Somatostatinomas Workup

  • Author: Eric J Hanly, MD; Chief Editor: Julian Katz, MD   more...
 
Updated: Jan 11, 2010
 

Laboratory Studies

  • Obtain a fasting serum somatostatin level. The reference range is less than 100 pg/mL, but patients with somatostatinoma syndrome may have elevated levels measurable in nanograms per milliliter (this means increases of 1000-fold or greater). Somatostatinomas are very rare; hence, this test is only available in select centers.
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Imaging Studies

  • High-resolution spiral computed tomography (CT) scanning enhanced with oral and intravenous contrast is the initial imaging technique used to localize and stage somatostatinomas. Even with thin cuts (3-5 mm) through the pancreas, this inexpensive and noninvasive modality has failed to identify up to 70% of pancreatic endocrine tumors. Many patients require more invasive and expensive localization techniques. Although no specific data exist regarding the sensitivity of CT scanning in localizing somatostatinomas, failure is probably less frequent because these tumors are relatively large at presentation compared with other pancreatic endocrine neoplasms. CT scanning is used to image the whole body and is therefore useful in the detection of metastatic disease.
  • Improvements in magnetic resonance imaging (MRI) techniques are making this noninvasive modality useful in the localization of somatostatinomas. Recent studies have demonstrated the usefulness of contrast-enhanced (eg, gadolinium), T1-weighted MRI when evaluating small primary and metastatic pancreatic endocrine tumors.
  • Somatostatin receptor scintigraphy (SRS) is a novel nuclear medicine imaging modality that takes advantage of the fact that many pancreatic endocrine tumors express large numbers of somatostatin receptors on their cell surfaces. Radiolabeled octreotide (an octapeptide somatostatin analogue) administered intravenously preferentially identifies such tumors by binding to somatostatin receptors. While the limited resolution of this technique does not afford the kind of detail necessary to determine the exact location of a primary tumor, SRS is particularly helpful in diagnosing small extrapancreatic metastases. Although SRS was originally thought to be a poor tool for localization of somatostatinomas, recent data suggest that many somatostatinomas exhibit radiopharmaceutical uptake of the tracer.
  • Endoscopic ultrasound (EUS) through the duodenum can be very helpful when localizing pancreatic endocrine tumors and assessing for lymph node metastases. This technique is particularly helpful in identifying small submucosal duodenal tumors and small pancreatic tumors. It cannot be used to detect hepatic or distant metastases.
  • Because of the improved techniques of CT scanning, MRI, and EUS, visceral angiography does not have an essential role in the evaluation of patients with somatostatinomas and other neoplasms of the endocrine pancreas.
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Other Tests

  • Selective transhepatic portal venous sampling is another test to consider. For this invasive test, blood is sampled from different locations within the portal venous drainage of the pancreas and pancreatic bed. Serum levels of somatostatin are determined from the blood samples to help localize the tumor based on anatomic venous drainage. The sample with the highest serum hormone level is presumed to have been drawn from the main venous drainage of the tumor.
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Procedures

  • Endoscopic evaluation of the upper gastrointestinal tract is useful for excluding other conditions that can produce similar constellations of symptoms. Gastric pH should be measured at the time of endoscopy to evaluate for hypochlorhydria. Intraoperative endoscopic transduodenal illumination may help localize small endocrine tumors that reside within the wall of the duodenum or within the pancreatic parenchyma.
  • Real-time intraoperative ultrasonography (IOUS) can provide additional information about the location and number of pancreatic endocrine tumors. It also can be used to detect small lymph node and hepatic metastases. This technique should always be used in patients who undergo exploration for tumors that could not be definitively localized preoperatively.
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Histologic Findings

When visualized via light microscopy, somatostatinomas appear similar to other types of Apudomas (including other pancreatic endocrine tumors and carcinoid tumors). Routine histologic examination does not predict the biologic behavior of these neoplasms, and malignancy is typically determined by the presence of tumor spread to regional lymph nodes or by the existence of hepatic or distant metastases.

