A large volume of echogenic peritoneal effusion distends the abdomen. Several rounded anechoic fluid-filled cystic structures are present on the surface of the liver, spleen, bladder, bowel, and omentum. These cystic structures are present  free-floating in the fluid as well. The cystic structures are numerous and all similar in size. In some areas, particularly along the inner peritoneal lining, linear hyperechoic regions may represent areas of fibrin or peritoneal thickening.  Sludge is in the gallbladder. Kidneys are normal. Spleen is heterogeneous, without definite nodules. Urinary bladder is normal.

• Severe volume of peritoneal effusion with probable peritonitis.
• Multifocal cystlike nodules free floating in the peritoneum and adhered to serosal margins

• The free fluid was aspirated and the contents were clear fluid with small white fragments.
• PCR examination of the aspirates confirmed the diagnosis of Mesocestoides sp. infection.  The feces were negative.
• Treatment with Fenbendazole at a dosage of 100 mg/Kg q12h was instituted until there was complete absence of parasites based on ultrasound exam.

Mesocestoides are tapeworms that infect dogs, cats, and wild carnivores in North America, Europe and Asia.  Blood and fecal exams are not usually helpful for the diagnosis and several authors suggest cytology and PCR of larval tissue are essential for the diagnosis (in this case, peritoneal fluid sampling).