Abdominal Imaging - 9 Topics in 90 min

Transcription

1 Abdominal Imaging 9 topics in 90 min Antonio C. Westphalen, MD PhD Departments of Radiology and Biomedical Imaging, and Urology Liver Biliary tree Gallbladder Pancreas Kidneys Small bowel Colon Abscess? Tubes and lines Outline Focus on most common problems faced by the hospitalist Brief description of the problem advantages and disadvantages main imaging findings Additional imaging further characterization follow-up 2 Abdominal Imaging - 9 Topics in 90 min 1

2 Liver Non-alcoholic fatty liver disease Obese patient Elevated liver enzymes RUQ pain Non-alcoholic steatohepatitis? / cirrhosis? 3 Abdominal Imaging - 9 Topics in 90 min NALFD vs cirrhosis Ultrasound Computed tomography Magnetic resonance imaging Steatosis may be diffuse or focal; and it is a heterogeneous process. Non-alcoholic steatohepatitis cannot be diagnosed with imaging. Cirrhosis: morphologic changes and evidence of portal hypertension. 4 Abdominal Imaging - 9 Topics in 90 min 2

3 Ultrasound Usually the first option when NAFLD is suspected Inexpensive, safe, readily available on the bed side, and highly accurate Full assessment of the parenchyma may be limited in severe cases. Hepatomegaly echogenicity / smooth vs nodular (split image of spleen use same setup) Poor visualization of deep parts of the liver 5 Abdominal Imaging - 9 Topics in 90 min Computed tomography Usually best in advanced disease with suspected cirrhosis Non-contrast CT for steatosis, contrast-enhanced for cirrhosis (GFR>45) Radiation exposure Low density compared with spleen on non-contrast CT (difference > 10 HU) Cirrhosis: nodular contour, widened gallbladder fossa, large caudate Portal hypertension: large PV (> 12-15mm), collaterals, splenomegaly, ascites Classical HCC are hypervascular lesions that washout on the delayed phase. 6 Abdominal Imaging - 9 Topics in 90 min 3

4 Magnetic resonance imaging Option to CT when suspect cirrhosis Best to characterize atypical/focal steatosis or indeterminate liver nodules In general, more sensitive than US and CT to detect fat Longer scan, breath holds, susceptible to artifacts (e.g. motion of ascites) In- and out-of-phase imaging If suspect cirrhosis, better to use gadolinium (contraindicated if GRF<30) 7 Abdominal Imaging - 9 Topics in 90 min Biliary tree Biliary obstruction Patient with cholestasis Elevated bilirubin, direct > indirect Elevated alkaline phosphatase Borderline elevated AST and ALT Intra- or extrahepatic obstruction? Cause? 8 Abdominal Imaging - 9 Topics in 90 min 4

5 Intra- or extrahepatic obstruction? Cause? Ultrasound Computed tomography Magnetic resonance imaging Extrahepatic obstruction is suggested by the presence of dilated ducts Normal ducts do not exclude acute/new or intermittent obstruction. Double duct sign (biliary and pancreatic ducts): pancreas, ampulla, scarring 9 Abdominal Imaging - 9 Topics in 90 min Ultrasound Always the first option for the assessment of bile ducts and gallbladder Inexpensive, safe, readily available on the bed side, and highly accurate May not detect the specific cause and level of obstruction. Bowel gas may obscure visualization of the CBD. Limited in markedly obese individuals. Try to always use the liver as a window to visualize the entire biliary tree Change decubitus/position to move air away from the area of interest Sometimes water PO helps 10 Abdominal Imaging - 9 Topics in 90 min 5

6 Computed tomography Better than US to determine the specific cause and level of obstruction. Visualizes the liver parenchyma more consistently than US. Very limited for CBD stones most are radiolucent. Radiation (40-50 years old). More expensive than US. Good option when a tumor is suspected IV contrast helps to determine the cause (late arterial & portal venous phases) Planning of percutaneous drainage 11 Abdominal Imaging - 9 Topics in 90 min Magnetic resonance imaging + MR cholangiopancreatography MRI for parenchyma / MRCP for ducts MRCP noninvasive and sensitive to detect stones, strictures, or dilatations. Requires good breath holds, fluid in the duodenum or ascites usually cause artifacts and limit visualization of ducts with MRCP. Good option when a CBD stone is suspected, but not visualized with US Option when tumor is suspected & iodinated contrast contraindicated (allergy) Best option when tumor is suspected & IV contrast contraindicated (low GFR) 12 Abdominal Imaging - 9 Topics in 90 min 6

