Autoimmune pancreatitis with extrapancreatic manifestations

69-year-old male patient with hypertension. He noticed enlarged lymph nodes on his neck. Hoarseness since 2 weeks. Neck soft tissue US showed moderately enlarged submandibular hypoechoic lymph nodes: the largest hypoechoic lymph node was 22 mm in diameter. Histology was performed due to the enlarged lymph nodes in the neck and upper mediastinal region. Histological diagnosis: metastatic adenocarcinoma of the submandibular lymph node. Immunohistochemical tests confirmed primarily pancreato-biliary, upper gastrointestinal or salivary gland origin. The PET-CT confirmed circumscribed FDG accumulation in the pancreas, parotid gland and the prostate. Biopsy of the parotid, pancreas and the mediastinal lymph node (by thoracoscope) did not prove malignancy. Chronic fibrosing pancreatitis without IgG4 associated disease was diagnosed. Right submandibular salivary gland core biopsy showed chronic fibrosing sialoadenitis with IgG4 positive plasma cell infiltrate suggesting IgG4 associated salivary gland inflammation. Left superficial parotidectomy and neck block dissection are planned.

PET/CT: There is a suspicion of a malignancy at the border of the body and tail of the pancreas with mild FDG uptake, with possibly metastatic lymph nodes in its surroundings. Hypermetabolism in the left parotid and both submandibular salivary glands were confirmed. The mediastino-hilar hypermetabolic lymph nodes might be due to inflammatory/granulomatous origin.

Neck MRI: A 24 x 19 mm lymph node can be seen on the left side at the border of the submandibular-anterior jugular lymph region. On the right side, an 18 x 11 mm lymph node can be observed under the submandibular gland.

CT Thorax and Abdomen: Close to the left parotid gland, along the surface of the masseter muscle there are some contrast enhancing lymph nodes with a maximum transverse diameter of 7-8 mm. Some smaller lymph nodes can also be detected on the right side in a similar localization. The structure of the large salivary glands is preserved. Parajugularly, bilaterally enlarged lymph nodes below the abnormal size limit can be seen.

An increased number of lymph nodes with a shorter diameter of 15 mm can be observed in the mediastinum. There is widened cast-like soft tissue mass in the hilar region bilaterally with a maximum diameter of 12 mm in width.

The body and tail region of the pancreas is diffusely widened, the tail is 40 mm wide, the body is 35 mm wide, the glandular structure is blurred, and the structure of the pancreas is inhomogeneous. No Wirsung's duct dilatation. In addition, a circumscribed hypodense lesion of 7 mm in the tail, and a calcified and a hypodense lesion in the head region of the pancreas can be detected. There are several areas of isolated scattered, patchy non-enhancing regions in the cortical regions of the kidneys bilaterally. The left ureter is dilated. In summary, the outlook of the pancreas is mostly characteristic of autoimmune pancreatitis, which can be characterized by patchy contrast enhancement of the kidneys, mediastinal lymphadenomegaly, and the lesions described near the salivary glands.

Background

Autoimmune pancreatitis (AIP) is a special form of chronic pancreatitis, which is a rare diagnosis. Overall prevalence is 2.2 and 4.6 per 100,000, respectively. CT and MRI play a vital role in AIP diagnosis. Type 1 AIP is the pancreatic manifestation of IgG4-related systemic disease, which can manifest in other organs. Type 2 AIP is a rare subtype which occurs in younger patients [1].

Multidisciplinary decision, such as clinicoradiological and serological correlation and histological confirmation is required for the diagnosis of AIP. Usually, elderly males (mean age 60–70 years) are affected.

The effective therapy of the AIP is corticosteroid therapy [2].

Clinical Perspective

Symptoms of AIP are vague abdominal pain, jaundice, or weight loss, these are caused by compression of adjacent organs and damage to the exocrine and endocrine function of the pancreas. Differentiating AIP from pancreatic carcinoma can be very difficult because they can mimic each other clinically and radiologically, therefore, it is important to be familiar with the various imaging findings of AIP [3].

Imaging perspective

The most common manifestations include diffuse or focal sausage-like (focal or entire) pancreatic enlargement, sometimes appearing like a mass and pancreatic ductal strictures (duct-penetrating sign). Extrapancreatic manifestations are less common, such as sialadenitis, pulmonary interstitial fibrosis, mediastinal or retroperitoneal fibrosis and peripancreatic lymphadenopathy, orbital pseudotumor and tubulointerstitial nephritis [4,5].

CT and MR are the gold standard imaging modalities using contrast media because the fibrotic component of the tissues affected by AIP are enhancing the contrast material.

CT features of AIP include sausage-like swelling of the focal or entire pancreas, duct-penetrating sign, a low-attenuation rim-like capsule representing surrounding dense fibrosis, punctate, speckled, or dotted contrast enhancements and homogeneous delayed enhancement in the arterial or pancreatic phase, moreover contrast-enhanced area along the main pancreatic duct (enhanced duct sign) is also characteristic after iodinated contrast medium injection [6].

MRI shows high signal on fat-saturated T1-weighted images in the affected areas by AIP. Fibrosis is characterized by low signal intensity on T2-weighted images, the capsule-like rim demarcates the swollen pancreas with a low signal. The diffusion-weighted images (DWI) show high signal intensity [7].

Positron emission tomography (PET) shows intense, diffuse and heterogenous fluorine-18 FDG uptake. Solitary FDG uptake in the pancreas might occur, which often mimics pancreatic cancer. Concomitant FDG uptake by extrapancreatic organs also support the diagnosis of AIP [8].

Typical extrapancreatic lesions of AIP include sclerosing cholangitis, retroperitoneal fibrosis and interstitial nephritis [6,9].

Outcome

The early correct imaging diagnosis of AIP is important for early steroid therapy. Differential diagnoses include general pancreatitis, pancreatic ductal adenocarcinoma, lymphoma and other malignant disorders.

Take Home Message / Teaching Points

AIP is a special form of chronic pancreatitis mediated by autoimmunity. The clinical presentation is not specific, however, the CT and MRI characteristics of AIP may suggest the diagnosis.