Cardiac myxoma is a benign neoplasm which originates from mesenchymal cells and can differentiate into several other cell types. It is very common in human beings, but rarely reported in animals. The exact histogenesis is unknown, but it has some characteristics that do not exist in any other cardiac neoplasia, which serves to confirm the diagnosis. The clinical signs may vary, but generally involve classic signs of cardiopathy, like pleural effusion, ascites, exercise intolerance, syncope, among others. The surgical treatment has been reported, but with only one case of real success. The objective of the present work is to report a case of a dog, male, Shih-tzu, seven years-old, that was admitted with signs as apathy, inappetence, slimming and discrete increase of abdominal volume. A mass adhered to the tricuspid valve was visualized on the echocardiogram examination, which measured 3, 3 cm x 2, 3 cm in extension, besides other cardiac alterations. The option for supportive treatment was made to prolong the survival and provide quality of life to the animal. The animal had some periods of improvement but ended up dying six months after the initial presentation and had the diagnosis of myxoma after histopathological examination, a very uncommon neoplasm in dogs.

• Oncology; Cardiopathy; Benign; Neoplasm

Martinello Romão LM, de Souza FB, Romão FG (2021) Primary Cardiac Myxoma of Tricuspid Valve in a Dog: Case Report. J Vet Med Res 8(1): 1206

g: grams, mg: milligrams, kg: kilograms, dL: deciliters, SID: Semel in die, BID: Bis in die

The origin of cancer in human history is related to habits, environmental and cultural factors [1]. It has a similar pathogenic process both in human beings and in animals [2]. Neoplasms are the leading cause of death in dogs and may also be in cats [3].

Tumors with cardiac involvement are uncommon, occurring in only 0.19% of dogs, and are often incidental findings [4, 5]. Elderly dogs are usually affected, since most cases occur after 10 years-old. Only cardiac lymphomas are more common in animals under 7 years of age. Gender does not influence the occurrence of cardiac tumors, since males and females are equally affected, but spayed animals are at higher risk of developing the disease [6].

Cardiac myxoma is a benign neoplasm derived from multipotential mesenchymal cells that differentiate into several other cell types [4], which occurs in the subendocardial layer [7]. The first case of cardiac myxoma reported in dogs was in 1959. After that, there were some other reports mainly involving the right atrioventricular valve [8]. It is the most common primary cardiac tumor in humans, but rare in animals [4]. It is estimated that in people it represents almost half of benign cardiac tumors and a quarter of all tumors and cysts of the heart and pericardium [7].

Clinical signs will depend on the location and size of the tumor [8]. About 30 to 40% of people affected with myxomas on the left side of the heart have cerebral or visceralembolization into coronary arteries [4]. In cardiac myxomas on the right side of the heart, embolism is infrequent, but it can happen. These embolisms are not classified as metastases, since they do not have features of malignant neoplasia and do not spread to lymph nodes and viscera [7]. Depending on the size and location of the myxoma, signs of outflow tract obstruction may occur, which leads to the same signs of mitral or tricuspid valve stenosis. Myxomas of mitral valve differ from others because they cause fewer clinical manifestations [4].

The diagnosis may be suggested by diagnostic imaging, such as echocardiography, computed tomography or magnetic resonance imaging [4], but the confirmation is made by histological findings that only myxomas have [7].

The exact histogenesis is not yet clarified [8]; however, the microscopic appearance of myxomas is generally described as a hypocellular mass with an amorphous polysaccharide acid matrix covered by a single layer of endothelial cells supported by spindle to stellate and elongated cells, scattered in an abundant stroma, both in dogs and humans. Since no other cardiac neoplasm has these characteristics, it is possible to confirm the diagnosis in dogs with these histological findings [7].

The treatment of choice in humans is complete surgical removal of myxoma, despite reports of tumor recurrence a few months or even years after the first surgical removal [4]. In dogs, there are two reports of success in surgical removal; in one of them, a myxoma in the right atrium, the patient died one day after surgery; the other, affected by a myxoma in the right ventricle, had a two-year survival [8].

