Key anastomoses of GI circulation
Visceral branches of the abdominal aorta form robust connections to compensate for blood flow when major trunks are affected (e.g., in occlusive disease or aneurysms).
The most significant collateral pathways:
- Splenic flexure zone (flexura coli splenica). Proximal to this flexure, a major anastomosis forms between the superior mesenteric artery (SMA) and inferior mesenteric artery (IMA) territories. The connection is established via the middle colic branch (arising from the SMA) and the left colic branch (arising from the IMA).
- Pancreaticoduodenal arcades. These vascular loops provide communication between the celiac trunk and the superior mesenteric artery.
X-ray anatomy of mesenteric vessels
When analyzing angiograms, the physician sequentially evaluates the branching of three major vascular territories:
- Celiac trunk (truncus coeliacus). It gives rise to the left gastric (a. gastrica sinistra), splenic (a. splenica), and common hepatic (a. hepatica communis) arteries. The latter continues as the proper hepatic artery (giving off right and left branches) and the gastroduodenal artery (a. gastroduodenalis). The gastroduodenal trunk gives off the superior pancreaticoduodenal and right gastroepiploic arteries.
- Superior mesenteric artery (arteria mesenterica superior). Angiograms visualize its small bowel branches (jejunal and ileal arteries) as well as arteries supplying the right half of the colon: ileocolic, right colic, and middle colic.
- Inferior mesenteric artery (arteria mesenterica inferior). Supplies the distal bowel segments via the left colic, sigmoid, and superior rectal arteries.
Localization and causes of hemorrhage
Gastrointestinal bleeding is one of the major pathologies affecting the mesenteric bed. It is conventionally divided based on localization relative to the duodenojejunal flexure (flexura duodenojejunalis).
- Upper GI tract (proximal to the flexure). Bleeding here occurs frequently. Its main causes include peptic ulcers, inflammatory processes (e.g., acute pancreatitis), as well as complications following surgical, endoscopic, or percutaneous biliary interventions.
- Lower GI tract (distal to the flexure). Encountered significantly less often. Typical triggers include vascular angiodysplasias, diverticular disease, various neoplasms, and hemorrhoids.
Role of MSCT angiography
Multidetector CT angiography has radically changed the management algorithm for acute GI bleeding. It is the first-line method when endoscopy results are negative or equivocal.
Scanning protocol The procedure is performed strictly without oral contrast to avoid obscuring the picture within the bowel lumen. Scanning is performed in three phases:
- Native (non-contrast) — necessary to differentiate acute blood loss from radiopaque objects (surgical clips, suture material, coproliths).
- Arterial — allows confirmation of active contrast extravasation into the bowel lumen.
- Portal-venous — demonstrates how the spilled contrast increases in volume or pools.
Significance for surgery MSCT angiography detects the cause of bleeding even outside the moment of active blood extravasation (e.g., detecting a pseudoaneurysm). Scan data provide the interventional radiologist with a roadmap: the physician sees the target source branch and potential aberrant anatomy in advance. This accelerates selective catheterization, reduces patient radiation exposure, and decreases the required volume of iodinated contrast during subsequent embolization.
Briefly: answers to topical questions
Which arteries form the pancreaticoduodenal arcades?
Pancreaticoduodenal arcades are formed between the superior and inferior pancreaticoduodenal arteries.
Vessels from two systems participate in their formation:
- Superior pancreaticoduodenal arteries (aa. pancreaticoduodenales superiores) — anterior and posterior branches arising from the a. gastroduodenalis (celiac trunk territory, truncus coeliacus).
- Inferior pancreaticoduodenal arteries (aa. pancreaticoduodenales inferiores) — anterior and posterior branches arising from the superior mesenteric artery territory (a. mesenterica superior).
These loops provide an important anastomosis between the celiac trunk and the superior mesenteric artery, supplying the descending and inferior parts of the duodenum as well as the head of the pancreas.
To memorize the branches of the celiac trunk: "Celiac trunk Travels (Left gastric), Sprints (Splenic), and Embraces the Liver (Common hepatic)."
Class and exam questions
Where is the key anastomosis between the superior and inferior mesenteric arteries located?
It is located proximal to the splenic flexure of the colon, where the middle and left colic arteries connect.
Why is oral contrast not used in CT angiography for bleeding?
Oral contrast would fill the gastrointestinal lumen and obscure the extravasation (escape) of intravenous contrast from the damaged vessel, making the diagnosis of active bleeding impossible.
What is the minimum bleeding rate that MSCT angiography can detect?
The method has high sensitivity and is capable of detecting active arterial bleeding at rates starting from 0.35 ml/min.
Why is the native phase included in the MSCT angiography protocol?
It allows the physician to identify dense structures (coproliths, surgical clips, suture material) so they are not mistaken for fresh blood after contrast administration.
What else to study on this topic
- X-ray anatomy of aberrant arteries of the hepatobiliary zone
- Technique of selective catheterization of mesenteric arteries
- Radiological diagnostics of occlusive lesions of the mesenteric bed
- Interventional embolization for gastrointestinal bleeding
- CT semiotics of intestinal vascular angiodysplasias
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