Omental Caking

The omentum is a double layered extension of the peritoneum that connects the stomach to the adjacent organs. It serves both as boundaries for disease processes and as conduits for disease spread [1]. They are frequently involved with infectious, inflammatory, neoplastic, vascular and traumatic process . Omental neoplasm can originate either de novo from the peritoneal tissue (primary) or invade or metastasize from adjacent or distant organs. Most common cancers that metastasize to omentum are neoplasms from ovary, stomach, colon, pancreas and also described in cholangiocarcinoma [2]. On Grey scale sonography the normal omenta is extremely difficult to visualize. It is better visualized in the presence of ascites as the free edge of the greater omentum can be seen floating in the fluid which is a moderately Hyperechoic structure with a variable thickness [3]. When infiltrated by tumor it is thickened nodular and usually Hyperechoic the appearance which is described as Omental caking. Infiltrated omentum can present in several different ways. It can float freely in the ascetic fluid. The thickened omentum can be adhered to the parietal peritoneum, can be superficial or it can be deep in the peritoneal cavity attached to visceral peritoneum and small bowel loops. When it is superficial in location a careful evaluation with the high frequency transducer often can identify the abnormal omentum even in the absence of ascites [3]. CT although the major diagnostic tool for detecting peritoneal disease it has a low sensitivity in detecting lesions less than 1 cm in size and has features common to both benign and malignant disease [4]. The normal omentum on CT is usually imperceptible on routine scans and visualize only when involved with pathology or in the presence of free fluid [5]. The two indirect signs that help detecting involved pathology are the density of the omentum and the location of the small bowel loops. When it is infiltrated with neoplastic or infective process the normal fat density of the omentum is not appreciated and the thickened omentum will cause a mass effect to the surrounding bowel loops [5]. On CT infiltrated omentum or the Omental caking appear as a soft tissue mass with ill defined edges. The fat plane between the anterior abdominal wall and the intestinal loops will be obscured. Or if the omentum is not thickened the normal size omentum will show soft tissue masses within it or on it [5]. MRI scan with homogenously fat suppressed images there will be marked enhancement of the infiltrated peritoneum [5]. FDG PET had shown higher sensitivity in peritoneal carcinomatosis as the hypermetabolism of the malignancy will be avid for 18FDG and show positive uptake. The dual –time- point imaging found to be helpful in differentiating malignant disease from benign. The delayed images the standard uptake values of malignant disease increase over time compared to benign lesions which remain stable or decrease over time [6].