7 Additional imaging Endoscopic retrograde cholangiopancreatography (ERCP) Diagnostic and therapeutic modality Imaging and sampling / removal of stones, stents, drains, & sphincterotomy Limited visualization of bile ducts proximal to the obstruction. Complications (10% risk overall, most commonly pancreatitis) Standard of reference (high accuracy and excellent spatial resolution) Best for obstruction at or distal to the confluence of right and left ducts Consider EUS (+/- FNA) if distal CBD tumor is suspected but not seen by other methods 13 Abdominal Imaging - 9 Topics in 90 min Remember! Biliary ductal dilatation of no clinical significance Mild central intrahepatic and CBD dilatation in older patients and after cholecystectomy 14 Abdominal Imaging - 9 Topics in 90 min 7

8 Gallbladder Acute cholecystitis Biliary colic / acute RUQ pain / Murphy sign Nausea / vomiting +/- fever Leukocytosis / mild cholestasis Confirm diagnosis and determine cause Complications? 15 Abdominal Imaging - 9 Topics in 90 min Acute cholecystitis? Cause? Complications? Ultrasound Computed tomography Distension of the gallbladder, gallbladder wall thickening, pericholecystic fluid, and gallstones suggest the diagnosis. Biliary sludge and gallbladder wall thickening without distension and pericholecystic fluid are commonly seen with chronic illnesses. Ascitic fluid versus pericholecystic fluid 16 Abdominal Imaging - 9 Topics in 90 min 8

9 Ultrasound Always the first option for the assessment of bile ducts and gallbladder Inexpensive, safe, readily available on the bed side, and highly accurate Ultrasonographic Murphy sign Thick GB walls or pericholecystic fluid? Turn Doppler on and look for vessels! Are GS mobile? Change decubitus. An impacted stone increases the probability of acute cholecystitis. 17 Abdominal Imaging - 9 Topics in 90 min Computed tomography Best option for assessment of complications May identify extrabiliary causes of acute cholecystitis Use of IV contrast is recommended Perforation: decompressed GB, pericholecystic fluid, hyperemia liver tissue Pancreatitis Abscess 18 Abdominal Imaging - 9 Topics in 90 min 9

10 Additional imaging HIDA cholescintigraphy, or HIDA scan Equivocal US results or acalculus cholecystitis Opacification of the gallbladder excludes the diagnosis Failure to fill the gallbladder suggests acute cholecystitis FP results: TPN or prolonged NPO, severe liver disease, sphincterotomy Cannot assess most complications Cannot assess alternative diagnoses 19 Abdominal Imaging - 9 Topics in 90 min Pancreas Pancreatitis Acutely ill, hypotensive / tachycardic Upper / epigastric pain radiating to back Nausea / vomiting Elevated amylase & lipase / leukocytosis Diagnosis? Stage? Complications? Cause? (uncommonly) 20 Abdominal Imaging - 9 Topics in 90 min 10

11 Diagnosis? Stage? Complications? Cause? Computed tomography Magnetic resonance imaging Usually not indicated if no signs of severe pancreatitis or rapid improvement. The ideal time to assess complications is 72 hours after onset of symptoms. To exclude cancer in patients > 40 yo with first episode of pancreatitis without identifiable cause 21 Abdominal Imaging - 9 Topics in 90 min Computed tomography Primary imaging tool to assess patients with pancreatitis Part of the revised Atlanta classification as a diagnostic criteria Also useful to guide percutaneous drainages or other interventions IV contrast is required pancreatic protocol (noncon, arterial, portal venous) Interstitial edematous pancreatitis versus necrotizing pancreatitits Pancreatic and peripancreatic collections 22 Abdominal Imaging - 9 Topics in 90 min 11

