Pancreatic neuroendocrine tumors containing areas of iso- or hypoattenuation in dynamic contrast-enhanced computed tomography: Spectrum of imaging findings and pathological grading

• Most iso/hypo-PNETs show a rapid enhancement pattern, as well as hyper-PNETs.
• Iso/hypo-PNETs show various radiological features compared to hyper-PNETs.
• Iso/hypo-PNETs show higher pathological grading than hyper-PNETs.

PurposeTo evaluate dynamic contrast-enhanced computed tomography (CT) features of pancreatic neuroendocrine tumors (PNETs) containing areas of iso- or hypoattenuation and the relationship with pathological grading.Materials and MethodsBetween June 2006 and March 2014, 61 PNETs in 58 consecutive patients (29 male, 29 female; median-age 55 years), which were surgically diagnosed, underwent preoperative dynamic contrast-enhanced CT. PNETs were classified based on contrast enhancement patterns in the pancreatic phase: iso/hypo-PNETs were defined as tumors containing areas of iso- or hypoattenuation except for cystic components, and hyper-PNETs were tumors showing hyperattenuation over the whole area. CT findings and contrast-enhancement patterns of the tumors were evaluated retrospectively by two radiologists and compared with the pathological grading.ResultsIso/hypo-PNETs comprised 26 tumors, and hyper-PNETs comprised 35 tumors. Not only hyper-PNETs but also most iso/hypo-PNETs showed peak enhancement in the pancreatic phase and a washout from the portal venous phase to the delayed phase. Iso/hypo-PNETs showed larger tumor size than the hyper-PNETs (mean, 3.7 cm vs. 1.6 cm; P < 0.001), and were significantly correlated with unclear tumor margins (n = 4 vs. n = 0; P = 0.029), the existence of cystic components (n = 10 vs. n = 3; P = 0.006), intratumoral blood vessels in the early arterial phase (n = 13 vs. n = 3; P < 0.001), and a smooth rim enhancement in the delayed phase (n = 12 vs. n = 6; P = 0.019). Iso/hypo-PNETs also showed significantly higher pathological grading (WHO 2010 classification; iso/hypo, G1 = 14, G2 = 11, G3 = 1; hyper, G1 = 34, G2 = 1; P < 0.001).ConclusionPNETs containing iso/hypo-areas showed a rapid enhancement pattern as well as hyper-PNETs, various radiological features and higher malignant potential.