Rishniw M, Weidman J, Hornof WJ.
Hydrothorax was identified in a 14-year-old Siamese cat with a pre-existent perinephric pseudocyst. The pleural fluid was classified as a low-protein transudate. Intrapseudocystic scintigraphy confirmed a direct communication between the pseudocyst and the pleural space. The hydrothorax resolved following pseudocystectomy and unilateral nephrectomy, demonstrating that the pseudocyst caused the hydrothorax.