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Suspected osteoma in an eclectus parrot (eclectus roratus roratus).

Abstract: A 7-month-old, male eclectus parrot (Eclectus roratus roratus) was presented with a slow-growing mass over the chest and localized self-trauma to the area. Repeated sternal trauma secondary to an improper wing trim was observed in this case before development of the lesion. Surgical excision of the mass was performed for diagnostic and treatment purposes. On histopathologic examination, the mass was characterized by well-differentiated trabecular bone surrounded by a thin layer of periosteum. These findings were consistent with, but not exclusive to, a diagnosis of osteoma. This benign bone lesion is rare in human and veterinary medicine, with even fewer reports of this condition in avian patients. Trauma to the sternum from falling because of wing clipping was the most likely inciting cause in this parrot.

Key words: osteoma, neoplasia, eclectus, avian, eclectus parrot, Eclectus roratus roratus

Clinical Report

A juvenile, male eclectus parrot (Eclectus roratus roratus) was presented with a progressive, slow-growing mass on the sternum that the owner had been monitoring for 3 months. The bird had been purchased from a breeder at approximately 3 months of age. It had been hand-raised and weaned before sale. The breeder had trimmed the flight feathers of both wings on 2 occasions before sale of the bird because it continued to fly after the first wing trim attempt. The owner had no concerns regarding the health of the bird at the time of purchase.

The owner kept the bird in a covered outdoor area with no exposure to other birds or animals. It was allowed supervised excursions from the cage, and the owner had observed that the bird was unable to fly normally and occasionally sustained heavy falls during flight attempts. No bleeding or adverse reaction was observed after these events, and the bird had otherwise acted normally. The parrot was fed a diet consisting primarily of vegetables and fruits with additional seeds and nuts.

Three months before presentation, the owner had observed a thickening of the skin overlying the cranial aspect of the sternum. Subsequently, the owner noticed a firm mass developing in the region, which had slowly increased in size. The bird also began self-traumatizing the skin overlying the mass in the week before presentation, which resulted in the owner seeking veterinary attention.

On presentation, the bird was bright and alert, in good body condition, and weighed 313 g. Primary flight feathers 5 through 10 had been trimmed bilaterally to the level of the covert feathers by the breeder, which was deemed as a moderate trim in this species. There was an approximately 1-cm-diameter, firm, spherical, pedunculated mass on the sternum that appeared painful on palpation. The stalk was of similar material to the mass and appeared to be adherent to the sternal bone. The remainder of the sternum appeared normal. The skin overlying and surrounding this mass was thickened and alopecic.

Fine-needle aspiration of the nodule was attempted; however, manipulation appeared excessively painful, and the lesion was so firm that aspiration was not possible. Further diagnostic evaluation, including radiography and blood tests, were declined because of financial constraints.

From the physical examination findings, the lesion was suspected to be bony in origin, and the differential diagnoses included hyperplasia, infection, developmental malformation, or neoplasia. Surgical intervention was considered the most appropriate course of action because of the appearance of the lesion and the clinical effects on the bird.

The parrot was premedicated with butorphanol (1 mg/kg IM; Torbugesic, Fort Dodge Australia, Baulkham Hills, NSW, Australia) and midazolam (0.25 mg/kg IM). Induction was achieved with 4% isoflurane in 1 L/min oxygen administered via mask. After induction, the bird was intubated, and anesthesia was maintained via intermittent positive-pressure ventilation with a small-animal ventilator (Vetronic Services Ltd; Abbotskerswell, Devon, UK) on 2% isoflurane and 0.8 L/min oxygen. Intravenous fluids (Hartmanns Solution, Baxter Healthcare Pty Ltd, Toongabbie, NSW, Australia) were administered throughout the procedure via a 26-gauge catheter in the right basilic vein.

The lesion on the cranial aspect of the sternum was plucked and prepared aseptically with chlorhexidine gluconate diluted to 0.5%, and the area was draped with a sterile, plastic ophthalmic drape. The skin adjacent to the nodule was incised, exposing markedly thickened subcutaneous tissue. This was also incised to expose the stalk of the nodule, and rongeurs were used to transect the stalk, leaving a circular crater of approximately 2 mm depth in the sternal bone. The surgical area was irrigated with 0.5% bupivacaine (2 mg/kg). The periosteum was closed with a simple, continuous pattern with 40 polydioxanone suture material (PDS II, Ethicon; Johnson & Johnson Medical Pty Ltd, North Ryde, NSW, Australia). The skin was closed in the same fashion. An adherent wound dressing (Allevyn; Smith & Nephew Pty Ltd, Mount Waverley, VIC, Australia) was applied over the wound. The bird recovered uneventfully and was discharged on amoxicillin clavulanate (125 mg/kg PO q12h) and meloxicam (0.25 mg/kg PO q12h; Metacam 1.5 mg/mL, Boehringer Ingelheim, North Ryde, NSW, Australia).

