Page 595 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 26 Tumors of the Endocrine System 573

and hypertension. The diagnosis is confirmed by ruling out other most often was made incidentally at necropsy, but these tumors
causes of hypokalemia, together with finding a markedly increased are now likely to be detected antemortem because abdominal
156
imaging techniques are used routinely in small animal patients.
plasma aldosterone concentration.

VetBooks.ir Pheochromocytomas generally are considered malignant tumors
Metastasis is reported in up to 40% of affected dogs;
in dogs.
173
Feline Adrenocortical Tumors
sites include liver, spleen, lung, regional lymph nodes, bone, and
Hyperadrenocorticism in cats is rare, and only 15% to 20% of CNS. 171,172,174 Vascular invasion by the tumor has been reported
cases are due to a functional adrenocortical tumor. A recent case in as many as 82% of cases. 20,22,175 This finding is not specific for
series documented the clinical findings in 33 cats with adrenal pheochromocytoma because vascular invasion can also occur with
neoplasia that had a histopathologic diagnosis. 157 Thirty of the adrenocortical tumors.
33 cats were diagnosed with a cortical tumor, and only three had Pheochromocytoma usually is diagnosed in older dogs, and no
a pheochromocytoma. Of the 25 cats that underwent adrenal clear breed predilection has been found. Catecholamine release
function tests, 19 cats were diagnosed with a functional tumor, by pheochromocytomas typically is episodic, therefore clinical
and of these 16 cats had hyperaldosteronism, one had hypercor- signs may be intermittent and often are absent at the time of
tisolemia, one had high estradiol, and one had hypersecretion of physical examination. Signs can include weakness, episodic col-
multiple hormones. Increasing evidence indicates that primary lapse, panting, anxiety, restlessness, exercise intolerance, decreased
hyperaldosteronism (also termed primary aldosteronism or Conn’s appetite, weight loss, polyuria, and polydipsia. Physical examina-
syndrome) has been an underrecognized condition in cats. In tion findings may be normal because of the episodic nature of
fact, it has been suggested to be the most common adrenocorti- catecholamine release or may reveal tachypnea, panting, tachycar-
cal disorder in this species. 158 Affected cats are middle-aged or dia, weakness, pallor, cardiac arrhythmias, or hypertension. Some
older, and the most common clinical sign is muscle weakness dogs have signs referable to an abdominal mass, and acute collapse
resulting from hypokalemia. Arterial hypertension frequently may occur secondary to tumor rupture with abdominal or retro-
is detected in these patients and may be associated with ocular peritoneal bleeding. 140 No consistent abnormalities are seen on
changes. Routine laboratory testing often reveals hypokalemia the CBC, serum biochemistry profile, or urinalysis in dogs with
and sometimes metabolic alkalosis, but hypernatremia is uncom- pheochromocytomas. 83
mon, presumably because of intact water balance mechanisms in Diagnostic imaging is central to the evaluation of patients with
these patients. Some cats also may have evidence of concurrent pheochromocytoma. In many dogs evaluation for pheochromo-
renal disease. cytoma occurs after an adrenal mass is found when abdominal
Plasma aldosterone can be measured in cats, and normal ultrasonography is performed for other reasons. In addition to
or increased plasma concentrations in the face of hypokalemia revealing the presence of an adrenal tumor, abdominal ultrasonog-
would be regarded as inappropriate. However, definitive diagno- raphy may reveal metastatic disease, and it is sensitive and specific
sis using aldosterone levels is difficult without measurement of for detecting vascular invasion by adrenal tumors. 20,22 CT and
the plasma renin activity and calculation of an aldosterone:renin MRI are the imaging modalities of choice for humans with pheo-
ratio. 159 Unfortunately, a plasma renin activity assay is not read- chromocytomas, and experience with these techniques in canine
ily available. The oral fludrocortisone suppression test had been patients has been encouraging. 134,176 Unfortunately no ultrasound
shown to be useful in the diagnosis of feline hyperaldosteron- or CT findings can distinguish definitively between pheochromo-
ism. 160–163 Imaging of the adrenal glands often is performed in cytoma and other adrenal tumors. Thoracic radiographs or CT
the evaluation of these patients, 164,165 and this may distinguish scans are recommended to evaluate the cardiovascular system and
between unilateral and bilateral lesions and also reveal vascular for detection of pulmonary metastases in any patient with a sus-
invasion or metastatic disease. Most cats with hyperaldosteron- pected adrenal tumor. Abdominal radiographs sometimes may
ism have an adrenal adenoma or carcinoma. 157,166,167 Bilateral reveal the presence of a large adrenal mass, but they generally are
adenomas have been reported, 166 and some cats have adrenal less informative than ultrasonography or CT. Rare reports exist
hyperplasia. 159 of positron emission tomography (PET) or nuclear scintigraphy
Adrenalectomy is the treatment of choice for cats with uni- imaging in dogs with pheochromocytomas. 177,178 Immunohis-
lateral disease, and good outcomes have been reported both for tochemical staining for chromogranin-A can distinguish pheo-
adenomas and for carcinomas, in addition to tumors associated chromocytomas from adrenocortical tumors on tissue obtained at
with vena cava thrombosis. 157,166–170 Medical management with surgery or necropsy. 179
potassium supplementation, antihypertensive drugs, and the Plasma and urinary concentrations of catecholamines and their
aldosterone antagonist spironolactone can give reasonable STs in metabolites are measured routinely in humans for the diagnosis of
patients that are not surgical candidates. 156 pheochromocytoma, and these have also been evaluated in dogs
and cats. 180–188 The best differentiation between pheochromocy-
Adrenal Medullary Tumors toma and other diseases appears to be provided by measurement
of normetanephrine, either in urine or plasma. 174,187,188
Chromaffin cells are part of the sympathetic nervous system and Surgery is the only definitive treatment for pheochromocy-
are present in the adrenal medulla and other locations through- toma. Chemotherapy and RT have not been evaluated in dogs
out the body. Neoplastic chromaffin cells in the adrenal medulla with pheochromocytoma. Radiotherapy using 131 I-metaiodoben-
give rise to pheochromocytomas, which are tumors that predomi- zylguanidine was reported in one dog. 189 The prognosis for dogs
nantly secrete catecholamines. Chromaffin cell tumors (termed with pheochromocytoma depends on tumor size, the presence
paragangliomas or extraadrenal pheochromocytomas) can arise in of metastases, and local invasion. An MST of 374 days has been
other parts of the body, but these are rare in veterinary medicine. reported after surgical treatment of pheochromocytoma. 116 Dogs
Pheochromocytomas are uncommon in dogs and rare in without metastatic disease that survive the perioperative period
cats. 171,172 In past decades the diagnosis of pheochromocytoma appear to have a good prognosis. A pheochromocytoma-associated