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Image of the Month—Diagnosis
Arch Surg. 2005;140:612.
Answer: A Second Insulinoma
To establish a definitive diagnosis of insulinoma, the following 4 criteria must be met: (1) neuroglycopenic symptoms with a documented blood glucose level less than or equal to 45 mg/dL and relief of the patient’s symptoms with glucose administration, (2) concomitant inappropriately elevated insulin levels ( 6 µIU/mL by radioimmunoassay or 3 µIU/mL by immunochemiluminescent assay), (3) elevated C-peptide levels (0.2 nmol/L), and (4) absence of sulfonylurea in the plasma.1-2 Laboratory values in our patient effectively ruled out Munchausen syndrome because of a negative sulfonylurea screen and an appropriately elevated C-peptide value. Therefore, endogenous causes for recurrent hypoglycemia were sought.
Data from our institution indicate that 3% (6/185) of patients with sporadic insulinoma have multiple tumors.3-4 Transabdominal ultrasound was repeated but failed to detect any abnormality within the gland. An ultrasound is our initial preoperative test of choice for the identification of insulinoma because it has a sensitivity approaching 65% and a positive predictive value of 90%, however this test is highly operator dependent and potentially limited by the patient’s body habitus. Based on the recommendation from our radiology colleagues, a pancreas protocol computed tomography study was obtained on a research 64-slice multidetector scanner (Siemens Medical Solutions, Malvern, Pa). Coronal and sagittal reconstructions of the pancreas revealed a 1.2-cm lesion consistent with an islet cell tumor (Figure 2). This tumor had been obscured on prior computed tomography scans owing to its adjacency to the splenic vessels. The patient returned to the operating room for enucleation of a 1-cm insulinoma and recovered without complication. Her postoperative blood glucose levels remained greater than 100 mg/dL.
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Figure 2. Sagittal reconstruction of the pancreas demonstrating a 1.2-cm hypervascular mass that is distorting the splenic artery consistent with a second islet cell tumor. Images were obtained on a 64-slice multidetector computed tomography scanner at a thickness of 1.5 cm utilizing intravenous contrast during arterial, venous, and delayed phases.
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Preoperative localization of an insulinoma continues to evolve with new technology. Transabdominal ultrasound was our first test of choice because of the expertise of our radiologists, however, the sensitivity of endoscopic ultrasound has been reported as high as 70% to 90%.5 Angiography had been the gold standard for localization of insulinoma owing to the vascular nature of the tumor, but because of the invasiveness of this procedure, it has been reserved as the second test of choice. Spiral computed tomography and magnetic resonance imaging have historically had poor sensitivity for the detection of insulinoma. Recent technologic advances in hardware, such as the 64-slice multidetector, have improved the spacial resolution of these tests and allowed image reconstruction, which may improve their sensitivity.
Noninsulinoma pancreatogenous hypoglycemia syndrome is a rare clinical entity characterized by endogenous hyperinsulinemic hypoglycemia following ingestion of a meal. Pathologically, islet cell hypertrophy and nesidioblastosis were found. This entity has been identified in conjunction with documented insulinoma, however, this combination is extraordinarily rare.6
AUTHOR INFORMATION
Correspondence: Clive S. Grant, MD, Department of Surgery, Mayo Clinic, 200 First St SW, Rochester, MN 55905 (cgrant{at}mayo.edu).
Accepted for Publication: December 8, 2004.
Previous Presentation: This study was presented in part at the International Association of Endocrine Surgeons; June 15, 2004; Uppsala, Sweden.
REFERENCES
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1. Grant CS. Surgical aspects of hyperinsulinemic hypoglycemia. Endocrinol Metab Clin North Am. 1999;28:533-554.
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2. Service FJ. Classification of hypoglycemic disorders. Endocrinol Metab Clin North Am. 1999;28:501-517.
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3. Thompson GB, Service FJ, van Heerden JA, et al. Reoperative insulinomas, 1927 to 1992: an institutional experience. Surgery. 1993;114:1196-1206.
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4. Service FJ, McMahon MM, O’Brien PC, Ballard DJ. Functioning insulinoma-incidence, recurrence, and long-term survival of patients: a 60-year study. Mayo Clin Proc. 1991;66:711-719.
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5. Thompson NW, Czako PF, Fritts LL, et al. Role of endoscopic ultrasonography in the localization of insulinomas and gastrinomas. Surgery. 1994;116:1131-1138.
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6. Service FJ, Natt N, Thompson GB, et al. Noninsulinoma pancreatogenous hypoglycemia: a novel syndrome of hyperinsulinemic hypoglycemia in adults independent of mutations in Kir6.2 and SUR1 genes. J Clin Endocrinol Metab. 1999;84:1582-1589.
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SECTION EDITOR: GRACE S. ROZYCKI, MD
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