This report presents the clinical course of a 61-year-old man with rectal cancer positive for extramural vascular invasion (EMVI). Preoperative MRI suggested cT₃N₁ disease with positive EMVI, while CT did not show distant metastasis. Radical surgery in July 2025 revealed pT₃N_1b disease with vascular invasion, perineural invasion, tumor deposits, and high-grade tumor budding. Chemotherapy was postponed because of postoperative fatigue, poor intake, and reduced performance status. During reassessment in September 2025, a small lesion was found in the left liver. Partial hepatectomy and ileostomy closure were performed, and intraoperative exploration also identified a peritoneal nodule near the splenic flexure. Pathology confirmed colorectal metastases in both lesions, and the stage was revised to pT₃N_1bM_1c. Next-generation sequencing showed KRAS p.G13D mutation and microsatellite stable (MSS) status, and immunohistochemistry indicated proficient mismatch repair (pMMR). The patient subsequently received 8 cycles of capecitabine and oxaliplatin (CAPEOX) plus bevacizumab, with no definite progression on imaging at the eighth cycle on May 26, 2026. This case indicates that negative routine CT findings do not fully exclude small-volume liver or peritoneal metastases in rectal cancer with MRI-detected EMVI. Careful intraoperative exploration and molecular testing may help refine staging and guide subsequent treatment.