Long Road to Identifying Peritoneal Mesothelioma: An Elusive Diagnosis.

Peritoneal mesothelioma is a rare and aggressive malignancy that often presents with non-specific abdominal symptoms such as ascites, leading to delayed diagnosis and treatment. It poses significant diagnostic challenges, especially in the absence of classical risk factors like asbestos exposure. We report the case of a 60-year-old woman with a background of coeliac disease and no known asbestos exposure, who presented with progressive abdominal distension and ascites. Initial investigations, including imaging, paracentesis, cytology and liver biopsy, failed to reveal a definitive cause. Despite multiple evaluations and treating a presumptive diagnosis of sarcoidosis, her symptoms persisted. One year after the initial presentation, imaging revealed peritoneal nodularity and enhancement. Following biopsy and immunohistochemistry, a multidisciplinary team discussion led to the diagnosis of peritoneal mesothelioma. The patient was commenced on chemotherapy which showed clinical improvement. This case underscores the importance of maintaining a high index of suspicion for rare malignancies such as peritoneal mesothelioma in patients with recurrent unexplained ascites, even in the absence of classical risk factors. Early multidisciplinary involvement and persistence in diagnostic evaluation are essential for timely diagnosis and management, which may improve patient outcomes in complex presentations.