BLOOD SUPPLY - SMA & IMA

Question 1

Label

Answer 1

Question 2

Describe what happens in SMA syndrome

List some symptoms and causes

Answer 2

Gastro-vascular disorder: distal third of duodenum compressed between abdominal aorta and overlying SMA → bowel obstruction

Symptoms: early satiety, N/V, stabbing postprandial pain, abdominal distention and tenderness, burping, reflux

Lots of causes including sudden weight loss. Mimics eating disorder → important to distinguish

Question 3

Label

At what vertebral level does inferior mesenteric artery come off aorta?

Answer 3

L3

Question 4

Explain the dual pancreaticoduodenal blood supply

Answer 4

• Superior pancreaticoduodenal artery → branch of celiac
• Inferior pancreaticoduodenal artery → branch of SMA

These arteries anastomose creating a dual blood supply between celiac and SMA → important protection against ischaemia

Question 5

What is significant about bloodflow to marginal artery of Drummond?

Why is it less likely to suffer from ischaemia due to vessel occlusion?

comment on location

Answer 5

Receives blood supply from both SMA and IMA → anastomoses

NOTE: junction of SMA and IMA is at splenic flexure. Anastomoses often weak or absent, hence marginal artery here (Griffiths point) is often discontinuous. For this reason, splenic flexure is a watershed (border zone) area prone to ischaemia.

Question 6

Why is rectal ischaemia from vessel occlusion rare?

Answer 6

Dual blood supply: superior rectal (IMA) merges with middle rectal (iliac) arteries

Question 7

Define mesenteric ischaemia and compare with Ischaemic colitis

​comment on prognosis of both

Answer 7

Mesenteric ischaemia: ischaemia of small intestine (often life-threatening)

Ischaemic colitis: ischaemia of colon (may spontaneously resolve)

Question 8

What is the most common cause of mesenteric ischaemia? What is the second most common cause?

what part of the intestine is most commonly affected? Comment on blood supply

Answer 8

Embolism: often cardiac origin

Arterial thrombosis: usually at site of atherosclerosis (“heart attack” in GIT)

often affects jejunum via superior mesenteric artery

Question 9

How can venous thrombosis cause mesenteric ischaemia? What type of patients are at risk?

Answer 9

Clot develops causing resistance to outflow of mesentary

→ those in hypercoagulable states e.g. malignancy

Question 10

Explain how non-occlusive ischaemia occurs in the GI tract and which parts are most affected

Answer 10

Usually caused by underperfusion (shock)

Affects watershed areas of colon often resulting in ischaemic colitis

Question 11

Abdominal pain out of proportion to abdominal exam is indicative of which condition? Describe the typical exam findings in this situation

Answer 11

Mesenteric ischaemia

• Usually mild tenderness
• No rebound tenderness or peritoneal signs
• Occult blood in stool

Question 12

What are the two watershed areas of colon making them vulnerable to ischaemia?

Answer 12

• Splenic flexure (marginal artery at Drumond)
• Rectosigmoid junction (narrow branches of IMA)

Question 13

Chronic mesenteric ischaemia has the same pathophysiology as which cardiac condition? Which symptoms does the patient typically present with?

Answer 13

Angina (same risk factors)

Plaque builds up in major arteries, including celiac and SMA

• Weight loss
• Pain with eating ⇒ fear of eating

Left untreated, blockages can decrease blood flow so much that the tissues in intestines die.

Question 14

A 60-year-old man on ITU develops severe abdominal pain and passes bright red blood and mucus in his rectum. Abdominal x-ray shown. What is your top differential?

Answer 14

Ischaemic colitis, likely in a watershed area such as splenic flex tire

Thumbprinting sign can be seen on x-ray