General Principles

Ultrasound

• Ultrasound is an excellent screening study for the abdomen.
• Ultrasound is exquisitely sensitive in evaluating the right upper quadrant of the abdomen, particularly when looking for disease of the gallbladder, liver or pancreatic head.
• Ultrasound of the pelvis is superior to CT scanning in evaluating the uterus and adnexa, especially given the availability of endovaginal techniques.
• Most obese patients can be adequately imaged using ultrasound technology.

Computed Tomography

• Combination CT abdomen and pelvis are appropriate only when the disease to be imaged is likely to span both anatomical areas.
• CT scanning of the abdomen and pelvis exposes patients to significant amounts of radiation and should never be ordered unless the results are likely to impact patient management.

Magnetic Resonance Imaging

• MRI has limited utility in imaging the abdomen because respiration, aortic pulsation and peristalsis may adversely affect the image.
• MRI is more expensive than US and CT.

General 

• The initial evaluation of asymptomatic patients with mild elevations in liver function tests should include repeat testing off alcohol and hepatotoxic medications and evaluation for conditions such as hemochromatosis, hepatitis and Ebstein Barr virus infection.
  
• CT scanning is rarely indicated in the initial workup, unless the patient has an underlying condition, such as malignancy, which may be associated with liver pathology and the results of the study might impact management.

Metastatic Liver Disease

• MRI is somewhat more sensitive than CT for evaluating known or suspected liver metastases.
  
• CT is superior for evaluating the extra-hepatic organs and spaces and calcifications.
  
• MRI and CT scan may both miss lesions < 1 cm in diameter.
  
• An important drawback of CT in imaging of the liver is the requirement for iodinated contrast.
  
• MRI is useful for imaging hyper-vascular liver metastases such as islet cell CA, thyroid CA, carcinoid, melanoma and neuroendocrine tumors.

Cavernous Hemangioma

• US, CT and radionucleotide scan are all good studies for imaging cavernous hemangioma.
  
• Lesions < 2 cm or multiple lesions may require MRI imaging.

Fatty Liver 

• US and CT can diagnose fatty infiltration. US is more cost effective and does not expose the patient to radiation.
• MRI can distinguish between focal fatty infiltration and other hepatic masses (e.g., metastases).

Cirrhosis

• MRI is useful in distinguishing the regenerative nodules of cirrhosis from hepatocellular carcinoma.
• MRI shows the secondary changes of portal venous hypertension well (splenomegaly, upper abdominal varices and portal vein changes).

Iron Overload

• Ultrasound is not as specific as CT or MRI in detecting diffusely infiltrative processes of the liver such as hemochromatosis.
• MRI can distinguish between parenchymal (primary hemochromatosis) and reticuloendothelial (transfusion related) overload.
  

Bowel

Colon Cancer

• Most colon cancer is intraluminal, with subtle findings on CT. Barium enema or endoscopy are more appropriate first steps than CT when colon cancer is suspected.

Irritable Bowel Syndrome

• Initial workup includes history and physical, labs, stool studies and possibly endoscopy or barium enema.
• CT scan is indicated only if symptoms persist despite conservative measures and workup is nondiagnostic.

Iron Deficiency Anemia 

• Symptoms generally correlate with the region the lesion is found in.
  Upper or lower endoscopy +/- enteroclysis reveals the majority of causes, so additional imaging may not be indicated.

Chronic Diarrhea 

• Diagnostic imaging is not indicated in the evaluation of acute diarrhea (< 4 weeks).
• The evaluation of patients with > 4 weeks of diarrhea for chronic diarrheal diseases includes a history and physical, followed by selected labs and stool studies.
• Signs and symptoms suggestive - but not diagnostic - of an organic rather than functional etiology include:

• Plain films and flexible sigmoidoscopy with biopsy, UGI and/or barium studies of the small bowel and colon may be appropriate in the initial evaluation.
• If the initial workup is non-diagnostic, additional labs and endoscopic techniques such as colonoscopy/ileoscopy with biopsy may be useful.
  CT has no role in the evaluation of diarrhea, unless the initial workup is negative and the patient has signs or symptoms of organic disease.

Small Bowel Obstruction 

• Plain film radiography is the method of choice for imaging patients with suspected small bowel obstruction.
• CT plays a role in determining the cause when plain film shows obstruction and the results will impact patient management.

Gallbladder

Ultrasound 

• Ultrasound is the study of choice in the workup of biliary colic and will diagnose both cholelithiasis and cholecystitis.
• Ultrasound is 95-98% accurate in detecting gallstones.
• Ultrasound is 70% sensitive in diagnosing choledocholecystitis

KUB

• Shows gallstones 15-20% of the time.

Oral Cholecystogram

• OCG is the primary test to determine the number and size of stones, the patency of the cystic duct and gallbladder wall integrity.
• In emergent situations, ultrasound and radionucleotide examinations are more efficient than OCG for the diagnosis of gallstones/cystic duct obstruction.
• OCG may be useful when the result of ultrasound are non-diagnostic in the light of strong clinical symptoms or when US shows nonspecific abnormalities.

