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, the head being spared. If no cause is identified, suspicion of a small imaging-occult cancer may be warranted. OBJECTIVE. The purpose of this study was 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, that showed acute pancreatitis without identifiable explanation. Studies were classified as showing distal or nondistal acute pancreatitis on the basis of consensus. The Fisher exact test was used to compare the frequency of subsequent histologic diagnosis of pancreatic cancer between groups. Negative classification required 6 or more months of imaging follow-up and/or 12 or more 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 (54%) had no identifiable explanation and formed the study sample. A total of 100 of 116 (86%) patients (59 men, 41 women; mean age, 57 ± 18 [SD] years) had nondistal acute pancreatitis; 16 of 116 (14%) patients (10 men, six women; mean age, 66 ± 14 years) 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 having negative follow-up 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 having negative follow-up for pancreatic cancer. The frequency of pancreatic cancer was higher (p < .001) in patients with distal pancreatitis (9/14 [64%; 95% CI, 35-87%]) than in with those with nondistal pancreatitis (0/62 [0%; 95% CI, 0-6%]). Interreader agreement on classification of distal versus nondistal pancreatitis was almost perfect (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.