Feline Pheochromocytoma (Adrenal Medullary Tumor)

Feline pheochromocytoma is a rare neoplasm originating from chromaffin cells of the adrenal medulla, capable of secreting catecholamines (epinephrine, norepinephrine, and dopamine) in an unregulated manner. In cats, this tumor is considered significantly less common than in dogs, and its clinical presentation is often subtle, making antemortem diagnosis challenging. The excess catecholamine secretion drives a constellation of cardiovascular, metabolic, and systemic signs that can mimic other feline endocrine and cardiac diseases. Histopathological and cytological examination remain cornerstone tools for definitive diagnosis, as distinguishing pheochromocytoma from adrenocortical tumors on clinical grounds alone is inherently difficult [1].

Pheochromocytomas arise from chromaffin cells, which are specialized neuroendocrine cells residing in the adrenal medulla and, less commonly, at extra-adrenal paraganglionic sites (termed paragangliomas). In cats, the etiology is poorly understood and is considered sporadic; a hereditary basis analogous to the human RET proto-oncogene mutations has not been clearly established in feline medicine. These tumors may be benign or malignant; malignant forms can invade locally (e.g., into the caudal vena cava or surrounding retroperitoneal tissues) or metastasize to regional lymph nodes, liver, spleen, lungs, and bone.

The core pathophysiological mechanism centers on the uncontrolled synthesis and secretion of catecholamines—principally norepinephrine and epinephrine. Norepinephrine acts predominantly on α-adrenergic receptors to cause vasoconstriction and hypertension, while epinephrine stimulates both α- and β-adrenergic receptors, accelerating heart rate, increasing cardiac contractility, and promoting hyperglycemia through glycogenolysis and gluconeogenesis. Chronic catecholamine excess leads to myocardial hypertrophy, hypertensive end-organ damage (kidney, retina, central nervous system), and a hypermetabolic catabolic state. The secretory pattern may be continuous or paroxysmal, accounting for intermittent "crisis" episodes seen clinically.

Distinguishing adrenomedullary from adrenocortical tumors is critically important because management and prognosis differ substantially, yet the two cannot reliably be differentiated on clinical signs, imaging characteristics, or routine laboratory findings alone [1]. Cytological assessment of adrenal masses has been investigated as a minimally invasive diagnostic approach, with specific cytomorphological features described to help differentiate pheochromocytoma from adrenocortical tumors in companion animals including cats [1].

Clinical Assessment Diagnosis requires integration of history (episodic hypertensive crises, weight loss), physical examination (cranial abdominal mass, hypertension, tachycardia, ocular lesions), and targeted diagnostics.

Blood Pressure Measurement Persistent or episodic hypertension (systolic blood pressure >160–180 mmHg) is a cardinal finding. Multiple measurements are recommended to distinguish white-coat hypertension from true sustained hypertension.

Routine Hematology and Biochemistry Laboratory abnormalities are nonspecific but supportive. Relevant parameters include:

• ·HCT: May be elevated (stress erythrocytosis) or within normal limits; anemia can develop with chronic disease or blood loss into the tumor.
• ·WBC: Leukocytosis with a stress leukogram (mature neutrophilia, lymphopenia, eosinopenia) may be present due to chronic catecholamine elevation.
• ·BUN / CREA: May be elevated reflecting hypertensive nephropathy or pre-renal azotemia; renal function should be carefully assessed before surgery.
• ·ALT: Hepatic enzyme elevation can occur secondary to hypertensive hepatopathy or hepatic metastases.
• ·Glucose: Hyperglycemia may be noted, driven by catecholamine-mediated glycogenolysis and gluconeogenesis; must be differentiated from diabetic ketoacidosis.
• ·ALB / GLOB: Hypoalbuminemia may develop with prolonged anorexia and catabolism.
• ·PLT: Thrombocytopenia is possible in the context of disseminated intravascular coagulation (DIC), which can complicate severe or ruptured tumors.
• ·TBIL: Mild elevations may be present with hepatic involvement.

Urinary Catecholamines and Metabolites Measurement of urine or plasma catecholamines (epinephrine, norepinephrine), metanephrines, and normetanephrines is the biochemical gold standard for diagnosis in humans and dogs. In cats, validated reference intervals are less well-established, and the clinical utility of these assays is less thoroughly documented; however, elevated urinary catecholamine-to-creatinine ratios can provide supportive evidence.

Diagnostic Imaging

• ·Abdominal Ultrasound: The primary imaging modality; identifies an adrenal mass (unilateral or bilateral), heterogeneous echogenicity, vascular invasion, or metastatic lesions in the liver/lymph nodes. Adrenal gland measurements exceeding normal reference ranges are diagnostically relevant.
• ·Computed Tomography (CT): Provides superior anatomical detail, delineates vascular invasion (particularly caudal vena cava thrombus), evaluates the contralateral adrenal gland, and stages the disease prior to surgery.
• ·Echocardiography: Essential to assess myocardial hypertrophy, left ventricular function, and other hypertension-related cardiac changes prior to anesthesia.

Cytology Fine-needle aspirate (FNA) cytology of the adrenal mass—guided by ultrasound—can assist in differentiating pheochromocytoma from adrenocortical tumor. Cytological key features allowing this distinction in companion animals, including cats, have been described [1]. Pheochromocytoma cells typically display neuroendocrine morphology: round to polygonal cells with granular cytoplasm, prominent vascularity, and a plasmacytoid or "zellballen" arrangement. However, FNA carries inherent risks including hypertensive crises from tumor manipulation; this procedure must be performed with caution and appropriate pre-medication.

