大腸のMetaplastic Polyp（化生性ポリープ）についての一考察―その病理組織像と鑑別診断

The Histopathological Aspects of Metaplastic Polyps of the Large Bowel

　大腸，直腸に発生する隆起性病変のうち，metaplastic polyp（Morson）¹⁾またはhyperplastic polyp（Lane）²⁾と呼ばれる病変は日常しばしば遭遇し，とくに高齢者に高頻度に認められ，Alterspolypen（Westhues）³⁾とも呼ばれている．この病変の本態に関しての研究は数少く，腺腫あるいは癌との関連を指摘するものもあるが，大方の考えは非腫瘍性病変であって，腺腫，癌とはまったく関係がないというものである^1)～3)．しかし，その本態に関しては未だ不明な点が多い．近年，疫学の立場から剖検例を用いて大腸癌と大腸ポリープ（metaplastic polypを含む）の関連性が論じられているが⁴⁾⁵⁾，metaplastic polyp（hyperplastic polyp）の診断基準は諸学者の間で必ずしも完全に一致していないようである．

　ここで，Morsonのもとで約2年間過した経験をもとに，metaplastic polyp（hyperplastic polyp）の臨床病理学的問題点を明かにしてみたい．

　Histological appearances of metaplastic polyps of the large bowel were described in detail after the idea by Morson. Tubular elongation with sawtooth appearance, some cystic dilatation of the tubules, hyperchromatism of the lower one third of the tubules and goblet cell depletion are characteristic features of metaplastic polyps. It is a non-neoplastic lesion, having an increasing incidence with increasing age and has no relation to adenoma or carcinoma.

　It was emphasized that mucosal nodules consisting of almost normal tubules with some elongation were to be distinguished from metaplastic nodules. The presence of non-neoplastic as well as non-metaplastic tubules in adenomas and in the mucosa immediately adjacent to carcinoma was also described. Although these tubules had some cytological similarity to metaplastic one, their histological features were quite different from those of metaplastic tubules, and they were to be distinguished from metaplastic tubules.

　It was suggested that some adenomas with very minimum dysplasia tend to be called hyperplastic polyps erroneously. The term “metaplastic” was thought to be better than the term “hyperplastic”.

　A new hypothesis on histogenesis of metaplastic polyp by Hayashi and Stemmermann was introduced.