Malignant peritoneal mesothelioma

Clinical History

A 47-year-old male presented with recent complaints of an abdominal distension and a right upper quadrant pain with shoulder tip radiation.

Imaging Findings

A 47-year-old male presented with recent complaints of an abdominal distension and a right upper quadrant pain with shoulder tip radiation. He had no history of having undergone radiotherapy or environmental exposure to asbestos. The laboratory work-up at presentation showed mildly elevated levels of liver enzymes (alanine aminotransferase and aspartate aminotransferase) and increased values of erythrocyte sedimentation rate. An abdominal ultrasonogram when taken revealed a right subphrenic heterogeneous mass with cystic and solid portions, limited by an irregular wall. A small amount of intraperitoneal fluid was present in the pelvis. A computed tomographic scan demonstrated the presence of a large right subphrenic mass measuring 13 x 17,5 x 11cm. It was well defined, multilobulated and of heterogeneous soft tissue attenuation, with peripheral enhancement, after adminisration of an intravenous contrast. Multiple enhancing peritoneal plaques and nodules were also visualized along the peritoneal surface, predominantly over the liver and in the epigastrium. In addition, there were several round, low-density lesions in the liver, representing metastases, and pleural effusion was detected in the right pleural space just above the diaphragm. After doing an exploratory laparotomy an omental mass was detected, adhering to the diaphragm and invading the liver. The lesion was unresectable, and a biopsy was only performed for histologic study. There were also implants in the parietal and visceral peritoneum covering the small bowel and the colon. The histological features were consistent with a malignant mesothelioma of the epithelial type and papillary subtype. Four weeks later the patient died.

Discussion

Mesotheliomas are known to be rare mesenchymal neoplasms arising from the serosal linings of the pleura and the peritoneum and may rarely even originate in the pericardium, tunica vaginalis or the ovarian epithelium (1,2). While simultaneous peritoneal and pleural involvement is found in 30%–45% of cases of mesotheliomas, solitary peritoneal involvement accounts for only 10%–20% (3). The malignant peritoneal mesothelioma (MPM) was first described in 1908 by Miller and Wynn and register an overall incidence of one to two cases per million (3). Currently, about 50% of the patients have occupationally been exposed to asbestos (1). The relationship between asbestos exposure and the malignant mesothelioma is an established fact, especially crocidolite fibers which appear to be much more carcinogenic than amosite and more easily degraded. This suggests that a chronic irritation of mesothelial cells is important in the tumoral development. Strikingly, peritoneal mesotheliomas are found more frequently in employees in the shipping industry. The precise pathogenesis of the peritoneal mesothelioma is not known. Animal studies show there is an evident migration of asbestos fibers through the intestinal mucosa. However, transportation of asbestos particles from the lungs to the peritoneal cavity by the lymph system is also described (2). More recently, radiation has been recognized as an etiologic factor. Most post-radiation mesotheliomas occur within prior radiation treatment fields, and the mean time between radiation exposure and mesothelioma formation is approximately 19.5 years (4). A paraneoplastic syndrome has rarely been reported in the case of this tumor (1). Before the third decade, no risk factor is usually found (5). Some investigators argue that MPM may be related to a more prolonged and heavy asbestos exposure than those with primary pleural tumors. The disease is more commonly found in men, possibly because of the higher male occupational exposure to asbestos, in the fifth and sixth decades, although it can be seen inthose of any age group (1). The main clinical symptoms are a diffuse abdominal pain, cramps, increasing girth and weight loss (3). Histopathologically, MPM is divided into three specific types: epithelial, fibrous (sarcomatoid) and mixed or biphasic (5). The epithelial type, the most common, is subdivided into four subtypes: papillary, tubulopapillary, cord-like and sheet-like or solid (5). Most non-invasive diagnostic efforts are not helpful. Chest radiographs reveal evidence of asbestosis in fewer than 45% of cases. CT scanning of the lower thorax may be helpful in revealing pleural plaques, which are compatible with asbestosis. The abdominal radiographic appearance is non-specific and includes fixation and serosal changes of bowel loops, areas of dilatation and a narrowing of the small bowel with or without partial obstruction and fixed segments of small bowel loops. Such a picture is similar to implants seen from many neoplasms. Ultrasound studies have shown that there is an associated thickened peritoneum, peritoneal nodules, omental mass and ascites (4). In the literature, there are reports of metastatic liver and bone involvement. At abdominal CT, MPM typically appears as a solid, enhancing soft-tissue mass within the mesentery, omentum or the peritoneum. It may also appear as an infiltrating mass or multiple nodules, varying from a few millimeters to several centimeters in diameter in any location within the omentum, mesentery and peritoneal folds. It has a tendency to spread along serosal surfaces and for a direct invasion of both solid and hollow intra-abdominal organs, most commonly the colon and the liver (1). Contrast-enhanced, fat-saturated MR imaging is a useful method for identifying the peritoneal involvement (4), in a malignant mesothelioma. In fact, increased peritoneal permeability resulting from peritoneal carcinomatosis causes peritoneal enhancement. Also, imaging in the coronal plane is particularly useful for showing subdiaphragmatic and paracolic peritoneal implants and for delineating the extension of the peritoneal tumor. Low et al has been indicated that the malignant peritoneal tumors are generally thicker and more lobular or masslike than benign peritoneal tumors (4). Early stage MPM may present only as peritoneal thickening, with no associated gastrointestinal symptoms, ascites or omental nodules (3). Massive ascites is not commonly associated; however, a small to moderate amount of fluid collections in peritoneal and pleural spaces are frequently seen, because of the transdiaphragmatic spread. The initial diagnosis of malignant mesothelioma is time consuming and arduous in the absence of evident symptoms. Examination of the ascitic fluid could lead to dubious interpretation, becoming positive only in the late phases (8). Radiological methods can contribute to the formulation of a diagnosis, but obtaining a biopsy specimen during laparoscopy or laparotomy is still procedure of choice. Findings of an image-guided fine needle aspiration biopsy should be interpreted with caution because the results may be misleading. That is why some authors favor the use of a laparoscopic biopsy as it permits direct visualization and abdominal staging (3). The differential diagnosis includes peritoneal carcinomatosis, lymphomas and tuberculous peritonitis. Treatment, including systemic and intraperitoneal chemotherapy, abdominal radiotherapy and surgical debulking have all been used with little success, resulting in short median survival (4–12 months) (3). The nonspecific nature of the symptoms often leads to a delay in making a diagnosis, which contributes to the high mortality rate, irrespective of the modality of treatment. However, it is hoped that with earlier diagnosis and radical treatment, the survival rate of patients may be improved (3).

Differential Diagnosis List

Final Diagnosis

Malignant peritoneal mesothelioma.

URL:	https://www.eurorad.org/case/2522
DOI:	10.1594/EURORAD/CASE.2522
ISSN:	1563-4086