Type:
Educational Exhibit
Keywords:
Abdomen, Pancreas, CT, MR, Ultrasound, Diagnostic procedure, Inflammation
Authors:
R. P. Patel1, T. M. Chandler1, S. Barrett2, J. Coyle3, C. Zwirewich1, A. Harris4; 1Vancouver, BC/CA, 2Dublin /IE, 3Cork/IE, 4BC/CA
DOI:
10.1594/ecr2013/C-2649
Imaging findings OR Procedure details
- Multi-modality imaging and enhancement characteristics of pancreatic features.
- Multimodality imaging of extrapancreatic pathological processes;
- biliary tree dilatation
- lacrimal adenitis
- siladenitis
- renal inflammatory pseudotumour
- prostatitis
- aortitis
- retroperitoneal fibrosis
- Follow up imaging after steroid therapy.
Pancreatic features
- Autoimmune pancreatitis (AIP) is a rare form of chronic pancreatitis accounting for 1.5-11% of all cases
- Pathogenesis is though to involve antibodies,
hypergammaglobulinemia and evidence of lymphoplasmocytic inflammation and fibrosis
- Highly responsive to steroids
- The role of imaging is to make a prompt diagnosis so that steroids can be implemented in a timely fashion
- Three recognized patterns; Diffuse,
focal and multifocal
- Signs and symptoms: Can be fluctuating obstructive jaundice,
vague abdominal pain,
weight loss,
steatorrhea and diabetes
- Focal; painless jaundice,
weight loss
- Diffuse; epigastric pain radiating to back
- AIP can clinically mimic pancreatic adenocarcinoma
Diagnostic evaluation
- Clinical features alone not helpful
- A short-term trial of high-dose steroid therapy with repeat imaging can be utilized to look for a reduction in size of the pancreatic parenchymal and normalization of the pancreatic duct.
- Serology; Serum IgG4 is statistically higher in patients with AIP than in other populations (e.g.
pancreatic cancer),
other autoantibodies are raised (rheumatoid factor and antinucleur)
- Imaging; Mayo clinic: utilizes CT features only,
Japan relies on ERCP and CT features
- Histology; Core biopsies can be used to confirm the presence of abundant IgG4 positive plasma cells and lymphocyte infiltration
Diffuse parenchymal enlargement Fig 1-8
- Pancreatic borders become featureless with effacement of the lobular contour
Typical imaging features:
- CT;
- A halo of soft tissue attenuation present in 12-40%
- Enhancement characteristics
- Hypoattenuating in early phase
- Hyperattenuating in the late phase
- MRI;
- T1 diffusely hypointense
- T2 mildly hyperintense
- Early phase heterogeneously diminished enhancement
- Late phase delayed enhancement
- USS
- Diffusely enlarged and hypoechoic
Focal,
mass like or segmental enlargement of the pancreas Fig 9-17
- Most commonly pancreatic head involvement
- Can mimic pancreatic adenocarcinoma radiologically
- Enhancement characteristics
- Focal mass like enlargement
- Iso or hypoattenuating to the spared non enlarged segment
- Parenchymal atrophy
- 5-20% pts
- Likely represents a late burn out phase of disease
- Also seen after steroid therapy
AIP vs.
Pancreatic adenocarcinoma: Distinguishing features
- Capsule-like rim around the pancreas
- Contrast enhancement
- BOTH adenocarcinoma and focal AIP are hypoattenuating on arterial phase
- ONLY adenocarcinoma is hypoattenuating on PV phase,
whereas AIP on delayed imaging demonstrates retention of contrast with near- normal enhancement (and appears nearly isoattenuating to the normal pancreatic parenchyma).
- Duct dilatation
- The pancreatic duct within the lesion is not visible in either AIP or adenocarcinoma - NOT a useful feature
- Upstream main pancreatic duct dilatation (e.g.> 5mm) seen more often in adenocarcinoma.
Extrapancreatic features
- Prevalence of extrapancreatic findings is 92%
- Familiarity with these findings can help to make the diagnosis of AIP when the pancreatic findings are ambiguous.
- Distribution:
- Retroperitoneum (retroperitoneal fibrosis,
AAA) 20%
- Renal (renal pseudotumours) 14%
- Biliary (wall thickening and multifocal strictures) 78%
- Prostate(enlargement) 10%
- Salivary/ lacrimal gland (enlargement),
lymph nodes - 48%
- Lung (inflammatory nodules,
chronic bronchitis,
NSIP,
LIP) 13%
Retroperitoneal fibrosis Fig 18-20
- Present in 10%-20% of patients
- Similar imaging characteristics as those of retroperitoneal fibrosis
- Manifestations
- Soft tissue mass surrounding the abdominal aorta (and branches) and IVC
- Soft tissue mass surrounding the ureters (may result in hydronephrosis)
- Paravertebral mass
- Pelvic retroperitoneal mass
- May be difficult to distinguish from periaortitis as some cases of AIP are associated with AAA
Renal pseudotumors Fig 21,22
- renal lesions associated with AIP may be difficult to differentiate from pyelonephritis or infarcts - look for ancillary pancreatic and extra-pancreatic findings to help make the diagnosis
- Pathophysiology:
- Due to dense lymphocytic infiltration of the renal interstitium
- Lesions vary from tubulointerstitial nephritis (TIN) to tumor like masses depending on the distribution
- Most lesions progress to cortical scars at follow up evaluation
- Appearance:
- Bilateral and multiple
- Poorly enhancing,
mild enhancement on delayed phase images
- 4 patterns:
- Round or wedge shaped renal cortical nodules
- Peripheral cortical lesions
- Mass like lesions
- Renal pelvic involvement
Biliary abnormalities Fig 23,
24,
25
- The most common form of extrapancreatic involvement which can occur in the absence of pancreatic findings. May progress and lead to biliary cirrhosis
- AIP associated biliary involvement may mimic primary sclerosing cholangitis (PSC),
therefore look for ancillary pancreatic and extrapancreatic findings to aid diagnosis
- CT;
- Focal or diffuse thickening and enhancement of the bile duct wall
- Rarely soft tissue mass that can resemble cholangiocarcinoma
- GB involvement appears as diffuse thickening of GB wall
- ERCP
- Multifocal intra +/- extrahepatic bile duct strictures or thickening
Prostate Fig 26
- May be difficult to distinguish from prostate cancer and prostatitis. A trial of steroids or a biopsy may be needed to confirm abundant IgG4 positive plasma cell and lymphocytic infiltration
- Imaging:
- Prostate enlargement
- Hypodense
- Surrounding fat stranding
Salivary gland/lymph nodes Fig 27,
28,
29
- Distribution
- Submandibular 76%
- Lacrimal 75%
- Parotid 13%
- Sublingual 5%
- Affected lymph nodes may be as large as 2cm (exhibit infiltration by IgG4 positive plasma cells)
- Salivary gland involvement in AIP may clinically mimic Sjogren’s syndrome. MRI may provide useful distinguishing features; In Sjorgren’s the lesions tend to have a ‘salt and pepper’ appearance,
a feature which is not seen in AIP – salivary involvement
- MRI; Bilateral homogenous swelling of the glands without a discernible mass
- USS; Multiple hypoechoic nodules