Presumptive metastatic leiomyosarcoma in a feedlot steer.

A 14-month-old feedlot steer was depressed and died while being examined. The gross post-mortem examination of the steer conducted at the feedlot identified numerous masses within the abdomen and thorax, including a large mass in the liver that eroded into the vena cava. Many masses in the lungs appeared to be the result of hematogenous distribution. Histologic examination of the masses confirmed the presence of neoplasia. Although the histologic appearance of the neoplasms was not typical of well-differentiated leiomyosarcoma, immunohistochemical staining supported that diagnosis. Leiomyosarcomas are rare among North American cattle. In this case, the primary neoplasm appears to have originated in the wall of the vena cava within the liver. Key clinical message: This report adds to the limited information on leiomyosarcomas in cattle, while highlighting both the challenges faced by veterinarians conducting post-mortem examinations on large animals in below freezing temperatures, as well as the current methods available to arrive at a diagnosis of a rare disease.

Léiomyosarcome métastatique présumé chez un bouvillon de parc d'engraissement. Un bouvillon de parc d'engraissement âgé de 14 mois était abattu et est mort pendant son examen. L'examen macroscopique du bouvillon réalisée au parc d'engraissement a identifié de nombreuses masses dans l'abdomen et le thorax, y compris une grosse masse dans le foie qui s'est étendue dans la veine cave. De nombreuses masses dans les poumons semblaient être le résultat d'une distribution hématogène. L'examen histologique des masses a confirmé la présence d'un néoplasme. Bien que l'aspect histologique du néoplasme ne soit pas typique d'un léiomyosarcome bien différencié, la coloration immunohistochimique a corroboré ce diagnostic. Les léiomyosarcomes sont rares chez les bovins nord-américains. Dans ce cas, le néoplasme primaire semble provenir de la paroi de la veine cave dans le foie.Message clinique clé :Ce rapport s'ajoute aux informations limitées sur les léiomyosarcomes chez les bovins, tout en soulignant à la fois les défis auxquels sont confrontés les vétérinaires effectuant des examens post-mortem sur de grands animaux à des températures inférieures au point de congélation, ainsi que les méthodes actuelles disponibles pour arriver à un diagnostic d'une maladie rare.(Traduit par Dr Serge Messier).

Gene expression profiles of beta-adrenergic receptors in canine vascular tumors: a preliminary study.

Beta adrenergic receptors (ß-AR) play a key role in regulating several hallmark pathways of both benign and malignant human and canine tumors. There is scarce information on the expression of ß-AR in canine vascular tumors. Therefore, the purpose of the present research work was to study the mRNA expression levels of the three subtypes of the ß-AR genes (ADRB1, ADRB2, ADRB3) in hemangiosarcoma (HSA) and hemangioma (HA), as well as in vascular hamartomas (VH) from dogs.Fifty samples (n = 50) were obtained from 38 dogs. Twenty-three animals had HSA, eight animals HA and seven animals VH. HSA were auricular (n = 8), splenic (n = 5), cutaneous (n = 6), auricular and splenic (n = 2), cutaneous-muscular (n = 1) and disseminated (n = 1). There were seven cases of HSA that were divided into primary tumor and secondary (metastatic) tumor. Skin and muscle samples with a normal histological study were used as control group. ADRB gene expression was determinate in all samples by real-time quantitative PCR. Results showed that ADRB1, ADRB2 and ADRB3 were overexpressed in HSA when compared to the control group. ADRB2 was overexpressed in HA when compared to the control group. HSA express higher values of ADBR1 (p = 0.0178) compared to VH. There was a high inter-individual variability in the expression of the three subtypes of ADBR. No statistically significant difference in the expression of ADBR genes were observed between HSA primary when compared to metastatic or in different anatomical locations. In conclusion, canine HSA overexpress the three ß-AR subtypes and canine HA ß2-AR. High variability was observed in ß-AR mRNA levels amongst HSA cases.

Primary Hepatic Vascular Neoplasm in a Houston Toad (Anaxyrus houstonensis).