Immunofluorescence techniques and the peroxidase-antiperoxidase procedure allow the demonstration of somatostatin within neoplastic cells, but positive findings on immunohistochemical staining only confirm that a particular tumor can synthesize somatostatin. Such a finding, however, does not provide information about whether the synthesized hormone is released into the bloodstream. Thus, an important distinction must be made between true somatostatinomas (ie, tumors that are associated with documented elevation of somatostatin levels) and tumors that merely stain positively for somatostatin.

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Staging

Prognosis is primarily based on the presence or absence of liver metastases. The presence of regional lymph node spread does not necessarily connote decreased patient survival. The standard TNM classification scheme is not used to stage somatostatinomas.

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Contributor Information and Disclosures
Author

Eric J Hanly, MD  Resident, Department of Surgery, The Johns Hopkins University School of Medicine; Fellow, Department of Surgery, The Johns Hopkins University School of Medicine

Eric J Hanly, MD is a member of the following medical societies: American Medical Association, Association of Military Surgeons of the US, MedChi, Phi Beta Kappa, and Society of USAF Flight Surgeons

Disclosure: Nothing to disclose.

Coauthor(s)

Michael Cooperman, MD  Clinical Associate Professor of Endocrinology, Temple University; Chair, Department of Internal Medicine, Division of Endocrinology, Jeanes Hospital

Michael Cooperman, MD is a member of the following medical societies: Alpha Omega Alpha, American Association of Clinical Endocrinologists, and Endocrine Society

Disclosure: Nothing to disclose.

Michael R Marohn, DO  Associate Professor, Department of Surgery and Surgical Sciences, John Hopkins University School of Medicine

Disclosure: Nothing to disclose.

Leon W Kundrotas, MD, Col, USAF, MC  Chief, Medical Staff 48th Medical Group, Malcolm Grow Medical Center; Assistant Professor, Department of Medicine, USAF Hospital

Leon W Kundrotas, MD, Col, USAF, MC is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, and American Society for Gastrointestinal Endoscopy

Disclosure: Nothing to disclose.

Charles J Yeo, MD  Samuel D Gross Professor and Chair of Surgery at Jefferson Medical College of Thomas Jefferson University and at Thomas Jefferson University Hospital

Charles J Yeo, MD is a member of the following medical societies: Alpha Omega Alpha, American Association of Endocrine Surgeons, American College of Surgeons, American Gastroenterological Association, American Hepato-Pancreato-Biliary Association, American Surgical Association, Association for Academic Surgery, Johns Hopkins Medical and Surgical Association, Pancreas Club, Phi Beta Kappa, Sigma Xi, Society for Surgery of the Alimentary Tract, and Society of University Surgeons

Disclosure: Nothing to disclose.

Specialty Editor Board

Mounzer Al Al Samman, MD  Department of Internal Medicine, Division of Gastroenterology, Assistant Professor, Texas Tech University School of Medicine

Mounzer Al Al Samman, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, and American Gastroenterological Association

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Senior Pharmacy Editor, eMedicine

Disclosure: eMedicine Salary Employment

Noel Williams, MD  Professor Emeritus, Department of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada; Professor, Department of Internal Medicine, Division of Gastroenterology, University of Alberta, Edmonton, Alberta, Canada

Noel Williams, MD is a member of the following medical societies: Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Alex J Mechaber, MD, FACP  Associate Dean for Undergraduate Medical Education, Associate Professor of Medicine, University of Miami Miller School of Medicine

Alex J Mechaber, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, and Society of General Internal Medicine

Disclosure: Nothing to disclose.

Chief Editor

Julian Katz, MD  Clinical Professor of Medicine, Drexel University College of Medicine; Consulting Staff, Department of Medicine, Section of Gastroenterology and Hepatology, Hospital of the Medical College of Pennsylvania

Julian Katz, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, American Geriatrics Society, American Medical Association, American Society for Gastrointestinal Endoscopy, American Society of Law, Medicine & Ethics, American Trauma Society, Association of American Medical Colleges, and Physicians for Social Responsibility

Disclosure: Nothing to disclose.

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