岡庭 信司¹, 岩下 和広²

Shinji OKANIWA¹, Kazuhiro IWASHITA²

¹飯田市立病院消化器内科, ²飯田市立病院超音波室

¹Department of Gastroenterology, Iida Municipal Hospital, ²Department of Radiological Technology, Iida Municipal Hospital

キーワード : ultrasound, macroscopic findings, cystic lesion, differential diagnoses

膵病変はその肉眼像から充実性病変と嚢胞性病変に分類され，充実性病変には膵管癌，神経内分泌腫瘍（neuroendocrine tumor: NET），SPN（solid-pseudopapillary neoplasm），腫瘤形成性膵炎などが，嚢胞性病変には漿液性嚢胞性腫瘍（serous cystic neoplasm: SCN），粘液性嚢胞性腫瘍（mucinous cystic neoplasm: MCN），膵管内乳頭粘液性腫瘍（intraductal papillary mucinous neoplasm: IPMN）などが含まれる．超音波検査（Ultrasound: US）は膵病変の病理肉眼像を詳細に反映するため，SCNの蜂巣状構造，MCNのcyst in cyst構造，IPMNのcyst by cyst構造などそれぞれの嚢胞性腫瘍に特徴的な構造を理解することは鑑別診断にも有用である．嚢胞性病変の鑑別診断に有用なUS所見には，①病変の占居部位，②病変の数，③輪郭，④内部構造，⑤内容液の性状，⑥膵管との交通の有無，⑦充実部分の有無といった所見がある．充実部分の有無は病変の悪性度の評価にも有用である．さらに，5 mm以上の膵嚢胞は膵管癌の高危険群としても認識されており，初診時に精検を行うとともに定期的に経過観察をしていく必要がある．

Pancreatic lesions are generally classified as solid or cystic lesions. Solid neoplasms include pancreatic ductal carcinoma, neuroendocrine tumor (NET), solid pseudopapillary neoplasm (SPN), and tumor-forming pancreatitis. Cystic neoplasms include serous cystic neoplasm (SCN), mucinous cystic neoplasm (MCN), and intraductal papillary mucinous neoplasm (IPMN). As ultrasound (US) reflects macroscopic pathological findings precisely, we should acknowledge the characteristic structures of each type of pancreatic cystic lesion, such as the honeycomb structure of SCN, the cyst-in-cyst structure of MCN, and the cyst-by-cyst structure of IPMN, to make correct diagnoses. Their location, number, contour, internal structure, internal echo texture, communication with MPD, and presence of solid components are useful US findings to make differential diagnoses. The presence of solid components is related to the malignant potential of cystic lesions. We also emphasize pancreatic cysts that are more than 5 mm in size as a high-risk sign for pancreatic carcinoma and recommend regular follow-up for early detection of pancreatic ductal carcinoma.