Usefulness of computed tomography during arteriography in a selective arterial calcium agent injection test for pancreatic gastrinoma: a case description.

Abstract

Pancreatic gastrinoma is a rare pancreatic neuroendocrine tumor with an incidence of about 0.5–21.5 cases per million people worldwide. The most common sites are the duodenum (75%), pancreas (20%), and other organs (5%). Gastrinomas are malignant in about 60–90% of cases (1-5). Malignant gastrinomas originating beneath the duodenal mucosa often metastasize to the liver, even if the tumor diameter is ≤1 cm. Therefore, in patients with gastrinoma and Zollinger–Ellison syndrome, it is important to determine the number and site(s) of gastrinoma(s), as well as the presence or absence of liver metastases. However, the detection sensitivity of computed tomography (CT) and magnetic resonance imaging is about 10–50%, that of angiography is 20–50%, and that of somatostatin receptor scintigraphy is 30–70%. Tumor size is strongly correlated with the detection sensitivity of any examination modality, and tumors of <1 cm in diameter are often difficult to detect (1,2). Therefore, the selective arterial calcium agent injection (SACI) test was developed as an effective method to detect small gastrinomas (2,6,7). In the SACI test, calcium gluconate is injected via a microcatheter into selected arterial branches to stimulate gastrin secretion from the gastrinoma located in the corresponding arterial territory. Generally, calcium gluconate is selectively injected into the gastroduodenal artery (GDA), superior mesenteric artery (SMA), distal or proximal portion of the splenic artery (distal SpA, proximal SpA), and the proper hepatic artery (PHA). The subsequent increase in the serum gastrin level is monitored using blood samples taken from the hepatic vein before and at 30, 60, 90, and 120 s after the injection. The location of the gastrinoma is determined based on a significant increase in serum gastrin levels in response to calcium gluconate (maximum serum gastrin level after calcium injection/serum gastrin level before calcium agent injection; with a median change of about 4.21 times baseline) (8). However, there are two limitations of the SACI test. First, the distribution of calcium varies between individual patients due to anatomical differences in the pancreatic arterial branches and the arterial territories. Second, there are many false positives following the injection of calcium gluconate into the GDA (median change of 4.15 times the baseline value) because calcium gluconate may stimulate normal gastrin-secreting cells in the gastric prepylorus and duodenal bulbus (8,9). It is possible to visualize the distribution of calcium following its injection by performing CT during arteriography (CTA). Here, we report a case in which the SACI test was combined with CTA for the diagnosis of a gastrinoma located in the pancreatic head and to exclude the presence of liver metastases.