ABSTRACT. A 4-year-old female Miniature Dachshund was referred with a chief complaint of right periorbital swelling that had not responded to antibiotic therapy. Ultrasonography and fine-needle aspiration revealed that the periorbital lesion had a cystic structure without any inflammatory or neoplastic cells. Computed tomography (CT) showed that the cyst occupied a defect in the periorbital maxillary, lacrimal, and frontal bones and had invaded the nasal cavity. The lesion was histologically suspected by incisional biopsy as an epithelial cyst. KEY WORDS: canine, computed tomography, periorbital cyst.J. Vet. Med. Sci. 68 (7): [747][748] 2006 A few reports have described cystic lesions around the eye or in the maxilla [2][3][4][5]. Surgery is the treatment of choice for a periorbital cyst. Either marsupialisation or enucleation is performed, depending on various factors-the size of the cyst, its status(unilocular or multilocular), and anatomical structures that are adjacent to the cysts [1,6].Computed tomography (CT) is one of the useful modalities for evaluating lesions in the human orofacial area [1]. However, to our knowledge, CT imaging of canine orofacial cysts has not yet been reported. Therefore, in the present case, we utilized CT imaging to identify the morphological characterization of the cyst.A 4-year-old, female Miniature Dachshund was referred to the Animal Medical Center of Nihon University with a chief complaint of right periorbital swelling. A swelling of the medial lower lid of the right eye had been observed for 2 months. An ophthalmic examination, including a fluorescein dye passage test, no abnormalities. The swelling had recurred despite antibiotic therapy and intermittent fine needle aspiration of the periorbital cyst.On physical examination, a fluctuant swelling with a diameter of 2 cm was palpated in the medial canthus and medial lower lid of the right eye. Ultrasonography revealed that the swelling had an echolucent cystic structure. Sterile serosanguineous fluid was derived from the cyst by fineneedle aspiration. Cytological examination did not provide any evidence for a significant inflammatory process or neoplastic cell infiltration. CT was designed to clarify the morphological structure of the cyst.Under general anesthesia, CT was performed by CT-W450-10A (Hitach Medical Co., Tokyo) with the following scan parameters: 50 mA, 120 kVp, 4.5 s scan, 2-mm continuous slices, and 512 × 512 matrix size. CT imaging revealed a circumscribed and smooth cystic structure (Fig. 1). The cyst had expanded primarily within the right orbital region, invading the nasal cavity and cribriform plate. A periosteal reaction was not observed around the lesion, and the internasal septum, palatine bone, and teeth that were adjacent to the cyst were intact. The subsequent contrast CT * CORRESPONDENCE TO: ASANO, K., Laboratory of Veterinary Surgery, Department of Veterinary Medicine, College of Bioresource Sciences Nihon University, 1866 Kameino, Fujisawa 252-8510, Japan. Fig. 1. Transverse CT imaging at the...