Somatostatinomas Workup

Updated: Jun 29, 2015
  • Author: Praveen K Roy, MD, AGAF; Chief Editor: Julian Katz, MD  more...
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Workup

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.

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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Imaging Studies

Computed tomography scanning

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.

Magnetic resonance imaging

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

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.

Ultrasonography

Endoscopic ultrasonography (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.

Angiography

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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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.

Cytologic evaluation with endoscopic ultrasonography-guided (EUS) fine-needle aspiration (FNA) may be helpful in the preoperative diagnosis of somatostatinomas. [13, 14, 15]

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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 tumor/node/metastasis (TNM) classification scheme is not used to stage somatostatinomas.

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