The objective of this work is to report a case of a Shih tzu dog, with a diagnosis of myxoma of tricuspid valve, that underwent palliative treatment, when it had some improvements in its clinical scenario, but with recurrence of clinical signs after certain follow-up periods. After six months of treatment, the animal died due to complications of right congestive heart failure; in general, the patient had a 13-months survival after initial diagnosis, higher than that reported by literature.

A 7-year-old male Shih tzu was admitted on a referral center with apathy, inappetence, weight loss and discrete increase in abdominal volume. Six months before, he was diagnosed with a neoplasm in the tricuspid valve, and furosemide (2.6 mg/kg/IDB), pimobendan (0.25 mg/kg/Bid) and benazepril hydrochloride (0.5 mg/kg/SID) were prescribed by the clinician for one month. The patient began to present the signs mentioned above after the administration of these medications.

On physical exam, grade V/VI murmur was auscultated on tricuspid focus; also, pale mucous membranes, tachycardia and discrete ascites were noted. On the electrocardiogram, sinus rhythm was detected, with the presence of left anterior fascicular block, while on the echocardiogram a spherical structure of heterogenous aspect and defined contours was visualized, adhered to the tricuspid valve, measuring 3.3 cm x 2.3 cm in length. There was a turbulent flow within the right ventricle (secondary to possible obstruction), significant increase in right atrium, left ventricular pseudohypertrophy (secondary to decreased preload) and diastolic dysfunction due to abnormal myocardial relaxation. Additionally, on hematology, mild thrombocytosis and azotemia (creatinine 1.8 mg/dL and urea 94 mg/dL) were observed. Liver function was normal, as were electrolyte concentrations.

After these findings, furosemide administration was suspended; also, benazepril hydrochloride was maintained, in addition to the prescription of spironolactone (2 mg/kg/ BID), because of mild ascites. Daily subcutaneous fluid therapy was also performed for one week and then weaned to every 48 hours; additionally, pimobendan was ta, because the tutor reported anorexia, apathy and emesis after administration of the medication; after its suspension, the animal improved these signs.

The patient remained in a stable clinical condition for approximately one month until he became apathetic again and with a large increase in abdominal volume. Abdominocentesis was performed, and furosemide (1.8 mg/kg/SID), pimobendan (0,1 mg/kg/BID) was gradually redirected and spironolactone was maintained. Benazepril hydrochloride was suspended because the tutor reported that the animal was dull after its administration. After that, the animal started eating by himself, and the only abnormalities observed on biochemical panel were increased serum creatinine levels (1.7 mg/dL) and hypoalbuminemia (2.0 g/dL).

After another month, the tutor reported worsening in the patient’s condition once again, with signs as apathy and anorexia. Due to apathy and pale mucous membranes, the pimobendan dose (0.15 mg/kg/BID) was gradually increased to 0.25 mg/kg/ BID; also, a hypercaloric diet was recommended.

Five months after the first visit, during a period that the animal was clinically well, the ascites was aggravated and weekly abdominocentesis was necessary, in which it was drained around 900 to 1000 mL in each procedure. Owners reported hyporexia, progressive weight loss, and then anorexia. The following medications were prescribed: silymarin (20 mg/kg/ SID) and S-adenosyl-methionine (20 mg/kg/SID), in addition to maintenance of spironolactone, furosemide and pimobendam.

The animal died seven months after initial presentation. On post mortem exam, a 5.5 × 5 × 3 cm, white and brownish, firm to elastic smooth-surfaced pedunculated mass (Figure 1) was found arising from the tricuspid valve. Microscopically (Figure 2), histological sections of the heart and tricuspid valve were analyzed. The neoplasm was multinodular, not encapsulated and composed of spindle mesenchymal cells immersed in a stroma with abundant amount of myxoid matrix. The cells presented cytoplasm of different limits, homogeneous acidophilic, oval to round nuclei, with fine chromatin and indistinct nucleoli. The atypia index was low and there were rare mitoses. The surface was coated with a single layer of endothelium cells, which sometimes formed vessel-like structures. At some points, there was ulceration with deposition of fibrin and an abundant amount of hemosiderophages inside the tumor. Based on these results, myxoma diagnosis was confirmed.