Radionucleotide Cholescintigraphy/Hepatobiliary Scintigraphy 

• Most specific method for diagnosing cystic duct obstruction, often used when US results are equivocal.
• Scintigraphy should be the initial study when clinical suspicion is great.

CT Scan 

• Can be useful in diagnosing acute calculous or acalculous cholecystitis.
• Especially useful in patients with atypical abdominal symptoms.
• When indolent or chronic obstruction is suspected based on laboratory findings or the patient has symptoms or findings more consistent with pancreatic disease than stones (e.g., weight loss, mass or back pain).
• The cost of CT scanning generally does not warrant its use in evaluating stone composition.

MRCP/ERCP
(Magnetic Resonance & Endocsopic Retrograde Cholangiopancreatography) 

• Detects small, distal bile duct stones not seen on US.
• ERCP is invasive, but allows for urgent stone removal (sphincterotomy).
• MRCP is noninvasive and also images the biliary tract and pancreatic duct. It is useful in diagnosing pancreatic duct stones, pancreatitis, primary sclerosing cholangitis, congenital duct anomalies, malignant obstructions and biliary calculi.

Uterus, Ovaries & Adnexa

• US of the pelvis is superior to CT scanning evaluating the uterus and adnexa, especially given the availability of endovaginal techniques.
• US is an excellent study to look for ovarian cysts, PID, fibroids, ovarian tumors, ovarian torsion, ectopic pregnancies, and other pathology.
• MRI of the pelvis is the best study for detailed imaging of the uterus/uterine wall to look for things like adenomyosis or endometriosis.

Appendix

• Diagnostic imaging is only indicated to look for appendicitis when the clinical findings are equivocal.
• US is recommended as the initial study to diagnose appendicitis in children and pregnant women, especially during the first trimester, due to its lower cost, lack of ionizing radiation and high positive predictive value.
• Un-enhanced helical CT scan is a useful study to evaluate adult, non-pregnant patients with atypical symptoms when appendicitis is suspected.

Adrenal Gland

• CT scan is an excellent study to image the hyperfunctioning adrenal medulla and cortex (can show tumors as small as 10 mm) and primary adrenal insufficiency (Addisons disease).
• MRI of the adrenals rarely provides information not seen on CT scan. In selected circumstances, however, MRI may help further define incidental adrenal tumors seen on CT scan of the abdomen because metastases give off higher signal intensities than benign adenomas.
• Adrenal carcinoma is generally visible on CT scan, although MRI will show a high signal intensity which may help support a malignant diagnosis.
• Sonography may be useful in imaging children for MEN syndromes, where lack of retroperitoneal fat makes CT evaluation difficult.
• CT is the most reliable way to image adrenal hemorrhage (sonography used to detect it in children).
• MRI is useful when looking for pheochromocytomas involving the bladder wall or paracardiac region and in postoperative patients where the retroperitoneal tissue planes are disrupted.

Pancreas

• Advances in ultrasound technology have significantly improved the sensitivity of US in identifying diseases of the pancreas.
• US is the most sensitive study to evaluate the biliary tract in acute pancreatitis.
• Contrast CT is the imaging method of choice in evaluating complications of pancreatitis.
• US is preferred over CT scan (due to lower cost) for follow-up of patients with pseudocysts < 4 cm or following percutaneous or surgical drainage of larger pseudocysts, except when distended loops of bowel or surgical dressings make US impossible.
• ERCP or MRCP may be useful in diagnosing patients in whom no definite cause of pancreatitis can be found on initial history taking and imaging.

  In the evaluation of chronic pancreatitis, if the serum trypsin level and/or plain film are markedly abnormal, there is no need for additional studies. If not, then abdominal CT scan, bentiromide testing or secretin stimulation testing may be indicated prior to ERCP. ERCP should be reserved for patients whose diagnosis is still unclear or for whom therapeutic rather than diagnostic information is required.

• US is the best method for screening masses in the region of the pancreas, demonstrating bile duct dilatation and revealing intra- and extra-pancreatic fluid collections (and tracking known fluid collections such as pseudocysts).
• US may demonstrate small pancreatic tumors (e.g., functioning islet cell adenomas) that do not alter pancreatic contour better than CT scan.
• CT with contrast visualizes biliary and pancreatic duct abnormalities, parenchymal changes and lymph nodes in the pancreatic bed and/or in lymphatic drainage sites remote from the pancreas.
• MRI does not provide a clear advantage over CT except in the evaluation of small islet cell tumors, vascular invasion and pancreatic transplants.
• CT is best modality for tumor staging because it has better resolution and is superior to US at imaging the retroperitoneum.
• CT is useful in detecting retroperitoneal hemorrhage, but angiogram is needed to detect exact site of bleeding if embolization is planned.
• CT scans can detect splenic or portal vein thrombosis

