Neuroendocrine tumors of the pancreas: Spectrum of appearances on MRI

We reviewed our 8.5 year experience with magnetic resonance imaging (MRI) i n the demonstration of neuroendocrine tumors of the pancreas using precontr ast fat-suppressed T1-weighted, fat-suppressed T2-weighted, and serial post -gadolinium T1-weighted images, to describe the spectrum of appearances of these tumors. All MR examinations of patients with histogically proven neur oendocrine tumors were retrospectively reviewed, Histological type, tumor l ocation, tumor diameter, signal intensity on precontrast images, enhancemen t patterns, and presence and appearance of metastases were determined, Twen ty-two patients had histologically proved neuroendocrine tumors detected by MRI over the 8.5 year period, Histological types were gastrinoma (n = 8), insulinoma (n = 3), glucagonoma (n = 2), somatostatinoma (n = 1), VIPoma (n = 1), ACTHoma (n = 1), carcinoid (n = 1), and five untyped tumors. Primary tumors ranged in diameter from 1 to 6.2 cm. There was one histopathology-p roven false-positive neuroendocrine tumor, The positive predictive value fo r MRI in the detection of these tumors was 96%. The most common appearance on precontrast images was low signal intensity on T1-weighted images and hi gh signal intensity on T2-weighted images, which was observed in tumors in 18 of 22 patients. Moderate or intense early enhancement of all or portions of the primary tumors was observed in tumors in 19 of 22 patients either a s uniform homogeneous, ring, or diffuse heterogeneous enhancement, Enhancem ent was minimal on these images in the other three patients, Gastrinomas en hanced in a ring pattern in 7 of 8 patients whereas the majority (9 of 11 p atients) of noninsulinoma-nongastrinoma and untyped tumors enhanced in a di ffuse heterogeneous fashion, Liver metastases were present in 13/22 patient s including 3/8 with gastrinoma and 9/11 with noninsulinoma-nongastrinoma t umors, Most neuroendocrine tumors of the pancreas are low signal intensity on fat-suppressed T1-weighted images and moderately high in signal intensit y on fat-suppressed TP-weighted images, although variations do exist, Tumor s most often enhance in an early moderately intense fashion, Gastrinomas ar e often different in appearance than other neuoendocrine tumors in that the y usually enhance in a ring fashion whereas nongastrinoma-noninsulinoma tum ors usually enhance in a heterogeneous fashion. (C) 2000 Wiley-Liss, Inc.