Myxoma is the most common primary cardiac tumor in adult human patients, but extremely rare in animals. It is usually reported its occurrence in the atriums, mainly left atrium, and less often in ventricles and valves [4]. Usually, myxomas arise from the dermis, and rarely primarily in the heart; to our knowledge, there are only reports of five primary cardiac myxomas in dogs to date [7-11].

Apparently, there is no breed, size or gender predilection associated to myxomas. Cases have been reported in adult or elderly dogs, and the dog reported in this study was 7 yearsold, thus similar to the age of the dogs reported by other studies [7,8,10].

Clinical signs will depend on where the myxoma is located, its size and mobility [4]. In the present case report, signs of right CHF were observed, as the myxoma was located in the tricuspid valve, also described by other authors [8].

It has also been described that animals with neoplasms of tricuspid valve usually present ascites as a result of CHF [8], as occurred in the case reported, when abdominocentesis procedures were necessary to relieve symptoms, draining between 900 and 1000 ml of free fluid on a weekly basis.

Although surgical removal is the treatment of choice in humans, in veterinary medicine there was only one case of real success in surgery, with a 2-year survival recurrence free after tumor removal [10]. The choice for clinical treatment was made by the owner, due to the high cost and relative unavailability of cardiac surgery in Brazil.

Therapy prescribed included furosemide, pimobendan, benazepril (chosen instead of enalapril, because of renal parameters) and spironolactone, which aimed to attenuate the clinical signs of CHF, as described by other authors [3,12]. The option of adding silymarin and S-adenosyl-methionine at the end of treatment was due to the liver injury that the patient presented. There is paucity of data regarding survival time of patients with myxoma. Sudden death in a dog with the disease was reported [8], while other colleagues [4] opted for palliative treatment, with a 11-months-survival after diagnosis (owners opted for euthanasia after this due to complications caused by CHF), a period similar to the case reported in this study, in which the patient lived just over 1 year after diagnosis, with palliative treatment.

The microscopic appearance of myxomas was described as a hypocellular mass with an amorphous polysaccharide acidophilic matrix covered by a single layer of endothelial cells, supported by an abundant stroma composed of fusiform, stellated and elongated cells [7]; histopathological exam of the mass had these features, which made it possible to confirm the diagnosis of cardiac myxoma in the tricuspid valve.

1. Daleck CR, De Nardi RB, Rodaski S. Oncologia em cães e gatos. São Paulo: Roca. 2010.

2. Villalobos A, Kaplan L. Canine and feline geriatric oncology. 2018.

3. Nelson RW, Couto CG. Small animal internal medicine. Elsevier. 2015.

4. Palacio MJFD, Sanchez J, Talavera J, Martinez C. Left ventricular inflow tract obstruction secondary to a myxoma in a dog. J Am Anim Hosp Assoc. 2011; 47: 217-223.

5. Treggiari E, Pedro B, Dukes-McEwan J, Gelzer AR, Blackwood L. A descriptive review of cardiac tumours in dogs and cats. Vet Comp Onco. 2017; 15: 273-288.

6. Tilley LP, Goodwin JK. Manual de cardiologia para cães e gatos. Sao Paulo. 2002.

7. Machida N, Hoshi K, Kobayashi M, Katsuda S, Yamane Y. Cardiac myxoma of the tricuspid valve in a dog. J Comp Pathol. 2003; 129: 320-324.

8. De Nijs MI, Vink A, Bergmann W, Szatmári V. Left ventricular cardiac myxoma and sudden death in a dog. Acta Vet Scand. 2016; 58: 41.

9. Darke PG, Gordon LR. Cardiac myxoma in a dog. Vet Rec. 1974; 95: 565-567.

10. Bright JM, Toal RL, Blackford LM. Right ventricular outflow obstruction caused by primary cardiac neoplasia. J Vet Int Med. 1990; 4: 12-16.

11. Akkoc A, Ozygit MO, Cangul IT. Valvular cardiac myxoma in a dog. J Vet Med. 2007; 54: 356-358.

12. Jericó MM, Neto JPA, Kogika MM. Tratado de medicina interna de cães e gatos. Guanabara Koogan; 2017.