[A Small Rectal Neuroendocrine Tumor of Less Than 5mm with Lymph Node Metastasis].

According to the treatment guideline for rectal neuroendocrine tumor(NET), tumor with a diameter ofC10mm should be resected endoscopically, while tumor with a diameter of>10mm should be resected surgically with lymph node dissection. We experienced a case of a rectal NET with a diameter of 5mm with lymph node metastasis. A 69-year-old man underwent colonoscopy for positive fecal occult blood test. The colonoscopy revealed a submucosal tumor(SMT)with a diameter of 5 mm in the lower rectum. An endoscopic mucosal resection(EMR)was performed after SMT was diagnosed as NET by biopsy. Histopathological findings were NET-G1, 4.5×2.5 mm, v(+), ly(+). Then, laparoscopically assisted rectal resection with D2 lymph node dissection was performed. In histopathological examination, no tumor residue was observed in the specimu; however, a regional lymph node metastasis was detected. Risk factors of lymph node metastasis with rectal NET are a diameter of>10 mm, recessed or ulcerated surface, and lymphovascular invasion. However, we have to keep in mind that lymph node metastasis may occur even in small rectal NET with a diameter of ≤10mm.