A 37-year-old woman complains of watery diarrhea, abdominal cramps and periodic facial flushing for the last six months. Examination reveals bilateral wheezing and slightly enlarged liver. Urine analysis shows high levels of 5-hydroxyindoleacetic acid (5-HIAA). Multiple tumors are detected by a CT scan.
What is the most likely primary site of these tumors?
This is a typical presentation of carcinoid tumors which arise from the neuroendocrine cells. The most common site of these tumors is the small intestine (50%). Other less common sites are the colon and the tip of the appendix. They secrete serotonin and histamine which are responsible for these symptoms. Serotonin secreted by these tumors is inactivated to 5-HIAA by the liver which excreted in urine. When the tumors spread to the liver, the secretion of serotonin bypass the inactivation of it resulting in carcinoid syndrome which is featured in this patient.
The correct answer is C