Prospective comparative study of ability of MR imaging and other imaging modalities to localize tumors in patients with Zollinger-Ellison syndrome

Abstract

The role of magnetic resonance (MR) imaging in patients with pancreatic endocrine tumors such as Zollinger-Ellison syndrome (ZES) is controversial. In the present study we have examined the ability of current MR imaging compared with other imaging modalities, to localize gastrinomas in 43 patients with ZES. All results were subsequently assessed at exploratory laparotomy (N = 34) or by liver biopsy (N = 9). For the 18 patients with metastatic gastrinoma in the liver, MR imaging had a sensitivity of 83%, ultrasound 50%, CT 56%, and angiography 61%. The combination of MR imaging, ultrasound, and CT were the same as MR imaging alone. For MR imaging, both T1 and STIR sequences had equal sensitivity, although tumors were more easily seen with STIR sequences. Specificity of MR imaging was slightly lower (88%) than the other modalities (96-100%) because MR imaging incorrectly identified small hemangiomas as possible tumors in four patients. MR imaging was better than CT in identifying metastatic lesions in the liver. For the localization of primary gastrinoma, assessed in 32 patients, MR imaging had a sensitivity of 25%, ultrasound 19%, CT 28%, all three together 38%, and angiography 59%. Localization of metastatic gastrinoma in the liver or primary gastrinomas in 16 patients was assessed before and after gadolinium-DTPA (0.1 mmol/kg). The sensitivity and specificity of MR imaging was unchanged but bolus injection and rapid MR acquisition techniques were not used. These results indicate that recent advances in MR imaging have greatly improved its sensitivity for the detection and assessment of the extent of metastatic gastrinoma. MR imaging is now the imaging study of choice to assess metastatic pancreatic endocrine tumors in the liver. In contrast, the detection of primary tumors by MR imaging has not improved; therefore, angiography remains the study of choice.

Fig 1.

Comparison of the ability of CT and MR imaging to demonstrate hepatic metastases. CT scan (top panel) of the inferior right hepatic lobe on a bolus-enhanced dynamic scan shows no hepatic lesion. By comparison, the T1 sequence MR imaging (middle panel) shows multiple low-signal-intensity foci within the liver that cannot be distinguished from vessels. The STIR sequence MR imaging (bottom panel) shows multiple foci of high signal intensity (the largest two lesions identified by arrows). Exploratory laparotomy demonstrated multiple small (<1 cm) metastatic gastrinomas throughout both the right and left hepatic lobes.

Fig 2.

Comparison of CT and MR imaging in a patient with multiple hepatic metastases. The top panel shows a CT with one clearly distinguishable hypodense area (arrow) and one other questionable focus that cannot be distinguished from the hepatic vein. The lower panel is a STIR sequence MR image at the same level of the liver unequivocally showing three hyperintense lesions (T = tumor) confirmed by biopsy to be metastatic gastrinomas.

Fig 3.

Comparison of CT and MR imaging. Bolus-enhanced dynamic CT (top panel) demonstrates suspicious low-density areas (arrows) in the posterior segment of the right lobe and the medial segment of the left lobe. STIR sequences (bottom panel) unequivocally demonstrate a small focus of high signal intensity compatible with metastatic gastrinoma (T). Biopsy of this lesion confirmed the lesion to be gastrinoma. On the T1-weighted image (middle panel) it was difficult to distinguish the tumor (T) from normal vasculature.

Fig 4.

MR imaging of a primary gastrinoma in the head of the pancreas. The two panels show MR imaging at the same level, demonstrating a primary gastrinoma (PRIM) that was later confirmed at surgery. The top panel is a T1-weighted MR image showing a hypointense lesion in the head of the pancreas (PRIM). The bottom panel shows the corresponding STIR MR image, demonstrating the hyperintense tumor in the pancreatic head (PRIM).