An 11-year-old captive, female Houston toad (Anaxyrus houstonensis) became lethargic and reluctant to move. This toad had been administered human chorionic gonadotropin (HCG) and luteinizing hormone-releasing hormone (LHRH) annually as part of a hormone-assisted captive propagation programme for 8 years. Due to poor prognosis, euthanasia was elected. At necropsy, the liver was moderately enlarged, diffusely dark red and had a nodular superficial appearance. Microscopically, the hepatic nodules consisted of poorly demarcated, non-encapsulated, paucicellular infiltrative neoplastic growths. These consisted of spindle cells, similar to sinusoidal endothelial cells, that formed irregular blood-filled vascular channels resembling sinusoids separated by thin bands of collagen and reticulin fibres. Neoplastic cells dissected through and replaced hepatic cords and bile ducts. Based on the cytohistomorphological features and analogy with vascular neoplasms in other vertebrates, a diagnosis of low-grade angiosarcoma was made. To the best of our knowledge, this is the first record of primary hepatic vascular neoplasia in an amphibian. It is not known if the long-term administration of HCG and LHRH had any oncogenic role in this animal. Vascular neoplasia should be included in the differential diagnosis of hepatomegaly and non-specific lethargy and health decline in amphibian species.

Gastric Intravascular Lymphoma in a Dog: Case Report and Literature Review.

Intravascular lymphoma (IVL) is a rare, high-grade, extranodal lymphoma characterized by selective proliferation of neoplastic lymphocytes within the lumen of small vessels. A 10 yr old female intact mixed-breed dog was presented with a 7 mo history of vomiting and anorexia. Physical examination revealed abdominal discomfort. Ultrasonography and endoscopy identified a submucosal gastric mass. Excision was performed by partial gastrectomy and histopathology and immunohistochemistry confirmed a T-cell IVL. The owner declined chemotherapy, and the dog was instead treated palliatively with prednisolone. Two months after surgery, vomiting recurred and abdominal ultrasonography revealed a large gastric ulcer with focal peritonitis. The dog was euthanized 4 mo after initial presentation and postmortem examination confirmed IVL recurrence in the stomach and an isolated nodule of neoplastic cells in the omentum. No involvement of other organs was found following histopathological examination. This is the first description of primary gastric intravascular lymphoma causing chronic vomiting in a dog.

Canine, feline, and equine corneal vascular neoplasia: A retrospective study (2007-2015).

Corneal vascular neoplasms (hemangioma and hemangiosarcoma) are rare in all species. Reported cases are single case reports in a single species. Archived cases of corneal hemangioma and hemangiosarcoma from dogs, cats, and horses were obtained from the Comparative Ocular Pathology Lab of Wisconsin (COPLOW, Madison, WI), tabulated, and examined. This retrospective study describes the breeds, ages, tumor types, and characteristics of vascular neoplasms that appeared to be primarily corneal in location, in feline, canine, and equine patients, with gross and histologic images. There is a discussion of predisposing factors and speculated association with chronic ocular surface disease.

Canine Cerebral Intravascular Lymphoma: Neuropathological and Immunohistochemical Findings.

Intravascular lymphoma (IVL) is a rare angiotropic large-cell lymphoma in which neoplastic lymphocytes proliferate within the lumina of small blood vessels in the absence of a primary extravascular mass or leukemia. This study included 10 cases of canine IVL restricted to the CNS. Dogs had an average age of 8 years and neurological signs mainly referred to brain involvement such as depression, seizures, and ambulatory deficits. Gross examination at necropsy showed focal extensive or multiple hemorrhagic areas mainly distributed in the telencephalon and diencephalon. Histopathologically, numerous veins and capillaries were filled with neoplastic lymphoid cells, accompanied by edema, hemorrhage, and thrombosis. Immunohistochemistry (IHC) for CD3, CD20, and PAX5 was performed to phenotype the neoplastic lymphocytes. IHC for CD44 and CD29 were used to investigate the pathogenetic mechanism leading to the intravascular aggregation of the neoplastic lymphocytes. The same IHC panel was applied to 8 cases of primary and metastatic canine CNS lymphoma in order to compare IVL immunoreactivity. Three IVLs were typified as T-cell, 3 as B-cell, and 4 as non-T non-B. Neoplastic lymphocytes showed marked expression of CD44 in all IVL cases, and CD29-immunolabeled cells were observed in 4 IVLs. CD44 immunoreactivity was consistent with the findings reported in human IVL, suggesting a predisposition to the formation of lymphocyte aggregates. CD29 was inconsistently immunonegative in canine IVL, confirming only partially the pathogenetic mechanism suggested for the human counterpart.

