What Is Your Diagnosis?
A free-living, second-year red-tailed hawk (Buteo jamaicensis) was presented to the Carolina Raptor Center after being seen down on the ground by a member of the public. It was approachable and captured easily.
On presentation, the bird was bright, alert, and responsive and in good body condition (829 g, with a body condition score of 3/5). Results of the physical examination were unremarkable with the exception of a large (6x4 cm), soft, subcutaneous mass over the lateral aspect of the right tibiotarsus.
The mass had a large, bloody laceration on the lateral aspect that appeared to be a talon-related injury. A small swelling was present on the lateral aspect of the left tibiotarsus.
The bird was anesthetized with isoflurane administered by mask at 2%-3%, and radiographs were taken (Fig 1). The bird was treated with lactated Ringer's (30 mL SC) and started on enrofloxacin (15 mg/kg PO q12h; Baytril, Bayer Healthcare, Shawnee Mission, KS, USA), meloxicam (0.5 mg/kg PO q12h), and terbinafine (15 mg/ kg PO q12h) as a preventative for aspergillosis.
The next day, the bird was premedicated with butorphanol (2 mg/kg IM) and lactated Ringer's (30 mL SC). The bird was then induced with 3% isoflurane via mask and intubated with a 3.0-mm uncuffed endotracheal tube. The leg was aseptically prepared (Fig 2) and draped for surgery, and an elliptical incision was made near the circumference of the mass. The overlying skin was undermined from around the perimeter, and the mass was quickly removed with blunt dissection. The mass was mostly well-encapsulated with minimal attachments to the underlying fascia and muscle. Bleeding was minimal, and the blood that was seen was pink, very opaque, and milky (Fig 3). The wound was partially closed after a large area of redundant skin was removed. The dead space was packed with gauze, and the ventral end was left open to drain. The entire procedure was completed in 23 minutes; however, during closure, the bird's heart rate began to decline and its respiration became shallow. The isoflurane was turned off, 2 doses of doxapram (9 mg IM/intratracheal) were administered, and manual positive pressure ventilation was begun. The heart rate normalized but normal respirations did not return, and the bird was euthanatized after not regaining consciousness after 30 minutes.
The mass weighed 120 g and had a thick fibrous wall and necrotic, cavernous interior. At gross postmortem examination, the bird was in relatively good condition (score of 2.5/5), and all internal organs appeared normal except the intestines, which were very pale, appearing almost white. Symmetrical, 34-mm subcutaneous masses were present on the ventral side of each elbow; a similar mass adhered to the intestines, and a 3-4-cm mass was on the lateral aspect of the left tibiotarsus. All masses appeared identical to each other and to the larger excised mass. The blood that leaked from the larger transected vessels was pink and milky in consistency.
Histopathologic examination of a section of the wall of subcutaneous mass was examined. The wall consisted of large, intact, and ruptured foamy cells, with capillaries arranged in perpendicular fashion. In the deep layer of the wall was an area of dense heterophilic exudate. An area in the wall had extensive deposits of eosinophilic proteinaceous material. The diagnosis based on these findings was subcutaneous xanthoma.
In the veterinary literature, inconsistent terminology, including xanthoma, xanthomatosis, and xanthogranuloma have all been used interchangeably when referring to this disease process. A xanthoma has been described as a distinct mass composed of lipid-laden macrophages, free cholesterol, giant cells, and fibrosis. These tend to be yellow, friable, firm masses and may be featherless, ulcerated, or both. (1) A xanthoma is not neoplastic. Xanthomatosis is an inflammatory response and is similar but lacks discrete margins, and xanthogranulomas include characteristics of both xanthomas and granulomas. (2) In green water dragons (Physignathus cocincinus), the lesions were described as cholesterol granulomas. (3) The common characteristic of these lesions is the presence of vacuolated or foamy macrophages. Although individual lesions may have various histologic components, it has been proposed that these 3 terms be replaced with xanthogranulomatosis to describe any syndrome where intracytoplasmic lipid is found within macrophages. (4)
In human medicine, xanthomas often arise in areas of repeated trauma or pressure points, such as knees and elbows. They are also present in tendons, with the most common site being the Achilles tendon, but they can also be located in the tendons of the hand, the elbow, and the patellar tendon/
The exact epipathogenesis of xanthogranulomatosis is unknown. They are most commonly associated with abnormal levels of lipoproteins such as primary or secondary hyperlipidemia. Therefore, the preferred treatment in these cases involves treating the metabolic disorder of lipid metabolism. (6) Conversely, while commonly caused by familial hypercholesterolemia, tendon xanthomas are not always associated with elevated levels of lipids. (7) Similarly, a case study of a cutaneous xanthoma in a normolipemic cat suggested a link between pruritus and xanthoma formation. (8)
Avian xanthomatosis is relatively common in psittacine and gallinaceous birds, possibly because of high lipid diets and their more sedentary lifestyles. (9,10) In a great white pelican (Pelecanus onocrotalus) with subcutaneous xanthomatosis (11) and a goose (Anser anser) with atypical multiple, xanthomatous, cutaneous neoplasia, (12) hyperlipidemia was thought to be a potential cause. Other studies have shown presentation of these lesions in normolipemic animals, such as tracheal granulomatosis in a red-tailed hawk, (4) a periosseous xanthogranulomatosis in a fledgling great horned owl (Bubo virginianus), (2) and cutaneous xanthoma in a cat. (8) In these cases, trauma was suggested as the primary cause. Results of a histopathologic study in rabbits found that vasculature-rich conditions combined with mechanical stress on an area led to xanthoma formation. (13)
Whatever the ultimate cause, treatment typically involves surgical resection of the lesions, as well as treatment of the underlying lipid disorder, if present. A case study of xanthomatous neoplasia in a goose found that treatment with chemotherapy was ineffective. (12)
Of additional interest in this case is that this bird did not survive the surgical procedure. The procedure itself was relatively short, did not have any complications, and had very little blood loss. The bird was stable throughout the procedure but became apneic and never recovered despite attempts at resuscitation. Possibly, severe lipemia may have led to cardiovascular compromise or an embolic event. In this case, a plasma biochemical analysis was not obtained, so the actual levels of cholesterol and triglycerides are not known. However, the gross appearance of the blood during surgery and postmortem examination were indicative of significant lipemia. In retrospect, preoperative blood tests may have been helpful. In this case, the bird was young and in apparently very good health (other than the mass), and the surgical procedure was expected to be relatively uncomplicated, so blood tests were not done.
