Somatostatinoma is a functional pancreatic neuroendocrine tumor (PanNET). Other tumors of this class include insulinomas, gastrinomas, VIPomas, and glucagonomas. Somatostatinomas are relatively rare and make up less than 5% of PanNETs.
Somatostatin is mainly produced by pancreatic delta cells. It reduces the production of other hormones including gastrin, secretin, cholecystokinin, glucagon, and insulin. Somatostatin is also produced by the hypothalamus where it inhibits growth hormone secretion.
Steatorrhea is characterized by excessive fat in the stool. This occurs due to mechanical compression of biliary and pancreatic duct drainage by a somatostatinoma. Decreased gastrointestinal motility also plays a role in this process. The result is a malfunction of the pancreas presenting as fat malabsorption. Fat then deposits in the stool.
Somatostatin suppresses cholecystokinin, resulting in decreased motility of the gallbladder. This will increase the risk of gallbladder stone formation.
Hyperglycemia or hypoglycemia can be seen in patients with somatostatinomas. This occurs due to the suppression of insulin and glucagon. Notably, somatostatin suppresses insulin more than glucagon. Thus, hyperglycemia will dominate. Another clinical feature that can be seen is hypochlorhydria. The decrease of gastrin production by somatostatin causes hypochlorhydria.
Increased somatostatin levels are virtually diagnostic of somatostatinoma.
Abdominal CT or MRI can help visualize the tumor. The initial diagnostic tool to be considered is multiphasic contrast-enhanced CT of the abdomen. MRI helps to recognize small liver metastasis.
Octreotide is a somatostatin analog. Its indication seems paradoxical because of the high somatostatin levels seen in these patients. However, octreotide has proven to be effective at relieving patient's symptoms and reducing plasma levels of somatostatin.
Surgical resection is the only curative treatment. It is recommended and effective in patients with localized cases. Because some cases are complicated by advanced stage and metastasis, surgical cure is not possible.
Chemotherapy can be considered in somatostatinoma patients. Fluorouracil is the most common chemotherapeutic agent used, and is often combined with other drugs such as streptozocin and doxorubicin. Half of cases benefit from chemotherapy.
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