Imaging Acute Abdomen (part 1)

Imaging Acute Abdomen Part 1: General Concepts Rathachai Kaewlai, M.D. www.RiTradiology.com Updated: May 2009

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Overview

Role, indications and limitations of each imaging modality: radiography, US, CT, MR imaging, scintigraphy Appropriateness criteria

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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

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Acute Abdomen: A Clinical Challenge

Require all resources to reach accurate diagnosis, timely management and proper disposition

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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

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Conventional Radiography

Helpful for the detection of: Pneumoperitoneum Bowel obstruction Pneumonia mimicking abdominal pain Suspected emphysematous pyelonephritis or emphysematous cholecystitis on ultrasound

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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

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

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)

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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-yearold man who had perforated gastric ulcer. 10

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

Ultrasound

Right upper quadrant (RUQ) ultrasound Renal ultrasound Abdominal ultrasound Limited ultrasound

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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

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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.

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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

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

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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)

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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.

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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.

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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)

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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.

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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

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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

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4 2

1 3

Diagram showing the areas included in FAST (focused abdominal sonography for trauma). These four areas are 1) perihepatic and hepatorenal space, 2) perisplenic, 3) pelvis, and 4) pericardium.

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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 fluidfilled tubular structure, which is non-compressible. (B) Color Doppler image shows hyperemia of the inflamed appendix. Surgically- and pathologically-proven acute appendicitis.

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mass

mass

A

intussuscepted omental fat

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.

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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)

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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

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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.

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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

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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.

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CT - IV Contrast Reactions Predisposing Factors1

x Risk

History of asthma or bronchospasm

6-10

Previous reaction to iodinated contrast medium

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History of allergy of atopy

3

Dehydration, cardiac disease, hematologic/metabolic conditions, very young or old age, use of medications such as b-blockers, IL-2, aspirin, NSAIDs 1. Morcos SK, Thomsen HS. Eur Radiol 2001;11:1267-1275.

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N/A

CT - Premedication If the risk exists - the patient should be premedicated. Regimen 1

Regimen 2

Prednisolone

Methylprednisolone

Route

oral

IV

Dose

50 mg

125 mg

13, 7, and 1 hour prior to CT

6 and 1 hour prior to CT

Medication

Schedule Diphenhydramine

50 mg oral or IV 1 hour prior to CT

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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

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

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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

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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

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

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CT - IV Contrast and Metformin

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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: http://home.caregroup.org/centralLineTraining/

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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.

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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 = http://www.radiologyinfo.org/en/safety/index.cfm?pg=sfty_xray#3 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.

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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

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

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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.

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Scintigraphy Major drawback is limited availability in acute setting; requires efforts to gather a team offhours; 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.

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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

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

Appropriateness

1 Criteria Most Appropriate

2nd Most Appropriate

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

Scintigraphy

X-ray, CT

US

CT

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

US

CT with contrast

CT with contrast

X-ray, US, CT without contrast

Clinical Variant Non-localizing pain, fever, no recent operation

RUQ pain, suspected acalculous cholecystitis RUQ pain, no fever, normal WBC RUQ pain, no fever, normal WBC, US shows only gallstones

LLQ pain, woman of childbearing age LLQ pain, obese patient

1 = Adapted from the American College of Radiology Appropriateness Criteria. Available at URL: http://www.acr.org/ SecondaryMainMenuCategories/quality_safety/app_criteria/pdf/ExpertPanelonGastrointestinalImaging.aspx

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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

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