European Journal of Radiology, 14 (1992) 46-51 0
46
EURRAD
1992 Elsevier Science Publishers
B.V. All rights reserved. 0720-048X/92/$05.00
00218
MRI in insulinomas: preliminary findings Guido Liessi
‘,
Claudio Pasquali 2, Alfonso Alfano D’Andrea2, Pedrazzoli *
Cesare Scandellari 3, Sergio
‘Servizio di Radiologia, Ospedale Civile, Castelfranco Veneto, TV, and 21stituto di Clinica Chirurgica, I Cattedra di: Patologia Speciale Chirurgica and ‘Istituto di Semeiotica Medica, Cattedra di Medicina Intema
(Received
Key words: Magnetic resonance
V, Padova. Italy
1 May 1991; accepted after revision 15 July 1991)
imaging, insulinoma;
Magnetic resonance
imaging, pancreas;
Pancreas,
neoplasm;
Pancreas,
MRI
Abstract After establishing the diagnosis of an insulinoma, most surgeons prefer preoperative localization. Selective arteriography is usually considered the gold standard for this purpose. Recently, computed tomography (CT) and preoperative US have contended the role to angiography. MRI has been used in few cases of endocrine pancreatic tumors, and its role in this particular field has to be defined. Between November 1988 and September 1990 we evaluated 7 adult patients who had had surgery in our Surgical Department. Eight tumors were resected in 6 patients who were cured; in an l&year-old woman surgical treatment was unsuccessful. Arteriography, CT, preoperative US, MRI and intraoperative US detected 2,6,6,5 and 6 tumors, respectively. Two insulinomas (0.2 and 0.7 cm) were found at histologic examination in resected specimen. The ability ofintraoperative US and careful surgical exploration to resolve more than 90% of cases makes the preoperative use of arteriography and CT of questionable value. If further experience confirms these findings, US and MRI may sufftce.
Introduction The insulinoma is the most common islet-cell neoplasm of the pancreas [ 11. Insulin secretion may produce severe symptoms that lead to an early detection of the disease. Despite the use of several available imaging techniques, the precise localization of an insulinoma inside the pancreatic parenchyma is sometimes very difficult because lesions may be multiple and are usually very small. Once the diagnosis has been made on the basis of the characteristic clinical symptoms and glucose/insulin ratio, an accurate localization is accomplished by radiologic techniques such as CT scan, US scan, arteriography and, if needed, venography and transhepatic venous sampling [ 2,3]. Recently, the ability of MR to evaluate pancreatic diseases has been stressed by some, but few reports are present in the literature [4-81.
Address for reprints: Prof. Sergio Pedrazzoli, Via Giustiniani 2, 35128, Padova, Italy.
Clinica Chirurgica I,
MR detection of insulinomas are seldom represented by typical signs and the characteristic signal intensities have not been investigated in any detail. We describe six patients with histologically proven pancreatic insulinoma and one patient with hyperinsulinemia whose symptoms remained unchanged after resection of the pancreatic tail. These patients were preoperatively evaluated with US, arterial CT, and MR imaging. Intraoperative US was also performed. In this study MR imaging was employed to detect insulinomas, and the results were compared with those obtained by other imaging techniques and with the surgical findings. In addition, we examined the most characteristic findings of this neoplasm on Tl- and T2-weighted images. Materials and Methods Between November 1988 and September 1990, we evaluated 7 patients with clinical and biochemical evidence of pancreatic insulinoma. Five patients were males and 2 were females ; age range: from 18 to 75 years. All patients had biochemical and clinical findings typical for insulin hyperproduction syndrome.
