. 18
  19. 19. dilated CBD CBD stones Common bile duct stone not detected on ultrasound: An ultrasound image of the right upper quadrant shows a dilated common bile duct (CBD), and intrahepatic duct (not shown) in a 76-year-old man with acute pain and mild jaundice. Follow-up ERCP shows multiple CBD stones obstructing the CBD. 19
  20. 20. Renal Ultrasound Evaluation of kidneys and bladder Acute indications: Hydronephrosis Renal infection (pyelonephritis is not an imaging diagnosis although US can occasionally suggest the diagnosis) 20
  21. 21. hydronephrosis hydroureter Hydronephrosis due to obstructed upper ureteric stone: Sagittal ultrasound image of the right kidney shows dilated renal collecting system and proximal ureter in a 57-year-old man presenting with acute renal failure. He had bilateral hydronephrosis due to obstructing ureteric stones. 21
  22. 22. Abdominal Ultrasound Evaluation of hepatobiliary tract, both kidneys, spleen, +/- aorta and IVC Acute indications: Patients contraindicated or unable to undergo CT or MR imaging Pregnant patients with trauma Pediatric patients with abdominal pain 22
  23. 23. Limited Ultrasound Ultrasound performed at specific anatomic location(s) according to clinical suspicion Free fluid in trauma patients (FAST) Suspected appendicitis Suspected intussusception in pediatric patients 23
  24. 24. 4 1 2 3 Diagram showing the areas included in FAST (focused abdominal sonography for trauma). These four areas are 1) perihepatic and hepato- renal space, 2) perisplenic, 3) pelvis, and 4) pericardium. 24
  25. 25. hyperemia of appendix non-compressible appendix A B Acute appendicitis: (A) Transverse ultrasound image of the right lower quadrant, using a “graded compression” technique, shows a dilated fluid- filled tubular structure, which is non-compressible. (B) Color Doppler image shows hyperemia of the inflamed appendix. Surgically- and pathologically-proven acute appendicitis. 25
  26. 26. mass mass intussuscepted omental fat A B Ileocolic intussusception: (A) Transverse ultrasound image of the right lower quadrant of a 6-month-old boy shows a mass containing several concentric rings of hyperechogenicity. (B) Longitudinal scan of the “mass” shows a “pseudo-kidney” sign of intussusception. Hyperechoic region inside the mass represents intussuscepted mesenteric fat. 26
  27. 27. Computed Tomography (CT) Evaluation of the whole abdomen and pelvis is required Options: Without oral or IV contrast (urinary tract stone, retroperitoneal hematoma) With oral and without IV contrast (cannot receive IV contrast) With IV and without oral contrast (mesenteric ischemia, high-grade small bowel obstruction) With both oral and IV contrast (most indications) With rectal contrast (appendicitis, colonic pathology i.e. penetrating trauma) 27
  28. 28. Computed Tomography (CT) Indications Contraindications Inappropriate use History of severe contrast reaction (CECT*) Renal insufficiency (CECT) Concerns Use of iodinated contrast medium: nephrotoxicity, adverse reactions Radiation exposure *CECT = contrast-enhanced CT 28
  29. 29. Value of CT in Acute Abdomen Changes leading diagnosis Changes were shown to be as high as 1/3 of all cases in prospective investigations1,2 Increases physician’s diagnostic certainty CT doubled diagnostic certainty of ED physicians, particularly in the elderly Changes patient management plan CT influenced disposition in up to 60% of cases1,2 1. Nagurney JT, Brown DF, Chang Y, et al. J Emerg Med. 2003;25:363-371. 2. Rosen MP, Sands DZ, Longmaid HE, et al. AJR Am J Roentgenol. 2000;174:1391-1396. 29
  30. 30. CT - Intravenous Contrast Often required in acute abdomen imaging Iodinated contrast medium enhances visibility of vascular structures and organs Characters Water-based Non-ionic (mostly used at present) vs. ionic Less osmolality - decreases adverse reactions and side effects More hydrophilic - less tendency to cross cell membranes 30
