Giant paraovarian cyst causing abdominal distention in a Swiss mouse (Musmusculus)

A 9-month-old unsterilized female Swiss mouse (Mus musculus), housed in the Central Animal Facility of the Federal University of Mato Grosso, presented with a 1-month history of progressive abdominal distention. Occupying most of the abdominal cavity was a prominent oval-shaped, 30 g (constituting 38% of the bodyweight), 4.5 cm × 3.5 cm × 3.2 cm nodule with an irregular surface that was compressing the liver, diaphragm and thoracic cavity cranially, the right kidney laterally and the intestinal loops caudally. Histological examination confirmed a multilocular paraovarian cyst closely resembling the giant paraovarian cysts described in women. Paraovarian cysts should be suspected as a differential diagnosis in cases of marked abdominal distention in mice.