Aortic body tumours, also called chemodectomas, are slow-growing neoplasms that arise from chemoreceptor cells located near the base of the heart, close to the aorta. In dogs they are typically locally expansive masses that cause trouble by compressing adjacent cardiovascular structures rather than by invading the heart chambers themselves. Intracavitary or intracardiac involvement is genuinely uncommon, and previous reports of intracardiac extension did not describe tumour debulking under cardiopulmonary bypass. Cardiopulmonary bypass, or CPB, has been used in dogs for selected intracardiac procedures, including removal of a left atrial paraganglioma and a tricuspid valve myxoma, but a partial-bypass palliative debulking of a heart-base tumour protruding into the right atrium had not previously been documented.

The patient was a seven-year-old, 15.2-kilogram castrated male French Bulldog referred for lethargy, poor appetite, exercise intolerance and abdominal distension of roughly two weeks’ duration. Ultrasound had revealed free fluid in the abdomen, and echocardiography showed severe right-sided cardiac enlargement together with a mass measuring 3.2 by 3.1 centimetres occupying most of the right atrial lumen. The mass was heterogeneously echogenic with an irregular surface, appeared to originate from the heart base adjacent to the aorta, and was associated with significant tricuspid regurgitation and paradoxical septal motion. Abdominal imaging showed hepatic venous congestion and a large volume of ascites, and roughly 600 millilitres of fluid was drained to relieve the distension. The fluid was classified as a modified transudate, consistent with back-pressure from an obstructed right atrium rather than primary abdominal disease.

The clinical picture was one of mechanical obstruction of venous return. Blood attempting to flow from the caudal vena cava into the right atrium was blocked by the intracavitary mass, raising right atrial pressure, congesting the hepatic veins and driving fluid out into the peritoneal cavity. Medical management with pimobendan, furosemide and low-molecular-weight heparin failed to resolve the ascites or improve the dog’s activity and appetite, which strengthened the suspicion that the problem was structural rather than functional. Differential diagnoses included neoplasia, thrombus and tumour-associated thrombus, but antithrombotic therapy produced no reduction in the mass. Preoperative biopsy was judged too hazardous because the mass sat within the right atrium adjacent to critical structures, so the team proceeded without a definitive tissue diagnosis, informing the owner that the operation would be palliative rather than curative.

The surgical plan was deliberately unconventional. After premedication with midazolam, fentanyl and cefazolin, anaesthesia was induced with propofol and maintained with sevoflurane. The right jugular vein and right carotid artery were exposed for cannulation: a 14-Fr venous drainage cannula was advanced through the cranial vena cava to near the right atrial junction, and an 8-Fr arterial cannula was placed in the carotid artery. A right fifth intercostal thoracotomy exposed the heart. Notably, the team attempted additional venous cannulation from the right atrium toward the caudal vena cava but could not advance the cannula because the mass was in the way. Partial CPB was therefore run on the cervical cannulas alone, with heparin achieving activated clotting times above 400 seconds and later around 1000 seconds. Pump flow was set at 60 to 80 millilitres per kilogram per minute, and the dog was cooled to a lowest recorded oesophageal temperature of 28 degrees Celsius.

The authors made two decisions that reveal the improvisational nature of the procedure. First, the azygos vein was deliberately left unoccluded. Although temporarily occluding it would have reduced venous return into the operative field, venous return from the caudal body was already compromised by the mass, so preserving collateral drainage through the azygos system was considered preferable even at the cost of some surgical visibility. Second, after debulking improved caudal vena caval return, the team chose not to pursue additional cannulation, instead managing venous blood with two suction lines whose contents were returned to the extracorporeal circuit. Perfusion was judged adequate on the basis of arterial pressure, serial blood gas analyses and lactate concentrations, which remained between 1.0 and 2.5 mmol/L throughout.

