胃悪性リンパ腫診断の変遷―臨床の対応―画像診断の面から

Clinical Diagnosis of Gastric Malignant Lymphoma: From the Viewpoint of Image Diagnosis

要旨　切除胃の肉眼所見で顆粒状粘膜所見を呈し，病巣が粘膜，粘膜下層に拡がる表層型に分類される胃悪性リンパ腫4症例のX線・内視鏡所見を検討した．X線所見は大小不揃いの顆粒状粘膜所見で，その中に不整小陥凹が認められた．そして，顆粒状粘膜を呈する部分に軽度の伸展不良が見られた．そして，内視鏡所見では，柔らかい感じのする凹凸不整粘膜，陥凹部に滲み出るような白苔の付着が見られ，また，易出血性粘膜が認められた．この顆粒状粘膜所見は，切除胃の病理組織標本の割面の所見でみると悪性リンパ腫の腫瘍細胞が浸潤性，一部，濾胞性に増殖して粘膜が肥厚した所見で，リンパ腫の本質的な所見と考えられる．このような肉眼所見を呈する例では反応性リンパ細網細胞増殖症（RLH）との鑑別が難しい．これらの例は病理組織学的にはLSG分類でびまん性・中細胞型が2例，びまん性・混合型が1例，濾胞性・中細胞型が1例であった．そして，これらの症例の病理組織診断をIsaacsonらの提唱したMALT型リンパ腫の概念で見直すと，全例MALT型リンパ腫の所見を備えていた．本邦でRLHと診断される例はMALT型リンパ腫であるという考え方は，臨床診断をする側にとってはすっきりした考え方である．これらの症例の集積が多い本邦での検討結果が待たれる．それまでは，臨床診断をする側は今回検討した顆粒状粘膜を呈する症例の診断を正確に行い，適切な治療を行う中で，十分な情報を得るように努めることが重要である．

　Radiological and endoscopic findings were studied in four cases of the superficial-spreading type of gastric malignant lymphoma with the granular mucosa on the resected specimens.

　Radiologically, various-sized granules on the mucosa were demonstrated as irregular-shaped small or minute barium flecks by double contrast radiography. Endoscopically, the surface of the gastric mucosa was uneven accompanied by tiny depressions and fibrin excudates, and seemed to be soft and friable. This granularity of the mucosa, which was caused by the infiltration and follicular proliferation of tumor cells, was thought to be an essential morphological finding of the superficialspreading type of gastric malignant lymphoma. Still, the differential diagnosis between this type of gastric malignant lymphoma and reactive lymphoreticular hyperplasia (RLH) is difficult in many cases, even by pathohistological examinations.

　Histological diagnosis of the four cases according to LSG classification was as follows; two cases of medium-sized cell type and one case of mixed type of diffuse malignant lymphoma, and one case of medium-sized cell type of follicular malignant lymphoma. These cases also had some histological findings of malignant lymphoma of the mucosa-associated lymphoid tissue (MALT lymphoma) proposed by Isaacson et al.

　Clinically, differential diagnosis should be made clearer if we identify RLH with MALT lymphoma. For the settlement of this issue, further investigation is needed, and clinicians are expected to obtain sufficient information through an acurate diagnosis and proper treatment of the disease, especially in cases which demonstrate the granular surface of the gastric mucosa.