Other Sporadic Islet Cell Tumors

Most other functional islet cell tumors such as glucagonomas, vasoactive intestinal polypeptide tumors (VIPomas), and somatostatinomas are too large at diagnosis to be amenable to enucleation and require resection when feasible.21"23 More than half of these tumors are malignant with either local invasion or hepatic metastases at the time of diagnosis. Whenever feasible, debulking of tumors is desirable short of Whipple's procedure even when hepatic metastases are present. When local invasion of the superior mesenteric vein is the only apparent factor preventing complete tumor resection, the proximal portion of the vein and portal vein, if uninvolved, can be mobilized and clamped and either an autologous jugular vein or a ribbed Gore-Tex graft used for replacement after the tumor has been resected. Another option is the use of the distal right renal vein as a graft for the resected superior mesenteric vein. Although we would not usually perform superior mesenteric vein resection for an adenocarcinoma of the pancreas, local venous involvement by an islet cell tumor may lead to portal hypertension and mesenteric thrombosis in the absence of disseminated disease. Every effort should be made to free the mesenteric vessels of malignancy in patients without liver metastases. When the superior mesenteric vein is locally invaded proximal to the confluence with the splenic vein, it may be possible to use the splenic vein as graft, swinging it down to the proximal transected superior mesenteric vein and anastomosing it end to end (Fig. 81-2). We have used this simple bypass on three occasions with success.

One lesson learned when there is complete occlusion of the vein is that the superior mesenteric vein should be shunted or bypassed to the portal vein with an elongated graft over and around the tumor before resecting the pancreas. Incisions into the pancreas filled with venous collaterals in these cases can result in massive blood loss unless decompressed by shunting. An elongated graft can be clamped, divided, and shortened to an appropriate length and anastomosed after the tumor has been excised. We have not been as aggressive in resecting an involved superior mesenteric artery, but we currently have several patients without liver metastases in whom resection and bypassing the artery are being considered because of the development of visceral angina. In both cases, the only residual islet cell tumor is in the superior mesenteric artery after an 85% resection of the pancreas. In neither case was the aorta invaded, although the superior mesenteric artery was encased within 1 cm of its origin.

When functional islet cell tumors are associated with liver metastases, we resect those that can be readily excised and use radiofrequency ablation for those still remaining. The occasional patient with a single large liver metastasis, usually involving the right lobe, however, is a candidate for a liver lobectomy. The effectiveness of somatostatin analogs in the treatment of both metastatic glucagonoma and VIPoma has lessened the need for more radical excisions of metastatic deposits in the liver.2425 Somatostatin analogs may cause tumor regression in some VIPoma cases and can control the secretion of VIP in nearly all cases. In patients with progressive enlargement of liver metastases in both liver lobes, we recommend hepatic arterial embolizations in two stages, which may prove effective for 6 months to 1 year or even longer. Because a somatostatin analog (octreotide) is used eventually in the treatment of most incurable islet cell tumors, cholecystectomy should always be considered in the patient found to have liver metastases at exploration. Long-term use of octreotide has been associated with a high incidence of cholelithiasis and cholecystitis in those patients with retained gallbladders.

Nonfunctional Sporadic Islet Cell Tumors

The general principles applied to the surgical treatment of nonfunctional islet cell tumors are essentially the same as those identified for the treatment of tumors associated with clinical syndromes. Most nonfunctional tumors are diagnosed after

FIGURE 81-2. A, Neuroendocrine tumor of head, neck, or uncinate region encasing or invading the superior mesenteric vein proximal to the confluence of the splenic and portal veins. B, Distal splenic vein mobilized and clamped in preparation for transposition as graft involvement. C, Proximal superior mesenteric vein transection is oversewn, and splenic vein is transposed and anastomosed end to end with proximal superior mesenteric vein. A 95% pancreatectomy is performed. (A to C, From Thompson NW, Eckhauser F. Malignant islet cell tumors of the pancreas. World J Surg 1984;8:946.)

they have attained a size large enough to cause local symptoms.2123,26 These include jaundice, pancreatitis, steatorrhea, gastrointestinal bleeding, duodenal obstruction, abdominal pain, and palpable abdominal mass. Most are malignant, as manifest by local invasion, liver metastases, or lymph node involvement. Nevertheless, even some of the largest tumors are resectable for cure, and most can be resected with expectation of palliation for extended periods. Many of the nonfunctional tumors arise in the pancreatic head, and a Whipple procedure is frequently feasible. This operation should not be withheld because of local lymph node metastases. An octreotide scan should be done preop-eratively in all patients with suspected nonfunctional islet cell tumors to confirm the diagnosis (when positive), for staging, and to determine whether octreotide may be useful as adjunctive therapy.

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