直腸の粘膜脱症候群―病理の立場から

Morphogenesis of Mucosal Prolapse Syndrome of the Rectum

要旨　直腸の粘膜脱症候群（mucosal prolapse syndrome；MPS）99病変（腸切除例，病変部切除例，ポリペクトミー例，鉗子生検例を含む）を対象として，その肉眼型別（隆起型・平坦型・潰瘍型）に発生部位・組織学的病期・組織学的特徴を検討した．隆起型66病変は96.3％（26/27病変発生部位を明確にしえたもののみ）が歯状線と連続して口側3cm以内にみられ，低線維筋症期72.7％（48/66）・血管期273％（18/66）で，平坦型17病変は100.0％（16/16）が歯状線から口側2.3cm以内にみられ，81.3％（13/16）が歯状線と連続しており，低線維筋症期64.7％（11/17）・血管期29.4％（5/17）であった．一方，潰瘍型16病変は，68.8％（11/16）が歯状線と連続性を持たず口側3～17cmにみられ，高線維筋症期50.0％（8/16），低線維筋症期43.8％（7/16）であった．隆起型・潰瘍型では，粘膜下層にみられる動脈の内膜肥厚や硝子化が認められ，潰瘍型でその変化がより高度であった．MPSは平坦型を初期病変として，歯状線近傍では全壁性の直腸脱が起こらず，粘膜の反応性過形成が主体の隆起型に，歯状線遠位では全壁性の直腸脱のため高度の虚血を来し潰瘍型に移行すると考えられた．

　Ninety-nine lesions with mucosal prolapse syndrome (MPS) of the rectum were examined concerning the incidence of each macroscopic type (polypoid, flat and ulcerative type), the location, histological features and stage of development in each macroscopic type. There were 66 polypoid-type lesions. In 27 of them the precise location was able to be verified. 26 (96.3%) occurred continuously to and within 3 cm oral from the dentate line. 48 of the 66 lesions (72.7%) belonged to a lowgrade fibromuscular stage, and none to a high-grade fibromuscular stage. There were 17 flat-type lesions, in 16 of which the location was able to be verified. All of the 16 lesions were located within 2.3 cm oral from the dentate line, though direct connection with the dentate line was 81.3% (13/16 lesions). 64.7% (11/17 lesions} belonged to a low-grade fibromuscular stage and 5.9% (1/17 lesions) to a high-grade fibromuscular stage. On the other hand, 16 ulcerative-type lesions were located in the rectum within 3-17 cm distance from the dentate line (68.8%). They were distinct from the other types in that they disclosed a higher incidence of fibromusculosis (93.8%) at a highgrade stage (50.0%). In both the polypoid type and the ulcerative type, arteries showed a thickening of the wall and hyalinous degeneration in the submucosa. These findings were conspicuous in the ulcerative type. We conclude that MPS initially occurs as a flat type, and then changes into a polypoid (mucosal hyperplasia) type especially at and near the dentate line by the process of mucosal prolapse, or changes into an ulcerative-type especially at the area more proximal to the rectum by total prolapse which causes more severe ischemic changes.