大腸腺腫性ポリープにおけるPseudocarcinomatous invasion―その組織像と成因について

Pseudo-carcinomatous Invasion in Adenomatous Polyps of the Colon and Rectum

　大腸直腸の腺腫性ポリープの組織学的検索に際して，腺腫性組織が粘膜筋板を越えてポリープの粘膜下へ侵入している像が見出された．一見，浸潤癌を疑わせるこの所見も，詳細に観察すると一定の組織学的特徴を具えた非癌性の病変であることが明らかになったので，これをpseudo-carcinomatous invasionと呼ぶことにした¹⁾．

　この奇妙な所見が浸潤癌と診断される可能性は十分にあり，特に粘膜下腺腫組織に異型が強い場合はその可能性が高い．文献上にも既にその実例と思われるものが散見される²⁾³⁾．本病変の組織学的特徴を詳細に述べて浸潤癌との相違を明かにし，合わせてその成因について多少の考察を試みた．

　The histology of pseudo-carcinomatous invasion in adenomatous polyps of the colon and rectum is described and the appearances are contrasted with those seen in malignant polyps. Prominent features of preudo-carcinomatous invasion are summarized as follows: 1) Aadenomatous tubules are found in the submucosal layer in continuity with the neoplastic tissue in the head of the polyp. 2) The submucosal glands are surrounded by lamina propria without any desmoplastic reaction to the epithelial cells. 3) Cystic change is very pronounced in many of the pseudocarcinomatous glands. 4) There are deposits of pigment with the staining characteristics of haemosiderin around the submucosal glands. 5) The gland-like structures are usually surrounded by a narrow rim of granulation tissue composed of collagen and inflammatory cells. 6) There are marked branching and excess of muscularis mucosae in some pseudo-carcinomatous polyps.

　The recognition of pseudo-carcinomatous invasion is important in the differential diagnosis of benign and malignant polyps of the large bowel. Failure to distinguish it from carcinoma may lead to wrong treatment and false reports of the incidence and prognosis of cancer of the colon and rectum.

　The polyps with pseudo-carcinomatous invasion are mostly situated in the sigmoid part of the colon with large size and exceptionally long stalks. The evidence suggest that pseudo-carcinomatous invasion may be the result of repeated twisting of the stalk of a polyp which causes haemorrhage and this facillitates the passage of non-malignant adenomatous epithelium through the muscularis mucosae.