Results
All patients were studied with US, arteriography, arterial CT, MRI and intra-operative US (Table 1) Preoperative US scans were performed with a realtime apparatus (GE RT 3600 and Platinum Philips) using mechanical and phased-array 3.5 and 5 MHz probes. Angiographic procedures were performed by catheterization of the celiac axis and the mesenteric artery with superselective injection in the splenic and gastroduodenal arteries using digital techniques (DVI 2 Philips). After angiography, the patients were examined on a CT scanner (GE 9800). Scans were obtained through the upper abdomen at 5 mm intervals without injection of contrast medium; afterwards, additional scans of the pancreatic area were performed during injection of lOO- 150 ml of non-ionic contrast medium in small multiple boli through the catheter placed in the celiac axis. MR imaging was performed on a Fonar B-3000 Machine operating at a 0.3 T resistive magnet. Images were obtained with a spin-echo sequence with the Tlweighted (TR 390/TE 16) and TZweighted (TR 2000-2200/TE 85-l 10). Four to six NEX were used for T l-weighted images and two NEX for T2-weighted, using circular surface coils of various diameter. Motion artifacts were reduced by compression belt and by injection of 4 ml Buscopan. A section thickness of 8 mm with a. .3 mm gap between the sections and a matrix of 256 x 256 pixels were used. Intraoperative US scans (IOUS) were performed with a real-time apparatus (GE RT 3600 Philips and Toshiba, SAL 32B) using 5 and 7.5 MHz probes. A prospective examination of the images was performed by two skilled radiologists who were unaware of the findings of the other tests.
TABLE
Results of preoperative and intraoperative imaging are summarized in Table 1. In 6 of 7 patients preoperative US examinations showed a round, sharp lesion that was always hypoechoic (Figs. l-3). In 3 obese patients the examination, although very difTicult, was positive. Angiography was performed by means of a digital technique. Subselective injection of the contrast medium revealed a hypervascular lesion in cases 5 (Fig. 1) and 6. Angiography was not performed in case 2. A hyperdense lesion in the pancreatic parenchyma (Figs. 1 and 2) was demonstrated in 6 patients by arterial CT. MR examinations revealed the insulinoma in 5 patients, showing a hypointense lesion on Tl-weighted images and hyperintense pattern on TZweighted sequences. In one patient (case 7) the tumor was not discovered even during surgical exploration, while in patient 2 the MR was positive although the images were partially obscured by several motion artifacts.. In one case (case 1) transhepatic venography and venous sampling were performed and were negative. All patients underwent surgery and the tumor was felt in 6 of 7 cases. Intraoperative US was also performed and in each case showed a single hypo-echoic mass, largely corresponding in size and location to the preoperative images. Six were true positives, and one was false positive (Fig. 3). The size of neoplasms detected by intraoperative US ranged from 1.2 to 2.1 cm. In two patients local excision of the tumor was performed. All but one of the others had a left pancreatectomy with preservaton of the spleen.
1
Preoperative
location and surgical treatment
of seven insulinomas
Patient No.
US
CT
MRI
ART
IOUS
Surgical procedure
Pathological analysis
Follow-up
1 2 3
+ + +
+ + +
+ + FN
FN NP FN
+ + +
Enucl. LP LP
cured 2 years cured 2 years cured 2 years
4 5 6
+ + +
+ + +
+ + +
FN + +
+ + +
LP Enucl. LP
1
FP
FP
-
-
FP
LP
2cmI 1.2 cm I 1.2 cm I 0.2 cm I 1.5 cm I 1.4 cm I 2.1 cm I 0.7 cm I Normal
Abbreviations: I, insulinoma; LP, left pancreatectomy; WP, not performed; ART, arteriography; true-positive; - , true-negative; FP, false-positive; FN, false-negative; Enucl., enucleation.
IOUS, intraoperative
cured 2 years cured 2 years cured 6 months unchanged ultrasonography;
+,
48
Fig. 1. Case 5, Insulinoma of the pancreatic body 1.4 cm in diameter. The neoplasm is hypoechoic (arrowheads) hyperdense on arterial CT (b). Superselective injection of the splenic artery shows the hypervascular insulinoma at pancreatic body(c). MR scan reveals a hypo-intense (arrowheads) lesion on Tl-weighted (TR 390/TE 16) images (d) and pattern (arrowheads) on TZ-weighted images (TR 2000/TE 85); the mass is aho depicted by means of ‘chemical
In 6 of 7 patients the insulinoma was histologically confirmed. Moreover, histologic examination of the specimen revealed 2 cases of multiple insulinoma (cases 3 and 6). Both of the second insulinomas were located in the tail of the pancreas and measured 0.2 and 0.7 cm in diameter. In both cases the second insulinoma was an incidental finding which had not been suspected or localized by preoperative or intraoperative imaging, nor felt by the surgeon. The site and diameter of the tumors felt and resected largely corresponded to the images produced by various localizing procedures. In case 7, where apparently a lesion was seen, the segment of the pancreas containing the suspected area was removed. Sonography of the resected specimen confirmed the same area, while a further intraoperative ultrasonography showed only
on sonogram (a) and the upper edge of the a relative hyperintense shift’ artifact (e).
