大腸T1b癌を完全一括切除するために必要な内視鏡的切除技術

Endoscopic Resection Technique Used for Complete En Bloc Resection of T1b Colorectal Cancer

要旨●内視鏡的粘膜下層剝離術（ESD）の技術の進歩に加え，高齢化や併存疾患の存在から，大腸cT1b癌に対して診断的切除の意味を含めESDを施行する頻度は増加している．特に直腸ではその傾向が顕著であるが，追加手術の要否を決定するためには浸潤距離，脈管侵襲の有無，組織型，簇出Gradeを正確に判定する必要がある．しかし，T1b癌は粘膜下層に高度な線維化やMR signを伴っていることがあり，技術的に困難であるのみならず剝離中にこれらの重要な転移リスク因子を損傷する可能性が高い．筆者らは，PCMの導入と，食道におけるPOEM/POETの経験からMR signを呈する周囲の内輪筋を輪状に切開し内輪筋と外縦筋の間で切離するPAEMを考案した．内輪筋ごと切除することで確実に粘膜下層全層を含む切除標本を得ることが可能である．PAEMにより，T1b癌を完全一括切除する内視鏡的切除技術はRbにおいては確立されたと言えるが，T2癌の正確な診断などが今後の課題と考えられる．

　The frequency of ESD（performing endoscopic submucosal dissection）in the treatment of cT1b colorectal cancer, including its use in diagnostic resection, has increased because of the advancement of ESD, aging of population, and the presence of comorbidities. This trend is particularly apparent in cases with rectal cancer, in which accurate assessment of the depth of invasion, presence/absence of lymphatic/blood vessel invasion, histological classification, and budding grade is required to determine the need for additional surgery. However, T1b cancer lesions can be associated with severe fibrotic changes and MR（muscle retracting）signs in the submucosal layer, which not only make ESD technically difficult but also are important metastatic risk factors that are likely to be damaged during dissection. Based on the introduction of PCM（the pocket creation method）and the experience with POEM（per-oral endoscopic myotomy）/POET（per-oral endoscopic tumor resection）in the esophagus, we devised PAEM（per-anal endoscopic myectomy）, for rectal lesions with severe fibrosis, in which dissection is performed between the inner circular and outer longitudinal muscles. The resected specimens that include the entire submucosal layer can be obtained by resecting the inner circular muscles together. Although PAEM is an reliable endoscopic resection technique for complete en bloc resection of T1b cancer in the lower rectum, future use in the accurate diagnosis of T2 cancer should be established.