12 Interstitial edematous versus necrotizing pancreatitits Interstitial edematous pancreatitis Localized or diffuse enlargement Normal homogeneous or slightly heterogeneous enhancement (edema) Normal or mild inflammation of the peripancreatic tissues Marked heterogeneous enhancement within the first 5-7 days of onset could be IEP or ill-defined necrosis. CT performed after 5 7 days permits definitive characterization. 23 Abdominal Imaging - 9 Topics in 90 min Interstitial edematous versus necrotizing pancreatitits Necrotizing pancreatitis Parenchymal necrosis alone: < 5% Peripancreatic necrosis alone: 20% Parenchymal and peripancreatic necrosis: 75-80% Lack of enhancement on contrast-enhanced CT a week after onset Less than 30% and greater than 30% Heterogeneous areas with lack of enhancement that contain nonliquefied components 24 Abdominal Imaging - 9 Topics in 90 min 12

13 Pancreatic and peripancreatic fluid collections Pancreatic collections Acute necrotic collection 4 weeks walled-off necrosis Acute peripancreatic fluid collection 4 weeks pseudocyst Sterile or infected Acute: conform to the anatomic boundaries and have no discernable wall Chronic: round or oval surrounded by a well-defined enhancing wall Infection: diagnosed by the presence of gas (in the absence of GI tract fistula) 25 Abdominal Imaging - 9 Topics in 90 min Magnetic resonance imaging Suspected choledocholithiasis not yet visualized Characterize collections - nonliquefied material may mimic fluid of CT CT is contraindicated (eg, allergy to iodinated contrast or pregnancy) Cost and availability Accuracy MRI = CT CT is used to guide procedures 26 Abdominal Imaging - 9 Topics in 90 min 13

14 Additional imaging Ultrasound Gallstones and/or choledocholithiasis Guide drainage of collections Vascular assessment (venous thrombosis / pseudoaneurysms) 27 Abdominal Imaging - 9 Topics in 90 min Chronic pancreatitits Computed tomography and magnetic resonance imaging Parenchymal atrophy, PD dilatation and calcifications (CT only) Acute on chronic? Peripancreatic fluid/necrosis > parenchymal findings! Pancreatic cancer? Stenosis of the duct? 28 Abdominal Imaging - 9 Topics in 90 min 14

15 Adrenals Adrenal nodules Incidental findings Associate with endocrine symptoms Subclinical with hormonal imbalances Known primary cancer Diagnosis? Nest step? 29 Abdominal Imaging - 9 Topics in 90 min Diagnosis? Next step? Computed tomography Magnetic resonance imaging The goal of imaging is to characterize and adenoma versus a nonadenoma Dx of adenomas: intracytoplasmatic lipid and/or enhancement characteristics 1/3 of adenomas are lipid-poor 30 Abdominal Imaging - 9 Topics in 90 min 15

16 Computed tomography Primary imaging tool to diagnose adenomas Adrenal protocol: unenhanced CT plus/minus PV & delayed phases ( 12 min) Imaging guided biopsy Low density (< HU) on unenhanced CT: very high specificity and PPV Contrast washout characteristics (40% to 60% on delayed phase) 31 Abdominal Imaging - 9 Topics in 90 min Magnetic resonance imaging Generally used to characterize indeterminate lesions on CT Detection of microscopic lipid Breath holding, not useful if unenhanced CT density > 30 HU Relative signal loss from in-phase to out-of-phase images Virtually diagnostic of adenoma 32 Abdominal Imaging - 9 Topics in 90 min 16

17 Additional imaging PET-CT Reserved for patients with known primary cancer to exclude metastasis Indicated to investigate of masses > 4 cm, in lieu of biopsy Meta-analysis (patients with known primary cancer): Sensitivity = 97% / Specificity = 91% LR = 11.1 / LR = Abdominal Imaging - 9 Topics in 90 min Beware! Computed tomography Metastases of renal cell carcinoma may have washout equivalent to adenomas Magnetic resonance imaging Metastases of hepatocellular carcinoma may have microscopic fat 34 Abdominal Imaging - 9 Topics in 90 min 17

18 Kidneys Urolithiasis Flank pain / renal colic Hematuria History of urolithiasis Diagnosis Obstruction? Probability stone passage? Complications? 35 Abdominal Imaging - 9 Topics in 90 min Urolithiasis Ultrasound Computed tomography KUB Consider history of urolithiasis and characteristics of symptoms Consider patient s age (radiation exposure) Consider pre-test probability of alternative diagnosis 36 Abdominal Imaging - 9 Topics in 90 min 18