normal pancreas tissue. Pathologic study of the resected specimen showed a normal pancreas. All patients but one, in whom no insulinoma was found after resection of the pancreatic tail, were normoglycaemic after surgery. They are in good health and can be considered cured, Discussion Hyperinsulinism-related syndrome is an endocrine disease due, in most cases, to a surgically resectable islet-cell adenoma. The diagnosis is established by clinical findings and laboratory data. Prompt localization of the tumor is mandatory and requires radiological and, eventually, interventive radiological procedures.
kg. 2. Case 4: Insulinoma of the pancreatic 1.5 cm in diameter: a hypoechoic pattern (Towheads) (a) and a hyperdense small mass on arterial CT can be seen (white arrows) (b); digital celiac angiography was unable to demonstrate the lesion (c). MR scan at the anterior edge of the pancreatic body shows a small mass with low signal on Tl-weighted (TR 390jTE 16) images (arrowheads)(d) and relatively intense (arrow-heads) on TZ-weighted sequences (TR 2000/TE 110) (e). Intraoperative sonogram shows the lesion (arrow-heads) (f).
Good results from preoperative radiologic localization of insulinoma have been reported [ 9,101. Currently, angiography and CT are the procedures of choice [ 9- IO]. Transhepatic venography with venous sampling [ 2,3,11], are seldom required for a correct localization of the insulinoma inside the pancreatic parenchyma. US is widely available, and islet-cell tumors usually appear as a well-defined round or oval mass which is generally hypoechoic. The rates of successful detection of insulinoma reported in the literature, range between 30%, for early studies primarily done with static scanners [ 121, and approximately 60% [9,10] using real-time US equipment. In this study we found all 6 tumors were greater than 1 cm in diameter. Two small insulinomas (0.7 and 0.2 cm) escaped detection, and a false-positive result was obtained in case 7 (Fig. 3). No hypodense pattern was observed in our experience. Detection rates of insulinomas by CT are also variable (40 - 60%) [ 91, and the proper protocol for scanning is controversial. Repeated scans could be performed after intravenous or intraarterial injection of contrast medium. The characteristic feature of islet-cell
tumor is a circumscribed enhancement in the pancreatic parenchyma. Angiography has been the most commonly used imaging method for the evaluation of insulinoma. Successful localization rates are reported to range between 29% and 90% [9]. In the present series angiography detected only 2 of the 5 insulinomas greater than 1 cm in diameter with no false positives. Angiography was not performed in case 2. Transhepatic portography with venous sampling has a successful localization rate of 83.6% [3,11]. This technique was employed in the first patient of the present series and was negative. Intraoperative US has dramatically reduced the need for this procedure. MR imaging of the pancreas is technically difficult for several reasons including .motion artifacts, low SNR, and poor contrast between small neoplasms and normal pancreas. According to the few reports in the literature [4-81, insulinomas revealed a hypointense pattern with Tl-weighted images, although a higher signal intensity was achieved with TZweighted sequences (Figs. 1 and 2). In our group of patients, insulinomas 1 cm in diameter or larger were correctly
d
_f
Fig. 3. Case 7: False-positive localization of the inseulinoma in the pancreatic tail. A small hypoechoic lesion can be seen in the pancreatic tail (arrowheads) (a); CT scan reveals a small hump at the anterior profile of the pancreatic tail (white arrow) (b). Super selective injection of the splenic artery is inconclusive (arrowhead) c); MR scan is negative both on Tl-weighted (TR 400/TE 16) (d), and T2-weighted (TR 1800/TE 85) (c)images. Intraoperative sonogram shows a small lesion (f) that was resected with the tail ofthe pancreas. Pathologic study showed normal pancreas.
