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Surgical removal of a retrobulbar adenoma in an African grey parrot (Psittacus evithacus).

Abstract: An African grey parrot (Psittacus erithacus) was presented with exophthalmos and a semisolid mass dorsomedial to the left eye that led to ventrotemporal deviation of the globe. Ultrasonography of the eye revealed a well-demarcated mass of cystic appearance, retrobulbar to the left eye. Cultures of samples of the mass acquired by fine needle aspiration were negative for bacteria and Mycoplasma species. Metaplasia of a periorbital gland caused by hypovitaminosis A was suspected, and vitamin A supplementation was initiated. Because of unresponsiveness to therapy, the cystic mass was surgically removed. The histologic diagnosis was adenoma. The surgical wound healed well, and no recurrence was observed 10 months later. To our knowledge, this is the first report of surgical removal of a retrobulbar adenoma in this species with the eye remaining intact and functional.

Key words: retrobulbar adenoma, neoplasia, ophthalmology, psittacine bird, avian, African grey parrot, Psittacus erithacus

Clinical Report

A 20-year-old African grey parrot (Psittacus erithacus), weighing 470 g, was presented to the Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, with a history of slowly progressive deviation of the left eye. According to the owner, the parrot did not show any irritation or scratching and had a normal appetite and behavior. At presentation, the parrot was in good nutritional and clinical condition. Clinical examination revealed a semisolid tissue swelling dorsonasal to the left eye, with epiphora and ventrotemporal deviation of the globe (Fig 1). No conjunctival swelling or ocular discharge was observed. Ophthalmologic examination included slit lamp biomicroscopy (Kowa SL-15, Kowa Company Ltd, Tokyo, Japan) and indirect ophthalmoscopy (Heine Omega 500, Heine Optotechnik, Herrsching, Germany). All visible eye structures appeared normal, and no abnormalities of the right eye were observed. Results of a complete blood cell count and plasma biochemical analysis revealed a slightly decreased concentration of total calcium (1.95 mmol/L [7.8 mg/dL], reference range 2.00-3.49 mmol/L [8.0-13.9 mg/dL]) (1) and an increased concentration of creatinine kinase (597 U/L, reference range 140-411 U/L). (1) All other hematologic and biochemical results were within reference ranges. Radiographs were taken with the bird under isoflurane anesthesia and revealed a soft-tissue swelling medial to the left globe, with no involvement of bony structures. Results of ultrasonography revealed a well-defined hypoechoic cavernous cystic structure, 8 x 11 mm in diameter, dorsonasal and caudal to the left eye (Fig 2). A fine needle aspirate of cystic cavities within the mass was performed, and samples of aspirated serosanguineous fluid were submitted for cytologic analysis, bacterial culture, and sensitivity testing. Results revealed a low number of free macrophages and blood cells, compatible with the presence of a noninflammatory cyst, without evidence of a malignant neoplasia. Culture results for mycoplasma, mycobacteria, and other bacteria were negative. Because metaplasia of the gland of the nictitating membrane caused by hypovitaminosis A could not be excluded as a differential diagnosis, therapy with vitamin A (Vitamin A Streuli, Streuli Pharma AG, Uznach, Switzerland) was initiated at 6000 IU/kg IM once, followed by 500 IU/kg IM for 3 days and 200 IU/kg IM for another 3 days. On reexamination after completing the therapy, the size of the mass was unchanged, and surgical excision was elected.

