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786 Pheochromocytoma

• Abdominal ultrasonography: usually provide additional proof of diagnosis. No Drug Interactions
unilateral adrenal tumor with normal-size histologic features (e.g., invasion of blood Avoid administering monoamine oxidase inhibi-
VetBooks.ir intraabdominal metastasis or tumor invasion of metastatic behavior. exacerbate hypertension.
contralateral adrenal gland; may also identify
vessels or surrounding tissue) are predictive
tors and metoclopramide because either may
of adjacent structures (see Video). Careful
Possible Complications
evaluation of the regional vena cava using
Doppler ultrasound is important to identify TREATMENT • Sudden blindness, seizures, or death from a
tumor thrombi (basis for anticoagulation; Treatment Overview hypertensive crisis
prognosis more guarded); large thrombi are Adrenalectomy is the preferred treatment • Perioperative complications include hyperten-
possible. if there is no evidence of (nonresectable) sion, hypotension, arrhythmias, respiratory
• Tests for hyperadrenocorticism (p. 485) metastasis. Surgical removal should always distress, and hemorrhage. Most animals
should be normal. be preceded by initial medical stabilization to become normotensive 24-48 hours after
control patient’s BP and cardiac arrhythmias. surgery.
Advanced or Confirmatory Testing Medical therapy for 1-3 weeks before surgery
• Contrast radiography (nonselective venogra- with an orally administered alpha-antagonist Recommended Monitoring
phy or excretory urography) for evaluating (phenoxybenzamine) is indicated to limit • In hospital: monitor BP and central venous
tumor invasion of the caudal vena cava or intraoperative complications associated with pressure perioperatively.
kidney, respectively sudden catecholamine release (hypertensive • After discharge: assess BP and ECG monthly.
• Abdominal CT or MRI (p. 1132) with or crisis, cardiac arrhythmias, pulmonary edema, Given tendency for pheochromocytomas
without contrast: strongly recommended and cardiac ischemia). Mortality rates after to be malignant, routine follow-up with
when surgical intervention is planned; usually adrenalectomy are significantly lower after pre- ultrasound is recommended q 3 months.
shows an adrenal mass and helps identify any treatment with phenoxybenzamine. Concurrent
local invasion or distant metastasis within vena caval venotomy is required when caudal PROGNOSIS & OUTCOME
the abdomen and to the lungs. vena caval invasion is present.
• Increased serum and urine catecholamines • Prognosis depends on tumor size, metastasis
and urinary catecholamine metabolites Acute General Treatment or local tumor invasion, perioperative com-
(e.g., normetanephrine): high-performance • Alpha-antagonist: phenoxybenzamine plications, and concurrent diseases, which
liquid chromatography superior technique 0.25 mg/kg PO q 12h initially, then are common (older animals).
but not available in North America at this increased to every few days until hypertension • Animals with a surgically excisable tumor
time. A nonvalidated species-specific assay controlled, without lethargy/weakness/signs have a guarded to good prognosis. If animals
is available. of hypotension, for the 1-3 weeks preceding survive the immediate postoperative period,
○ Urine normetanephrine concentration (≥4 surgery. Maximal dosage 1.5 mg/kg PO q a survival time of 18-24 months is possible.
times normal) in dogs and high plasma 12h in dogs (cats, maximum of 0.5 mg/
normetanephrine concentration in cats kg PO q 12h) can be reached. Prazosin or PEARLS & CONSIDERATIONS
strongly suggest pheochromocytoma. amlodipine are alternatives.
○ Stress associated with hospitalization, • Beta-blocker drugs (e.g., atenolol beginning Comments
critical illness, hyperadrenocorticism, at 0.5 mg/kg PO q 12h and titrating up to Pheochromocytomas are difficult to diagnose
and some medications (e.g., opioids, high- 1 mg/kg PO q 12h if needed) may be used antemortem, and perioperative management is
dose dexamethasone) can increase urine for controlling sinus tachycardia but only complex. Referral to an experienced surgeon
catecholamine excretion (i.e., false-positive after alpha-adrenergic blockade has been and anesthesiologist team is recommended.
result); urine collection should occur at initiated.
home after a few days of adaptation to Technician Tips
the sampling procedure. Urine must be Chronic Treatment Preoperatively and immediately postoperatively,
acidified, chilled, and protected from light. • Careful anesthetic selection is needed to patients may have marked fluctuations in BP
It is recommended to call the laboratory minimize intraoperative complications; and arrhythmias. Close monitoring and prepara-
ahead of time for instructions on collec- isoflurane or sevoflurane are typically used tion for treatment when necessary (monitoring
tion and shipping of samples. for maintenance. Direct arterial BP and ECG parameters/guidelines should be made clear)
• Although experimental, functional imaging should be monitored during surgery and for are essential.
123
using I-labeled metaiodobenzylguanidine at least 24 hours postoperatively.
(MIBG), octreotide-DTPA scintigraphy, or • If surgical resection is incomplete or not SUGGESTED READING
positron emission tomography scan with possible, long-term treatment with an alpha- Gostelow R, et al: Plasma-free metanephrine and free
18 F-MIBG may be useful for detecting a antagonist ± beta-blockade is indicated. normetanephrine measurement for the diagnosis
pheochromocytoma not found on CT or • Other treatments used in people for non- of pheochromocytoma in dogs. J Vet Intern Med
MRI. resectable pheochromocytoma include the 27:83-90, 2013.
• Histopathologic exam and positive immu- radioisotope 131 I-MIBG and metyrosine. AUTHOR: Elisabeth Snead, DVM, MSc, DACVIM
nohistochemical staining for chromogranin Metyrosine inhibits tyrosine hydroxylase, the EDITOR: Ellen N. Behrend, VMD, PhD, DACVIM
A and synaptophysin of the excised tumor rate-limiting step in catecholamine synthesis,
are required for a definitive diagnosis. and is used in patients with signs refractory
Biochemical testing for catecholamines can to phenoxybenzamine.

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