Non-hyperfunctioning pancreatic endocrine tumors: multimodality imaging features with histopathological correlation.

PURPOSE

To evaluate the multimodality imaging features of non-hyperfunctioning pancreatic endocrine tumors (NF-PNET) with histopathological correlation.

METHODS

Preoperative imaging (CT: n = 23; MRI: n = 14; (111)In-octreotide: n = 8) of 28 patients (17 female; mean age 55 years) with resected NF-PNET were evaluated for tumor location, size, morphology, attenuation/signal intensity, (111)In-octreotide uptake, cystic degeneration, and enhancement. Tissue specimens were assessed for the extent of stromal fibrosis, vascular density, presence of a fibrous pseudocapsule, and tumor grading. Correlation between imaging and histopathology was made using the Fisher-Freeman-Halton exact test.

RESULTS

NF-PNET arose from the pancreatic head/neck (n = 10), body (n = 7), and tail (n = 11). On CT, NF-PNET (mean largest diameter: 4.4 cm) appeared predominantly solid (69.6%), well defined (91.3%), and oval (47.8%) in shape. In the late arterial phase, NF-PNET appeared mainly hypovascular (55.5%). Septations (30.4%) and calcifications (21.7%) were relatively uncommon. On MRI, NF-PNET (mean size: 2.6 cm) appeared most commonly as solid (57.1%), encapsulated (71.4%), oval (64.2%) lesions that were hyperintense on T2-WI (64.3%), and hypo- or isovascular to pancreas (66.7%) during the late arterial phase. Cystic NF-PNET (3.8 cm) were not significantly larger than solid (3.5 cm) NF-PNET (CT, p = 0.758; MRI, p = 0.451). (111)In-octreotide uptake was demonstrated in 5/8 (62.5%) patients. At histopathology, NF-PNET were predominantly encapsulated (69.2%); stromal fibrosis comprised <33% of the tumor (69.2%), and vascular density was average (46.1%). A significant association was demonstrated between the degree of fibrosis and hypointensity on T2-WI (p = 0.003). Vascular density, tumor grade, and degree of fibrosis did not significantly relate to the pattern of enhancement.

CONCLUSIONS

NF-PNETs have variable imaging appearances but are most commonly oval shaped, solid, and well-defined/encapsulated masses, and hypovascular on late arterial and portal venous phase. Cystic degeneration in NF-PNET appears independent of tumor size. Low signal intensity on T2-WI correlates with extensive intratumoral fibrosis.