Melena means smelly black tarry stool that is caused by presence of large quantities of digested blood in feces. It is a very serious symptom that must lead to an urgent medical examination.
Melena is caused by bleeding into upper GI tract, i.e. into mouth, esophagus, stomach and the upper part of small intestine. If blood flows through this path, it is partially digested causing its black color and very unpleasant characteristic odour. Main causes of bleeding into the upper digestive tract are follows:
Bleeding into the oral cavity
Stronger bleeding into oral cavity may exhibit by melena when blood is swallowed. Personally, I have encountered this case in a patient who was bleeding for several days after dental surgery.
Esophageal varices are dilated blood veins in the wall of esophagus that bulge into esophageal cavity. They usually emerge due to portal hypertension in liver cirrhosis. In portal hypertension blood flow through liver tissue is difficult and blood flows by collateral veins. Unfortunately, some of these veins are located just in the wall of esophagus. Esophageal varices are especially deadly because their bleeding is usually massive and it is not easy stoppable. In addition to melena, blood vomiting is often present.
Gastroesophageal reflux disease is a condition when the acidic stomach content returns back into the esophagus and damages its wall. Usually it is asymptomatic or it manifests as heartburn. If the lining of the esophagus is damaged seriously, it can bleed.
This is often a dramatically-looking situation caused by a tear of mucosa of lower esophagus (typically in area where esophageal mucosa turns into stomach mucosa). It usually follows an episode of vomiting. Affected person starts to vomit blood and melena may be also present. Luckily the condition is not serious and bleeding quickly stops. When gastroscopy is performed, the tear may be well-visible.
Tumors of upper digestive tract
Tumors in oral cavity, pharynx, esophageal cancer and stomach cancer may cause bleeding when their growth damages major blood vessels. Tumor of upper small intestine can have the same effect, but these are very rare. Small intestine, however, can be affected by metastases of other tumors and these metastases can bleed as well.
Drugs inhibiting blood clotting mechanisms can cause bleeding into different organ systems including digestive tract.
Classical melena has appearance of black, tarry stool that smells. When taking iron supplements in iron-deficiency anemia the stool is also black, but the color is a little bit more greenish and the typical smell is absent. That is not a melena!
When there is suspicion of melena, we have to be cautious. Digital rectal exam must be done to rule out or confirm the diagnosis unless clearly melenous stool has been already seen. If the patient manifests symptoms of sudden blood loss (weakness, pallor, accelerated heart rate, blood pressure drop), he or she must be stabilized before further diagnostics. Basic examination method is upper endoscopy of GI tract. This method allows to view the digestive tract from esophagus to the upper part of small intestine and, if necessary, the doctor can use the endoscopic device to treat bleeding lesions. Blood test is important especially for determination of red blood cell numbers and hemoglobin concentration (i.e. anemia diagnosis).