Vol. 3 No. 2 - June 2017

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Evaluating the Sensitivity of Arterial Phase CT Images for Detection of Hepatic GIST Metastases Mikin Patel, Danial Jilani, Aytekin Oto, and Pritesh Patel Department of Radiology, The University of Chicago Medicine, Chicago, Illinois Corresponding Author: Mikin Patel, MD, MBA 5841 S Maryland Avenue, MC 2026, Chicago, Illinois 60637; E-mail: Key Words: gastrointestinal stromal tumor, hypervascular tumors, liver imaging, arterial phase CT, multiphasic CT Abbreviations: Gastrointestinal stromal tumor (GIST), computed tomography (CT), portal venous (PV), multidetector computed tomography (MDCT) Gastrointestinal stromal tumor (GIST) frequently metastasizes to the liver, and conventional staging computed tomography (CT) protocols use multiphasic contrast enhancement for detection of hepatic lesions. We evalu- ated the sensitivity of arterial phase CT imaging for hepatic GIST metastases compared with that of standard (portal venous [PV]) phase imaging. We conducted a retrospective review of patients who presented with hepatic GIST metastases identified on staging CT examinations between 2005 and 2015. Arterial and PV phase CT images were randomized and reviewed by 2 radiologists blinded to clinical history, correlative imaging, and number of controls. In total, 32 patients had hepatic metastases identified on multiphasic (arterial and PV) staging CT examinations. There was no significant difference in identification of metastases between arterial and PV phase imaging (31 vs 32, P 5 .32). Lesion size measurements did not significantly differ (P 5 .58). Arterial phase CT imaging did not significantly increase the sensitivity for hepatic GIST metastases compared with PV phase imaging alone. INTRODUCTION Gastrointestinal stromal tumors (GISTs) account for 90% of mesenchymal tumors in the gastrointestinal tract with incidence of 14 –20 cases per million and prevalence of 130 cases per million (1-3). GISTs most commonly occur in the stomach ac- counting for 2%–3% of all gastric malignancies and most com- monly metastasize to the liver and peritoneum (4, 5). GISTs are generally considered to be hypervascular tumors (6, 7). Ac- cordingly, the literature suggests that arterial phase computed tomography (CT) imaging may be helpful for detection of hy- pervascular liver metastases (1, 8). Conventional literature also states that GIST metastases can become isoattenuating to liver parenchyma and therefore occult on portal venous (PV) phase imaging, necessitating multiphasic enhanced CT imaging for detection (9-14). Current consensus guidelines support the use of multiphasic enhanced CT to stage newly diagnosed GISTs but state that monophasic studies are adequate for follow-up evaluations (9-15). However, outside of anecdotal support for the practice, there is a paucity of data showing the necessity of arterial phase imag- ing for detection of hepatic GIST metastases. In fact, large series have characterized primary and metastatic GIST with only PV phase imaging (16). Some literature studies state CT imaging during PV phase is adequate for detection of primary GIST, vascular encasement, and hepatic metastases (17). Even advo- cates of multiphasic CT for evaluation of GIST acknowledge that further study is necessary to support its use (11). This study aims to determine whether arterial phase imaging augments the sen- sitivity of standard PV phase imaging when evaluating for hepatic GIST metastases. MATERIALS AND METHODS A retrospective review of all patients with new diagnosis of GIST at a single academic institution between September 1, 2005 and August 31, 2015, was performed. Of these, 61 patients had hepatic metastases identified on initial staging CT. After exclu- sion of patients with monophasic staging CT, 32 patients were included. All procedures were in accordance with the ethical standards of the Institutional Review Board, and the waiver of need for informed consent was approved. All CT examinations were performed on either 16-multi- detector computed tomography (MDCT) or 64-MDCT scanners (Brilliance, Philips Healthcare, Amsterdam, Netherlands). The institutional protocol for CT staging of GIST includes PV phase images (reconstructed section thickness 5 3 mm) of the entire abdomen and pelvis with additional arterial phase images (sec- tion thickness 5 3 mm) of the liver, which are optional and obtained as per the physician's discretion. Iohexal (120 mL; 4 –5 mL/s through peripheral venous access; Omnipaque 350; GE Healthcare) was administered to the patients. Arterial phase RESEARCH ARTICLE ABSTRACT © 2017 The Authors. Published by Grapho Publications, LLC This is an open access article under the CC BY-NC-ND license ( ISSN 2379-1381 TOMOGRAPHY.ORG | VOLUME 3 NUMBER 2 | JUNE 2017 101

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