[FIGURE 1 OMITTED]

For the procedure, the parrot was premedicated with butorphanol (2 mg/kg IM; Morphasol-4, Dr E. Graeub AG, Bern, Switzerland), enrofloxacin (15 mg/kg SC in a fluid pocket; Baytril, Bayer, Provet AG, Lyssach, Switzerland), and meloxicam (0.5 mg/kg SC; Metacam, Boeringer Ingelheim GmbH, Basel, Switzerland). Anesthesia was induced by a face mask with 5% isoflurane, and the bird was intubated and maintained on 1.5% isoflurane. A 24-gauge intravenous catheter was placed in the vena basilica and lactated Ringer's solution (10 ml IV) was administered slowly over 20 minutes. The bird was positioned in ventral recumbency, and the head was placed on the right lateral side so that the left eye was positioned dorsally. After surgical preparation of the site, a 1-cm skin incision was made above the mass, and the mass was carefully dissected from the surrounding connective tissue with Stevenson scissors. The well-defined and encapsulated cystic mass, which was in close contact to the wall of the globe and attached to the periosteum of the orbit, was removed en mass without affecting the eye. During surgery, there was only minor bleeding (Fig 3). The resulting surgical defect was closed with single interrupted sutures by using a 1.5 metric glyconate, synthetic, monofilament, absorbable suture material (4/0 Monosyn, B. Braun Aesculap AG & Co KG, Sempach, Switzerland) (Fig 4a). Recovery from anesthesia was uneventful. The cystic mass was submitted for histopathologic examination. To prevent scratching, an avian spherical cervical collar (GHN, Inc, Fort Myers, FL, USA) was placed around the neck of the bird.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The day after surgery the bird was in good general condition and showed minor swelling at the surgical site. The parrot was discharged with diclofenac sodium and gentamicin solution (Voltamicin, OmniVision AG, Neuhausen, Switzerland) applied topically to the eye (1 qtt OS q 12h for 5 days), enrofloxacin (15 mg/kg PO q12h for 7 days) and meloxicam (0.5 mg/kg q12h for 3 days). On reexamination 1 week after surgery, the surgical wound was healing well and the collar was removed (Fig 4b).

[FIGURE 4 OMITTED]

Histologic examination of the excised mass revealed a well-demarcated proliferative mass composed of highly differentiated simple, squamous-to-cuboidal epithelial tissue forming round to bizarre-shaped cysts surrounded by a dense stroma rich in collagen. Inside the cystic structures, normally differentiated macrophages were present in low numbers. On the basis of these findings, the diagnosis was adenoma (Fig 5a, b). Ten months after the surgical procedure, the parrot was reexamined. No abnormalities were detected during the ophthalmologic examination of both eyes. Phenol red thread tear test (PRT) was performed to evaluate tear production as described in a previous study. (2) The operated left eye had a PRT value of 18 mm/15 s and the right eye had a PRT value of 15mm/15s. No recurrence of the mass was observed.

[FIGURE 5 OMITTED]

Discussion

Most cases of ocular neoplasia in birds have been described as single case reports or small series; various investigators reviewed the literature and added personal experiences. (3-10) Retrobulbar neoplasia is rarely reported in avian species. The limited reports include retrobulbar rhabdomyosarcoma, (11) adenocarcinoma, (5) carcinoma, (12-14) lipoma, adenoma, and adenofibroma in a

budgerigar (Melopsittacus undulatus), (15) teratoma in a great blue heron (Ardea herodias), (16) and a single case report of cystadenoma in an African grey parrot, (9) in which the exact origin of the neoplasia could not be determined. Most of these reports include findings obtained on postmortem examination. The clinical presentation of reported cases of retrobulbar neoplasia includes exophthalmia, dislocation of the palpebral fissure, and epiphora, with affected eyes described as visual and intact. (15) In the present case, displacement of the palpebral fissure with epiphora was detected as well.