  31. 31. CT - IV Contrast Reactions Can range from minimal (e.g. hives) to anaphylactoid reactions; mostly idiosyncratic (unpredictable, not dose-dependent) Acute or delayed Delayed reaction = 1 hour to 7 days after injection; usually mild Incidence1 Mild reactions up to 3% (LOCM), 15% (HOCM) Severe reactions 0.04% (LOCM), 0.22% (HOCM) Fatal reactions exceedingly rare in both (1:170,000) LOCM = low-osmolar contrast medium; HOCM = high-osmolar contrast medium 1. Morcos SK, Thomsen HS. Eur Radiol 2001;11:1267-1275. 31
  32. 32. CT - IV Contrast Reactions Predisposing Factors1 x Risk History of asthma or bronchospasm 6-10 Previous reaction to iodinated contrast medium 5 History of allergy of atopy 3 Dehydration, cardiac disease, hematologic/metabolic conditions, very young or old age, use of N/A medications such as b-blockers, IL-2, aspirin, NSAIDs 1. Morcos SK, Thomsen HS. Eur Radiol 2001;11:1267-1275. 32
  33. 33. CT - Premedication If the risk exists - the patient should be pre- medicated. Regimen 1 Regimen 2 Medication Prednisolone Methylprednisolone Route oral IV Dose 50 mg 125 mg Schedule 13, 7, and 1 hour prior to CT 6 and 1 hour prior to CT Diphenhydramine 50 mg oral or IV 1 hour prior to CT 33
  34. 34. CT - IV Contrast Nephrotoxicity “Increase in serum creatinine by more than 25% or 44 umol/l occurring within 3 days following IV contrast administration and in the absence of alternative etiology.” Reduces renal perfusion and injured renal tubular cells Manifestations Reduced GFR, proteinuria, oliguria Persistent nephrogram on conventional radiography or CT Usually self-limiting and resolve within 1-2 weeks but it can increase risk of severe non-renal complications and prolong hospital stay 34
  35. 35. CT - IV Contrast Nephrotoxicity Incidence 0-10% in normal population (normal renal function) 12-27% in patients with pre-existing renal impairment Predisposing factors Patient factors: Pre-existing renal impairment, particularly diabetic nephropathy, dehydration, congestive heart failure, concurrent nephrotoxic medications, e.g. NSAIDs Large dose of IV contrast medium, injection in renal arteries 35
  36. 36. CT - IV Contrast Nephrotoxicity Prevention Adequate hydration Use low- or iso-osmolar contrast media Stop administration of nephrotoxic medications for at least 24 hours prior to contrast administration Consider alternative imaging methods 36
  37. 37. Contrast-induced nephropathy: Coronal CT image of the abdomen without IV contrast in a 76-year-old man, status post cardiac catheterization 24 hours ago, shows persistent renal nephrograms. 37
  38. 38. CT - IV Contrast and Metformin Patients with pre-existing renal impairment and are on Metformin are at risk of developing Metformin-associated lactic acidosis (MALA). The use of IV contrast in this patient subset could lead to contrast-induced nephropathy that in turn worsens MALA The American College of Radiology recommends checking the renal function and patient’s comorbidities for lactic acidosis before determining if IV contrast could be given 38
  39. 39. CT - IV Contrast and Metformin 39
  40. 40. CT - IV Contrast: IV Access Peripheral IV should be used. Most PICC lines CANNOT be used for IV contrast administration Not designed to allow rapid injection Risk of line disruption ‘Power PICC’ (as shown in picture on the right) can be used. Image credit: 40
  41. 41. CT - Radiation Exposure CT accounts for 5% of radiologic examinations but contributes 34% of collective radiation dose, worldwide1 Risk of radiation exposures Deterministic effect: cell death; threshold level specified when effects would occur; rarely seen with diagnostic x-ray and CT Stochastic effect: cancer, genetic effects; “linear, non-threshold” model generally believed; seen with diagnostic x-ray and CT 1. United Nations Scientific Committee on the Effects of Atomic Radiation. 2000 report to the General Assembly, Annex D: medical radiation exposures New York, NY: United Nations, 2000. 41
