cap polyposisの病理組織学的特徴―粘膜脱症候群との比較

Analysis of Clinicopathological Features of Cap Polyposis, in Comparison with Mucosal Prolapse Syndrome

要旨　cap polyposisの臨床病理学的特徴を明らかにするために粘膜脱症候群（MPS）と比較検討した．cap polyposisではほとんどの症例で病変が直腸のみならずS状結腸や下行結腸にも認めるが，MPSでは病変は直腸のみであった．組織学的には両者では炎症細胞浸潤の程度と分布および線維筋症の程度が異なり，MPSで比較的高率に認める粘膜内血管の変化（筋性血管の出現，血管壁内フィブリン滲出，血栓形成）やdiamoid-shaped cryptの出現がcap polyposisでは低率であった．さらに，cap polypの詳細な組織学的観察により，これらの発育進展様式が以下のように推察された．①それらの初期像は平坦な粘膜に生じた粘膜表層性かつ限局性慢性活動性炎症細胞浸潤．②その後陰窩の延長と軽度の線維筋症，肉芽組織増生，うっ血（血管拡張），循環不全による陰窩上皮の壊死（びらん）が起こり小隆起性病変を形成．③そしてこれらの小さな隆起が集簇して大きな隆起を形成．④さらに粘膜脱が高度な症例ではさらに陰窩が延長し線維筋症が著明となる．このように両疾患は臨床病理学的に異なり，本質的には病因が異なる疾患群であることが示唆されたが，cap polypの進展過程で粘膜脱が関与している可能性も考えられた．

　The Clinicopathological features of cap polyposis were reviewed, comparing them with mucosal prolapse syndrome (MPS). Cap polyps were distributed not only in the rectum but also in the sigmoid and descending colon, while lesions of MPS were restricted to the rectum. Histologically, there was a difference between cap polyposis and MPS in the degree and distribution of inflammation and the degree of fibromusculosis. Microvascular abnormalities such as the presence of muscularised capillaries, thrombosis and fibrin insudation and the presence of diamond-shaped crypts are characteristic in MPS, while they are rarely seen in cap polyposis. analyzing the histological features of cap polyposis, we speculated about its histogenesis and progression as follows: 1) First, the superficial and localized inflammation arises in flat mucosa. 2) Next, it grows into an elevated lesion (polyp) with elongation of crypts, mild fibromusculosis, overgrowth of granulation tissue, congestion and ischemic change of superficial crypts. 3) The aggregation of small cap polyps makes a large sessile polyp. 4) In addition, the mucosal prolapse increases the degree of elongation of crypts and fibromusculosis. In conclusion, cap polyposis and MPS are essentially different in histogenesis and clinicopathological features, but mucosal prolapse may be associated with the progression of cap polyposis.