What Do I Have? Carcinoid Tumors to the Liver
Carcinoid is a relatively uncommon type of cancer that most commonly arises from special cells in the gastrointestinal tract; occasionally, special cells in the lung, the ovaries, and the thymus can get a carcinoid tumor as well. These special cells are called amine precursor uptake and decarboxylation (APUD) cells, and they make compounds which affect other cells. Because they produce these compounds, these cells have a characteristic appearance under the microscope: they contain vesicles (sacs within cells) in which these compounds are stored. The most characteristic compound which is found in these vesicles is serotonin.
Sometimes these tumors spread (metastasize) to the liver.
One of the primary tasks of the liver is to metabolize and detoxify substances originating from the gastrointestinal tract. These substances are delivered to the liver via the portal vein. Because of this, any compounds released by a carcinoid tumor in any location proximal to the portal vein (before the liver) will be metabolized before they can pass into the heart; thus it will never reach the rest of the body. However, carcinoid tumors which have migrated to and invaded into the liver (i.e. metastasized) may release active compounds (such as serotonin and others called tachykinins) into the hepatic veins and inferior vena cava, thereby bypassing the detoxification cells of the liver. These compounds may then reach the systemic circulation (circulation of the body) in active form and may cause symptoms such as flushing, diarrhea, abdominal pain, heart palpitations, and asthma. Any or all of these symptoms taken together describe the carcinoid syndrome, which is highly diagnostic for carcinoid disease metastatic to the liver. Often, patients present to the doctor with these symptoms and are diagnosed with metastatic disease without knowing exactly where the primary tumor is. The primary tumor at a gastrointestinal site may only cause vague symptoms such as intermittent abdominal pain or intermittent diarrhea. In fact, up to half of the time, a carcinoid tumor is found incidentally during another abdominal operation or during routine endoscopy.
Once a carcinoid tumor is diagnosed, a computed tomography (CT) scan is next performed in order to assess the liver for metastatic disease. If a suspicious lesion is found, the radiologists can biopsy it via a needle passed trough the skin under ultrasound guidance. The pathologists then study the biopsy to make the diagnosis. Another scan that may be performed is the radiolabeled metaiodobenzylguanidine (MIBG) scan. Carcinoid cells selectively take up this substance, and significant uptake in the liver is evidence of metastatic disease.