Hemangiosarcoma at the base of the left atrium of a dog with mitral and tricuspid valve degeneration ­ case report / Hemangiossarcoma na base do átrio esquerdo de um cão com degeneração da válvula mitral e tricúspide ­ relato de caso

Hemangiosarcoma (HSA) is a malignant neoplasm originating from the vascular endothelium, with high metastatic power and commonly described in the spleen, liver, and right atrium. Thus, the objective of the present study is to report the occurrence of HSA at the base of the left atrium of a male, elderly, Lhasa Apso dog, treated with cyanosis, orthopedic position, cough. In the physical examination, the presence of crackling was observed in pulmonary lobes, murmur in focus of mitral and tricuspid grade IV\VI. The recommended emergency therapy was performed until the clinical improvement of the animal. After echocardiography, mitral and tricuspid valvular degeneration was confirmed, as well as the presence of an irregular, mixed echocardiogram, extra-cardiac, immobile at the base of the left atrium, measuring 2.9 x 1.44 cm in diameter. The clinical therapy established stabilized the clinical picture for 128 days, with recurrence of pulmonary edema and severe hemorrhagic pleural effusion, with the owners opting for euthanasia of the animal and necropsy confirming the definitive diagnosis of extrahepatic SAH at the base of the left atrium.(AU)

O hemangiossarcoma (HSA) é uma neoplasia maligna originada no endotélio vascular, com alto poder metastático e comumente descrito no baço, fígado e átrio direito. Assim, o objetivo deste trabalho é relatar a ocorrência do HSA na base do átrio esquerdo de um cão, macho, idoso, da raça Lhasa Apso, atendido apresentando cianose, posição ortopneica e tosse. No exame físico foi observado presença de crepitação em lobos pulmonares e sopro em foco de mitral e tricúspide grau IV\VI. Foi realizada terapia emergencial preconizada até a melhora clínica do animal, e após a ecocardiografia confirmou-se a degeneração valvular mitral e tricúspide, bem como a presença de uma imagem irregular, de ecogenicidade mista, extracardíaca e imóvel na base do átrio esquerdo, medindo 2,9 x 1,44 cm de diâmetro. A terapia clínica instituída estabilizou o quadro clínico por 128 dias, havendo recidiva do edema pulmonar e efusão pleural hemorrágica grave, com os proprietários optando pela eutanásia do animal e a necropsia, confirmando o diagnóstico definitivo do HSA extracardíaco na base do átrio esquerdo.(AU)

Hemothorax in Three Dogs with Intrathoracic Extracardiac Hemangiosarcoma.

Intrathoracic extracardiac hemangiosarcoma (HSA) is rare in dogs. This report describes three dogs with acute onset dyspnea due to hemorrhagic pleural effusion resulting from intrathoracic extracardiac masses, which were confirmed as HSA by histopathology. The dogs were stabilized with thoracocentesis and intravascular fluid resuscitation. Computed tomography identified intrathoracic masses, which were not originating from the heart or pulmonary parenchyma. Surgical exploration was performed in all cases. Case 1 was euthanized intraoperatively as the tumor could not be dissected from the aorta. In cases 2 and 3, hemostasis and resection of the tumors was successful. Case 2 was euthanized 1 mo after surgery and case 3 was alive at the time of writing, 5 mo postoperatively. Intrathoracic extracardiac HSA should be considered as a differential for nontraumatic hemothorax and surgical treatment can be palliative.

Hemangiossarcoma ocular em um equino: relato de caso / Equine ocular hemangiosarcoma: case report

O hemangiossarcoma ocular na espécie equina é um tumor maligno, raro e agressivo, de origem vascular endotelial. No presente trabalho, descreve-se um caso de hemangiossarcoma ocular em uma égua de 10 anos que apresentava secreção serossanguinolenta advinda de uma massa, acometendo a conjuntiva bulbar e a terceira pálpebra do olho direito. O diagnóstico foi realizado com base na avaliação histopatológica e na imuno-histoquímica. Foi realizada a enucleação, assim como a completa excisão cirúrgica do tecido acometido, não sendo observada, após seis meses da terapia, a recidiva ou a metástase da lesão.

Equine ocular hemangiosarcoma is a rare and aggressive malignant tumor of vascular endothelial origin. We describe a case of ocular hemangiosarcoma in a 10-year-old mare with serosanguineous secretion arising from a mass involving the bulbar conjunctiva and third eyelid of the right eye. The diagnosis was based on histopathological evaluation and immunohistochemistry. Enucleation was performed as complete surgical excision of the affected tissue, with no recurrence or metastasis of the lesion being observed after six months of.

The use of novel lymphatic endothelial cell-specific immunohistochemical markers to differentiate cutaneous angiosarcomas in dogs.