Opening the right atrium revealed a mass firmly adherent to the septal aspect of the chamber, with marked induration suggesting neoplastic tissue. The surgeons used Babcock forceps to gently stabilise the intracavitary component and removed tumour primarily by blunt dissection with careful sharp dissection near the attachment site. No distinct dissection plane existed in the firmly adherent portion, so complete separation was not attempted. Residual tumour was intentionally left in place wherever further dissection risked perforation, uncontrollable haemorrhage or injury to critical structures such as the coronary sinus or atrioventricular junction. The atriotomy was closed in two layers with 6-0 polypropylene. Approximately ten minutes after atriotomy, ventricular fibrillation occurred; defibrillation after closure restored sinus rhythm. Total anaesthesia time was 410 minutes, surgical time 350 minutes, CPB time 140 minutes and intracardiac manipulation time just 40 minutes.

The haemodynamic payoff was immediate and measurable. Intermittently recorded central venous pressure fell from approximately 19 mmHg before debulking to approximately 5 mmHg afterwards, while systemic arterial pressure actually rose. Postoperatively, the mucous membrane pallor resolved, the ascites disappeared, and appetite and activity returned. Pimobendan and furosemide were discontinued, clopidogrel was prescribed for about a month, and follow-up echocardiography showed only minimal residual intracardiac tissue, reduced right-sided enlargement and no detectable tricuspid regurgitation. The dog was discharged on day 14. Histopathology of the resected tissue suggested a neuroendocrine neoplasm, and immunohistochemistry positive for synaptophysin and chromogranin A supported the diagnosis. Toceranib, a tyrosine kinase inhibitor with reported benefit in canine chemodectomas, was started on day 21.

The longer arc of the case tempers the enthusiasm. On day 360, a recurrent right atrial mass measuring 2.0 by 1.9 centimetres was documented, although without signs of right-sided heart failure. On day 390 the dog developed pancreatitis with biliary obstruction and died of multiple organ failure. Necropsy confirmed an aortic body tumour infiltrating from the endocardial surface into the right atrial myocardium, with pulmonary metastases and tumour emboli in the left caudal lung lobe. The authors are careful to note that they cannot determine whether the pulmonary spread represented spontaneous disease progression or was partly procedure-associated, because suctioned blood was returned to the circuit and standard filters cannot reliably remove individual tumour cells. They also acknowledge that the contribution of surgery, toceranib and the tumour’s naturally slow growth to the dog’s ten-month survival cannot be disentangled.

The team is equally clear that this should not be read as a new standard of care. Preoperative CT staging was not performed, central venous pressure was not monitored during bypass, and no strict numerical abort criterion was set, all acknowledged limitations. Total venous inflow occlusion was considered as a simpler alternative but rejected because the mass required careful stepwise debulking rather than rapid excision, and the 40-minute intracardiac manipulation exceeded the short window that technique allows. The authors frame the operation as an exceptional, high-risk rescue intervention justified only when severe intracardiac obstruction is the dominant life-limiting problem, medical and radiation options cannot provide rapid relief, and advanced cardiac surgical and perfusion support are available. Within those narrow boundaries, the case demonstrates that partial cardiopulmonary bypass can deliver real, if temporary, palliative benefit in veterinary patients facing obstruction that would otherwise be fatal.

Subject of Research: Palliative surgical debulking of a canine aortic body tumour with right atrial invasion under partial cardiopulmonary bypass

Article Title: Palliative Debulking of an Aortic Body Tumour With Right Atrial Invasion in a Dog Under Partial Cardiopulmonary Bypass

Article References: Suzuki, S., Tanaka, S., Kanno, N., Yogo, T., Harada, Y., Michishita, M., & Hara, Y. (2026). Palliative Debulking of an Aortic Body Tumour With Right Atrial Invasion in a Dog Under Partial Cardiopulmonary Bypass. Veterinary Medicine and Science, 12(5), Article e71244. https://doi.org/10.1002/vms3.71244

Image Credits: AI Generated

DOI: 10.1002/vms3.71244

Keywords: aortic body tumour, chemodectoma, cardiopulmonary bypass, right atrium, veterinary surgery, French Bulldog, cardiac tumour, ascites, toceranib, palliative care, echocardiography, neuroendocrine tumour

The cat arrived at the Colorado State University Veterinary Teaching Hospital after its owner noticed a growing mass in the neck. Two weeks earlier, the family veterinarian had measured it at 3.7 by 2.1 centimeters, but by the time of the referral examination it had expanded to roughly 5 centimeters long and 4 centimeters wide, filling the ventral part of the neck. The owner also described six months of gradually worsening snoring noises, lethargy, and a mildly reduced appetite. On physical examination, the cat was bright and alert but showed intermittent stertor and stridor, the harsh breathing sounds produced when the upper airway is partially obstructed. A large, fixed, painless mass dominated the left side of the throat.

