Tibiotarsal Subcutaneous Xanthogranuloma in a Rose-breasted Cockatoo (Eolophus roseicapilla): A Case Report

Case History
Xanthomas (also known as xanthogranulomas) are rare non-neoplastic and non-infectious granulomatous lesions. Grossly, they appear as variably sized, mostly nodular, yellowish (as the name implies) soft masses stemming from abnormal intracellular and extracellular cholesterol accumulation (Benoit-Biancamano & Langlois, 2020; Lennox, 2014; Mauldin & Peters-Kennedy, 2016; Schmidt et al., 2015). Histologically, they present as large lipid-laden foamy macrophages, multinucleated giant cells (sometimes Touton giant cells), and cholesterol clefts. Lymphocytic and heterophilic infiltrates are usually observed (Mauldin & Peters-Kennedy, 2016; Reavill & Dorrestein, 2018; Schmidt et al., 2015; Stacy et al., 2021). Xanthomas have been reported in humans (Benoit-Biancamano & Langlois, 2020) as well as a broad range of animals, such as frogs (Carpentear et al., 1986), fish (Béland et al., 2020), dogs (Harvey et al., 2020; Russell & Courtman, 2019), cats (Barachetti et al., 2021), cattle (Özmen et al., 2014), birds, and even reptiles, however, uncommon (Stacy et al., 2021). In recent years avian xanthomas have been reported in various species such as Japanese quails (Coturnix japonica) (Sasikala et al., 2018), blue and gold macaws (Ara ararauna) (Souza et al., 2009), cockatiels (Nymphicus hollandicus) (Lipar et al., 2011; Pazhanivel et al., 2018), great white pelicans (Pelecanus onocrotalus) (Di Girolamo et al., 2014), budgerigars (Melopsittacus undulatus) (Shokrpoor et al., 2019), and Eclectus parrots (Eclectus roratus) (Hanson et al., 2020). Xanthogranulomas have been reported in the cutaneous and subcutaneous tissues and tendons. Also, there are uncommon records of visceral involvement (Benoit-Biancamano & Langlois, 2020; Reavill & Dorrestein, 2018; Schmidt et al., 2015). Eyelids and the skin covering the face, wings, sternum, ventral abdomen, pubis, and thighs are the commonly affected anatomic regions in birds (Reavill & Dorrestein, 2018; Trupkiewicz et al., 2018). Despite the ambiguity on the underlying cause, mechanical stress (Stacy et al., 2021), chronic trauma (Lennox, 2014), and inflammation (Hanson et al., 2020) are suspected to be the predisposing factors to the disease. Genetic predisposition (such as storage disorders), metabolic impairments, renal disorders, endocrinopathies, and high-lipid feed consumption can lead to dyslipidemia (e.g. hypercholesterolemia and hyperlipidemia), thus increasing the risk of xanthomas (Barboza & Beaufrère, 2019; Hanson et al., 2020; Reavill & Dorrestein, 2018; Stacy et al., 2021). Lipoma, xanthoma, and spindle cell tumors (especially fibrosarcoma) are the primary differential diagnoses of such soft subcutaneous masses (Chang et al., 2019; Latimer & Rakich, 1995; Stacy et al., 2021). This paper presents a case of xanthogranuloma in an uncommon anatomic region in a rose-breasted cockatoo. The surgical excision process, macroscopic findings, histopathologic features, routine hematoxylin and eosin (H&E) staining, and Oil Red O special staining are described.

Clinical Presentation
In January 2022, a 350-g, 5-year-old, rose-breasted cockatoo (Eolophus roseicapilla) (Galah) was referred for assessment of a non-pruritus and non-painful soft subcutaneous mass on the medial aspect of the tibiotarsal region for the past 7 days (Figure 1). The animal’s diet was mainly composed of nuts and seeds (mostly pumpkin seed, sunflower seed, and hemp seed), boiled eggs, human food, and occasionally fruits. Upon physical examination, concurrent bacterial airsacculitis, most remarkable in thoracic and clavicular air sacs, was diagnosed in the bird. Due to the severity and urgency of the respiratory condition, antibiotic therapy took precedence over the surgical removal of the mass. During 3 weeks, aminophylline was administered in conjunction with enrofloxacin through nebulization. Surgical excision was planned because the mass grew significantly during the treatment course. 