The nodule was placed in 10% buffered formalin. On gross examination of the resected mass, it appeared to be of bone origin with an overlying capsule composed of multiple layers of tan-colored tissue sheets. In addition, the skin in the region of the mass was thickened, with a small focal area of superficial ulceration. The owner declined histopathologic examination initially, but on postoperative examination 10 days later, the surgical wound had developed a small amount of superficial crusting and subcutaneous soft tissue swelling. The owner had observed the bird fall onto wooden flooring during the healing time. Because of concern regarding reformation of the lesion, the owner at that time consented to histopathologic examination of the tissue sample.

[FIGURE 1 OMITTED]

Before routine processing, the sample was decalcified in formic acid and processed for paraffin-embedding and sectioning. The bony nodule seen in Figure 1 was composed of well-differentiated trabecular bone containing osteocytes and lined by osteoblasts and osteoclasts. Bone marrow spaces contained loosely packed, spindle-shaped cells and erythrocytes. The thick capsule of overlying periosteum and connective tissue surrounding the bony growth was primarily composed of an interweaving pattern consisting of spindle-shaped cells that resembled fibroblasts and merged with normal connective tissue, shown in Figure 2. Pale eosinophilic material resembling osteoid was observed in some areas of the tissue. The epidermal layer overlying the lesion exhibited evidence of a moderate, chronic, superficial perivascular dermatitis. Histiocytes and lymphocytes surrounded superficial dermal blood vessels, and the epidermis appeared to be acanthotic with orthokeratotic hyperkeratosis as well as a focal area of superficial ulceration of the keratin layer.

[FIGURE 2 OMITTED]

The lateral margins of the sample appeared clear of immature mesenchymal cells, although because of the difficulties in surgical removal, the deeper margin was unable to be adequately assessed. Based on these histologic findings, a tentative diagnosis of osteoma was made.

Aside from the initial postsurgical swelling, the owner has not reported a recurrence of the tumor in the 6 months after surgical treatment.

Discussion

Osteomas are rare, benign, slow-growing, monostotic, sclerotic tumors of membranous bone origin. (1-3) Histologically, these neoplasms comprise well-differentiated, mature lamellar bone, surrounded by connective tissue that often resembles periosteum. (4,5) Trabeculae of bone are often lined by normal osteoblasts and osteoclasts, and intertrabecular spaces are often filled with normal connective tissues, including adipose, cartilage, and hemopoietic tissue. (3) These features seen in osteoma are challenging to differentiate from other diseases of bone, including ossifying fibroma, fibrous dysplasia, and metaplastic ossification. (1,2,6,7) Diagnosis is usually best achieved with a combination of findings from physical examination, histopathologic examination, and imaging techniques. (7)

On histopathologic examination, osteomas appear to consist of more bone tissue than ossifying fibromas, with a less-dense area of cells in the intertrabecular connective tissues, (1,6,8) Osteomas arise from the surface of bone, have a distinct connective tissue border, and generally blend with normal bone tissue. (2) Ossifying fibroma lesions lead to replacement of the normal bone architecture. (2)

The features of fibrous dysplasia that differ from osteoma are poorly differentiated bone with woven bone spicules embedded in fibrous tissue and an absence of osteoblasts. (1,6,8) It has been suggested that fibrous dysplasia, ossifying fibroma, and osteoma are progressive stages of one disease process, ultimately resulting in osteoma. (1)

A primary osseous neoplasm was considered more likely than metaplastic ossification, given the well-formed trabecular bone core and the periosteal lining. Osteoma was considered the most likely of the benign mesenchymal tumors, which also include ossifying fibroma and fibrous dysplasia, because of the quantity of trabecular bone and the presence of osteoblasts and osteoclasts.

The use of radiography before surgical intervention may have provided additional information to aid in diagnosis, although financial restrictions did not permit this. The absence of aggressive neoplastic features, such as mitotic figures or a high nucleus to cytoplasmic ratio, precluded this lesion from being characterized as malignant.

