Autoimmune Pancreatitis Mimicking a Pancreatic Neuroendocrine Tumor: A Case Report with a Literature Review

Abstract

Autoimmune pancreatitis (AIP) is a rare chronic pancreatitis subtype that often mimics pancreatic cancer due to the overlapping clinical and radiological features, posing significant diagnostic challenges. Similarly, distinguishing AIP from pancreatic neuroendocrine neoplasms (PanNENs), which present with nonspecific symptoms, adds complexity to clinical evaluations. We present the case of a 46-year-old male with recurrent acute idiopathic pancreatitis. Abdominal computed tomography (CT) revealed a 25 mm hypodense mass in the pancreatic tail with mild arterial contrast enhancement. Magnetic resonance imaging (MRI) showed the mass to be hypointense on T2-weighted sequences, with no diffusion restriction and an enhancement pattern akin to normal pancreatic tissue. The endoscopic ultrasound-guided fine needle biopsy (EUS-FNB) was inconclusive. Gallium-68 DOTATATE positron emission tomography-CT (Ga-68 DOTATATE PET-CT) showed an increased tracer uptake, leading to a distal pancreatectomy with a splenectomy. Histopathology demonstrated chronic sclerotic pancreatitis with inflammatory infiltrates. Elevated serum IgG4 levels confirmed the diagnosis of type 1 AIP Differentiating AIP from pancreatic malignancies, including PanNENs, is both critical and complex. This case highlights a misdiagnosis of PanNENs in a patient with focal AIP, where neuroendocrine hyperplasia and islet cell clusters within fibrotic areas mimicked PanNENs, even on Ga-68 PET-CT. The findings emphasize the potential for false positives with Ga-68 DOTATATE PET-CT and the importance of integrating clinical, radiological, and histological data for an accurate diagnosis.

Keywords: autoimmune pancreatitis; chronic pancreatitis; pancreatic neuroendocrine tumors.

Figure 1

A CT scan performed with iodinated contrast media demonstrated a lesion in the distal pancreatic tail, measuring 23 mm × 18 mm (yellow arrow). The lesion appeared isodense to the surrounding pancreatic parenchyma across all contrast phases. It exhibited a compact glandular component with polylobulated margins. The spleen, liver, and surrounding retroperitoneal structures showed no abnormalities.

Figure 2

Increased tracer uptake in the pancreatic tail lesion was observed on Ga-68 DOTATATE PET-CT, suggestive of somatostatin receptor expression. The Ga-68 DOTATATE PET-CT was performed using an Omni Legend PET/CT scanner (GE HealthCare, Chicago, IL, USA).

Figure 3

A pseudonodular alteration was identified in the pancreatic tail, measuring approximately 25 mm. On T1-weighted post-contrast MRI sequences, the lesion appeared isointense relative to the surrounding pancreatic tissue, while on T2-weighted sequences, it was slightly hypointense (yellow arrows). The MRI was performed with a 1.5T magnet (Ingenia, Philips Healthcare, Amsterdam, The Netherlands). P = posterior.