Staging And Localization Of Tumor

Overall staging of the extent of disease usually relies on confirmation of the initial diagnosis as well as the integration of evidence from a number of imaging modalities. Conventional noninvasive localization studies may fail to detect tumor in as many as 40% of patients with ZES.5,7 As a first-line study, abdominal ultrasonography has a sensitivity of 30% and a specificity of 92%.8 The accuracy of computed tomography (CT) depends on the size of the gastrinoma. Tumors < 1 cm are seldom visualized, 30% of those between 1 and 3 cm are seen, and all > 3 cm are imaged. Overall, CT can identify approximately 80% of pancreatic and 35% of extrahepatic gastrinomas (Figure 14-3).9 It can also be used as a diagnostic modality by measuring gastrin levels in tissue following fine-needle aspiration (Figure 14-4). Magnetic resonance imaging may be useful in identifying small tumors and liver metastases and in distinguishing metastatic tumors from hemangiomas (Figure 14-5). However, it rarely images primary duodenal gastrinomas, only approximately 25%.8

Somatostatin receptor scintigraphy (SRS) is the imaging test of choice for localizing both primary

Figure 14-3. Computed tomographic appearance of a gastrinoma (arrows). The identification of the tumor is facilitated by the presence of contrast material in the small bowel adjacent to the lesion. No intravenous contrast is seen in the inferior vena cava (IVC) or aorta (A).

(Figure 14-6) and metastatic gastrinomas (Figures 14-7 and 14-8). This radiolabeled somatostatin analogue binds to the type 2 somatostatin receptor that is expressed in most gastrinomas. Ninety percent of tumors can be imaged by this modality with a specificity approaching 100%.10 However, it still may miss small primary duodenal gastrinomas.

Endoscopic ultrasonography (Figure 14-9) is a fairly new method to localize gastrinoma. It is rela

Figure 14-4. Use of computed tomography to guide fine-needle aspiration (arrowhead) of a mass lesion in a patient with ZollingerEllison syndrome. The gastrin level in the aspirate from the mass was 11,518 pg/mL (the peripheral venous gastrin level was 769 pg/mL), thus confirming it as a gastrinoma (arrow).

Figure 14-4. Use of computed tomography to guide fine-needle aspiration (arrowhead) of a mass lesion in a patient with ZollingerEllison syndrome. The gastrin level in the aspirate from the mass was 11,518 pg/mL (the peripheral venous gastrin level was 769 pg/mL), thus confirming it as a gastrinoma (arrow).

tively invasive and can detect small tumors by endo-scopically placing a high-frequency ultrasound transducer in the vicinity of the gastrinoma triangle and the liver. The procedure is operator dependent and has not been able to reliably identify small duodenal tumors. One study found the sensitivity of endoscopic ultrasonography to be 50 to 75% for duodenal, 75% for pancreatic, and 63% for lymph node gastrinomas.10

Because noninvasive studies may not image the gastrinoma, invasive imaging and regional localization studies have also been used extensively. Previously, selective angiography was the imaging study

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Figure 14-5. A, Magnetic resonance visualization of a metastatic gastrinoma in the liver (white arrows). In B, the same lesion is seen on computed tomographic scan (white arrow). The magnetic resonance image was obtained before contrast administration.

Figure 14-6. Somatostatin receptor scintigram showing isotope uptake by a gastrinoma (arrow). On exploration, the tumor was found in the duodenum. The large enhancing area on the right of the figure is the spleen.

of choice and was able to identify 60% of tumors. Primary or metastatic gastrinomas were seen as tumor "blush" within the liver, pancreas, or wall of the duodenum (Figure 14-10). This study has been largely supplanted by SRS. Another invasive localization study that has been used is portal venous

Figure 14-7. Another somatostatin receptor scintigram showing a metastatic gastrinoma in the liver (white arrow). Again, the enhancing area on the right of the figure is the spleen.

sampling for serum levels of gastrin (Figure 14-11, A).12 This is performed by transhepatic passage of a catheter into the portal vein and its tributaries with sampling of gastrin levels along the portal venous circulation. Alternatively, selective infusion of secretin can be combined with angiogra-phy in an attempt to identify the region of the pancreas that contained the gastrinoma (Figure 14-11, B). This approach became popular because it avoided the need for transhepatic portal venous sampling. In this study, secretin is selectively injected into arteries supplying specific regions of the pancreas and liver. Gastrin levels are then measured in

Figure 14-8. Correlation between somatostatin receptor scintigra-phy (SRS) and magnetic resonance imaging (MRI) in the detection of metastatic tumors in the liver. In A, SRS shows the presence of two distinct liver lesions (white arrows). In B, the presence of these lesions is confirmed on successive STIR (short tau inversion recovery) sequence MRI displays in the upper and lower panels (white arrows).

Figure 14-8. Correlation between somatostatin receptor scintigra-phy (SRS) and magnetic resonance imaging (MRI) in the detection of metastatic tumors in the liver. In A, SRS shows the presence of two distinct liver lesions (white arrows). In B, the presence of these lesions is confirmed on successive STIR (short tau inversion recovery) sequence MRI displays in the upper and lower panels (white arrows).

Figure 14-9. In A, endoscopic ultrasonography is used to image a large primary gastrinoma (white arrows). B, In this same patient, the location of the gastrinoma correlates with what is seen on computed tomography (white arrows). A = aorta.

may be able to directly visualize the gastrinoma (Figure 14-13), and, using transillumination, the tumor appears as a photo-opaque mass (Figure 14-14, A). Once identified, the tumor can be marked with a suture and removed with a small margin of normal duodenal tissue (Figure 14-14, B to D). Intraoperative secretin-stimulated gastrin levels have been used to determine when all of the gastrinoma has been removed.14

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