Where is the blood clot likely to form in a patient with compromised circulation from the duodenum (D1) to the upper rectum?

Location of Blood Clot in Compromised Circulation from D1 to Upper Rectum

The blood clot is most likely located in the superior mesenteric artery (SMA), either as an embolus lodged 3-10 cm distal to its origin or as a thrombosis at the vessel's origin, given that the SMA supplies the entire territory from the distal duodenum through the proximal colon including the upper rectum. 1

Anatomic Basis for SMA Involvement

The superior mesenteric artery is the primary vessel supplying blood to the duodenum (distal to D1), entire small bowel, and colon up to the splenic flexure, with collateral supply extending to the upper rectum via the ileocolic artery. 1

Most Likely Clot Locations Based on Pathophysiology:

Embolic Occlusion (50% of acute mesenteric ischemia cases):

• Emboli typically lodge 3-10 cm distal to the SMA origin at points of normal anatomic narrowing, which would spare the proximal jejunum but affect all bowel from the mid-jejunum through the proximal colon 1
• The SMA is particularly vulnerable to embolic events due to its relatively large diameter and low takeoff angle from the aorta 1
• Emboli originate from cardiac sources including atrial fibrillation, left ventricular dysfunction, or valvular endocarditis 1

Thrombotic Occlusion (25-40% of cases):

• Thrombosis occurs at the origin of the SMA in patients with pre-existing atherosclerotic disease 1
• These patients often have a history of chronic mesenteric ischemia with postprandial pain, weight loss, or "food fear" 1
• SMA thrombosis typically accompanies celiac artery occlusion due to progressive atherosclerotic plaque 1

Alternative Vascular Territories to Consider

Mesenteric Venous Thrombosis (<10% of cases):

• Thrombosis in the superior mesenteric vein (SMV) and its tributaries can cause the same distribution of ischemia 1
• This presents more subacutely with congestion and bowel distention before arterial compromise develops 1
• Associated with hypercoagulable states, inflammatory conditions (pancreatitis, IBD), or surgical trauma 1

Non-Occlusive Mesenteric Ischemia (20-25% of cases):

• No discrete clot present, but rather SMA vasoconstriction with low splanchnic blood flow 1
• Occurs in critically ill patients with cardiac failure, sepsis, or vasopressor use 1
• Also affects the proximal colon via ileocolic artery involvement 1

Critical Diagnostic Pitfall

The involvement of the ileocolic artery territory is key: When the ileocolic artery (a branch of the SMA) is compromised, necrosis extends to the proximal colon and potentially the upper rectum, which explains the extensive distribution from D1 to upper rectum described in your question. 1 This anatomic detail confirms SMA territory involvement rather than isolated celiac or inferior mesenteric artery pathology.

Clinical Context Determines Exact Location

• Acute presentation with atrial fibrillation: Suspect embolic occlusion 3-10 cm distal to SMA origin 1
• Subacute presentation with history of postprandial pain: Suspect thrombotic occlusion at SMA origin 1
• Critically ill patient on vasopressors: Consider non-occlusive mesenteric ischemia without discrete clot 1
• Hypercoagulable state or recent abdominal surgery: Consider superior mesenteric vein thrombosis 1