19 Ultrasound Possibly the first option if known urolithiasis and classical symptoms Inexpensive, safe, readily available on the bed side Limited assessment of midureter due to gas in the GI tract Hydronephrosis Scan pelvis with bladder slightly full to better visualize distal ureter and UVJ Change patient decubitus to move gas / slow and continue pressure 37 Abdominal Imaging - 9 Topics in 90 min Computed tomography First option if nonclassical symptoms and need to exclude other causes of pain Visualizes virtually all stones, sensitivity 90% Radiation exposure young patients with repeated episodes of renal colic Noncontrast CT suffices in the vast majority of cases / IV if no urolithiasis Scan prone to more completely assess UVJ stones 6 mm threshold (axial plane) for spontaneous passage 38 Abdominal Imaging - 9 Topics in 90 min 19

20 Ultrasound or computed tomography? Westphalen AC. Acad. Emerg. Med Jul;18(7): Abdominal Imaging - 9 Topics in 90 min Ultrasound or computed tomography? Westphalen AC. Acad. Emerg. Med Jul;18(7): Abdominal Imaging - 9 Topics in 90 min 20

21 Ultrasound or computed tomography? Smith-Bindman R. N Engl J Med 2014; 371: Abdominal Imaging - 9 Topics in 90 min KUB Option to assess passage of stones after treatment (PNL of staghorn calculus) Easy to obtain in the bed side, little radiation Limited for the initial assessment of suspected urolithiasis overlap of bowel content and bones 42 Abdominal Imaging - 9 Topics in 90 min 21

22 Additional imaging Intravenous pyelography Rarely used nowadays 43 Abdominal Imaging - 9 Topics in 90 min Complications Calyceal rupture and pyonephrosis Calyceal rupture is a minor complication, usually treated with stenting Contrast-enhanced CT (delayed/excretory phase) Pyonephrosis is a medical emergency and requires immediate drainage Limited renal ultrasound Interventional radiology 44 Abdominal Imaging - 9 Topics in 90 min 22

23 Small bowel SBO versus ileus Abdominal distension / pain Nausea / vomiting History of abdominal surgery Diagnosis? If SBO, cause? Management? 45 Abdominal Imaging - 9 Topics in 90 min SBO vs ileus Computed tomography KUB Initial assessment = computed tomography KUB may be an option for follow-up 46 Abdominal Imaging - 9 Topics in 90 min 23

24 Computed tomography Better first option for initial assessment of suspected SBO Fast, more sensitive than KUB, identifies a cause in ~ 80% of cases IV contrast (nonadhesive causes), PO contrast (transition point) SBO = proximal dilated loops of SB (> 3 cm), decompressed distally (RLQ) Ileus = diffuse distention, often borderline, normal stool/air in colon SBO in developed countries = adhesions (> 2/3 of cases) SBO in developing countries = incarcerated hernias (up to 80% of cases) 47 Abdominal Imaging - 9 Topics in 90 min KUB May be used for follow-up of patients with SBO 50-60% sensitive for SBO, does not identifies cause of SBO Abdominal series (at least one standing or left lateral decubitus) SBO = air fluid levels at various heights, central predominance, with paucity of gas distally and in colon SBO = gasless abdomen if dilated and fluid filled SB, or after vomiting Ileus = borderline dilatation with air found throughout SB and in colon 48 Abdominal Imaging - 9 Topics in 90 min 24

25 Additional imaging KUB with PO Gastrografin (Diatrizoate Meglumine) Not for diagnostic use Predict the need of surgery and (?) shortens the course of partial SBO Usually done 48 hours after unsuccessful conservative therapy Contrast reaches the colon in 4-6 hours = conservative treatment Contrast does not reach the colon in 12 hours = surgery 49 Abdominal Imaging - 9 Topics in 90 min Closed loop obstruction Computed tomography 25% risk of strangulation and infarction Marked segmental distension of bowel, often C or U shape "beak sign": tapering bowel loops at the point of obstruction whirl": tightly twisted mesentery Contrast enhanced CT, due to high risk of ischemia and infarction 50 Abdominal Imaging - 9 Topics in 90 min 25