Hypercholesterolemia has been shown to have adverse cardiovascular effects, although the literature is sparse with respect to avian physiology. Toda et al (14) demonstrated significant vascular pathology in chickens with hyperlipidemia, and Xu et al (15) showed that hypercholesterolemia has adverse effects in people during general anesthesia with sevoflurane. It is unclear if the anesthetic death was due to the severe lipemia in this bird.
Xanthogranulomatosis should be considered a differential diagnosis for any subcutaneous mass in a bird. A definitive diagnosis must be made by histopathologic examination; however, the distinct yellow, friable appearance is very indicative of this type of lesion. The masses can be quite large and surgical resection can often be curative. However, careful consideration should be given to underlying causes, such as hypercholesterolemia, and efforts (either dietary or medical) should be made to correct any elevations. Finally, avian practitioners should be aware of possible anesthetic risks associated with surgical removal of masses in potential hypercholesterolemic patients.
This case was submitted by David Scott, DVM, Carolina Raptor Center, Huntersville, NC 28078, USA.
(1.) Chitty J, Lierz M, eds. BSAVA Manual of Raptors, Pigeons and Passerine Bird. Gloucester, UK: British Small Animal Veterinary Association; 2008:290.
(2.) Raynor PL, Kollias GV, Krook L. Periosseous xanthogranulomatosis in a fledgling great horned owl (Bubo virginianus). J Avian Med Surg. 1999; 13(4):269-274.
(3.) Kummrow MS, Berkvens CN, Pare JA, Smith DA. Cerebral xanthomatosis in three green water dragons (Physignathus cocincinus). J Zoo Wildl Med. 2010;41 (1): 128-132.
(4.) Monks DJ, Zsivanovits HP, Cooper JE, Forbes NA. Successful treatment of tracheal xanthogranulomatosis in a red-tailed hawk (Buteo jamaicensis) by tracheal resection and anastomosis. J Avian Med Surg. 2006;20(4):247-252.
(5.) Tsouli SG, Kiortis DB, Argyropoulou MI. et al. Pathogenesis, detection and treatment of Achilles tendon xanthomas. Eur J Clin Invest. 2005;35(4): 236-244.
(6.) Malleshappa A, Sonoli S, Jabannavar V, Manjunathswamy BS. Xanthoma-cutaneous marker for lipo-protein disorder. Int J Innov. 2013;4(3): 13-16.
(7.) Koopal C. Visseran FLJ, Marais AD, et al. Tendon xanthomas: not always familial hypercholesterolemia. J Clin Lipidol. 2016:10(5): 1262-1265.
(8.) Ravens PA, Vogelnest LJ, Piripi SA. Unique presentation of normolipaemic cutaneous xanthoma in a cat. Aust Vet J. 2013:91(11):460-63.
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(11.) Di Girolamo N, Lane EP, Reyers F, et al. Subcutaneous xanthomatosis in a great white pelican (Pelecanus onocrotalus). J Zoo Wildl Med. 2014:45(1): 153-156.
(12.) Jaensch SM, Butler R. O'Hara A, et al. Atypical multiple, papilliform, xanthomatous, cutaneous neoplasia in a goose (Anser anser). Aust Vet J. 2002;80(5):277-280.
(13.) Nakano A, Kinoshita M, Okuda R, et al. Pathogenesis of tendinous xanthoma: histopathological study of the extremities of Watanabe heritable hyperlipidemic rabbits. J Orthop Sci. 2006:11(1): 75-80.
(14.) Toda T, Leszczynksi D, Nishimori 1, Kummerow F. Arterial lesions in restricted-ovulator chickens with endogenous hyperlipidemia. Avian Dis. 1981:25(1): 162-178.
(15.) Xu Y, Ma LL, Zhou C, et al. Hypercholesterolemic myocardium is vulnerable to ischemic-reperfusion injury and refractory to sevoflurane-induced protection. PLoS ONE. 2013;8(10):e76652.
Caption: Figure 1. Ventral-dorsal radiograph of a free-living red-tailed hawk that was presented for examination after being found down on the ground. A large mass is visible on the lateral aspect of the right tibiotarsus, and a small swelling is present over the lateral aspect of the left tibiotarsus.
Caption: Figure 2. The red-tailed hawk described in Figure 1 showing the leg mass being aseptically prepped for surgery.
Caption: Figure 3. Intraoperative photograph of the red-tailed hawk described in Figure 1, with the leg mass partially resected. The blood has a pink, opaque appearance because of severe hyperlipidemia.
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|Publication:||Journal of Avian Medicine and Surgery|
|Date:||Mar 1, 2019|
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