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Figure 13-7. A, Pathologic specimen from a patient with a large, well-circumscribed, pancreatic neuroendocrine tumor. B, Microscopic specimen of this tumor. The appearance of benign and malignant lesions may be very similar. The tumor consists of cells arranged in trabeculae and nests. C, Electron micrograph shows ■ JIUI|im|llll|lll||!l|limijlllll]]]![HII|imjllll|i!Ilj abundant dense core neurosecretory granules. A i . . ? ^ -i rv 6

Figure 13-7. A, Pathologic specimen from a patient with a large, well-circumscribed, pancreatic neuroendocrine tumor. B, Microscopic specimen of this tumor. The appearance of benign and malignant lesions may be very similar. The tumor consists of cells arranged in trabeculae and nests. C, Electron micrograph shows ■ JIUI|im|llll|lll||!l|limijlllll]]]![HII|imjllll|i!Ilj abundant dense core neurosecretory granules. A i . . ? ^ -i rv 6

of each sample is graphically noted, and simultaneous peripheral samples are taken as controls.

The drawback to the THPVS is that it is invasive and uncomfortable for the patient and is associated with appreciable complications. In addition, it only regionalizes and does not localize the site of the tumor. The exact location of the tumor still must occur intraoperatively. This procedure has been replaced by a variation of the Imamura procedure, which uses intra-arterial stimulation with calcium.26 We recommend the Imamura-Doppman procedure for patients with persistent or recurrent insulinoma, although some experts use it for most patients. This procedure has been recommended by some authors to be especially useful in patients with beta-cell hyperplasia or with nesidioblastosis (Figure 13-10).27

Figure 13-8. A, Pathologic specimen from a 72-year-old woman with islet cell hyperplasia. B, This microscopic specimen shows a marked focal enlargement of islet A compared with islet B, which suggests islet cell hyperplasia.

Figure 13-9. Preoperative localization of an insulinoma of the head of the pancreas by celiac artery angiography. Subtraction technique during the arterial phase. The tumor (arrows) is clearly seen. Reproduced with permission from Kaplan EL, Lee CH. Recent advances in the diagnosis and treatment of insulinomas. Surg Clin North Am 1979;59:119.

Figure 13-9. Preoperative localization of an insulinoma of the head of the pancreas by celiac artery angiography. Subtraction technique during the arterial phase. The tumor (arrows) is clearly seen. Reproduced with permission from Kaplan EL, Lee CH. Recent advances in the diagnosis and treatment of insulinomas. Surg Clin North Am 1979;59:119.

Preoperative Endoscopic Ultrasonography

A retrospective analysis from various medical centers showed that endoscopic ultrasonography detected at least 80% of insulinomas that were not visible in transabdominal ultrasonography or computed tomography (CT).28 In one of the studies, endoscopic ultrasonography correctly identified 32 of the 39 surgically verified tumors, with accurate prediction of its size and site. Twenty-two underwent both endoscopic ultrasonography and angiography, and the former was significantly more sensitive for tumor localization (82% versus 27%). No other tumors were detected in 18 of 19 control patients (specificity of 95%). However, these results are limited for tumors localized to the head of the pancreas, whereas sensitivity achieved for tumors in the body is 78% and for those in the tail of the pancreas only 60%.29 We believe that this is the preferred preoperative localization study (Figure 13-11). We are using it in most patients as it enables one to laparo-scopically remove most of the identified tumors.

There have been several case reports in the literature describing successful use of preoperative intraductal ultrasonography.30 However, more evidence is

Figure 13-11. Endoscopic ultrasonographic image shows a well-circumscribed, 1 cm hypoechoic mass in the pancreatic head (arrows). The probe lies within the second portion of the duodenum. Note the dilated distal common bile duct (C). Reproduced with permission from Buetow P. Islet tumors of the pancreas: clinical, radio-logic and pathologic correlation in diagnosis and localization. Radi-ographics 1997;17:453-72. Copyright 1997 Radiologic Society of North America.

Figure 13-10. Percutaneous transhepatic portal venous sampling. Insulin radioimmunoassay demonstrates peak levels (227 and 329 |jU/mL) in the area of the tail of the pancreas. Reproduced with permission from Bottger TC and Junginger T.31

Figure 13-11. Endoscopic ultrasonographic image shows a well-circumscribed, 1 cm hypoechoic mass in the pancreatic head (arrows). The probe lies within the second portion of the duodenum. Note the dilated distal common bile duct (C). Reproduced with permission from Buetow P. Islet tumors of the pancreas: clinical, radio-logic and pathologic correlation in diagnosis and localization. Radi-ographics 1997;17:453-72. Copyright 1997 Radiologic Society of North America.

needed before recommending this procedure to be of standard use in insulinoma localization.