Lymphangiosarcomas are uncommon vascular neoplasms that arise from lymphatic endothelial cells (LECs). They efface and replace normal subcutaneous tissue and are characterised by arborising, vascular channels lined by a single layer of pleomorphic endothelial cells and a paucity of erythrocytes. Lymphangiosarcomas are architecturally similar to hemangiosarcomas, a common malignancy of vascular origin arising from blood vascular endothelial cells. Common immunohistochemical markers for vascular endothelium, such as Factor VIII-related antigen (F8RA) and CD31, have traditionally been used to confirm the diagnosis of tumours of vascular origin. However, these markers fail to differentiate between lymphangiosarcoma and hemangiosarcoma, which often show overlapping morphologic features, disparate clinical behaviour and require different treatment modalities. Here we describe the use of two novel LEC-specific markers, lymphatic vessel endothelial receptor-1 (LYVE-1) and prospero-related homeobox gene-1 (PROX-1), to further differentiate between vascular tumours of lymphatic (lymphangiosarcoma) and blood (hemangiosarcoma) endothelial cell origin in the dog.

IMAGING DIAGNOSIS-MULTIMODALITY FINDINGS IN AN ADULT DOG WITH PRIMARY SARCOMA OF THE PULMONARY ARTERY AND MYOCARDIAL METASTASES.

Intravascular pulmonary artery sarcomas in combination with myocardial metastasis are rare in dogs. We describe the radiographic, echocardiographic, and electrocardiographic-gated (ECG-gated) computed tomographic angiography (CTA) findings in a dog with pulmonary artery sarcoma. All imaging studies demonstrated severe main pulmonary artery enlargement. Echocardiography and ECG-gated CTA revealed a mass occluding the lumen of the right pulmonary artery. In addition, CTA revealed focal left ventricular myocardial contrast enhancement and parenchymal lung changes. Postmortem examination confirmed the presence of a large thrombus associated with arteriosclerosis and an intravascular sarcoma in the right pulmonary artery with metastases to the myocardium, lungs and brain.

Vascular hamartoma in the right ventricle of a dog: Diagnosis and treatment.

A 6-month old Labrador retriever was presented with an acute history of collapse during exercise. A grade III/VI left basilar systolic murmur and thoracic radiographs showing severe right heart enlargement with an enlarged main pulmonary artery were most consistent with a clinical diagnosis of pulmonic stenosis. Echocardiography revealed an intracardiac mass partially obstructing the right ventricular outflow tract. The mass was surgically excised, and histopathology diagnosed a benign vascular hamartoma of the right ventricle. Short-term follow-up showed resolution of clinical signs with no evidence of local recurrence. Intracardiac masses should be considered a differential diagnosis for patients with acute-onset syncope.

Growth Factors and COX2 Expression in Canine Perivascular Wall Tumors.

Canine perivascular wall tumors (PWTs) are a group of subcutaneous soft tissue sarcomas developing from vascular mural cells. Mural cells are involved in angiogenesis through a complex crosstalk with endothelial cells mediated by several growth factors and their receptors. The evaluation of their expression may have relevance since they may represent a therapeutic target in the control of canine PWTs. The expression of vascular endothelial growth factor (VEGF) and receptors VEGFR-I/II, basic fibroblast growth factor (bFGF) and receptor Flg, platelet-derived growth factor B (PDGFB) and receptor PDGFRß, transforming growth factor ß1 (TGFß1) and receptors TGFßR-I/II, and cyclooxygenase 2 (COX2) was evaluated on frozen sections of 40 PWTs by immunohistochemistry and semiquantitatively scored to identify their potential role in PWT development. Statistical analysis was performed to analyze possible correlations between Ki67 labeling index and the expression of each molecule. Proteins of the VEGF-, PDGFB-, and bFGF-mediated pathways were highly expressed in 27 (67.5%), 30 (75%), and 19 (47.5%) of 40 PWTs, respectively. Proteins of the TGFß1- and COX2-mediated pathways were highly expressed in 4 (10%) and 14 (35%) of 40 cases. Statistical analysis identified an association between VEGF and VEGFR-I/II (P = .015 and .003, respectively), bFGF and Flg (P = .038), bFGF and PDGFRß (P = .003), and between TGFß1 and COX2 (P = .006). These findings were consistent with the mechanisms that have been reported to play a role in angiogenesis and in tumor development. No association with Ki67 labeling index was found. VEGF-, PDGFB-, and bFGF-mediated pathways seem to have a key role in PWT development and growth. Blockade of tyrosine kinase receptors after surgery could represent a promising therapy with the aim to reduce the PWT relapse rate and prolong the time to relapse.

