USMLE® Step 1 style questions USMLE
A 50-year-old woman comes to the emergency department because of hematemesis. After waking up this morning, she vomited blood several times. The bleeding has since resolved, but she feels nauseous and dizzy. She denies any pain. She has a history of osteoarthritis, gastroesophageal reflux, hypertension, and dyslipidemia. She has not received medical care and has not been taking any prescription medications for several years. The patient denies any tobacco or alcohol use. An esophagogastroduodenoscopy (EGD) reveals oozing esophageal and gastric varices. Later, a liver biopsy shows normal liver histology. Which of the following is the most likely pathophysiology underlying her bleeding varices?
Content Reviewers:Viviana Popa, MD
Most commonly, this happens because of hepatic cirrhosis, which is when the liver tissue is replaced by fibrotic, functionless tissue.
This blood contains all the nutrients absorbed in the GI tract, but it also carries toxins that the liver metabolizes so that they can be safely excreted by the kidneys.
Now, there’s a few points in the boundaries of the hepatic portal system, where it could be connected with the systemic venous system that collects blood from the rest of the body: the inferior portion of the esophagus, the superior portion of the anal canal, and the round ligament of the liver - which used to be the umbilical vein during fetal life.
At birth, the umbilical cord is cut, and the umbilical vein collapses to form the round ligament.
Normally, the round ligament stays shut because pressures in the portal venous system and the systemic venous system are the same, between 5 and 10 Millimeters of Mercury
But in some situations, an obstruction may prevent blood flow from the portal vein towards the inferior vena cava.
When this happens, venous blood accumulates in the hepatic portal system, causing pressure to rise above 5 to 10 12 mmHg - which defines portal hypertension of mercury.
Portal hypertension leads to the formation of portosystemic shunts - which is when blood is diverted away from the portal venous system and backs up into systemic veins.
So first, less blood gets to the liver, causing diminished liver function and decreased blood detoxification, which leads to a buildup of toxic metabolites, like ammonia, in the blood.
Second, blood backing up in the systemic veins leads to portosystemic shunts, which happens in the three points where the systemic venous system and the hepatic portal system are connected.
In fact, portal hypertension is the most common cause of esophageal varices.
These varices are very fragile, and could easily rupture, causing massive upper GI bleeding.
Finally, portal hypertension causes the round ligament to re-channel, allowing blood from the portal system to pass into the systemic veins of the abdomen, which dilate, making the abdomen look like the head of the greek mythological creature “Medusa” - the one with snakes for hair.
So this consequence is frequently termed caput medusae.
Another consequence of portal hypertension is that the endothelial cells lining the blood vessels release more nitric oxide.
The reason behind this is unclear, but nitric oxide makes peripheral arteries dilate, so blood pressure drops.
This stimulates the release of aldosterone, which tries to bring blood pressure back up by telling the kidneys to retain more sodium and water.
The accumulation of fluid in the peritoneal cavity is called ascites.
As if that wasn’t enough, bacteria can also invade the peritoneal cavity, causing spontaneous bacterial peritonitis.
So, the features of portal hypertension can be remembered as ABCDE: where “A” stands for Ascites, “B” for Bleeding, “C” for Caput medusae, “D” for Diminished liver function, and “E” for Enlarged spleen.
Now, causes of portal hypertension can be classified as prehepatic, intrahepatic or posthepatic, depending on where the obstruction is.