Natural history of branch duct intraductal papillary-mucinous neoplasms of the pancreas without mural nodules: long-term follow-up results

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Abstract
Background and aim: Although branch duct intraductal papillary-mucinous neoplasms (IPMNs) of the pancreas without mural nodules are frequently observed in asymptomatic subjects, the natural history of these lesions has never been studied. The aim of this study was to elucidate the natural history of branch duct IPMNs without mural nodules. Methods: Eighty-two patients who had no apparent mural nodules on initial examination were selected for follow-up. All subjects underwent examinations by imaging modalities including endoscopic retrograde pancreatography, and were followed-up by regular examinations once or twice a year. Serial changes of the maximum cystic diameter and the appearance of mural nodules were studied during the observation periods ranging from 14 to 148 months (median, 61 months). Results: Nine (11.0%) of 82 patients exhibited obvious progression of cystic dilatation (median, 59 months). Of these nine patients with cystic enlargement, six continued with regular follow-up examinations. Three cases underwent surgical resection, and were pathologically diagnosed as adenoma in two and borderline in one. Four patients (4.9%) showed newly developed mural nodules in dilated branch ducts (median, 105 months). Histological analysis revealed three cases classified as adenoma and one as carcinoma in situ. None of the remaining 69 patients (84.1%) showed any changes in dilated branch ducts (median, 57 months). Conclusions: Most branch duct IPMNs without mural nodules remained unchanged during long-term follow-up. Although follow-up with careful examination is required to detect newly developed mural nodules in dilated branch ducts, branch duct IPMNs without mural nodules can be followed-up without surgery.