localized in 5 cases while arterial-CT and preoperative US localized the tumor in 6 cases. Furthermore, no false positives were obtained. In our opinion these results suggest a possible role for MR imaging in detecting insulinomas; however, further experience is needed for defining the specific MR features of this pathology and also for evaluating other acquisition sequences, such as gradient-echo images. Intraoperative US has improved surgical detection of insulinoma. In a recent series [ lo] all 29 insulinomas were identified by a combination of intraoperative US and palpation. In the present series only two small (0.2 and 0.7 cm) insulinomas were not found by these means. Both tumors were in the resected specimen, and the two patients were nonetheless cured. This failure of intraoperative US and palpation may be due to the fact that exploration of the pancreas left in place has been more accurate than that of the pancreas to be resected along with the detected tumor. Furthermore, a falsepositive localization in the tail of the pancreas suggested a wider left resection of the tail than previously planned
(from 2 to 6 cm). In fact in a case in which no tumor is found the only justification for limited resection would be to diagnose a nesidioblastosis in a young patient. Histologic examination of the resected specimen showed only normal pancreas and the patient was not cured. When a patient has clinical and biochemical evidence of insulinoma, preoperative US examination and, eventually, MR imaging may be the non-invasive techniques we need. The ability of intraoperative US and careful surgical exploration to resolve more than 90% of cases makes the use of additional, more invasive or expensive studies of questionable value. References Buchanan KD, Collins JSA, Varghese A, Johnston CF, Shaw C. Sandostatin and the Belfast experience. Digestion 1990; 45 (Suppl 1): 11-16. Ingemansson S, Lunderquist A, Lundquist I, Lovdal R, Tibblin S. Portal and pancreatic vein catheterization with radioimmu-
51
3
4
5
6
7
8
nologic determinationofinsulin. Surg Gynecol Obstet 1975; 141: 705-11. Pedrazzoli S, Pasquali C, Miotto D, Feltrin GP, Petrin P. Transhepatic portal sampling for preoperative localization of insulinomas. Surg Gynecol Obstet 1987; 165: 101-6. Stark DD, Moss AA, Goldberg HI, Davis PL, Federle MP. Magnetic resonance and CT of the normal and diseased pancreas: a comparative study. Radiology 984; 150: 153-62. Tscholakoff D, Hricak H, Thoeni R, Winkler ML, Margulis AR. MR imaging in the diagnosis of pancreatic disease. AJR 1987; 148: 703-9. McHenry C, Newell K, Chejfec G, Barbato A, Lawrence AM, Brooks M, Emanuele MA, Paloyan E. Adult nesidioblastosis: an unusual cause of fasting hypoglycemia. Am Surg 1989; 55: 366-9. Steiner E, Stark DD, Hahn PF, Saini S, Simeone JF, Mueller PR, Wittenberg J, Ferrucci JT. Imaging of pancreatic neoplasms: Comparison of MR and CT. AJR 1989; 152: 487-91. Mallek R, Mostbeck G, Walter RM, Herold CH, Imhof H, Tscholakoff D. Contrast MRI in multiple endocrine neoplasia type 1 (MEN) associated with renal cell carcinoma. Eur J Radio1 1990; 10: 105-8.