  42. 42. CT - Radiation Exposure Effective radiation dose of one abdominal-pelvic CT scan equals to1 10 mSv, comparable to 3 years of natural background radiation 100 chest radiographs “Estimated risk of cancer death for those undergoing CT is 12.5/10,000 population for each pass of the CT scan through the abdomen”2 Any efforts to reduce radiation dose from CT should be done. 1 = 2 = Gray JE. Safety (risk) of diagnostic radiology exposures. In: Janower ML, Linton OW, eds. Radiation risk: a primer. Reston, Va: American College of Radiology, 1996; 15-17. 42
  43. 43. MR Imaging Advantages over CT High contrast resolution (good for imaging of pelvis, hepatobiliary tract and pancreas) No ionizing radiation Can be performed in pregnancy Total exam time usually <30 minutes. No contrast needed in most cases Limitations Contraindications for MR: pacemaker, claustrophobia, etc. Critically ill patients require MR-compatible life support equipments 43
  44. 44. MR Imaging Scientific evidence for MRI in acute abdomen still is not extensive Clinical applications Suspected acute appendicitis (particularly during pregnancy, and in children). Note that gadolinium-based contrast agent cannot be used in pregnant women. Good results shown for MRI in sigmoid diverticulitis, common bile duct stone, acute cholecystitis, pancreatitis 44
  45. 45. appendix Acute appendicitis: Axial STIR MR image of the pelvis in a young pregnant woman shows an enlarged appendix with high signal intensity of the wall and small periappendiceal fluid. 45
  46. 46. Scintigraphy Major drawback is limited availability in acute setting; requires efforts to gather a team off- hours; and limited resolution Clinical applications Acute cholecystitis: hepatobiliary scintigraphy1 Higher accuracy and specificity than ultrasound Reserved for patients whom diagnosis is unclear after ultrasound Acute pulmonary embolism: ventilation-perfusion (V/Q) scan Considered V/Q scan in patients with a normal chest radiograph suspected of having PE when there is a contraindication to CT scan (renal impairment, severe contrast reaction) 1. Strasberg SM. New Eng J Med 2008;358:2804-2811. 46
  47. 47. Acute cholecystitis: Anterior (A) and right lateral (B) images of a HIDA scan performed at 4 hours after radiotracer injection show no excretion into the gallbladder. Image credit: MedPixTM 47
  48. 48. Acute pulmonary embolism: 55-year-old man. Perfusion lung scan in right posterior oblique view shows multisegmental defects which do not match the findings seen on a ventilation scan obtained earllier (V/Q mismatch). Image credits: Radiographics 2003;23:1521-1539 48
  49. 49. Appropriateness Criteria1 Most 2nd Most Clinical Variant Appropriate Appropriate Non-localizing pain, fever, no recent operation CT with contrast X-ray, US, CT without contrast Non-localizing pain, pregnant, fever US MRI without contrast RUQ pain, fever, elevated WBC, positive Murphy sign US X-ray, CT RUQ pain, suspected acalculous cholecystitis Scintigraphy X-ray, CT RUQ pain, no fever, normal WBC US CT RUQ pain, no fever, normal WBC, US shows only gallstones Scintigraphy CT RLQ pain, fever, elevated WBC, adults, typical appendicitis CT with contrast CT without contrast RLQ pain, fever, elevated WBC, adults and adolescents, atypical presentation CT with contrast X-ray, US, CT without contrast RLQ pain, fever, elevated WBC, pregnant US MRI without contrast RLQ pain, fever, elevated WBC, atypical presentation in children (<14 years) US CT with contrast LLQ pain, typical diverticulitis, old age CT with contrast CT without contrast LLQ pain, acute, severe CT with contrast CT without contrast LLQ pain, woman of childbearing age US CT with contrast LLQ pain, obese patient CT with contrast X-ray, US, CT without contrast 1 = Adapted from the American College of Radiology Appropriateness Criteria. Available at URL: SecondaryMainMenuCategories/quality_safety/app_criteria/pdf/ExpertPanelonGastrointestinalImaging.aspx 49
  50. 50. Conclusions Imaging plays an increasingly important role in diagnosis of etiology of acute abdomen CT is widely used in several acute abdominal indications; along with ultrasound and MR imaging Limitations of each imaging method and appropriateness criteria should be considered before selecting an imaging test for a particular patient 50