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Preoperative Localization of Insulinoma by Intra-arterial Spiral CT LI Li, WU P e i h o n g , Xie C h u a n m i a o , LIN H a o g a o , C H E N Lin Objective To evaluate the value of intra-arterial dynamic spiral CT on preoperative localization of insulinoma. Methods Two patients with insulinoma proved by operative pathology were preoperatively localized by intra-arterial dynamic spiral

CT. Results In intra-arterial spiral CT, two small insulinomas ( 1.5 - 2.0 cm in diameter) demonstrated as a significantly high dense nodule 20 s later after initiation of injection of contrast medium. The course of high density lasted nearly 4 min. Conclusion Intra-arterial dynamic spiral CT could clearly detect small insulinoma, and might be one of most effective preoperative localization methods for small insulinoma. Key words insulinoma; anteriography; CT

he precise preoperative localization of a suspected insulinoma remains a difficult clinical and radiographic problem. Since 1998, two patients with small insulinoma were detected by dynamic CT performed with an intra-arterial injection of contrast medium, and proved by operative pathology in our hospital. In this paper, we reported our preliminary experience and evaluated the effect of intra-arterial dynamic CT in preoperative localization of insulinomas.

T

trast medium administered before CT scanning was limited to 5 ml injected by hand to facilitate proper catheter placement. Dynamic scanning was performed on the head of pancreas with 2 . 7 mm thick slices and scanned with an interval of 30 s or 60 s, till 10 min later after initiation of injection of contrast medium.

Results Materials and methods Materials Case 1: A 30-year-old male patient complained of repeated spontaneous unconsciousness in period of fasting for 8 months. In the period of paroxysm, serum sugar level dropped significantly, with the lowest up to 0.8 mmol/L - 1.9 mmol/L. The symptoms relieved rapidly after administration of glucose. The patient was normal at interval of paroxysm. Case 2: A 37 year-old male patient had complained of spontaneous unconsciousness and convulsion seizure for nearly one year. In the period of paroxysm, serum sugar level dropped to 2 . 9 mmol/L. The symptoms relieved rapidly after administration of glucose and diet. Methods Intra-arterial CT examination was done with incremental scanning of pancreas performed in cranial-to-caudal direction with 2 . 7 mm collimation on bi-spiral CT scanner (Pick Corp. ). CT images were obtained 8 s later after the initiation of transcatheter (5-F) celiac artery injection of 20 ml of non-ionic contrast medium (Omnipaque, 180 mg I / m l ) . Contrast medium was injected at a rate of 2 . 5 ml/s with an automatic power injector ( Medrad, Pittsburgh). During the catheterization, conDiagnostic Imaging & Interventional Center, Cancer Center, Sun Yat-sen University, Guangzhou 510060, China Correspondence: WU Peihong, Diagnostic Imaging & Interventional Center, Cancer Center, Sun Yat-sen University, Guangzhou 510060, China Tel : 0086-20-87343270 ; Fax: 0086-20-87343392 ; Email : jrkzl@ gzsums. edu. cn

Findings on CT images Two insulinomas demonstrated as well-edged, high dense nodule. One located right side of head with a diameter of 2 . 0 cm, another located posterior to head with a diameter of 1.5 em. Two insulinomas were successfully removed during operation. Histological analysis showed two small islet cell neoplasm with intact capsules without infiltrating the normal surrounding pancreas. The serum glucose of both patients returned to normal and symptoms of hypoglycemia disappeared after surgery. Curve of time-density In dynamic CT scanning of the case one, 8 s later after initiation of injection of contrast medium, the normal pancreatic parenchyma enhanced significantly and reached CT attenuation of 600 Housfield unit ( H u ) . Then, the density of pancreas decreased rapidly, 20 s later dropped to 80 Hu and 10 min later to 50 Hu (Fig. 1). The insulinoma was enhanced to an attenuation of 500 H u - 550 Hu, and could not be distinguished from the normal pancreatic parenchyma on scan of 8 s. 20 s later, the density of insulinoma slightly decreased to an attenuation of 350 Hu as a high dense nodule. However, the density of head of pancreas rapidly dropped to 80 Hu (Fig. 4 ) . 60 s later, the density of insulinoma dropped to 200 Hu and 180 s later, the density remained 100 Hu (the normal pancreas dropped to 55 Hu, Fig. 3). 10 min after initiation of intra-arterial injection of contrast medium,

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T i m e - d ~ i t y curve 7O0 - lasulinoma ~.Normal pancreatic parenchyma

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Fig. 1 The Time-density curve of insulinoma and normal parenehyma

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Fig. 2 An 30 year-old male patient complained of repeated spontaneous unconsciousness in period of fasting for 8 months. ( a ) suspected nodule was demonstrated unclearly at the lateral of head of pancreas and could not be distinguished from duodenum (b) The insulinoma (white arrow) was not demonstrated clearly on venous phase enhanced CT image (c) Intra-arterial CT image acquired 20 s later after initiation of injection of contrast medium demonstrating an insulinoma as a high dense nodule (black arrow) (d) Three minutes later, the insulinoma still mnifests as a high dense nokule (white arrow)

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1

A 37 year-old male patient with a suspected insulinoma. (a) Arterial phase enhanced CT failed to detect the tumor (b) A small insulinomawas demonstratedbehind head of pancreases on intra-arterial enhanced CT image acquired 20 sec later after initiation of injection of contrast material (white arrow) Fig. 3

the density of the tumor dropped to 50 Hu, and was isodense to the normal pancreatic parenchyma. Another case demonstrated as a high dense nodule 20 s later after administration of contrast medium (Fig. 4 ) . 60 s later, it became slightly higher density than normal head of pancreas.

