膵囊胞性病変の病理

Pathology of pancreatic cysts

要旨

膵囊胞性病変は多彩であり，本稿では囊胞性腫瘍の病理像について述べる。膵管内乳頭粘液性腫瘍は低異型度と高異型度に分類し，分化方向より胃型，腸型，膵胆道型に亜型分類する。組織亜型は腫瘍の広がり，浸潤癌の組織型，予後などと関連する。膵管内オンコサイト型乳頭状腫瘍，膵管内乳頭管状腫瘍が鑑別となる。粘液性囊胞腫瘍は卵巣様間質を有する粘液産生性の囊胞性病変であるが，非粘液性の膵胆道型上皮がみられることがある。漿液性腫瘍は多数の囊胞を形成する漿液性囊胞腺腫が最も多い。囊胞性変化を示す充実性腫瘍も鑑別が必要で，充実性偽乳頭状腫瘍は腫瘍の変性により偽乳頭状構造を示し囊胞化する。神経内分泌腫瘍は変性により囊胞化する場合と，腫瘍の広がりが膵管に及び尾側膵管が拡張する場合がある。膵囊胞性腫瘍の理解には，真の囊胞性病変かどうか，膵管由来かどうか，どのような細胞が囊胞を裏打ちして増殖しているかが重要である。

　Pancreatic cystic lesions are a diverse group, and this article describes the pathology of cystic neoplasms. Intraductal papillary mucinous neoplasms (IPMNs) are histologically classified as low grade or high grade and subclassified into gastric, intestinal, and pancreatobiliary types based on the predominant cell differentiation pattern. Histological subtyping is related to the extent of spread, the histological type of the invasive carcinoma, and the prognosis. IPMNs must be differentiated from intraductal oncocytic papillary neoplasms (IOPNs) and intraductal tubulopapillary neoplasms (ITPNs). Mucinous cystic neoplasms (MCNs) are mucin-producing epithelial neoplasms with ovarian-type subepithelial stroma but may have a nonmucinous epithelium of the pancreatobiliary type. Among serous neoplasms (SNs), serous cystadenomas (SCNs) are encountered more frequently and form numerous cysts composed of cuboidal or flat epithelium. Solid neoplasms that exhibit cystic changes must also be differentiated. Solid pseudopapillary neoplasms (SPNs) have pseudopapillary architecture due to degeneration. Neuroendocrine tumors (NETs) may become cystic as a result of tumor degeneration, or the spread of the tumor may affect the pancreatic duct, resulting in dilatation of the caudal pancreatic duct. To understand pancreatic cystic neoplasms, it is important to clarify whether or not they are true cysts, whether or not they originate from the pancreatic duct, and to determine the type of cells that line and proliferate in the cyst.