CT and operative images for evaluation of right colectomy with extended D3 mesenterectomy anterior and posterior to the mesenteric vessels Summary Background Surgical techniques like complete mesocolic excision (CME) and D3 mesenterectomy, D3 refering to the N3 lymph node groups central in the mesentery removed at surgery, were introduced without proper evaluation of the lymphadenectomy. The aim of this study was to measure the vascular stumps and evaluate the extent and quality of lymphadenectomy after right colectomy with extended D3 mesenterectomy anterior/posterior to the mesenteric vessels. We also compared the investigation methods. Methods Residual vascular stumps were measured using three-dimensional (3D) reconstructed anatomy from follow-up computed tomography (CT) datasets and images taken during surgery. The quality of central lymphadenectomy was evaluated on the images. Results In total, 31 patients (15 females), median age 67 years (50–78), with stage I (n = 7), stage II (n = 13), and stage III (n = 11) disease, were operated. Tumor locations were: 14 (45%) in the cecum, ten (32%) in the ascending colon, three (10%) in the hepatic flexure, and four (13%) in the transverse colon. The middle colic artery (MCA) was divided at its origin (13 patients) or its right branch (18 patients). Median lengths (range) of residual vascular stumps measured on 3D reconstructed CT and photographic images taken during surgery were: right colic artery: 0.0 mm (0.0–1.8)/0.0 mm (0.0–1.1), ileocolic artery: 0.0 mm (0.0–7.2)/0.0 mm (0.0–3.0), ileocolic vein: 0.0 mm (0.0–7.5)/0.0 mm (0.0–0.0), MCA: 0.0 mm (0.0–18.1)/1.0 mm (0.0–8.0), and right branch of the MCA: 0.0 mm (0.0–1.8)/0.0 mm (0.0–2.0). There was no significant difference between average lengths measured with the two techniques. The extent of lymphadenectomy was deemed acceptable in all patients. No differences in stump lengths were found in patients with different vascular crossing patterns in the central mesentery and presumably different degree of difficulty at surgery. Conclusion The results demonstrate very short residual vascular stumps and together with operative photographs provide objective evidence for superior lymphadenectomy in right colectomy with extended D3 mesenterectomy.