Melena overview
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Melena Microchapters
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Melena overview On the Web |
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American Roentgen Ray Society Images of Melena overview |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Melena or melaena refers to the black, "tarry" feces that are associated with gastrointestinal hemorrhage. The black color is caused by oxidation of the iron in hemoglobin during its passage through the ileum and colon.
Pathophysiology
Melena, is stool with blood, that has been altered by the gut flora, and appears black/"tarry".
Melena vs. hematochezia
Bleeding originating from the lower GI tract (such as the sigmoid colon and rectum) is generally associated with the passage of bright red blood, or hematochezia, particularly when brisk. Blood acts as a cathartic agent in the intestine, promoting its prompt passage. Only blood that originates from a high source (such as the small intestine), or bleeding from a lower source that occurs slowly enough to allow for oxidation, is associated with melena. For this reason, melena is often associated with hemorrhage in the stomach or duodenum (upper gastrointestinal tract), for example by a peptic ulcer. A rough estimate is that it takes about 14 hours for blood to be broken down within the intestinal lumen; therefore if transit time is less than 14 hours the patient will have hematochezia and if greater than 14 hours the patient will exhibit melena. One often-stated rule of thumb is that melena only occurs if the source of bleeding is above the ligament of Treitz.
Causes
The upper part of the GI tract will usually cause black stools due to:
- Abnormal blood vessels (vascular malformation)
- A tear in the esophagus from violent vomiting (Mallory-Weiss tear)
- Bleeding stomach or duodenal ulcer
- Inflammation of the stomach lining (gastritis)
- Lack of proper blood flow to the intestines (bowel ischemia)
- Trauma or foreign body
- Widened, overgrown veins (called varices) in the esophagus and stomach
Diagnosis
Symptoms
Physical Examinations
- Patients present with signs of anemia.
- Vital signs.
- Pulse.
- Blood pressure
- Respiratory rate.
- Core body temperature.
Laboratory Findings
- Blood studies, including a complete blood count ( CBC) and differential, serum chemistries, clotting studies.
- The presence of blood must be confirmed with either a positive hemoccult slide on rectal exam, frank blood on the examining finger, or a positive stool guaiac from the lab.
X Ray
- Chest X Ray should be ordered to rule out perforated viscus, aspiration pneumonia.
- Barium studies.
- X Ray of the abdomen.
CT
Other Imaging Findings
- Bleeding scan (nuclear medicine)
- Colonoscopy
- Esophagogastroduodenoscopy
Other Diagnostic Studies
- Stool culture.
- Tests for the presence of Helicobacter pylori infection.
- Nasogastric lavage.
Medical Therapy
Following options should be considered:
- Blood transfusions
- IV Fluids
- Medications to decrease stomach acid.
- Interventional radiography embolization.
Surgery
Surgery should be done if bleeding does not stop.