Sporadic Gastrinomas

Unlike insulinomas, most gastrinomas are malignant. However, unless detected at a stage in which hepatic metastases are already present, most patients are candidates for a curative procedure. The surgical treatment of gastrinoma is dependent on its location, whether within the pancreatic parenchyma or arising within the duodenal wall. Our experience is similar to that of others who have noted that sporadic gastrinomas are always solitary tumors; those within the pancreas causing Zollinger-Ellison syndrome (ZES) are invariably larger than 1 cm in diameter and can be readily identified at exploration.10

Although most gastrinomas are within the gastrinoma triangle, a pancreatic gastrinoma can arise from the neck or body of the pancreas as well. For these unusual patients, a distal pancreatectomy is preferable to enucleation because of the greater likelihood that the neoplasm is malignant. When the gastrinoma is within the pancreatic head or uncinate, we attempt enucleation and reserve resection (pancreatoduodenectomy) for when there is local infiltration and absence of hepatic metastases.411 Surprisingly, in nearly all gastrinomas of the head without liver metastases, it has been possible to enucleate the tumor. When no neoplasm is found within the pancreas after its complete mobilization and exploration, it should be assumed that the tumor is within the duodenum.12 A duodenotomy should be performed routinely in sporadic patients with ZES when the pancreatic exploration is negative.1216

Before this is performed, the duodenum should be carefully palpated from the pylorus to the level of the superior mesenteric vein. However, fewer than half of sporadic duodenal gastrinomas are palpable. Because a sporadic gastrinoma is singular, the duodenectomy can be placed for its excision when it is palpable. In these cases, the neoplasm is usually 0.5 cm or larger and may locally infiltrate the sub-mucosa. As a result, its excision with a full-thickness margin of duodenal wall is required.1214 When no tumor is palpable, we make a 6- to 8-cm vertical duodenotomy centered in the second portion of the duodenum. After inspection and gentle finger palpation circumferentially, a small submucosal lesion can usually be identified in the first, second, or proximal third portion of the duodenum. When no tumor is initially palpable, the duodenal wall, both proximally and distally, is everted into the duodenotomy for further inspection and palpation. Tumors as small as 1.5 mm can be detected by these maneuvers.12 Once identified, we place a stay stitch on either side of the tumor, make an elliptical incision through the mucosa around the tumor, and enucleate the tumor from the underlying submucosa. If this cannot be easily accomplished, a full-thickness excision of the duodenal wall around the tumor is performed. It has been our experience that nearly all gastrinomas that are 0.5 cm or smaller can be enucleated. When a full-thickness excision has been performed, unless it is at the edge of the duodenotomy, two separate closures are required. We prefer a two-layer closure with a running full-thickness absorbable stitch followed by an interrupted Lembert silk closure. Our duodenotomies are closed vertically rather than in a transverse direction.

Regardless of a duodenal tumor's size, a regional lymph node dissection is indicated. Gastrinomas as small as 1 mm may be associated with one or more metastatic nodes. We excise any visible nodes on both surfaces of the pancreatic head and those along the common bile duct and along the common hepatic artery to the level of the celiac axis.

When any of them are positive for metastatic disease, we excise all of the lymph nodes in the porta hepatis as well. A complete exploration of the pancreas and duodenum is currently rarely negative. Although for a decade we routinely used percutaneous transhepatic selective venous sampling in localizing gastrinomas, we currently rely on EUS after screening for hepatic metastases with a computed tomographic (CT) scan.61718 We also routinely obtain an octreotide scan, primarily to identify any liver metastases or otherwise occult distant metastases. Most gastrinomas 2 cm or larger (either primary or metastatic) have sufficient somatostatin receptors to be detectable with an octreotide scan. Most primary duodenal gastrinomas are too small to be identified by octreotide scans or any other localization techniques, although their larger metastatic lymph nodes may be detectable.

During the past 15 years, more than 70% of sporadic gastrinomas, in our experience have been duodenal in origin with about 60% having associated metastatic lymph nodes in the periduodenal or pancreatic region. Only one of these patients had a liver metastasis (<10%). During this time, we recognized that tumors arising in the third or fourth portions of the duodenum may also metastasize to lymph nodes along the superior mesenteric vein and in the base of the mesentery. These nodes are also now routinely resected for primary tumors in these locations. Because of the likelihood of recurrence in patients with malignant metastatic gastrinoma and the possible future need for long acting somatostatin therapy, we routinely perform a cholecystectomy as well.

If EUS is negative for a pancreatic tumor, it may be assumed that a duodenal primary is present. Nevertheless, it is reassuring to confirm regionalization with a selective arterial secretin stimulation test.19 20 In such cases, the liver not only is palpated but also is examined by ultrasonography for a rare primary hepatic gastrinoma. The distal duodenum and proximal jejunum should also be evaluated as well as the ovaries in a female patient. Although some have recommended a blind Whipple procedure after a negative exploration in a patient with proven localized gastrin hypersecretion in the region of the head or duodenum, we do not favor that approach. However, the possibility of re-exploration after 1 or 2 years should always be considered after a complete re-evaluation in the patient with rising gastrin levels.

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