CT pancreas.pptx

Imaging of pancreas

1. Imaging of Pancreas Dr. Shireen Ahmed Assistant professor Dept. of GHPD

2. CT pancreas protocol The  CT pancreas protocol  serves as an outline for a dedicated examination of the  pancreas. As a separate examination, it is usually conducted as a biphasic contrast study and might be conducted as a part of other scans such as  CT abdomen-pelvis, CT chest-abdomen-pelvis.

3. Indications Typical indications include an evaluation of the following: jaundice evaluation of  pancreatic tumors  and/or  cystic lesions acute  or  chronic pancreatitis complications of pancreatic diseases unclear findings on ultrasound or  CT abdomen pancreatic interventions (e.g.  CT-guided biopsy ,  drainage )

4. Purpose The purposes of a pancreatic CT includes the following  : detection and characterization of pancreatic tumors arterial phase:  hypervascular lesions  e.g.  neuroendocrine tumors , vascular lesions pancreatic phase: depiction of hypoattenuating tumors such as  pancreatic ductal adenocarcinoma portal venous phase: depiction of  hepatic metastases ,  venous thrombosis  etc. detection and characterization of cystic pancreatic lesions

5. acute pancreatitis staging and severity assessment (best-done ≥2-3days after symptom onset) search for etiology ( choledocholithiasis ,  autoimmune pancreatitis ,  etc.) detection of complications in early and late phases including extrapancreatic complications confirmation of the diagnosis of pancreatitis (only if clinically unclear - rare) chronic pancreatitis identification and characterization of  pancreatic calcifications Purpose

6. Technique patient position supine position, abdomen centered within the gantry both arms elevated scout diaphragm to the iliac crest (or symphysis ) scan extent arterial/pancreatic phase: mid diaphragm to the iliac crest venous phase: above the diaphragm to the iliac crest, might be extended to include the whole pelvis scan direction - craniocaudal

7. oral contrast neutral contrast agent: 800 ml water 20-30min before the scan contrast injection considerations non-contrast (rarely indicated) biphasic pancreatic ± venous acquisition (pancreatic mass) contrast volume: 70-120ml  (1 mL/kg) with 30-40 mL saline chaser at 3-5 mL/s pancreatic phase: scan delay 15-20 sec after trigger or 35-40 sec after contrast injection portal venous phase: 30 sec after the pancreatic phase or 65-70 sec after contrast injection

8. biphasic arterial ± venous acquisition (neuroendocrine tumors) contrast volume: 70-120ml  (1 mL/kg) with 30-40 mL saline chaser at 4-5 mL/s arterial phase: minimal scan delay portal venous phase: 40 seconds after the arterial phase or 60-70 seconds after contrast injection single acquisition with a monophasic injection (venous phase) contrast volume: 70-120ml  (1 mL/kg) with 30-40 mL saline chaser at 3-5 mL/s portal venous phase: 65-70 sec after contrast injection

9. respiration phase single breath-hold: inspiration multiplanar reconstructions slice thickness: soft tissue ≤2,5 mm, bone ≤2 mm overlap 20-40%

10. Acute pancreatitis The role of imaging is manifold:  to clarify the diagnosis when the clinical picture is confusing to assess severity (e.g. Balthazar score) and thus to determine prognosis to detect complications to determine possible causes

11. Imaging studies of acute pancreatitis may be normal in mild cases. Contrast-enhanced CT provides the most comprehensive initial assessment, typically with a dual-phase (arterial and portal venous) protocol. However, ultrasound is useful for the follow-up of specific abnormalities, such as fluid collections and  pseudocysts . Radiographic features

12. Plain radiograph Radiographs are insensitive for evidence of acute pancreatitis: many patients have normal exams. Moreover, none of the signs is specific enough to establish the diagnosis of pancreatitis. Abdominal radiographs may demonstrate: localized ileus of the small intestine (sentinel loop) spasm of the descending colon (colon cut-off sign) Chest radiographs may demonstrate: Pleural effusion, usually left-sided  Hemi-diaphragm elevation Basal atelectasis pulmonary edema suggestive of acute respiratory distress syndrome

13. S entinel loop A  sentinel loop  is a short segment of  adynamic ileus  close to an intra-abdominal inflammatory process.

14. Colon cut-off sign The  colon cut-off sign  describes gaseous distension seen in the proximal colon associated with abrupt termination of gas within the colon usually at the level of the  splenic flexure  and decompression of the more distal part of the colon.