Kidney

• Ultrasound is the appropriate first study in the evaluation of renal failure and can diagnose hydronephrosis and irreversible end-stage renal disease.
• US is a noninvasive and inexpensive way to show a dilated collecting system without requiring contrast or exposing the patient to radiation. It may also show the level/cause of obstruction. Additional functional data can be obtained by adding a duplex Doppler ultrasound.
• Non-contrast CT scan is highly sensitive for the detection of renal or ureteral calculi but, unlike IVP, non-contrast CT provides no functional or physiologic information.
• Disadvantages of CT scan include higher radiation dose than IVP, inability to provide functional information, and greater difficulty distinguishing between a stone or dilated ureter and neighboring structures such as calcifications or blood vessels.
• US is the best study to detect pyonephrosis (CT cannot distinguish between infected and uninfected hydronephrosis), but CT scan is best for identifying emphysematous pyelonephritis.
• CT is the study of choice to evaluate patients with blunt renal trauma when significant renal injury or hemorrhage is suspected.
• In stable, asymptomatic patients thought to have minor injury, excretory urography should be sufficient to exclude significant renal damage.
• Renal vein thrombosis can be detected on duplex and color Doppler sonography, contrast CT (if normal renal function) and on MRI.
• Acute unilateral obstruction is most reliably diagnosed by excretory urography; US is a useful first exam during pregnancy, in patients with reactions to contrast and in those with renal failure.

Bibliography

1. Balthazar EJ, Birnbaum BA, Yee J , et al. Acute appendicitis: CT and US  correlation in 100 patients. Radiology 1994;190:31-35.
2. Balthazar EJ, Ranson JHC, Naidich DP et al. Acute pancreatitis: prognostic value of CT. Radiology 1985;156:767-772.
3. Birnbaum BA, Jeffrey RB. CT and sonographic evaluation of acute right lower quadrant abdominal pain. AJR 1998;170:361-771.  
4. Donowitz M, Kokke FT, Saidi R. Evaluation of patients with chronic diarrhea. NEJM 1995; 332(11): 725-729.
5. Dunnick NR. Adrenal imaging: current status. American Journal of Roentgentology 1990;154:927-936.
6. Forsmark CE, Toskes PP. What does an abnormal pancreatogram mean. Gastrointest Endosc Clin N. Am 1995;5(1):15-123.
7. Huntington DK, Hill SC, Hill MC. Sonographic manifestations of medical renal disease. Seminars in Ultrasound, CT and MR 1991;12(4):290-307.
8. Jain KA, Quam JP, Albin DS, et al. Imaging findings in patients with right lower quadrant pain: alternative diagnoses to appendicitis. Journal of Computer Assisted Tomography 1997;21(5):693-698.
9. Johnson CD. Magnetic resonance imaging of the liver: Current clinical applications. Mayo Clin Proc 1993; 68:147-156.
10. Lane MJ, Katz DS, Ross BA,et al. Unenhanced helical CT for suspected acute appendicitis. Amer J or Roentgenology 1997;168:405-409.
11. Levine E. Acute renal and urinary tract disease. Radiologic Clinics of North America 1994;32(5):989-1004.
12. Lynn RB, Friedman LS. Irritable Bowel Syndrome. NEJM 1993; 329: 1940-1945.
13. Maglinte DDT, Reyes B, Harman BH, et al. Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR  1996;167: 1451-1455.
14. Maglinte DDT, Torres WE, Laufer I. Oral cholecystography in contemporary gallstone imaging: a review. Radiology 1991;178:49-58.
15. Platt JF. Urinary obstruction. Radiologic Clinical of North America 1996;34(6):1113-1129.
16. Rockey DC, Cello JP. Evaluation of the gastrointestinal tract in patients with iron-deficiency anemia. NEJM 1993; 329(23):1691-1695.
17. Sivit CJ. Imaging children with acute right lower quadrant pain. Pediatric Clinics of North America 1997;44(3):575-589.
18. Soiva M, Haveri M, Taavitsainen M, Suramo I. The value of routine  sonograpphy  in clinically suspected acute cholecystitis. Scand J  Gastroenterol 1986; 21:70-74.
19. Weltman DI, Zeman RK. Acute diseases of the gallbladder and biliary ducts.
20. Smith RC, Rosenfield AT, Choe KA, et al. Acute flank pain: comparison of non-contrast-enhanced CT and intravenous urography. Radiology 1995;194:789-794.
21. Steinberg W, Tener S. Acute pancreatitis. NEJM 1994;330:1198-1210.
22. Thoeni RF, Blankenberg R. Pancreatic imaging: computed tomography and magnetic resonance imaging. Radiologic Clinics of North America 1993; 31(5):1085-1112.
23. Weltman DI, Zeman RK. Acute diseases of the gallbladder and biliary ducts.

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