Unexplained Acute Distal Pancreatitis: Association With Subsequent Diagnosis of Pancreatic Cancer.

Background: Distal pancreatitis is an atypical imaging subtype of acute pancreatitis involving only the pancreatic body and tail, with sparing of the head. If no cause is identified, then suspicion for a small imaging-occult cancer may be warranted. Objective: To determine the frequency of subsequently diagnosed pancreatic cancer in patients with unexplained acute distal pancreatitis and to compare this frequency to that found in patients with unexplained nondistal pancreatitis. Methods: This retrospective study included patients who underwent contrast-enhanced CT between January 1, 2019 and December 31, 2020 showing acute pancreatitis without identifiable explanation. Studies were classified as showing distal or nondistal acute pancreatitis using a consensus process. Fisher's exact test was used to compare frequency of subsequent pancreatic cancer histologic diagnosis between groups; negative classification required ≥6 months of imaging follow-up and/or ≥12 months of clinical follow-up. Interreader agreement among seven readers of varying experience was assessed by Fleiss kappa. Results: Among 215 patients with acute pancreatitis, 116/215 (54%) had no identifiable explanation, forming the study sample. A total of 100/116 (86%) (57±18 years; 59 men, 41 women) patients had nondistal acute pancreatitis; 16/116 (14%) (66±14 years; 10 men, 6 women) had distal acute pancreatitis. Among patients with nondistal pancreatitis, none were subsequently diagnosed with pancreatic cancer; 62 had sufficient follow-up (median, 2.5 years) to be classified as negative for pancreatic cancer. Among patients with distal pancreatitis, nine were subsequently diagnosed with pancreatic cancer (median interval to suspected cancer on subsequent CT, 174 days); five had sufficient follow-up (median, 3.1 years) to be classified as negative for pancreatic cancer. Frequency of pancreatic cancer was higher (p<.001) in patients with distal (9/14 [64%]; 95% CI 35-87%) than with nondistal (0/62 [0%]; 95% CI, 0-6%) pancreatitis. Interreader agreement for distal versus nondistal pancreatitis classification was excellent (κ=0.81). Conclusion: Distal pancreatitis without identifiable cause on CT is an uncommon but unique imaging subtype of acute pancreatitis that is associated with a high frequency of pancreatic cancer. Clinical Impact: In patients with acute distal pancreatitis without identifiable cause, endoscopic ultrasound-guided biopsy should be considered to evaluate for an underlying small cancer.