9 Galiber AK, Reading CC, Charboneau JW, Sheedy PF II, James EM, Gorman B, Grant CS, Van Heerden JA, Telander RL. Localisation of pancreatic insulinoma: comparison of pre and intraoperative US with CT and angiography. Radiology 1988; 166: 405-8. 10 Grant CS, Van Heerden J, Charboneau JW, James EM, Reading CC. Insulinoma: the value of intraoperative uhrasonography. Arch Surg 1988, 123: 843-8. 11 Passariello R, Feltrin GP, Miotto D, Pedrazzoli S, Rossi P, Simonetti G. Transhepatic portal catheterization with pancreatic venous sampling versus angiography in the localization of pancreatic functioning tumors. Frontiers Eur Radio1 1982; 1: 51-69. 12 Shawker TH, Doppman JL, Dunnick NR, McCarthy DM. Ultrasonic investigation of pancreatic islet cell tumors. J Ultrasound Med 1982; 1: 193-200. 13 Norton JA, Cromack DT, Shawker TH, Doppman JL, Comi R, Gorden P, Maton N, Gardner JD, Jensen RT. Intraoperative ultrasonographic localization of islet ceil tumors: a prospective comparison to palpation. Ann Surg 1988; 207: 160-8.
46
EURRAD
1992 Elsevier Science Publishers
B.V. All rights reserved. 0720-048X/92/$05.00
00218
MRI in insulinomas: preliminary findings Guido Liessi
‘,
Claudio Pasquali 2, Alfonso Alfano D’Andrea2, Pedrazzoli *
Cesare Scandellari 3, Sergio
‘Servizio di Radiologia, Ospedale Civile, Castelfranco Veneto, TV, and 21stituto di Clinica Chirurgica, I Cattedra di: Patologia Speciale Chirurgica and ‘Istituto di Semeiotica Medica, Cattedra di Medicina Intema
(Received
Key words: Magnetic resonance
V, Padova. Italy
1 May 1991; accepted after revision 15 July 1991)
imaging, insulinoma;
Magnetic resonance
imaging, pancreas;
Pancreas,
neoplasm;
Pancreas,
MRI
Abstract After establishing the diagnosis of an insulinoma, most surgeons prefer preoperative localization. Selective arteriography is usually considered the gold standard for this purpose. Recently, computed tomography (CT) and preoperative US have contended the role to angiography. MRI has been used in few cases of endocrine pancreatic tumors, and its role in this particular field has to be defined. Between November 1988 and September 1990 we evaluated 7 adult patients who had had surgery in our Surgical Department. Eight tumors were resected in 6 patients who were cured; in an l&year-old woman surgical treatment was unsuccessful. Arteriography, CT, preoperative US, MRI and intraoperative US detected 2,6,6,5 and 6 tumors, respectively. Two insulinomas (0.2 and 0.7 cm) were found at histologic examination in resected specimen. The ability ofintraoperative US and careful surgical exploration to resolve more than 90% of cases makes the preoperative use of arteriography and CT of questionable value. If further experience confirms these findings, US and MRI may sufftce.
Introduction The insulinoma is the most common islet-cell neoplasm of the pancreas [ 11. Insulin secretion may produce severe symptoms that lead to an early detection of the disease. Despite the use of several available imaging techniques, the precise localization of an insulinoma inside the pancreatic parenchyma is sometimes very difficult because lesions may be multiple and are usually very small. Once the diagnosis has been made on the basis of the characteristic clinical symptoms and glucose/insulin ratio, an accurate localization is accomplished by radiologic techniques such as CT scan, US scan, arteriography and, if needed, venography and transhepatic venous sampling [ 2,3]. Recently, the ability of MR to evaluate pancreatic diseases has been stressed by some, but few reports are present in the literature [4-81.
Address for reprints: Prof. Sergio Pedrazzoli, Via Giustiniani 2, 35128, Padova, Italy.
Clinica Chirurgica I,
MR detection of insulinomas are seldom represented by typical signs and the characteristic signal intensities have not been investigated in any detail. We describe six patients with histologically proven pancreatic insulinoma and one patient with hyperinsulinemia whose symptoms remained unchanged after resection of the pancreatic tail. These patients were preoperatively evaluated with US, arterial CT, and MR imaging. Intraoperative US was also performed. In this study MR imaging was employed to detect insulinomas, and the results were compared with those obtained by other imaging techniques and with the surgical findings. In addition, we examined the most characteristic findings of this neoplasm on Tl- and T2-weighted images. Materials and Methods Between November 1988 and September 1990, we evaluated 7 patients with clinical and biochemical evidence of pancreatic insulinoma. Five patients were males and 2 were females ; age range: from 18 to 75 years. All patients had biochemical and clinical findings typical for insulin hyperproduction syndrome.
