Anatomic Extent of Colon Resection by Procedure Type
Left hemicolectomy removes approximately 30-40% of the colon (from the distal transverse colon through the sigmoid colon), descending colectomy removes approximately 15-20% (the descending colon segment), and sigmoidectomy removes approximately 10-15% (the sigmoid colon only).
Left Hemicolectomy
Anatomic boundaries and extent:
The resection extends from the left/distal transverse colon to the sigmoid colon, encompassing the splenic flexure, entire descending colon, and proximal sigmoid 1, 2.
This represents removal of approximately 30-40% of the total colon length, as the procedure includes multiple anatomic segments 2, 3.
The splenic flexure is a critical landmark that must be mobilized and included in the resection 2, 4.
High ligation of the inferior mesenteric artery with removal of associated mesocolon containing lymphatic channels is standard 1, 5.
Technical considerations:
The left branch of the middle colic artery and left colic artery are typically ligated, with preservation of blood supply to the remaining transverse colon via the middle colic vessels 2, 4.
Proper mobilization of the splenic flexure is critical for achieving a tension-free anastomosis 5, 4.
The anastomosis is typically performed between the transverse colon and the remaining sigmoid or upper rectum 2, 4.
Descending Colectomy
Anatomic boundaries and extent:
This procedure removes only the descending colon segment, from below the splenic flexure to above the sigmoid colon 2, 3.
This represents approximately 15-20% of total colon length, as it is a more limited segmental resection 2.
The splenic flexure may or may not be included depending on tumor location and vascular anatomy 2, 3.
Key distinction from left hemicolectomy:
Unlike left hemicolectomy, descending colectomy preserves more of the transverse colon proximally and the sigmoid colon distally 2, 3.
The inferior mesenteric artery may be preserved with selective ligation of the left colic artery only 2.
Sigmoidectomy
Anatomic boundaries and extent:
Sigmoidectomy removes only the sigmoid colon, typically from the rectosigmoid junction to the junction with the descending colon 1, 6.
This represents approximately 10-15% of total colon length, making it the most limited of these three procedures 6.
The procedure is commonly performed for sigmoid-specific pathology including diverticular disease, volvulus, or localized cancer 1, 6.
Critical technical point:
- The entire length of redundant sigmoid must be removed to prevent recurrence in conditions like sigmoid volvulus, where inadequate resection leads to 45-71% recurrence rates 6.
Important Clinical Caveats
Anatomic variation significantly impacts these procedures:
Sigmoid colon variation (regular vs. variable type) significantly affects the feasibility and type of anastomosis after left-sided resections 7.
Splenic flexure anatomy (mesenteric, mobile, or adhesive type) influences surgical approach and anastomotic options 7.
When extended resection is required:
In patients with concomitant megacolon and sigmoid pathology, subtotal colectomy is required (removing approximately 80-90% of colon from terminal ileum to rectosigmoid junction), as limited sigmoid resection alone results in 82% recurrence 6, 8.
For malignant obstruction requiring subtotal colectomy, this represents a much more extensive resection than standard left hemicolectomy 1.
Oncologic considerations: