胃MALTリンパ腫の生検組織診断―経過観察例の見直しから

Point of Biopsy Diagnosis of Gastric MALT Lymphoma, through a Review of Followed up Cases

要旨　胃生検で経過観察された後に胃全摘が行われた，胃MALTリンパ腫の3例を提示し，経過中の生検組織像の見直しを通して得られた，生検診断での注意点，着目すべき点，生検診断の限界について触れた．MALTリンパ腫のH・E染色標本を用いての生検組織診断で最も問題となるのは，①異型リンパ球の認識，②小型リンパ球あるいは形質細胞が粘膜全層に浸潤している病変の評価，③複数回の生検の総合的評価，の3点であろう．①に関しては，核のくびれや小さいながらも核クロマチンが濃縮せずに核小体が見られるような核を，われわれの施設では重視している．②に関しては，この所見だけではMALTリンパ腫の診断根拠とならないが，RLHを含めたリンパ増殖性疾患を念頭に置くための手掛かりとなると考えられ，経過中に同じ部位からより有意な所見が得られれば，MALTリンパ腫を積極的に疑う必要がある．③に関しては，1回の生検で，例えば5検体中に1検体，明らかなcentrocyte-like cellやlymphoepithelial lesionなどの有意な所見が見られ，次の生検で同じ部位から5検体中2検体に有意な所見が見られたような場合の評価である．それぞれの回に単に異型リンパ球の記載のみにとどめたり，いたずらにRLHの診断を繰り返すのではなく，それまで得られた生検標本を見直しつつ総合的に判断することが肝要と考えた．

　Three resected cases of gastric MALT lymphoma, which were followed up in our hospital where biopsy was performed repeatedly prior to gastrectomy, were discussed with a view to showing how to diagnose MALT lymphoma from gastric biopsy specimens. All biopsy materials were reviewed and compared with histological discriptions made at the time of biopsy.

　In the first case, a 46-year-old female, diffuse infiltration of small lymphocytes in the gastric mucosa was pointed out at the time of biopsy. However, these small cells were recognized as normal lymphocytes and were repeatedly diagnosed as reactive lymphoid hyperplasia. In this case, gastrectomy was performed until seven years later. Review of the first biopsy material revealed small irregular shaped nuclei and several convoluted nuclei which were characteristic of centrocyte-like cells of MALT lymphoma. The diagnosis from the operation material was malignant lymphoma, diffuse, mediumsized cell type, depth sm. The delay of accurate diagnosis was due to lack of recognition of atypical cells by pathologists.

　In the second case of a 49-year-old female, plasma cells infiltrated extensively the total thickness of the lamina propria of the mucosa with lymphoepithelial lesions. However, this plasma cell infiltration was recognized during the several biopsy as reactive lymphoid cell infiltration, and repeatedly diagnosed as reactive lymphoid hyperplasia. The diagnosis of the operation material was malignant lymphoma, diffuse, mediumsized cell type, depth sm. This is a case in which the significance of prominent plasma cell infiltration in the mucosa is shown.

　In the third case of a 48-year-old female, as〔cases 1 and 2〕, as well plasma cells and small lymphocytic infiltration was prominent in the first biopsy material In this case, such phenomena were recognized quickey from the first biopsy as part of a MALT lymphoma, and gastrectomy was performed only four months after the first biopsy. The diagnosis of the operation material was malignant lymphoma, diffuse, small cell type, depth sm.

　By reviewing these three cases, we recognized several check points to attain accute diagnosis of MALT lymphoma by biopsy examination. The first was to recognize nuclear atypia of the small lymphocyte in the specimens. The next was to be careful to evaluate the extensive infiltration of plasma cells in the mucosa. And the last was to check all the previous biopsy materials from the same case.