The anesthesia was induced by delivering isoflurane through a face mask connected to an Ohmeda anesthesia machine (Ohmeda Inc, United States). Then, an endotracheal catheter was placed and connected to a Mapleson-F Open Respiratory Circuit, delivering isoflurane to the patient for maintaining anesthesia. The mass was finely dissected from the underlying tissues and excised thoroughly from the region. There were some invasions to the underlying tissues and muscles, which were freed easily. The bone was intact with no grossly evident invasion. The bird was recovered from anesthesia and discharged after 2 hours. The wound healed after 10 days with no gross appearance of relapse of the mass, but unfortunately, the bird died after 1 month due to respiratory disorders. 
The excised tissue was immersed in 10% neutral buffered formalin. Following the gross inspection, representative sections were obtained, processed routinely, embedded in paraffin, cut at 5-µm thickness, and stained with H&E for histopathologic evaluation. Frozen sections were also obtained from the mass and stained with Oil Red O to detect lipid accumulation. 

Diagnostic testing
Subcutaneous connective tissue and muscle invasion were noted throughout the surgery, sparing the bones. Upon gross inspection, a 2×1.5×1.2 cm irregular, yellowish tan, soft, and friable mass was detected with multifocal superficial hemorrhage. The cut surface showed a vivid yellow material deposition (Figure 2).

Histopathologic scrutiny revealed sheets of densely packed foamy and lipid-laden macrophages, heterophilic inflammatory infiltrates (Figure 3), numerous multinucleated giant cells, and cholesterol clefts (Figure 4).

Lipid-laden macrophages and extracellular lipid deposits were positively stained with Oil Red O (Figure 5).

 Assessment
Xanthogranulomas are sterile granulomatous lesions composed of finely vacuolated macrophages, multinucleated giant cells, cholesterol clefts, and crystals, with occasional necrosis (Mauldin & Peters-Kennedy, 2016; Stacy et al., 2021), matched with the findings in the present case. Xanthomas may be single or multiple (xanthomatosis) (Mauldin & Peters-Kennedy, 2016; Trupkiewicz et al., 2018), nodular (Mauldin & Peters-Kennedy, 2016), or disseminated (Carpentear et al., 1986; Hanson et al., 2020). Diagnosis can be made by histopathology. Surgical excision (Koski, 2002), radiation therapy, hyperthermia (Filippich, 2004; Koski, 2002), and sufficient dietary vitamin A (Reavill & Dorrestein, 2018) have been proposed for treatment. Xanthomas may lead to focal feather loss without feather-picking (Koski, 2002). This lesion is more frequent in psittacine (Psittaciformes order), predominately in older budgerigars and cockatiels (Reavill & Dorrestein, 2018). However, other avian orders, including Columbiformes, Anseriformes, and Accipitriformes, have also been affected (Hanson et al., 2020). Budgerigars and cockatoos, especially galah or rose-breasted cockatoos (Eolophus roseicapilla), are prone to developing lipomas (Filippich, 2004; Koski, 2002). Despite the benign nature, the surrounding tissues may be massively invaded by xanthomas (Kubiak, 2021), which was seen in our patient. In terms of etiology, the lipid-rich diet of this bird (majorly composed of pumpkin seed, sunflower seed, hemp seed, and boiled eggs) and lack of any clinical signs related to renal diseases or endocrinopathies explain the propensity of developing xanthogranuloma. It is well-established that high-fat diets and hyperlipidemia are linked to developing xanthomas (Stacy et al., 2021). Moreover, the owner rejected any previous local trauma, inflammation, or irritation; such lesions were absent in the patient’s health records. It can be concluded that stress, dietary imbalance, and consumption of lipid-rich feed are the leading underlying causes of the development of xanthogranuloma in this patient.

Ethical Considerations

Compliance with ethical guidelines
The patient’s owner provided written informed consent for the treatment and diagnostic work-up, follow-up of their pet, and participation in this case report.

Funding
This research received no financial support for this research, diagnostic work-up, authorship, or publication.

Authors' contributions
Supervision, investigation and funding acquisition: Farhang Sasani; Conceptualization, methodology, investigation, resources, original draft preparation: Diba Golchin; Data collection and investigation: Mohammad Yasan Bangash, Soheil Khorasaninejad and Sanaz Banifazl; Review & editing: All authors.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
The authors would like to thank Fahimeh Babaahmadi Milani for her invaluable technical support.

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