Results
All patients were studied with US, arteriography, arterial CT, MRI and intra-operative US (Table 1) Preoperative US scans were performed with a realtime apparatus (GE RT 3600 and Platinum Philips) using mechanical and phased-array 3.5 and 5 MHz probes. Angiographic procedures were performed by catheterization of the celiac axis and the mesenteric artery with superselective injection in the splenic and gastroduodenal arteries using digital techniques (DVI 2 Philips). After angiography, the patients were examined on a CT scanner (GE 9800). Scans were obtained through the upper abdomen at 5 mm intervals without injection of contrast medium; afterwards, additional scans of the pancreatic area were performed during injection of lOO- 150 ml of non-ionic contrast medium in small multiple boli through the catheter placed in the celiac axis. MR imaging was performed on a Fonar B-3000 Machine operating at a 0.3 T resistive magnet. Images were obtained with a spin-echo sequence with the Tlweighted (TR 390/TE 16) and TZweighted (TR 2000-2200/TE 85-l 10). Four to six NEX were used for T l-weighted images and two NEX for T2-weighted, using circular surface coils of various diameter. Motion artifacts were reduced by compression belt and by injection of 4 ml Buscopan. A section thickness of 8 mm with a. .3 mm gap between the sections and a matrix of 256 x 256 pixels were used. Intraoperative US scans (IOUS) were performed with a real-time apparatus (GE RT 3600 Philips and Toshiba, SAL 32B) using 5 and 7.5 MHz probes. A prospective examination of the images was performed by two skilled radiologists who were unaware of the findings of the other tests.
TABLE
Results of preoperative and intraoperative imaging are summarized in Table 1. In 6 of 7 patients preoperative US examinations showed a round, sharp lesion that was always hypoechoic (Figs. l-3). In 3 obese patients the examination, although very difTicult, was positive. Angiography was performed by means of a digital technique. Subselective injection of the contrast medium revealed a hypervascular lesion in cases 5 (Fig. 1) and 6. Angiography was not performed in case 2. A hyperdense lesion in the pancreatic parenchyma (Figs. 1 and 2) was demonstrated in 6 patients by arterial CT. MR examinations revealed the insulinoma in 5 patients, showing a hypointense lesion on Tl-weighted images and hyperintense pattern on TZweighted sequences. In one patient (case 7) the tumor was not discovered even during surgical exploration, while in patient 2 the MR was positive although the images were partially obscured by several motion artifacts.. In one case (case 1) transhepatic venography and venous sampling were performed and were negative. All patients underwent surgery and the tumor was felt in 6 of 7 cases. Intraoperative US was also performed and in each case showed a single hypo-echoic mass, largely corresponding in size and location to the preoperative images. Six were true positives, and one was false positive (Fig. 3). The size of neoplasms detected by intraoperative US ranged from 1.2 to 2.1 cm. In two patients local excision of the tumor was performed. All but one of the others had a left pancreatectomy with preservaton of the spleen.
1
Preoperative
location and surgical treatment
of seven insulinomas
Patient No.
US
CT
MRI
ART
IOUS
Surgical procedure
Pathological analysis
Follow-up
1 2 3
+ + +
+ + +
+ + FN
FN NP FN
+ + +
Enucl. LP LP
cured 2 years cured 2 years cured 2 years
4 5 6
+ + +
+ + +
+ + +
FN + +
+ + +
LP Enucl. LP
1
FP
FP
-
-
FP
LP
2cmI 1.2 cm I 1.2 cm I 0.2 cm I 1.5 cm I 1.4 cm I 2.1 cm I 0.7 cm I Normal
Abbreviations: I, insulinoma; LP, left pancreatectomy; WP, not performed; ART, arteriography; true-positive; - , true-negative; FP, false-positive; FN, false-negative; Enucl., enucleation.