Discussion Insulinomas originates from [3 cell, usually has hypoglycemia and high serum insulin levels. Wipple' s triad, a set of clinical features that should suggest the diagnosis, is as follow: (~) spontaneous hypoglycemia; (~) repeated serum sugar level below 50 mg/dl; (~) relief of symptom by administration of glucose Ell . Although insulinoma has typical clinical features, the localization depends mainly on imaging methods. Because the insulinsecreting tumors are generally small (usually less than 2.0 cm in diameter) and have similar quality to normal pancreatic parenchyma, it is difficult for surgeons to palpate the tumors during operation. The precious preoperative localization is fundamental important, for the tumors are usually proved by consecutive histological slicing of resected pancreatic tissue, according to preoperative localization by imaging methods. Because of its similar quality to normal pancreatic parenchyma, the accuracy of conventional CT (contrast medium administrated intravenously) varies between 45% - 50% I1.21. Due to its hypervascularity, angiography was an effective method for localizing insulinoma with an accuracy of 62.8% [1] The typical angiographic finding is a vascular blush, beginning in arterial phase and persisting into the venous

phase. Some insulinomas are not visualized during arteriography because they are too small or obscured by surrounding structure. King et a l E3] suggested that dual phase spiral CT could improve the chance of detection of small insulinomas. However, both two insulinomas in our group were not clearly demonstrated on dual phase spiral CT. CT arterial portography (CTAP) and CT hepatic arteriography (CTHA) are one of the most sensitive methods of detecting hepatocellular carcinoma t4"sl . With the development of spiral CT technique, micro liver cancer with a diameter of less than 0.5 cm could also be detected by CTAP and CTHA Esl . By injecting contrast medium locally through the arteries supplied for the tumor, even small volume of contrast medium were used, the efficiency of enhancement in intra-arterial enhanced CT was greatly superior to that in intra-venous enhanced CT, and the noise of background in CT images was largely decreased. Intra-arterial enhanced CT might distinguish the nuance of enhancement of tumors from normal tissues. Ahlstsm et al E6] had reported their experience of intra-arterial dynamic CT in localization of insulinomas, and suggested insulinomas might be iso-density, low density, high density compared with normal pancreatic parenchyma. These signs probably related to different delayed time of scanning. Due to limit of non-spiral CT scanners and manual injection of contrast medium, the acquired CT images were not good enough for diagnosis in their studies, and the superiority of intra-arterial dynamic CT in localization of insulinomas was not proved in their studies. In our study, we acquired excellent CT images by using bi-spiral CT scanner ( Picker Corp. ) and an au-

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tomatic power injector (Medral, Pittsburgh). Two insulinomas were demonstrated clearly by dynamic intra-arterial spiral CT. According to our preliminary experiences of dynamic scanning, we suggested that somewhat delay scanning be needed for intra-arterial CT in detecting insulinomas. In our cases, the tumors were not detected 8 s later after initiation of injection of contrast medium through celiac artery because both insulinoma and normal pancreatic parenchyma were enhanced significantly (reached 500 - 6 0 0 Hu). However, 20 s later, the density of normal pancreatic parenchyma decreased rapidly to 80 Hu, and the lesion had a course of delayed dropping (20 s later, dropped to 350 Hu, 60 s later, to 200 H u ) , the tumor was demonstrated clearly as a high dense nodule. The course of delayed dropping lasted nearly 4 min. According to our experiences, we suggested that an insulinoma could be detected by intra-arterial CT was not because it was enhanced more than normal pancreatic parenchyma, but because it excreted contrast medium slower than the normal pancreatic parenchyma. In summary, our studies show that intra-arterial dy-

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namic spiral CT could clearly demonstrate small-insulinoma and its close anatomic relationship, and might be one of effective methods of preoperative localization of small insulinomas.

References 1

Haaga JR. Computed Tomography and Magnetic Resonance Imaging of the Whole Body. St. Louis: Missouri, 1994, 1037 - t130. 2 Zhao Y, Wang X, Yang B, et al. Pancreatic insulinomas: experience in 220 patients. Zhonghua Wal Ke Za Zhi, 2000, 38 : 10 - 13. 3 King AD, Ko GT, Yeung VT, et al. Dual phase spiral (IT in the detection of small insulinomas of the pancreas. Br J Radio, 1998, 71 : 20 23. 4 Li L, Wu PH, Lin HG, et al. Findings of non-pathologic perfusion defects by CT arterial portography and non-pathologic enhancement of CT hepatic arteriography. W J G , 1998, 4 : 513 - 515. 5 Li L, WuPH, MoYX, e t a l . CTarterialportography and CThepatic arteriography in detection of micro liver cancer. WJG, 1999, 5 : 2 2 5 227. 6 Ahlst~m H, Magnusson A, Grama D, et al. Preoperative localization of endocrine pancreatic tumors by intra-arterial dynamic computed tomography. Acta Radiol, 1990, 3 1 : 1 7 1 - 1 7 5 . ( Received 2002 - 07 - 29)