[A case of omental mesothelioma presenting with laminar thickening of omentum-appearances of diffuse malignant peritoneal mesothelioma].

A man in his 60's with no apparent history of asbestos exposure was admitted to our hospital with a chief complaint of abdominal fullness. CA125 levels in serum and ascites were veryhigh. Enhanced abdominal CT confirmed a large amount of ascites, inflexible intestinal canal, short mesentery and laminar thickening of the omentum. SPIO-enhanced MRI-T1WI slightly enhanced the thickened omentum. These T1WI images largely matched portal-phase contrast CT images. Furthermore, the thickened omentum was clearly visualized by lowering the signal for the liver and spleen by SPIO and by suppressing the ascites signal by fluid-attenuated inversion recovery (FLAIR). Gascintigraphy confirmed Ga accumulation in the same areas. Chemotherapy was ineffective, and the patient died of liver metastasis in February 2006. Autopsy confirmed biphasic malignant peritoneal mesothelioma. The involvement of asbestos is clear in the onset of malignant peritoneal mesothelioma. Therefore, it is possible that the patient unintentionally inhaled asbestos. Hence, when levels of CA125 in serum and/or ascites are high, it is important to differentiate malignant peritoneal mesothelioma from primaryserous papillary carcinoma of the peritoneum. Here, we experienced a case of biphasic diffused omental mesothelioma. While studies have documented laminar thickening of the omentum by abdominal incision, this is thought to be first case in Japan in which laminar thickening of the omentum was detected on diagnostic imaging. Laminar thickening of the omentum and short mesentery are thought to be characteristic features of diffused peritoneal mesothelioma when subjective symptoms appear. In addition, Gascintigraphy and FDG-PET are useful auxiliary diagnostic tools. In the future, we hope to differentiate epithelial, sarcomatous and biphasic types based on imaging findings.