Advanced imaging revealed the true scale of the problem. A triple-phase computed tomography scan showed a lobular, strongly and heterogeneously enhancing soft tissue mass measuring 5.2 by 4.1 by 3.9 centimeters that completely enveloped the common carotid artery, the main vessel supplying the head. The mass compressed and displaced the thyroid glands, pushed the pharynx, larynx, and hyoid apparatus markedly to the right, and extended toward the skull base near the tympanic bulla. Multiple branching vessels penetrated deep into the tumor interior, a hallmark of the rich blood supply characteristic of chemoreceptor tissue. A board-certified radiologist judged the growth pattern inconsistent with thyroid carcinoma, and the differential diagnosis narrowed to a carotid body tumor, a metastatic lymph node mass, or a primary soft tissue sarcoma.

Fine-needle aspiration cytology of the mass showed an epithelial neoplasm with endocrine and neuroendocrine morphology: densely cohesive clusters of round to polygonal cells with scant basophilic cytoplasm, ropey chromatin, and absent nucleoli. Critically, immunocytochemical staining for Thyroid Transcription Factor-1, a marker of thyroid origin, came back negative, making a thyroid tumor far less likely. The absence of any secretory phenotype, no hyperthyroidism and no hypercalcemia on bloodwork, further separated this tumor from the functional thyroid and parathyroid carcinomas that typically arise in the feline neck. Taken together with the tumor’s location hugging the carotid bifurcation, the team concluded the mass was most consistent with a paraganglioma of the carotid body, a tumor type never before documented in a cat.

That diagnosis matters because carotid body paragangliomas, also called chemodectomas, arise from the chemoreceptor organs that sense oxygen and carbon dioxide in blood. They are well described in dogs and humans, in whom they are notoriously invasive, enveloping major vessels at the base of the skull and causing retropharyngeal masses, difficulty swallowing, respiratory distress, stridor, gagging, and laryngeal paralysis. This cat’s presentation, including left-sided laryngeal paralysis and bilateral tonsillar protrusion noted on a sedated oral exam, matched that pattern almost exactly. Yet in cats, paragangliomas had only ever been reported in the abdomen, around the kidneys and retroperitoneum, at the aortic body, in the heart, and in the orbit, never at the carotid body, despite the fact that cats possess these normal anatomic structures.

Surgery was off the table. After reviewing the imaging, a board-certified surgical oncologist judged the mass unresectable because of its extensive involvement of the carotid artery, larynx, and hyoid apparatus, and warned that any biopsy attempt risked catastrophic hemorrhage and airway-compromising swelling. The oncology team instead offered definitive-intent stereotactic body radiotherapy, a technique that delivers ablative radiation doses in a handful of fractions with submillimeter targeting. The rationale was technical as much as biological: compared with a conventional 16 to 20 fraction course, a three-fraction protocol meant only three anesthesia episodes for a cat that was already difficult to intubate, with far less cumulative acute toxicity to the pharynx and trachea.

The treatment plan was built on the treatment planning system using pre- and post-contrast CT sequences. The gross target volume encompassed all abnormal contrast-enhancing tissue and abnormal vasculature, including the left tonsil. A 2-millimeter planning target volume expansion accounted for setup uncertainty, but was cropped away from organs at risk, the skin, pharynx, trachea, esophagus, brain, spinal cord, and eyes, to prioritize normal tissue sparing. Two coplanar arcs of 6-megavolt photons delivered 10 Gy per day for three consecutive days, for a total of 30 Gy, using volumetric modulated arc therapy. Dosimetry was calculated with the Acuros algorithm, and quality assurance with an electronic portal imaging device achieved a gamma passing rate above 95 percent at 3 millimeters and 3 percent, confirming the planned dose distribution matched delivery.

