Computed Tomographic and Magnetic Resonance Imaging Findings of Asymptomatic Intra-Abdominal Gastrointestinal System Lipomas Hakan Genchellac, MD, Mustafa K. Demir, MD, Huseyin Ozdemir, MD, Ercument Unlu, MD, and Osman Temizoz, MD Abstract: Lipomas are common benign mesenchymal neoplasms documented in literature. This study aimed to describe the computed tomographic (CT) and magnetic resonance imaging (MRI) findings of gastrointestinal system lipomas, all of which are incidentally found in routine abdominal imaging studies. Lipomas were depicted as homogeneous, nonenhancing, well-marginated lesions consistent with adipose tissue on CT and MRI. The density measurements on CT images consistent with fat are virtually diagnostic. Lipomas can incidentally be found and should be considered in the differential diagnosis of soft tissue gastrointestinal systemYrelated masses. Computed tomographic or MRI examinations can correctly diagnose a lipoma nonoperatively, thereby allowing better treatment planning. Key Words: computed tomography, magnetic resonance imaging, intra-abdominal, gastrointestinal system, lipoma (J Comput Assist Tomogr 2008;32:841Y847) L ipomas are slow-growing benign mesenchymal tumors consisting of mature fat. The tumor is composed of well- differentiated adipose tissue surrounded by a thin fibrous capsule. They usually arise in soft tissues and skeletal muscle but may also arise in any region of the body that contains fat, including the (GI) tract. Although generally single, they may be multiple. Approximately 90% to 95% of GI-system lipomas are defined to arise from the submucosal layer, and the subserosal and intermucosal layers account for the remaining 5% to %10. 1,2 Most are asymptomatic and discovered incidentally. They usually do not produce symptoms until they reach approximately 3 to 4 cm in diameter. There is no report of malignant transformation of a lipoma. Establishing a preoperative diagnosis of a lipoma related to GI system is clinically important because it often obviates further intervention in patients. Cross-sectional imaging methods have proven useful in the radiological evaluation of lipomas. Although there have been many case reports of the diagnostic imaging of GI-system lipomas with serious complications, there are only a few reports that describe their computed tomographic (CT) and magnetic resonance imaging (MRI) findings in asymptomatic patients. 3,4 The present review describes the most common CT and MRI appearances of incidental intra-abdominal lipomas related to GI system. GENERAL CT AND MRI FINDINGS Macroscopic fat is readily identified with both CT and MRI. Therefore, these imaging modalities are the radiological examinations of choice for making a specific diagnosis of lipoma. Identification of fat with CT is based on x-ray absorption and attenuation. Lipomas are sharply circum- scribed homogeneous tumors with uniform fat attenuation between j70 and j120 Hounsfield units on CT. They may contain a few thin internal septations. Magnetic resonance imaging is also reliable in the diagnosis of GI-system lipomas. They have short T1 and relatively long T2 relaxation and thus seem hyperintense on T1-weighted and intermediately intense to hyperintense on T2-weighted fast spin-echo and gradient- echo images relative to muscle. Because these signal intensity characteristics are not always specific, it is necessary to exploit the different resonance frequencies of water and fat protons. Several MRI techniques have been developed for this purpose. Two of the most widely available are spectroscopic fat saturation and chemical shift (in phase/opposed-phase) imaging. 5,6 Because frequency-selective fat suppression tech- niques effectively reduce macroscopic fat signal, it is preferred to diagnose lipomas. Lipoma signals are low on T1- and T2- weighted fat-suppressed MR images, providing the definitive diagnosis. Chemical shift (in phase/opposed-phase) imaging is more sensitive for detecting fat in those pathologic findings in which the fat is microscopic. However, chemical shift imaging is more confusing for less experienced readers because the signal intensity drop of the fat is not seen, but there is only a typical black rim-like artifact at the border between fat and water tissue. After intravenous contrast media administration, lipo- mas show no enhancement on both CT and MRI studies. The findings of our cases were summarized in Table 1. INDIVIDUAL SITES Stomach Gastric lipomas are rare lesions. They represent only 5% of GI-tract lipomas and 3% of all benign tumors of the stomach. Although the pyloric antrum is the most common location, they can occur anywhere in the stomach such as the REVIEW ARTICLE J Comput Assist Tomogr & Volume 32, Number 6, November/December 2008 841 From the Department of Radiology, Trakya University Faculty of Medicine, Edirne, Turkey. Received for publication July 4, 2007; accepted August 27, 2007. Reprints: Hakan Genchellac, MD, Trakya U ¨ niversitesi TNp Faku ¨ltesi, Gu ¨llapo?lu yerlezkesi, Radyodiagnostik AnabilimdalN, Edirne, Turkey (e-mail: hakangenchellac@gmail.com). Copyright * 2008 by Lippincott Williams & Wilkins Copyright @ 2008 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.