Arterial Supply of the Rectum
The rectum receives its primary arterial supply from the superior rectal artery (terminal branch of the inferior mesenteric artery), with variable contributions from the middle rectal artery (branch of the internal iliac artery) and the inferior rectal artery (branch of the internal pudendal artery).
Primary Arterial Supply
The superior rectal artery is the chief arterial supply to the rectum 1. This vessel provides the dominant blood flow and forms several important branches:
- Rectosigmoid branch - supplies the rectosigmoid junction
- Upper rectal branch - supplies the upper rectum
- Right and left terminal branches - these extend downward and forward around the lower two-thirds of the rectum to the level of the levator ani muscle 2
The superior rectal artery creates two distinct vascular patterns within the rectal wall 3:
- Annular pattern in the upper half via transverse rectal arteries
- Plexiform pattern in the lower half via terminal branches
Secondary Arterial Supply
Middle Rectal Artery
The middle rectal artery has highly variable presence and contribution. Key anatomical facts:
- Present in only 50-71.4% of individuals 3, 4
- When present, found bilaterally in 21.4% and unilaterally in 50% 4
- Originates most commonly from the internal pudendal artery (45.5%), inferior gluteal artery (22.7%), or gluteal-pudendal trunk (22.7%) 4
- Supplies a limited portion of the rectum in only 12% of specimens 2
- Its presence can be anticipated by observing the diameter of the superior rectal artery and its terminal branches 2
Inferior Rectal Artery
- Supplies the anal canal below the levator ani muscle 2
- Provides ample blood supply to the anal canal with good anastomotic connections 5
- Forms intramural anastomoses with the superior rectal artery at the dentate line level in the submucosa 6
Critical Anatomical Considerations
Vascular Watershed Zone
A vessel-deficient area consistently exists in the dorso-caudal sector of the rectal ampulla cranial to the levator muscle 5. This zone:
- Cannot be adequately compensated by other rectal arteries
- Explains the higher rate of anastomotic leaks after low anterior resection
- Is particularly relevant in patients over 50 years, where hypogastric artery contribution becomes minor 7
Anastomotic Patterns
- Extramural anastomoses between main rectal arteries are NOT typically present 2
- Intramural anastomoses exist primarily between superior and inferior rectal arteries at the dentate line in the submucosa 2, 6
- Anastomoses between the middle rectal artery and other vessels reported in 78.1% when the vessel is present 8
Clinical Pitfalls
The levator ani muscle serves as a critical vascular divide 5:
- Below the levator: inferior rectal artery predominates
- Above the levator: superior rectal artery predominates with the dorso-caudal watershed zone
The middle rectal artery's inconsistent presence (only 50-71% of individuals) means surgical planning cannot rely on this vessel for collateral circulation 4, 8. In patients over 50 years, the contribution from hypogastric arteries becomes increasingly minor, making the superior rectal artery even more critical 7.