IOUS, intraoperative
cured 2 years cured 2 years cured 6 months unchanged ultrasonography;
+,
48
Fig. 1. Case 5, Insulinoma of the pancreatic body 1.4 cm in diameter. The neoplasm is hypoechoic (arrowheads) hyperdense on arterial CT (b). Superselective injection of the splenic artery shows the hypervascular insulinoma at pancreatic body(c). MR scan reveals a hypo-intense (arrowheads) lesion on Tl-weighted (TR 390/TE 16) images (d) and pattern (arrowheads) on TZ-weighted images (TR 2000/TE 85); the mass is aho depicted by means of ‘chemical
In 6 of 7 patients the insulinoma was histologically confirmed. Moreover, histologic examination of the specimen revealed 2 cases of multiple insulinoma (cases 3 and 6). Both of the second insulinomas were located in the tail of the pancreas and measured 0.2 and 0.7 cm in diameter. In both cases the second insulinoma was an incidental finding which had not been suspected or localized by preoperative or intraoperative imaging, nor felt by the surgeon. The site and diameter of the tumors felt and resected largely corresponded to the images produced by various localizing procedures. In case 7, where apparently a lesion was seen, the segment of the pancreas containing the suspected area was removed. Sonography of the resected specimen confirmed the same area, while a further intraoperative ultrasonography showed only
on sonogram (a) and the upper edge of the a relative hyperintense shift’ artifact (e).
normal pancreas tissue. Pathologic study of the resected specimen showed a normal pancreas. All patients but one, in whom no insulinoma was found after resection of the pancreatic tail, were normoglycaemic after surgery. They are in good health and can be considered cured, Discussion Hyperinsulinism-related syndrome is an endocrine disease due, in most cases, to a surgically resectable islet-cell adenoma. The diagnosis is established by clinical findings and laboratory data. Prompt localization of the tumor is mandatory and requires radiological and, eventually, interventive radiological procedures.
kg. 2. Case 4: Insulinoma of the pancreatic 1.5 cm in diameter: a hypoechoic pattern (Towheads) (a) and a hyperdense small mass on arterial CT can be seen (white arrows) (b); digital celiac angiography was unable to demonstrate the lesion (c). MR scan at the anterior edge of the pancreatic body shows a small mass with low signal on Tl-weighted (TR 390jTE 16) images (arrowheads)(d) and relatively intense (arrow-heads) on TZ-weighted sequences (TR 2000/TE 110) (e). Intraoperative sonogram shows the lesion (arrow-heads) (f).
Good results from preoperative radiologic localization of insulinoma have been reported [ 9,101. Currently, angiography and CT are the procedures of choice [ 9- IO]. Transhepatic venography with venous sampling [ 2,3,11], are seldom required for a correct localization of the insulinoma inside the pancreatic parenchyma. US is widely available, and islet-cell tumors usually appear as a well-defined round or oval mass which is generally hypoechoic. The rates of successful detection of insulinoma reported in the literature, range between 30%, for early studies primarily done with static scanners [ 121, and approximately 60% [9,10] using real-time US equipment. In this study we found all 6 tumors were greater than 1 cm in diameter. Two small insulinomas (0.7 and 0.2 cm) escaped detection, and a false-positive result was obtained in case 7 (Fig. 3). No hypodense pattern was observed in our experience. Detection rates of insulinomas by CT are also variable (40 - 60%) [ 91, and the proper protocol for scanning is controversial. Repeated scans could be performed after intravenous or intraarterial injection of contrast medium. The characteristic feature of islet-cell
tumor is a circumscribed enhancement in the pancreatic parenchyma. Angiography has been the most commonly used imaging method for the evaluation of insulinoma. Successful localization rates are reported to range between 29% and 90% [9]. In the present series angiography detected only 2 of the 5 insulinomas greater than 1 cm in diameter with no false positives. Angiography was not performed in case 2. Transhepatic portography with venous sampling has a successful localization rate of 83.6% [3,11]. This technique was employed in the first patient of the present series and was negative. Intraoperative US has dramatically reduced the need for this procedure. MR imaging of the pancreas is technically difficult for several reasons including .motion artifacts, low SNR, and poor contrast between small neoplasms and normal pancreas. According to the few reports in the literature [4-81, insulinomas revealed a hypointense pattern with Tl-weighted images, although a higher signal intensity was achieved with TZweighted sequences (Figs. 1 and 2). In our group of patients, insulinomas 1 cm in diameter or larger were correctly
d
_f
Fig. 3. Case 7: False-positive localization of the inseulinoma in the pancreatic tail. A small hypoechoic lesion can be seen in the pancreatic tail (arrowheads) (a); CT scan reveals a small hump at the anterior profile of the pancreatic tail (white arrow) (b). Super selective injection of the splenic artery is inconclusive (arrowhead) c); MR scan is negative both on Tl-weighted (TR 400/TE 16) (d), and T2-weighted (TR 1800/TE 85) (c)images. Intraoperative sonogram shows a small lesion (f) that was resected with the tail ofthe pancreas. Pathologic study showed normal pancreas.
