Insulinoma localisation

- imaging techniques -

The necessity of preoperative insulinoma localisation after being biochemically proven has remained contradictory, even among experts in the field. Each new developement of imaging tewchnology has resulted in new investigations in order to detect insulinomas according to sensitivity and specificity of the procedure..

Internists and endocrinologists sometimes may face diagnostic uncertainties, radiologists claim the advantage of technical resolution capabilities, endocrine surgeons claim the strategy of exact localisation during surgery and in addition rely upon available intraoperative ultrasound. Diagnostic uncertainties only depend upon the quality and exactly controlled procedure ot the fasting test and its skilled and correct interpretation. Concern about quality control routine of the endocrine lab has to be taken into account.

Ref.: 1. Starke AAR, Frilling A, Becker H, et al. Are CAT-scans necessary for preoperative localization of insulinomas ? Eur J Med 1: 411-413, 199 2. Schumacher B, Lübke HJ, Frieling T, Strohmeyer G, Starke AAR. Prospective study on the detection of insulinomas by endoscopic ultrasonography. Endoscopy 28, 273-276, 1996 3. Röher HD, Simon D, Starke A, Goretzki PE. Special diagnostic and therapeutic aspects of insulinoma. Chirurg 68(2), 116-121, 1997 4. Simon D, Starke A, Goretzki PE, Röher HD. Reoperative surgery for organic hyperinsulinism: indications and operative strategy. World J Surg 22, 666-672, 1998

For more than 15 years we did not perform imaging procedures as a clinical routine in patients without earlier abdominal surgery and in whom the endocrine diagnosis of endogenous hyperinsulinism resp. insulinoma was definite. During the years the detection ratio of the endocrine surgeon remained at 100 %. Due to minor disturbance of the patient and its low cost we only would perform endoscopic endosonography. The use of CAT scans and NMR technique are helpful and remain the procedure of choice in cases of liver metastases being seen in cases of malignant insulinoma. Therapeutic options and consequences as such may appropriately be streamlined. In patients who have had abdominal surgery before, especially after a formerly unsuccessful search for an insulinoma, imaging procedures may be helpful in certain cases. Abdominal ultrasound, ordered to exclude or detect liver metastases before surgery, is always justified. Regular ultrasound investigation of the pancreas is rarely helpful in the localisation of an insulinoma. Octreotide scintigraphy (Octreoscan™, somatostatin-receptor-imaging - SRI) does not have an established role in the localisation of insulinoma in contrast to other neuroendocrine GEP-tumors. Insulinomas often do not express somatostatin receptors, specifically not the subtype 2 (sstr2), which is expressed in most neuroendocrine tumors (NET) of the pancreas. Intraarterial pancreatic calcium stimulation (SIPS = "selective intraarterial pancreatic stimulation") of relevant pancreatic arteries during angiography in addition to evaluation of an insulin concentration gradient from venous blood in the hepatic veins is invasive and only allows crude regionalisation. Its role or need in the localisation of insulinomas is controversial and disputed. The same is true for the even more invasive technique of transhepatic portal venous sampling (THPVS) involving transhepatic catheterisation of various tributaries.

Performance of mere imaging procedures, such as:   do not allow proof or exclusion of an insulinoma of the pancreas. Only proof or exclusion of a biochemical perturbation of insulin secretion does allow the correct diagnosis.

abdominal ultrasound endoscopic endosonography computed tomography (CAT-scan nuclear magnetic resonance tomography (NMR) arterial angiography, sometimes combined with arterial calcium provocation (SIPS) somatostatin receptor szintigraphy (octreotide scan)