Objectives: Celomic distention in birds may be caused by obesity, hepatomegaly, ascites, internal neoplasia, egg binding, intestinal severe parasitism, air sac distention, abdominal hernia and etc. A 4-year-old male homer pigeon (Columba livia) from a flock of 20 pigeons was referred to avian medicine and surgery division of Faculty of Veterinary Medicine, Ferdowsi University of Mashhad. The pigeon suffered from anorexia, lethargy, emaciation, and abdominal distention for 3 weeks. Palpation revealed a solid mass in the caudal celomic region. After clinical examination, radiology and ultrasonography were performed. Materials & Methods: Lateral and ventrodorsal plain radiographs were taken using mammographic films. Transabdominal ultrasonography was done by 8 MHz linear transducer. Acoustic coupling gel was used. Fasting for a 3 hours period was done for preparing before surgery. The patient had been wrapped loosely in a towel to prevent wing flapping and excessive struggling. Mask induction was carried out with 5% isoflurane for approximately 20–30 seconds. After stable plane of anesthesia had reached, the bird placed in dorsal recumbency and maintenance of anesthesia carried out using isofluran via a face mask at 2% concentration, with Oxygen flow rate at 2 liters/minute. In order to prevent hypothermia, a heat pad was used. After removing the mass, it was fixed in 10% neutral buffered formalin and processed routinely for histopathologic examination. Histologic slides were obtained and stained with hematoxylin and eosin staining. Results & Conclusion: In ventrodorsal radiograph, soft tissue mass was seen in caudal region of celomic cavity that displaced ventriculus and intestine, cranially, compressed air sacs and also obliteration of the caudal border of the heart. Ultrasonographic evaluation revealed hypoechoic and heterogenous mass with well define margin.These findings were suggestive of a abnormal space-occupying soft tissue mass. A firm, gray, solid mass measuring 6×6×5 cm was observed in the caudal region of the celomic cavity. The mass seemed to be attached to serous layer of small intestine. The external surface of the mass was smooth. The cut surface of the mass was white and smooth. The internal organs did not exhibit apparent lesions. Histological changes were characterized by well vascularized extensive connective tissue within macrophages as dominant cell type, lots of multinucleated giant cells, many lymphocytes and plasma cell, and a few heterophil around a central necrotic region. The histopathologic diagnosis was a well-organized encapsulated granuloma. Successful surgery of occupying lesion has not been described in pigeons and to our knowledge this is the first case report.

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