15. Ultrasound The main role of ultrasound is:  to identify  gallstones as a possible cause diagnosis of vascular complications, e.g. thrombosis identify areas of necrosis that appear as hypoechoic regions assessment of clinically similar etiologies of an acute abdomen

16. Typical ultrasonographic features with acute pancreatitis include: increased pancreatic volume with a marked decrease in echogenicity    volume increase quantified as a pancreatic body exceeding 2.4 cm in diameter, with marked anterior bowing and surface irregularity  decreased echogenicity secondary to fluid exudation, which may result in a marked heterogeneity of the parenchyma  displacement of the adjacent transverse colon and/or stomach secondary to pancreatic volume expansion  Ultrasound

17. Complications P ancreatic fluid collections are defined by presence or absence of necrosis (as described by the  Revised Atlanta Classification ): necrosis absent (i.e. interstitial edematous pancreatitis) acute peripancreatic fluid collections (APFCs)  (in the first 4 weeks) pseudocysts : encapsulated fluid collections after 4 weeks necrosis present (i.e. necrotizing pancreatitis) acute necrotic collections (ANCs) : develop in the first 4 weeks walled-off necrosis  (WON) : encapsulated collections after 4 weeks L iquefactive necrosis of pancreatic parenchyma (e.g.  necrotizing pancreatitis ) increased morbidity and mortality may become secondarily infected ( emphysematous pancreatitis )

18. Vascular complications hemorrhage: resulting from erosion of blood vessels and tissue necrosis pseudoaneurysm : autodigestion of arterial walls by pancreatic enzymes results in pulsatile mass that is lined by fibrous tissue and maintains communication with parent artery splenic vein thrombosis portal vein thrombosis Fistula formation with pancreatic  ascites : leakage of pancreatic secretions into the peritoneal cavity Abdominal compartment syndrome Complications

19. Abdominal compartment syndrome (ACS) is a severe illness seen in critically ill patients.  ACS results from the progression of steady-state pressure within the abdominal cavity to a repeated pathological elevation of pressure above 20mmHg with associated organ dysfunction. 

20. MRI Contrast-enhanced MRI is equivalent to CT in the assessment of pancreatitis.

21. CT severity index (CTSI) The  CT severity index (CTSI)  is based on findings from an enhanced CT scan to assess the severity of  acute pancreatitis . The severity of  acute pancreatitis  CT findings has been found to correlate well with clinical indices of severity.  The CT severity index sums two scores: Balthazar score : grading of pancreatitis (A-E)  grading the extent of pancreatic necrosis The necrosis scoring system was added to the traditional  Balthazar score  in 1990 Modifications have been made to the CTSI, resulting in the  modified CTSI  (2004 ).

22. CT severity index Grading of pancreatitis (Balthazar score) A:  normal pancreas : 0 B:  enlargement of pancreas : 1 C: inflammatory changes in pancreas and peripancreatic fat: 2 D: ill-defined single  peripancreatic fluid collection : 3 E: two or more poorly defined peripancreatic fluid collections: 4 Pancreatic necrosis  none: 0 ≤30%: 2 >30-50%: 4 >50%: 6

23. Balthazar score

24. CT severity index The CT severity index is the sum of the scores obtained with the Balthazar score and those obtained with the evaluation of pancreatic necrosis: 0-3: mild acute pancreatitis 4-6: moderate acute pancreatitis 7-10: severe acute pancreatitis

25. Peripancreatic fluid collection

26. Pancreatic pseudocyst

27. Necrotizing pancreatitis

28. Walled-off pancreatic necrosis

29. KEY POINTS 1 . CT is used to confirm the diagnosis of acute pancreatitis when the diagnosis is in doubt and to differentiate acute interstitial pancreatitis from necrotizing pancreatitis, which is a key element of the updated Atlanta nomenclature. The acute interstitial variety accounts for 90–95% of cases, with acute necrotizing pancreatitis accounting for the remaining cases.

30. 2. Necrosis due to acute pancreatitis is best assessed on IV contrast-enhanced CT performed 40 seconds after injection. Peripancreatic necrosis is a subtype of necrotizing pancreatitis in which tissue death occurs in peripancreatic tissues. This is seen in isolation in 20% of patients with necrotizing pancreatitis. KEY POINTS

31. 3. Simple fluid collections associated with acute interstitial pancreatitis are subdivided chronologically. A collection observed within approximately 4 weeks of acute pancreatitis onset is termed an “acute peripancreatic fluid collection (APFC).” A collection older than 4 weeks should have a thin wall and is termed a “ pseudocyst .” Both APFCs and pseudocysts can be infected or sterile. KEY POINTS

32. 4 . Fluid collections associated with necrotizing pancreatitis are labeled on the basis of age and the presence of a capsule. Within 4 weeks of acute pancreatitis onset, a fluid collection associated with necrotizing pancreatitis is termed an “acute necrotic collection (ANC)” whereas an older collection is termed an area of “walled-off necrosis (WON)” if it has a perceptible wall on CT. The term “ pseudocyst ” is not used in the setting of necrotizing pancreatitis collections. Although an ANC and a (WON can be infected or sterile, infection is far more likely compared with acute interstitial pancreatitis collections. KEY POINTS

33. 5. The severity of acute pancreatitis is graded on the basis of the presence of acute complications or organ failure. Mild acute pancreatitis has neither acute complications nor organ failure. Moderate-severity acute pancreatitis is associated with acute complications or organ failure lasting fewer than 48 hours. Severe acute pancreatitis is characterized by single- or multiorgan failure persisting for greater than 48 hours KEY POINTS