Adenomas are benign neoplasms that arise from a glandular epithelium. In birds, adenomas have been reported most often to arise from the pituitary gland in budgerigars (17,18) but have also been described to arise from the uropygial gland, pancreas, thyroid gland, (19) and kidney. (20) Retrobulbar adenoma may arise from one of the orbital glands. There are several glands described in the avian orbit: 1) glandula lacrimalis, 2) glandula membranae nictitantis/harderian gland, and 3) glandula nasalis. Pathologic involvement of any of these glands could affect the contents of the orbit. (21) In the present case, the exact glandular origin of the adenoma could not be identified on histologic examination. Because of the location of the neoplasm within the orbit, we suspect involvement of the harderian gland. Infectious causes should always be included as a differential diagnosis in lacrimal gland disease. Another noninfectious cause that can lead to hyperplasia of the nictitating/harderian gland is vitamin A deficiency. (15) Vitamin A deficiency is observed commonly in psittacine birds and often is a result of a low beta-carotene level in a seed-based diet. (22) Alimentary vitamin A deficiency can cause metaplasia of the glandular epithelium of the nictitating/harderian gland or of the lacrimal gland, which results in proliferative periocular tissue in the dorsorostral and ventrotemporal orbital area, respectively. (15) The proliferation, which in the beginning is soft but later becomes firm, may lead to a dislocation of the palpebral rim. As a sequel to metaplasia, lacrimal-duct openings may become obstructed, which results in epiphora. (15)

In the case we describe, the negative results of bacterial culture helped to rule out a possible infectious origin of the swelling, but metaplasia could not be excluded completely despite the lack of cytologic evidence. Hypovitaminosis A was suspected and the initial therapy with vitamin A was aimed to correct this assumed deficiency. Initial therapy with vitamin A did not improve the clinical signs, and the cytologic results led to the suspicion of a cystic formation, without evidence of malignant neoplasia. Because radiography ruled out the bony involvement of the orbit, surgical removal of the mass was considered. Surgical resection of retrobulbar masses is not always achieved without enucleating the affected eye, and relapse after enucleation may occur. (15) Further diagnostic investigations, such as ultrasonography, computed tomography, or magnetic resonance imaging, may be helpful to define the extent and location of the lesion and involvement of adjacent structures as well as to recognize the possible invasion into other organs. In this case, ultrasonography allowed us to assess the location and extent of the mass and helped to determine if the eye was involved. Because of the clear demarcations of the structure, magnetic resonance imaging or computed tomography was not considered necessary in the present case.

In this case, Monosyn was preferred for wound closure to polyglactin 910, which has been described to cause an intense inflammatory response. (23) Postoperative treatment consisted of diclofenac sodium and gentamicin topical solution at a dose of 1 drop OS twice daily (approximately 0.05 mg per application) for 5 days. This preparation was given twice daily and only for a short period, because we considered the possible toxic effect of diclofenac sodium after systemic resorption. (24) No clinical signs of toxicosis were observed with this schedule. One week after mass removal, the surgical site had healed, the eye was in its normal position, and the bird was doing well. When a large part of a tear-producing gland is excised, the possibility exists for reduced tear production to cause ocular-surface disease. Therefore, on follow-up ophthalmologic examination done 10 months later, the phenol red thread test was used to evaluate tear production in the operated eye. The PRT test has been performed in various psittacine birds, (2) but, because of the lack of reference values in African grey parrots, the test was performed in both eyes for comparison. The values of both the operated and clinically healthy eye were similar. Based on the results of the PRT test and the lack of ocular-surface disease, we concluded that the operated eye still had a satisfactory tear production. Therefore, the surgical removal of the retrobulbar neoplasia was considered successful. This procedure negated the need for enucleation, and it should be considered as a treatment option in similar cases.

References

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Stefka Simova-Curd, Dr MedVet, Marianne Richter, Dr MedVet, Dipl ECVO, Beat Hauser, Dr MedVet, Dipl ECVP, and Jean-Michel Hatt, Prof Dr MedVet, MSc, Dipl ACZV, Dipl ECAMS

From the Clinic for Zoo Animals, Exotic Pets and Wildlife (Simova-Curd, Hatt); Equine Department-Section of Ophthalmology (Richter); and Institute for Veterinary Pathology (Hauser), Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 268, 8057 Zurich, Switzerland.
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Title Annotation:Clinical Reports
Author:Simova-Curd, Stefka; Richter, Marianne; Hauser, Beat; Hatt, Jean-Michel
Publication:Journal of Avian Medicine and Surgery
Article Type:Report
Geographic Code:4EXSI
Date:Mar 1, 2009
Words:2455
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