Mesentery, Omentum, Peritoneum: Cystic Masses and Neoplasms

Abstract

There are many intra-abdominal processes which may mimic cystic masses within the peritoneal cavity. These include various fluid collections such as abscess, seroma, biloma, urinoma, or lymphocele. These are often recognized based on relevant clinical history, such as recent surgery or trauma. For example, penetrating or iatrogenic injury may result in intraperitoneal urine leak which may encapsulate and mimic a cystic mass. Even when not suspected clinically, the diagnosis of urinoma can be confirmed by demonstration of contrast collecting within the fluid collection on delayed post-contrast imaging. Alternatively, a thin-walled homogeneous fluid collection abutting surgical clips after lymphadenectomy is suggestive of the diagnosis of lymphocele (Fig. 103.1). Other specific characteristics of certain collections may also facilitate diagnosis: gas within abscess or infected collection; on MR, high T1 signal within a fluid collection on fat-suppressed images is suggestive of blood products, implying possibility of a hematoma or seroma. These collections need to be identified and differentiated from cystic masses as some of these collections (abscess, urinoma, or biloma) may require urgent intervention. At times surgical excision or an imaging-guided needle aspiration of a collection and laboratory evaluation of the fluid aspirated is needed to make a definitive diagnosis (Fig. 103.2).