Osteoma is rarely reported in the veterinary literature but has been documented in cattle, horses, sheep, dogs, mice, ferrets, pigs, cats, a camel, and a tawny nurse shark (Nebrius ferrugineus). (1,7,8-14) Reports in bird species are confined to budgerigars (Melopsittacus undulatus), domestic ducks (Anas platyrhynchos domestica), a chicken, a barred owl (Strix varia), and a yellow-collared lovebird (Agapornis personatus). (3,15-19) Osteomas in domestic mammals are commonly seen in the bones of the head, mandible, and nasal sinuses, whereas the tibia and femur are the most frequently recorded sites in humans. (1,2,20) The sternal location in this report is unusual. In the cases of osteoma that have been recorded in avian species, the affected sites have been described as the scapula, (16) humeroradial articulation, (17) tarsometatarsus, (15) foot-pad, (15) proximal radius, (3) or the cranium. (15,19) These tumors, although benign, can cause considerable morbidity in affected patients where the pressure of a lesion may disrupt the function and integrity of surrounding tissues. In domestic animals, tumors adjacent to the central nervous system have been reported to cause ataxia, paresis, and paralysis. (11-13) In humans, the most common presenting sign of osteoma is local pain, similar to this case. (21) Treatment of osteomas is reported to be curative, assuming the mass can be completely excised surgically. (3)

In humans, reported causes of osteomas are maldevelopment, trauma, and infection. (21,22) Additionally, a viral etiology has been proposed in mice and humans, after demonstration of viral inclusions in the osteoblasts within the studied osteomas. (13,23) In this case, a traumatic origin appears to be the most likely cause, with repeated trauma to the sternum observed by the owner. The location of the lesion is also comparable to the common skin tears, necrosis, and subcutaneous abscesses seen at the cranial and caudal sternal borders in pet birds because of poor flight management.

Falling and heavy landings in pet birds are commonly associated with inappropriate trimming of the flight feathers, often leading to a variety of injuries including sternal, pygostyle, beak, and leg injuries. (24) Although recommendations exist for the number of primary flight feathers that should be trimmed, (24) these should be considered in conjunction with additional factors, such as age and species. The bird in this case was probably prevented from flight at an early age, impeding the development of flight skills and leading to an increased risk of poor landing. Additionally, this species of bird often exhibits a heavy build compared with similar-sized psittacid birds and appears to require fewer feathers to be removed to prevent lift. (25) Allowing a young bird to learn the skills of flight before wing trimming and a staged wing-trimming procedure with test flying may be beneficial in preventing wing-trim related injuries.

Although a definitive diagnosis in this case could not be achieved by histopathology alone, a more aggressive process, such as malignant neoplasia, was eliminated from the possibilities based on histologic findings. From a clinical perspective, ruling out malignant neoplasia was the most useful information to be gained from histopathologic review of the tissue. An accurate diagnosis, however, would allow a more precise treatment plan if the mass recurred in the future. A traumatic origin is considered the most likely cause, regardless of the exact process, so recurrence of the lesion may be preventable by avoiding sternal trauma.

This case illustrates the difficulties that can occur when relying on a singular diagnostic modality, particularly when dealing with benign bone neoplasms. Osteoma is a rare diagnosis in humans and animals but should be considered by the clinician when presented with a bony lesion. This case also highlights the need for appropriate flight management in our captive birds.

References

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(24.) Doneley B. Wing clipping in birds. Aust Vet Pract. 2009;39:102-104.

(25.) Beaufrere H. A review of biomechanic and aerodynamic considerations of the avian thoracic limb. J Avian Med Surg. 2009;23(3):173-185.

Melinda Lee Cowan, BVSc (Hons), Pi-Jie Yang, BVSc, Deborah Jane Monks, BVSc (Hons), CertZooMed, Dipl ECAMS, FACVSc (Avian Medicine), and Shane Robert Raidal, BVSc (Hons), PhD, FACVSc

From the Brisbane Bird and Exotics Veterinary Service, Corner Kessels Rd and Springfield St, Macgregor, Queensland 4109, Australia (Cowan, Monks); and the Veterinary Diagnostic Laboratory, School of Animal and Veterinary Sciences, Charles Sturt University, Wagga Wagga, New South Wales 2678, Australia (Yang, Raidal).
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Author:Cowan, Melinda Lee; Yang, Pi-Jie; Monks, Deborah Jane; Raidal, Shane Robert
Publication:Journal of Avian Medicine and Surgery
Article Type:Case study
Date:Dec 1, 2011
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