Metastatic Atrial Infiltrative Chemodectoma in a Bitch

Abstract

Background: Cardiac neoplasms are rare in dogs, typically affecting those aged 7 to 15 years. These tumors can be primary or secondary, benign or malignant. Chemodectoma, a primary cardiac tumor, is uncommon in dogs. This report aims to describe the clinical signs, diagnostic approaches, and progression of a bitch with metastatic malignant chemodectoma.

Case: A 8-year-old spayed crossbred bitch, weighing  20 kg, was evaluated due to a 1-month history of weight loss, lymphadenomegaly, and edema in the face and submandibular region. The animal exhibited signs of apathy, muffled heart sounds, and a grade I-II systolic murmur. Chest X-rays revealed pleural effusion, which was drained. An echocardiogram identified a 4 cm x 6.89 cm mass in the aortic wall compressing the right atrium. Computed tomography examination identified a heart with a configuration and dimension within species' standards, and a 6.6 cm x 5.8 cm amorphous structure at the base of the heart, between the atria, with enhanced contrast uptake. The owner opted for palliative care, but the bitch's general condition deteriorated, leading to euthanasia after 2 months. Necropsy revealed a multilobulated mass at the cardiac base with atrial infiltration. Histology suggested a neoplasm consistent with metastatic malignant chemodectoma or pheochromocytoma. Immunohistochemistry with neuroendocrine markers confirmed the diagnosis of chemodectoma, showing strong positive results for synaptophysin and chromogranin.

Discussion: The diagnosis of cardiac neoplasms relies on clinical history, physical examination, chest radiographs, and echocardiography. The echocardiogram is considered to have high specificity and sensitivity for detecting and characterizing masses, especially with the presence of pericardial effusion, but is moderately accurate as a presumptive diagnosis concerning the type of tumor. In this case, all of these exams were performed, and computed tomography was also used to help determine the extent of the lesion and the involvement of adjacent structures. Although cytological examination of the pleural fluid was performed in the present case, the cells of the chemodectoma do not desquamate, so the examination of fluid drained from the pleural or pericardial cavity does not aid in the diagnosis. In turn, the collection of samples of cardiac masses, whether by fine needle aspirates or biopsies, although feasible, is often avoided due to the potential risk of arrhythmia and hemorrhage. For this reason, in vivo diagnosis of the disease is challenging. Despite histopathological findings in the present report resembling those previously described (such as oval or cuboidal to polyhedral cells with vacuolated granular cytoplasm, round to oval nuclei, and fibrovascular stroma), the findings were inconclusive, and immunohistochemical examination was necessary. Although non-specific, neuroendocrine markers indicated to characterize chemodectomas include chromogranin A, synaptophysin, and neuron-specific enolase, among others. In the current report, synaptophysin and chromogranin markers were used. The neuroendocrine marker synaptophysin is considered to have a broad spectrum and greater sensitivity, but it has less specificity than the chromogranin A antibody. In malignant tumors, chromogranin A may be less marked, since the number of secretory granules is reduced. In conclusion, this clinical case emphasizes that underdiagnosis of chemodectoma can be minimized through history and complementary exams, such as histopathology and immunohistochemistry, to achieve better guidance in the treatment and prognosis of the animal. 

Keywords: primary neoplasm, heart, chemoreceptors, immunohistochemistry.

Título: Quimiodectoma infiltrativo atrial metastático em uma cadela

Descritores: neoplasia primária, coração, quimiorreceptores, imunohistoquímica.