Analysis of genomic mutation and immunohistochemistry of platelet-derived growth factor receptors in canine vascular tumours.

We examined whether mutation of the platelet-derived growth factor receptor protein tyrosine kinase (PDGFR)-α and PDGFR-ß genes contributes to their overexpression in canine vascular tumours. Genomic sequences of trans- or juxtamembrane regions of PDGFR-α and PDGFR-ß were analysed with immunohistochemical staining and polymerase chain reaction-direct sequencing using DNA from paraffin-embedded neoplastic tissues of 27 hemangiosarcomas (HSAs) and 20 hemangiomas (HAs). Immunohistochemically, 75% of the HA cases were positive for PDGFR-α and almost most of the HA cases were negative for PDGFR-ß. Of the HSA cases, 55.6% were negative for PDGFR-α and 63% were strongly positive for PDGFR-ß. Among the HA cases, 1 missense mutation was detected in PDGFR-α exon 18 and 1 in PDGFR-ß exon 17. Two HSA cases had missense mutations in exon 14 and 1 in exon 17 of PDGFR-ß. Thus, genomic mutation of trans- or juxtamembrane regions of PDGFRs was not the main mechanism driving the activation of receptors in HSA and HA.

Paraparesis in a Golden Retriever.

A 7-year-old female spayed Golden Retriever dog presented with fever and a 10-day history of neurological signs, including ambulatory paraparesis and pelvic limb ataxia. Neurological examination initially revealed a T3-L3 myelopathy. Thoracic radiographs revealed a diffuse miliary pulmonary pattern. Endotracheal washes and fine-needle aspirates from several organs aimed at identifying a potential infectious agent or neoplastic process were all unsuccessful. Due to worsening of the clinical signs, euthanasia was elected. Necropsy findings included multifocal, pale to dark red, firm nodules infiltrating the lungs, heart, mesentery, pancreas, small intestine, brain, and spinal cord. Cytological examination of impression smears obtained from the pulmonary nodules during necropsy revealed clusters of epithelioid cells admixed with fewer spindle cells, erythrocytes, and scattered leukocytes. Clinical signs and cytological findings initially suggested the possibility of a widespread granulomatous disease or a metastatic epithelial neoplasm as possible clinical differentials in this case. The final diagnosis was based on the gross and histological findings, with confirmation following histochemistry and immunohistochemistry.

Diagnosis and treatment considerations in a case of malignant mesenchymoma in an African fur seal (Arctocephalus pusillus).

A 20-yr-old African fur seal (Arctocephalus pusillus) presented with a slowly growing mass located on the dorsum at the level of the last thoracic vertebrae. The mass was hard, 10 cm in diameter, and not adherent to the underlying tissues. Multiple biopsies were collected for histopathology and revealed extensive areas of necrosis, small nodules of malignant mesenchymal proliferation with areas of chondroid metaplasia, and atypical cells in vessel walls. The morphologic diagnosis was suggestive of malignant mesenchymal neoplasia originating from the vascular wall. The mass was removed 1 mo later due to ulceration and infection. Histologically, based on the World Health Organization's classification of neoplastic processes in domestic animals, the tumor was consistent with malignant mesenchymoma. The margins of resection revealed the presence of neoplastic cells. Based on these results, the particular species involved, the high local invasiveness, and the high metastatic index of this malignant tumor in domestic mammals and humans, the prognosis was poor. The animal died 6 mo later with metatastic disease.

Vascular hamartoma in the uterus of a female Sprague-Dawley rat with an episode of vaginal bleeding.

An annular, reddened lesion with mild serosal hemorrhage and no tumorous mass formation was detected in the right uterine horn of a 37-week-old female Sprague-Dawley rat that had postpubertal vaginal bleeding. Histological examination revealed prominent proliferation of the endometrium, which occupied the uterine lumen. There were numerous aberrant vascular spaces filled with erythrocytes, proliferation of stromal cells, and inflammatory infiltrates including hemosiderin-laden macrophages in the endometrium. These vasculatures extended into the myometrium, and in a transverse section of the lesion, they were mostly distributed throughout the circumference of the uterus. They were irregular in shape and interconnected, forming a large vascular sinus and anastomosing reticular channels. In the area with serosal hemorrhage, the muscular layer covering the large irregular vascular space had undergone degeneration and necrosis. The lining cells of the vasculatures were often plump, and they protruded into the lumen and were arranged in a tombstone or hobnail manner. Immunostaining revealed that these cells were positive for von Willebrand factor and CD34. The aberrant vasculatures were not accompanied by pericytes or muscular layer, although a discontinuous muscular wall was present around some of them. From these results, the uterine lesion was diagnosed as a vascular hamartoma.

