Gastrointestinal system additional information

SMA syndrome: Superior mesenteric artery syndrome (SMAS) occurs when the duodenum is compressed between the aorta and the superior mesenteric artery, causing partial or complete obstruction of the third part of the duodenum. It typically presents with crampy abdominal pain that may be relieved by the prone position, the knee-chest position, or lying on the left side. Other symptoms include fullness, nausea, vomiting of partially digested bile-like fluid, weight loss, and bloating.

The underlying anatomy explains the condition. The SMA branches from the aorta at an acute angle, and the duodenum lies within this angle. Normally, a fat pad in this region protects the duodenum from compression. If this fat pad is lost (for example due to weight loss, surgery - especially for scoliosis - or psychological disorders causing weight loss), the duodenum can become compressed, leading to SMAS.

If untreated, SMAS may lead to gastric or portal vein pneumatosis (gas in the walls), bezoar formation, gastric perforation, and electrolyte imbalances. On imaging, dilation of the first and second parts of the duodenum may be seen.

Box for Mc burney’s point: McBurney’s point was first described by Charles McBurney in 1891. It lies at two-thirds of the distance from the umbilicus on a line joining the umbilicus to the right anterior superior iliac spine. In acute appendicitis, tenderness is elicited on deep palpation at this point.

McBurney’s point tenderness may be absent in patients with a retrocaecal appendix or in some cases with a pelvic appendix. In these situations, the psoas sign or obturator sign may be positive.

How to identify bowel obstruction on imaging: Use the 3/6/9 rule: bowel is considered distended if it measures more than 3 cm for the small intestine, 6 cm for the colon, and 9 cm for the caecum.

You can distinguish small bowel from large bowel using these features:

Small intestine: identified by valvulae conniventes, which cross the entire width of the lumen.
Colon: identified by haustrations, which bulge from the wall and span only about a third of the diameter of the colon.

Typical locations and appearances also help:

Small bowel loops tend to be located centrally.
Large bowel loops are more peripheral.
Large bowel typically has a mottled appearance due to fecal material.

Distension is usually more severe with large bowel obstruction. Massive dilation of the colon - especially the caecum or sigmoid colon - suggests volvulus. The “bent inner tube” or coffee bean sign is seen in sigmoid volvulus.

Signs suggesting complications or specific causes include:

Strangulation: thumbprinting sign, thickened loops, pneumatosis intestinalis (air in the bowel wall).
Perforation: free air.
Gallstone ileus: pneumobilia (air in the biliary system).
Adhesions: fixed bowel loops that do not change position when the patient’s position changes.

Box for Couinaud segments of the liver: Claude Couinaud divided the liver into eight functional segments (I to VIII). Each segment has its own artery, bile duct, and tributaries of the hepatic and portal veins. In the Couinaud system, the hepatic veins are situated peripherally. This classification is especially useful in hepatic surgery, such as segmental resection.

Segments I to IV form the left hemiliver, while segments V to VIII form the right hemiliver. Segment I corresponds to the caudate lobe, which is unique because it receives branches from both the left and right hepatic arteries and portal veins, and it is drained by tributaries of both the right and left biliary ducts.

Gastrointestinal system additional information

SMA syndrome: Superior mesenteric artery syndrome (SMAS) occurs when the duodenum is compressed between the aorta and the superior mesenteric artery, causing partial or complete obstruction of the third part of the duodenum. It typically presents with crampy abdominal pain that may be relieved by the prone position, the knee-chest position, or lying on the left side. Other symptoms include fullness, nausea, vomiting of partially digested bile-like fluid, weight loss, and bloating.

Box for Mc burney’s point: McBurney’s point was first described by Charles McBurney in 1891. It lies at two-thirds of the distance from the umbilicus on a line joining the umbilicus to the right anterior superior iliac spine. In acute appendicitis, tenderness is elicited on deep palpation at this point.

McBurney’s point tenderness may be absent in patients with a retrocaecal appendix or in some cases with a pelvic appendix. In these situations, the psoas sign or obturator sign may be positive.

How to identify bowel obstruction on imaging: Use the 3/6/9 rule: bowel is considered distended if it measures more than 3 cm for the small intestine, 6 cm for the colon, and 9 cm for the caecum.

You can distinguish small bowel from large bowel using these features:

Small intestine: identified by valvulae conniventes, which cross the entire width of the lumen.
Colon: identified by haustrations, which bulge from the wall and span only about a third of the diameter of the colon.

Typical locations and appearances also help:

Small bowel loops tend to be located centrally.
Large bowel loops are more peripheral.
Large bowel typically has a mottled appearance due to fecal material.

Signs suggesting complications or specific causes include:

Strangulation: thumbprinting sign, thickened loops, pneumatosis intestinalis (air in the bowel wall).
Perforation: free air.
Gallstone ileus: pneumobilia (air in the biliary system).
Adhesions: fixed bowel loops that do not change position when the patient’s position changes.

Box for Couinaud segments of the liver: Claude Couinaud divided the liver into eight functional segments (I to VIII). Each segment has its own artery, bile duct, and tributaries of the hepatic and portal veins. In the Couinaud system, the hepatic veins are situated peripherally. This classification is especially useful in hepatic surgery, such as segmental resection.