Histopathology Definitive diagnosis requires histopathological examination of surgically excised or necropsy tissue, with immunohistochemical staining (chromogranin A, synaptophysin) to confirm neuroendocrine origin.

Pre-operative Medical Stabilization Medical management prior to surgical intervention is critical to minimize anesthetic and perioperative mortality from catecholamine-induced hemodynamic instability.

• ·Alpha-adrenergic blockade: Phenoxybenzamine (a non-competitive α-blocker) is the traditional agent of choice, administered for a minimum of 1–2 weeks preoperatively to normalize blood pressure and expand intravascular volume. Starting doses in cats are extrapolated from dogs (0.25–0.5 mg/kg PO q8–12h, titrated to effect). Prazosin (competitive α-blocker) is an alternative.
• ·Beta-adrenergic blockade: Beta-blockers (e.g., atenolol) may be cautiously added AFTER adequate alpha-blockade is established to control tachycardia and arrhythmias. Beta-blockers must never be initiated before alpha-blockade, as unopposed alpha-stimulation can precipitate a hypertensive crisis.
• ·Calcium channel blockers: Amlodipine, commonly used for feline hypertension, can be used as an adjunct or in cats intolerant of alpha-blockade.
• ·Volume expansion: Intravenous fluid therapy is used in the perioperative period to counteract the contracted plasma volume that develops chronically under catecholamine influence.

Surgery Unilateral or bilateral adrenalectomy is the definitive and preferred treatment. Surgical approach may be open laparotomy or, in select cases, laparoscopic adrenalectomy. Key intraoperative considerations include meticulous blood pressure and cardiac monitoring, readiness to treat hypertensive crises (sodium nitroprusside, phentolamine) or hypotension (IV fluids, vasopressors), and careful handling of the tumor to minimize catecholamine surges. Vascular invasion of the caudal vena cava significantly increases surgical complexity and risk.

Management of Intraoperative Crises

• ·Sodium nitroprusside CRI for acute hypertensive episodes.
• ·Phentolamine IV bolus for acute catecholamine surges.
• ·Lidocaine or other antiarrhythmics for ventricular arrhythmias.
• ·Norepinephrine or dopamine infusions for post-tumor-removal hypotension.

Post-operative Care

• ·Close monitoring for hypoglycemia (rebound after catecholamine removal) and hypotension in the first 24–72 hours.
• ·Cortisol supplementation if bilateral adrenalectomy is performed (necessitating life-long mineralocorticoid and glucocorticoid replacement).
• ·Continued antihypertensive therapy until blood pressure normalizes post-operatively.

Non-surgical / Palliative Management In cats that are poor surgical candidates due to advanced disease, comorbidities, or metastatic spread, long-term alpha-adrenergic blockade combined with supportive care may provide palliative benefit. Chemotherapy protocols for malignant pheochromocytoma in cats are not well-established; cyclophosphamide and vincristine have been used anecdotally based on neuroendocrine tumor protocols.

Data on long-term prognosis and survival statistics specifically for feline pheochromocytoma is limited in current veterinary literature; no peer-reviewed survival statistics specific to this disease in cats were identified in the references cited above. The following represents a synthesis of available clinical knowledge:

• ·Benign, surgically resected tumors: Cats undergoing successful adrenalectomy for non-invasive, non-metastatic pheochromocytoma may experience prolonged survival with resolution of hypertension and associated clinical signs, though precise median survival times are not established in feline-specific studies.
• ·Malignant or invasive tumors: Prognosis is considerably worse when vascular invasion (particularly caudal vena cava thrombus), local invasion, or distant metastasis is present. Surgical risk is substantially elevated, and recurrence or metastatic progression typically shortens survival.
• ·Perioperative mortality: Adrenalectomy for pheochromocytoma carries significant perioperative risk due to hemodynamic instability. In dogs, perioperative mortality rates for pheochromocytoma adrenalectomy have been reported to range from approximately 13% to over 25%, and feline cases are expected to carry comparable or higher risk given the relative rarity and limited institutional experience.
• ·Unresected/advanced disease: Without surgical intervention, sustained hypertension leads to progressive end-organ damage (hypertensive nephropathy, hypertensive heart disease, retinal detachment, stroke), and the prognosis is considered guarded to poor.
• ·Cytological diagnosis can help direct appropriate clinical decision-making by confirming the neoplasm's medullary origin prior to surgery [1], which may improve preoperative preparation and perioperative outcomes.

Overall, the prognosis is considered guarded, with outcome heavily dependent on tumor invasiveness, completeness of resection, and the cat's cardiovascular and renal status at presentation.

There are currently no known preventive measures, vaccines, or specific husbandry strategies proven to prevent feline pheochromocytoma, as the etiology is believed to be sporadic and is not linked to identified environmental, dietary, or heritable risk factors in cats.

• ·Routine veterinary screening: Annual or semi-annual physical examinations with blood pressure measurement in middle-aged and older cats (>8 years) facilitate early detection of hypertension, which may be the first clue to an underlying adrenal neoplasm.
• ·Early investigation of hypertension: Any cat presenting with unexplained systemic hypertension should undergo abdominal ultrasound to evaluate the adrenal glands, allowing earlier diagnosis before severe end-organ damage occurs.
• ·Monitoring at-risk individuals: Cats with known adrenal incidentalomas discovered on imaging for other reasons should undergo periodic reassessment, including blood pressure monitoring and repeat imaging, as functional transformation or growth may occur over time.
• ·Neutering: There is no established association between reproductive status and pheochromocytoma in cats; routine neutering is recommended for general health but not specifically for this disease.