Two canine malignant vascular tumours with features of human retiform haemangioendothelioma.

Within the human medical literature, retiform haemangioendothelioma (RHE) is an established and well-recognized histopathological variant of endothelial tumours, but to date RHE has not been reported in animals. These tumours are characterized by the presence of elongate, arborizing vascular channels lined by neoplastic endothelium with prominent, often bulging ('hobnail') nuclei supported by a dense collagenous matrix and accompanied by abundant lymphoplasmacytic inflammation. Immunohistochemically, the neoplastic cells typically express endothelial markers such as von Willebrand factor and CD31. Human RHEs are categorized as low-grade malignancies. This report describes two canine vascular tumours with features consistent with RHE. In both cases there was suspected or known widespread tumour metastasis.

Sonographic assessment of vessel invasion by cervical masses in dogs / Avaliação ultrassonográfica da invasão vascular por massas cervicais em cães

Tumor invasion of the vessels displays both therapeutic and prognostic implications and represents a challenge for head and neck surgeons. Although previous research has shown that ultrasound can detect such invasions, accurate sonographic parameters to do so have not yet been established. We sought to determine sonographic criteria which are able to characterize these invasions. A high-resolution transducer was used to perform ultrasound examinations of 15 patients selected from a group with inconclusive radiography and computed tomography diagnosis. We found that encasement of the vessel, tumor immobility or fixation in the vessel wall, and narrowing and/or deformity of the lumen were the best criteria. Indeed, when loss of hyperechoic interface of the vessel wall was used as a single criterion it generated false positive results. This study shows that a combination of parameters can be used to provide the best sensitivity and specificity values to produce conclusive diagnosis of vessel invasion by tumors in the cervical region.

Determinaram-se critérios ultrassonográficos capazes de caracterizar a invasão vascular por tumores em cães. Utilizaram-se transdutores de alta resolução para os exames ultrassonográficos realizados em 15 pacientes, selecionados de um grupo submetido previamente à radiografia e tomografia computadorizada, com resultados inconclusivos. Os melhores critérios encontrados foram: encarceramento do vaso, imobilidade do tumor ou aderência na parede vascular e estreitamento ou deformidade luminal. A perda de definição da interface hiperecoica da parede vascular quando foi usada como critério isolado produziu resultados falso positivos. O estudo demonstrou que uma combinação de parâmetros pode ser usada para aumentar a sensibilidade e especificidade diagnóstica, produzindo diagnósticos mais conclusivos e precisos pra definir a invasão vascular por tumores na região cervical ventral.

Surgical treatment of a pulmonary artery vascular hamartoma in a dog.

CASE DESCRIPTION: A 6-year-old Siberian Husky-mix dog was examined for episodes of collapse. CLINICAL FINDINGS: Physical examination, echocardiography, abdominal ultrasonography, ECG, and thoracic computed tomography with contrast were performed and revealed a 2.5 × 2.3 × 2.0-cm mass over the pulmonic valve leaflets, resulting in moderate pulmonic stenosis. Other abnormal findings included systemic hypertension, right bundle branch block, proteinuria, and a urinary bladder mass. TREATMENT AND OUTCOME: Pulmonary arteriotomy was performed under inflow occlusion, and the mass was resected with transesophageal echocardiographic guidance and direct visualization. Results of histologic examination of the mass revealed a vascular hamartoma. Sequential follow-up examinations and telephone contacts (at 0.5, 5, and 15 months after surgery) revealed that the patient had been free from episodes of collapse since surgery. No regrowth of the mass was noted on follow-up echocardiograms, and the pulmonic stenosis had resolved, although mild to moderate pulmonary insufficiency later developed. The bladder mass was excised 15 months after the first surgery when hematuria developed, and results of histologic examination of this mass revealed a vascular hamartoma. The dog was eventually euthanized 31 months after the initial surgery for reasons that could not be directly linked to any recurrence of the pulmonary artery mass. CLINICAL RELEVANCE: Hamartomas are benign tumors that can be located in various tissues, including large arteries. Computed tomography was helpful in predicting the resectability of the intracardiac mass in this dog. Treatment with arteriotomy under inflow occlusion and mild hypothermia resulted in a favorable outcome.