Completely Right‐Sided Sigmoid and Descending Colon in a Rectal Cancer Patient

A 66-year-old female with no significant medical history was diagnosed with low rectal cancer via CT scan and colonoscopy (Figure 1a). The initial tumor staging was T3N0, and was downgraded to T1N0 after neo-adjuvant therapy. During laparoscopic operation, the sigmoid was found extending obliquely from the lesser pelvis to the right lower quadrant; it continued as the descending colon along the right abdominal wall and became retroperitoneal; the highly mobile cecum and ascending colon were also right-sided with complete mesocolon (Figure 1b, lower panel). This unexpected morphological anomaly complicated the dissection and inferior mesenteric root node lymphadenectomy. A compromised TME procedure with D2 lymphadenectomy and ileostomy was performed. (a) CT coronal image and endoscopic view of the rectal cancer. (b) CT coronal images of the anomaly and their corresponding laparoscopic views. (c) Drawings presenting the normal large bowel and the reported anomaly. A, ascending colon; D, descending colon; R, rectus; S, sigmoid. The CT images showed that the left side of the abdomen was devoid of colon; the descending colon and the sigmoid were both right-sided, with the cecum and ascending colon positioned above on the same side (Figure 1b, upper panel). The patient recovered uneventfully and was discharged 7 days after the operation. The pathology revealed complete response of the tumor with no nodal metastasis. The positional anomaly of the intestine is very rare in adults, but may cause difficulties in endoscopic and surgical interventions [1, 2]. A completely right-sided sigmoid and descending colon was never documented before. The anomaly could be asymptomatic, but may be detected through endoscopy and confirmed via radiological methods such as CT scans or barium colonography. Recognition of such anomalies beforehand could have facilitated a more radical resection through adjustments to surgical approaches and surgeon positioning. The cause of this anomaly is puzzling. Perhaps during the hindgut development, it rotated accidentally and was then transposed to the right side and took the position of the ascending colon, forcing the ascending mesocolon to persist (Figure 1c). We thank Dr. Xiaoyuan Qiu and Dr. Xin Gao for their substantial contribution and support in the making of CT coronal images and schematic drawings which appear in the manuscript figure. Informed consent was obtained from the patient for the publication of their medical information and imaging. No patient identification details were included in the manuscript. The authors declare no conflicts of interest. Detailed clinical, radiological and surgical data of the patient are available in Supporting Information S1. Any request or question should be directed to the first author or corresponding author via e-mail. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.