Unexpected benign histopathology after pancreatoduodenectomy for presumed malignancy: accepting the inevitable.

Background: Differentiating malignant and benign disease in the pancreatic head and periampullary region is difficult. The aim of this retrospective study was to analyze patients with unexpected "benign" disease after pancreatoduodenectomy (PD) to evaluate the incidence, possible discriminating factors, and outcome. The role of preoperative pathology interpretation in diagnosing malignancy was also assessed.

Methods: Patients with unexpected benign disease were identified from a prospectively maintained database of 446 PDs for presumed malignancy from April 2006 to December 2013. Clinical, radiological, and pathological features were reviewed. Positive predictive values (PPVs) of preoperative pathology interpretation were analyzed. Short-term outcomes were compared.

Results: Incidence of unexpected benign disease was 6.5 % (29/446). Radiological diagnostic signs (except the double duct sign) suggestive of malignancy were seen in more than half of the benign cases. Preoperative pathology 'positive' or 'suspicious for malignancy' had a PPV of 97.6 % and 'indeterminate disease' and had a PPV of 90 % for malignancy. 'Benign' or 'negative' pathology had a PPV of 19 % for benign disease in strongly suspected malignancy. There was no significant difference in outcomes in PD for benign versus malignant disease except for a decreased rate of POPFs and a higher trend toward mortality. However, both outcomes were not independently associated with benign disease.

Conclusions: A small percentage of benign disease after PD for "strongly suspected malignancy" is inevitable. No radiological or pathological features can reliably discriminate benign from malignant in these patients. Trend toward higher mortality after PD for unexpected benign disease exists. Detailed preoperative pathological subclassifications are helpful in malignancy.