26 Bowel ischemia Computed tomography Imaging appearance similar independent of cause Unenhanced, late arterial phase, and portal venous phase of enhancement Contrast enhanced CT due to high risk of ischemia and infarction Wall thickening and free fluid Hyperemia or decreased enhancement of wall Pneumatosis intestinalis, pneumoperitoneum, pneumatosis portalis 51 Abdominal Imaging - 9 Topics in 90 min Colon Pseudomembranous colitis Diarrhea, fever, abdominal pain Abdominal distension Leukocytosis Broad-spectrum antibiotic use Diagnosis? C. difficile colitis? Or another cause? Complications? 52 Abdominal Imaging - 9 Topics in 90 min 26

27 Diagnosis? Complications? Computed tomography KUB Colonic distension (Diffuse) marked wall thickening, thumbprinting Toxic megacolon (perforation) 53 Abdominal Imaging - 9 Topics in 90 min Computed tomography More sensitive option for the diagnosis of colitis and its complications Etiology is suggested, but not necessarily definitively established Sensitivity and specificity approximately 85% and 48% (colonic abnormalities) IV contrast, no PO contrast (Diffuse) marked wall thickening, thumbprinting Paucity of pericolonic inflammation may help differentiate from other colitides 54 Abdominal Imaging - 9 Topics in 90 min 27

28 KUB Easy and quick exam, but normal early in the disease Useful for follow-up (q 12-24h); may identify development of toxic megacolon Bowel dilatation, mural thickening and thumbprinting on more advanced cases Underestimate the severity of disease Limited for detection of small pneumoperitoneum Abdominal series preferable to KUB 55 Abdominal Imaging - 9 Topics in 90 min Additional imaging Barium enema Limited role in the diagnosis Contraindicated in patients with severe (perforation) 56 Abdominal Imaging - 9 Topics in 90 min 28

29 Toxic megacolon KUB or CT Nonobstructive colonic dilatation plus systemic toxicity Marked distension > 6 cm transverse segment Loss of hautral markings, pseudopolyps, and air-fluid levels Risk of perforation high if cecum > 12 cm Ischemia Pneumoperitoneum 57 Abdominal Imaging - 9 Topics in 90 min Remember! Imaging findings often not specific for a particular etiology Must consider the clinical setting Interpretation of scans is improved with adequate history Song KS. Yonsei Med J (2): Abdominal Imaging - 9 Topics in 90 min 29

30 Abscess Post operative/trauma/infection/inflammation 1 to 3 weeks to develop Fever, abdominal pain, anorexia Nausea, ileus, weight loss Leukocytosis Diagnosis Treatment planning 59 Abdominal Imaging - 9 Topics in 90 min Diagnosis? Treatment planning? Computed tomography Ultrasound Walled-off collection Amenability to percutaneous drainage Exclude associated complications, e.g. venous thrombosis 60 Abdominal Imaging - 9 Topics in 90 min 30

31 Computed tomography Primary imaging modality (diagnosis and drainage) IV (diagnosis) and oral contrast (drainage) are helpful Collection with enhancing walls and mass effect (Complex) fluid attenuation Presence of gas is the most specific finding Adjacent inflammatory findings (fat stranding/fluid) 61 Abdominal Imaging - 9 Topics in 90 min Ultrasound Easy, fast, and cheap to perform in the bedside Better for superficial, rather than deep abscesses Operator dependent Collection with thick walls and flow on color Doppler Complex fluid (floating echos) Gas is the most specific finding (echogenic and mobile foci with dirty shadow) Turn on color Doppler to find vessels prior to any percutaneous interventions 62 Abdominal Imaging - 9 Topics in 90 min 31

32 Additional imaging 111 In-leukocyte scintigraphy? Equivocal US and CT results Elaborate procedure, requires strict patient collaboration ½ of abscesses are identified by 4 h after injection, more than 90% by 24 h FP results: interpretation must refer to CT findings FN results: chronic abscess (> 3 weeks); lymphocytic mediated infection, e.g. TB or other granulomatous processes; abscess in or adjacent to liver or spleen 63 Abdominal Imaging - 9 Topics in 90 min Thank You! antonio.westphalen@ucsf.edu 32