localized in 5 cases while arterial-CT and preoperative US localized the tumor in 6 cases. Furthermore, no false positives were obtained. In our opinion these results suggest a possible role for MR imaging in detecting insulinomas; however, further experience is needed for defining the specific MR features of this pathology and also for evaluating other acquisition sequences, such as gradient-echo images. Intraoperative US has improved surgical detection of insulinoma. In a recent series [ lo] all 29 insulinomas were identified by a combination of intraoperative US and palpation. In the present series only two small (0.2 and 0.7 cm) insulinomas were not found by these means. Both tumors were in the resected specimen, and the two patients were nonetheless cured. This failure of intraoperative US and palpation may be due to the fact that exploration of the pancreas left in place has been more accurate than that of the pancreas to be resected along with the detected tumor. Furthermore, a falsepositive localization in the tail of the pancreas suggested a wider left resection of the tail than previously planned
(from 2 to 6 cm). In fact in a case in which no tumor is found the only justification for limited resection would be to diagnose a nesidioblastosis in a young patient. Histologic examination of the resected specimen showed only normal pancreas and the patient was not cured. When a patient has clinical and biochemical evidence of insulinoma, preoperative US examination and, eventually, MR imaging may be the non-invasive techniques we need. The ability of intraoperative US and careful surgical exploration to resolve more than 90% of cases makes the use of additional, more invasive or expensive studies of questionable value. References Buchanan KD, Collins JSA, Varghese A, Johnston CF, Shaw C. Sandostatin and the Belfast experience. Digestion 1990; 45 (Suppl 1): 11-16. Ingemansson S, Lunderquist A, Lundquist I, Lovdal R, Tibblin S. Portal and pancreatic vein catheterization with radioimmu-
51
3
4
5
6
7
8
nologic determinationofinsulin. Surg Gynecol Obstet 1975; 141: 705-11. Pedrazzoli S, Pasquali C, Miotto D, Feltrin GP, Petrin P. Transhepatic portal sampling for preoperative localization of insulinomas. Surg Gynecol Obstet 1987; 165: 101-6. Stark DD, Moss AA, Goldberg HI, Davis PL, Federle MP. Magnetic resonance and CT of the normal and diseased pancreas: a comparative study. Radiology 984; 150: 153-62. Tscholakoff D, Hricak H, Thoeni R, Winkler ML, Margulis AR. MR imaging in the diagnosis of pancreatic disease. AJR 1987; 148: 703-9. McHenry C, Newell K, Chejfec G, Barbato A, Lawrence AM, Brooks M, Emanuele MA, Paloyan E. Adult nesidioblastosis: an unusual cause of fasting hypoglycemia. Am Surg 1989; 55: 366-9. Steiner E, Stark DD, Hahn PF, Saini S, Simeone JF, Mueller PR, Wittenberg J, Ferrucci JT. Imaging of pancreatic neoplasms: Comparison of MR and CT. AJR 1989; 152: 487-91. Mallek R, Mostbeck G, Walter RM, Herold CH, Imhof H, Tscholakoff D. Contrast MRI in multiple endocrine neoplasia type 1 (MEN) associated with renal cell carcinoma. Eur J Radio1 1990; 10: 105-8.
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