Satomi Kawamoto MD, Presenter: Research support, Siemens AG

Pamela Tecce Johnson MD, Abstract Co-Author: Research funded, Becton, Dickinson and Company

Chanjuan Shi MD, PhD, Abstract Co-Author: Nothing to Disclose

Ralph H. Hruban, Abstract Co-Author: Royalties, Myriad Genetics, Inc

Elliot K. Fishman MD, Abstract Co-Author: Research support, Siemens AG Advisory Board, Siemens AG Research support, General Electric Company Advisory Board, General Electric Company Co-founder, HipGraphics, Inc

Pancreatic neuroendocrine tumors (PanNETs) occasionally manifest as cystic lesions. When they are purely or partially cystic on CT, there is potential for misdiagnosis. The purpose of this study is to determine the incidence of small (≤3 cm) cystic PanNET on preoperative CT, and characterize the CT appearance of these neoplasms.

Seventy-four consecutive patients (average age: 55.5) with pathologically proven PanNET who underwent preoperative 64-MDCT exam were retrospectively reviewed, and 46 patients with small (≤3 cm) PanNET were included. Arterial and portal venous phase contrast enhanced CT images were reviewed by 2 radiologists. Cystic component was defined as an area less than 30HU within the mass, which demonstrated no contrast enhancement between arterial and portal venous phases. The size and incidence of cystic tumor were obtained. Cystic tumors were classified into purely (nearly 100%) cystic, or partially cystic (<50% or >50%). Additionally, rim enhancement and internal structure of the cystic component were recorded. The radiologist’s preoperative diagnosis was recorded based on the CT reports.

The mean size of the tumors in 74 patients was 3.0±2.6cm (0.5 to 13 cm). In 5 patients with insulinoma (average 0.9cm), tumor was not seen on CT, and these were excluded from the analysis. The mean size of small (<3cm) tumors was 1.7±0.6cm on CT. Twelve (26%) of these 46 small tumors were cystic on CT. Among them, 2 were purely cystic, and 10 were partially cystic (>50% cystic in 7, <50% cystic in 3). Average attenuation of cystic component was 18.5±7.4HU. Smooth or irregular rim enhancement was seen clearly (n=10) or equivocally (n=2) in the cystic PanNETs, and was often more apparent on arterial phase than portal venous phase (n=6), or seen equally on both phases (n=4). Preoperative CT diagnosis for cystic PanNET was most commonly "primary cystic neoplasm".

In this study, 26% of small PanNETs were cystic on CT, and 4% were purely cystic. Radiologists should be aware that PanNETs can simulate primary cystic neoplasm of the pancreas. Rim enhancement was commonly seen, and future studies comparing cystic PanNET to other cystic neoplasms should confirm the specificity of this finding for preoperative diagnosis.

Small cystic PanNETs are not uncommon, and they can be purely cystic. Cystic PanNET should be considered particularly when a cystic lesion is associated with rim enhancement.

Kawamoto, S, Johnson, P, Shi, C, Hruban, R, Fishman, E, Small (≤3 cm) Cystic Neuroendocrine Tumor of the Pancreas: Evaluation with MDCT.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11008642.html