Magnetic Resonance Imaging, Magnetic Resonance Imaging with Gadolinium, CT, and Preoperative Ultrasonography

In our medical center, the accuracy of magnetic resonance imaging (MRI), MRI with gadolinium, CT, and preoperative ultrasonography was 30%, 40%, 24%, and 50%, respectively. These sensitivities are similar to those reported in other medical centers.31,32 The frequency of use of these studies, as well as arteriography and THPVS, has changed over the years owing to the availability of newer and more sensitive localization procedures. The accuracy of MRI, MRI with gadolinium, CT, and preoperative ultrasonography increased as the size of the tumor increased. Thus, MRI accuracy increased from 0 to 75% as the

tumor size increased from < 1 cm to >2 cm.33 The accuracy of MRI with gadolinium increased from 0 to 50% and then to 100% as the tumor size increased from 1 cm, 3 cm, and 6 cm, respectively.33 Because most insulinomas are < 1 cm in diameter, the sensitivities of the above studies for these small tumors do not warrant their use in patients who have not had previous insulinoma operations. Presently, however, CT in our institution is used primarily for screening patients for malignant insulinomas with liver metastases rather than for localization of insulinomas (see Figure 13-12 for illustrations of MRI, preoperative ultrasonography, and CT).

Intraoperative Ultrasonography and Intraoperative Palpation

Intraoperative ultrasonography (IOUS) was introduced in 1985. It identifies insulinomas with 90 to

Figure 13-12. A, This T2-weighted magnetic resonance image demonstrates an insulinoma in a region of the pancreatic head (arrow). B, Preoperative sonogram demonstrates a small insulinoma. C, Axial contrast-enhanced computed tomographic scan demonstrates a hypervascular mass within the pancreatic head (arrows) that measured approximately 2.5 cm in diameter and produced mass effect on the superior mesenteric vein. Reproduced with permission from Buetow P. Islet tumors of the pancreas: clinical, radiologic and pathologic correlation in diagnosis and localization. Radiographics 1997;17:453-72. Copyright 1997 Radiologic Society of North America.

Figure 13-12. A, This T2-weighted magnetic resonance image demonstrates an insulinoma in a region of the pancreatic head (arrow). B, Preoperative sonogram demonstrates a small insulinoma. C, Axial contrast-enhanced computed tomographic scan demonstrates a hypervascular mass within the pancreatic head (arrows) that measured approximately 2.5 cm in diameter and produced mass effect on the superior mesenteric vein. Reproduced with permission from Buetow P. Islet tumors of the pancreas: clinical, radiologic and pathologic correlation in diagnosis and localization. Radiographics 1997;17:453-72. Copyright 1997 Radiologic Society of North America.

100% sensitivity,34 and 91% were identified among our patients.33 In our medical center, as well as in others, IOUS was significantly more sensitive than intraoperative palpation (91% versus 76% in our medical center).31-33 Some experts have suggested that this procedure eliminates the need for other preoperative localization procedures.31,32 In our medical center, as well as in others,31-33 IOUS before or after a careful mobilization of the pancreas in combination with intraoperative palpation gave the best results. Although it was formerly the only localization technique that we recommended for patients who had not had previous pancreatic operations, we now recommend preoperative transgastric ultra-sonography. Among the 20 tumors identified by IOUS in our patients, there were no false-positive diagnoses.33 The low false-positive rate makes this method more useful because it decreases the false diagnosis of adenoma in a nodular-feeling pancreas, in which nodularity and scarring may lead to unnecessary dissection. IOUS helped to identify 9 of the 11 nonpalpable and nonvisable tumors, thus preventing unsuccessful operations.33 It also decreases the risk of missing multiple tumors even after one tumor is identified. Additionally, IOUS and preoper-ative transgastric ultrasonography provide assistance in visualizing anatomic details during the operation, such as the relationship of the insulinoma to the pancreatic duct, thus helping the surgeon to decrease the risk of a postoperative fistula (Figure 13-13 for IOUS illustration).

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