The response was fast and durable. Two weeks after the final fraction, the tumor had shrunk roughly 30 percent in length and 37.5 percent in width on caliper measurement, the cat’s breathing signs had resolved, and its appetite had normalized. By three months, the mass was no longer palpable at all. Ultrasound at 15 months showed a residual soft tissue structure surrounding the left carotid artery, and a 24-month scan by a second radiologist documented a highly vascular mass measuring 3.2 by 2.2 centimeters, a persistent partial response under RECIST 1.0 criteria with no local or systemic progression for 755 days. Thyroid hormone values, which had been suppressed by euthyroid sick syndrome at presentation, returned to and remained within normal ranges through repeated monitoring.

Tolerability was equally striking. The only radiation-related adverse event was leukotrichia, whitening of the fur in the treatment field, graded as a mild VRTOG grade 1 late skin toxicity. A transient episode of hiding, drooling, and poor appetite after the first fraction resolved when gabapentin was stopped and an anti-nausea drug given. Later weight loss at 20 to 24 months was traced to newly diagnosed chronic kidney disease and a progressively enlarging hepatic cystadenoma, both judged unrelated to the cervical tumor or its radiation. At the time of manuscript submission, the cat was alive with no evidence of disease progression, more than two years after treatment.

The authors caution that without surgical histopathology, which was deliberately avoided given the hemorrhage risk, the diagnosis remains presumptive; cytology alone cannot fully exclude ectopic thyroid or parathyroid tumors, and the definitive classification would have required immunohistochemistry on tissue. Even so, the convergence of imaging, cytomorphology, TTF-1 negativity, and the non-secretory clinical picture makes carotid body origin the leading explanation. The team recommends that carotid body paraganglioma be added to the differential list for feline cervical neuroendocrine masses, and that endocrine function screening be built into both initial work-up and long-term follow-up, since radiation can induce endocrine changes, as seen in dogs. For veterinary oncologists facing cats with otherwise untreatable advanced neck tumors, the report suggests external beam radiotherapy, and stereotactic body radiotherapy in particular, can now be offered as a definitive local option rather than a palliative afterthought.

Beyond this single patient, the case fills a genuine gap in comparative oncology. In human medicine, carotid body paragangliomas are the most common head and neck paragangliomas, and while surgery remains the mainstay, definitive radiotherapy and stereotactic techniques are established alternatives for tumors encasing the carotid artery, where resection carries stroke risk. In dogs, these tumors are typically encountered as incidental, slowly growing masses at the heart base, and complete surgical excision is rarely achieved. The feline report suggests that the radiotherapy experience accumulated in those species may translate across species lines.

The diagnostic work-up also illustrates a subtlety of feline endocrinology. The cat’s low total thyroxine with inappropriately low thyroid-stimulating hormone was interpreted as euthyroid sick syndrome, a reversible suppression of thyroid hormone values caused by non-thyroidal illness, rather than true hypothyroidism. Recognizing this pattern prevented a misdiagnosis that could have steered the work-up toward thyroid disease, and the later normalization of thyroid values on follow-up confirmed the interpretation.

Finally, the durability of response matters for fractionation debates in veterinary radiation oncology. Ablative hypofractionated schedules trade convenience and reduced anesthesia exposure against uncertainty about late toxicity, and this report, with more than two years of follow-up and only grade 1 leukotrichia, provides early evidence that such schedules can be both effective and well tolerated in cats with deeply seated cervical disease.

Subject of Research: First reported use of stereotactic body radiotherapy to treat a suspected feline carotid body paraganglioma

Article Title: Locally advanced cervical neuroendocrine tumor of presumptive carotid body origin in a cat treated with stereotactic body radiotherapy (SBRT): a case report

Article References: Gualtieri, P., Benedict, W. M., Tremolada, G., & Boss, M.-K. (2026). Locally advanced cervical neuroendocrine tumor of presumptive carotid body origin in a cat treated with stereotactic body radiotherapy (SBRT): a case report. Veterinary Oncology, 3(1), Article 18. https://doi.org/10.1186/s44356-026-00071-6

Image Credits: AI Generated

DOI: 10.1186/s44356-026-00071-6

Keywords: cat, carotid body, paraganglioma, chemodectoma, neuroendocrine tumor, SBRT, stereotactic body radiotherapy, veterinary oncology, VMAT, cervical mass, TTF-1, radiation therapy