Intra-abdominal fat. Part I. The images of the adipose tissue localized beyond organs

Abstract

Unaltered fat is a permanent component of the abdominal cavity, even in slim individuals. Visceral adiposity is one of the important factors contributing to diabetes, cardiovascular diseases and certain neoplasms. Moreover, the adipose tissue is an important endocrine and immune organ of complex function both when normal and pathological. Its role in plastic surgery, reconstruction and transplantology is a separate issue. The adipose tissue has recently drawn the attention of research institutes owing to being a rich source of stem cells. This review, however, does not include these issues. The identifi cation of fat is relatively easy using computed tomography and magnetic resonance imaging. It can be more diffi cult in an ultrasound examination for several reasons. The aim of this paper is to present various problems associated with US imaging of unaltered intra-abdominal fat located beyond organs. Based on the literature and experience, it has been demonstrated that the adipose tissue in the abdominal cavity has variable echogenicity, which primarily depends on the amount of extracellular fl uid and the number of connective tissue septa, i.e. elements that potentiate the number of areas that refl ect and scatter ultrasonic waves. The normal adipose tissue presents itself on a broad gray scale: from a hyperechoic area, through numerous structures of lower refl ection intensity, to nearly anechoic regions mimicking the presence of pathological fl uid collections. The features that facilitate proper identifi cation of this tissue are: sharp margins, homogeneous structure, high compressibility under transducer pressure, no signs of infi ltration of the surrounding structures and no signs of vascularization when examined with the color and power Doppler. The accumulation of fat tissue in the abdominal cavity can be generalized, regional or focal. The identifi cation of the adipose tissue in the abdominal cavity using ultrasonography is not always easy. When in doubt, the diagnostic process should be extended to include computed tomography or magnetic resonance imaging, or sometimes biopsy (preferably the core-needle one).

Keywords

• intra-abdominal fat
• reflection patterns
• localization
• ultrasound
• diagnostic criteria