Somatostatin receptor scintigraphy in gastrinomas.

Recent studies report that the radiolabelled synthetic somatostatin analogue, [111In-DTPA-DPhe1]octreotide, is useful for imaging carcinoid tumours and pancreatic endocrine tumours. At present, it is unclear whether this method is superior to conventional imaging studies (computed tomography, magnetic resonance imaging, ultrasound, angiography) and what its role should be, if any, in the management of these patients. The aim of this paper is to review five recent studies performed at the National Institutes of Health in patients with Zollinger-Ellison syndrome to define the role of somatostatin receptor scintigraphy. Patients were from a tertiary referral centre, all had Zollinger-Ellison syndrome. In Study n. 1: the sensitivity of somatostatin receptor scintigraphy was assessed compared to conventional studies in 80 patients. Study n. 2: the effect of somatostatin receptor scintigraphy on management was determined in 122 patients. Study n. 3: ability of somatostatin receptor scintigraphy and other conventional methods to distinguish small hepatic metastases (< 2 cm) from hepatic haemangiomas was assessed in 29 patients. Study n. 4: somatostatin receptor scintigraphy, magnetic resonance imaging and bone scanning were compared in 115 consecutive patients to detect bone metastases. Study n. 5: ability of somatostatin receptor scintigraphy to detect gastrinomas found at surgery in 35 patients and its effect on cure rate and determinants of detection of gastrinomas by somatostatin receptor scintigraphy were analysed. Briefly, results showed: Study n. 1: somatostatin receptor scintigraphy is the most sensitive modality for detection of primary or metastatic gastrinomas; Study n. 2: somatostatin receptor scintigraphy changes management in 47% of cases; Study n. 3: somatostatin receptor scintigraphy is the only method to distinguish small liver metastases from small haemangiomas; Study n. 4: somatostatin receptor scintigraphy and magnetic resonance imaging have higher sensitivity and predictive values for bone metastases than bone scanning; Study n. 5: somatostatin receptor scintigraphy misses 33% of gastrinomas found at surgery, primarily small duodenal tumours. Size is the important factor. The use of somatostatin receptor scintigraphy does not increase cure rate. In conclusion, Somatostatin receptor scintigraphy is now the imaging method of choice in patients with Zollinger-Ellison syndrome for preoperative primary tumour localization, detection of bone or liver metastases, and to distinguish small liver metastases from small hepatic haemangiomas. Its specificity appears to be high but has been poorly studied as has the use of it in combination with endoscopic ultrasound. Studies by others suggest these recommendations will apply to carcinoid tumours and other pancreatic endocrine tumours except insulinomas.