Page 597 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 26 Tumors of the Endocrine System 575

coagulation (DIC), pulmonary thromboembolism, and death. 116– performed to rule out another primary tumor. Aspiration cytol-
118 Prognostic factors include the presence and size of a tumor ogy and ultrasound- or CT-guided biopsies are not routinely
recommended for incidentalomas because of the high risk of
thrombus, whether nephrectomy is performed, whether a transfu-
VetBooks.ir sion is performed, the tumor type (pheochromocytoma), and the complications and the inability to reliably differentiate benign
116–118
and malignant lesions
15,204
tumor’s size (>5 cm).
; however, a recent study suggested that
Dogs with preoperative HAC require a postoperative ACTH cytology can be valuable in distinguishing between cortical and
stimulation test, and it could be argued that this test should be medullary tumors. 205
performed after adrenalectomy in all cases because some tumors Adrenalectomy should be considered for masses that are func-
can secrete more than one hormone and the tumor type is not tional, locally invasive, or larger than 2.5 cm in maximum dimen-
always clearly defined before surgery. Dogs undergoing adrenal- sion. Masses smaller than 2 cm with no evidence of hormonal
ectomy for ADH need a supraphysiologic dose of corticosteroids activity should be monitored with regular imaging. A suggested
postoperatively that can be weaned down over several weeks. protocol is to repeat the sonogram monthly for 3 months after
ACTH stimulation tests can be used to monitor recovery of func- the initial study and then less frequently if no significant change
tion in the remaining adrenal gland. Even in cases with a pre- is noted, with further intervals determined by the appearance
sumptive pheochromocytoma, if a patient is not recovering as well of the mass and the clinical status of the patient. However, the
as expected postoperatively, an ACTH stimulation test should be growth of these masses is not necessarily predictable or uniform
considered to rule out a relative insufficiency of cortisol. TEG over time. 9,156
should be performed postoperatively and the result compared
to the preoperative status. Long-term survival is reported if the Thyroid Gland Neoplasia in Dogs
patient survives the perioperative period. 116–118
Compared with dogs, significantly fewer accounts are available Thyroid carcinoma is a tumor of middle-aged to older, medium
of adrenalectomy in cats. In one series of 33 cats with adrenal neo- to large breed dogs. 206 Siberian huskies, golden retrievers, and
plasia, 26 cats underwent adrenalectomy and 20 (77%) survived beagles are overrepresented. The median age is 10 to 15 years,
for at least 2 weeks postoperatively. 157 Causes of death included with no gender predilection. 206 Carcinomas or adenocarcinomas
euthanasia, hemorrhage and refractory hypotension, and acute were diagnosed in 90% of thyroid tumors. 206 Thyroid adenomas
kidney injury. The MST for cats undergoing surgery was 50 weeks. that cause clinical signs are very rare in dogs. 207 Carcinomas can
Complications included pancreatitis, lethargy and anorexia, and be further divided into follicular and medullary carcinomas with
significant hemorrhage. Three of the cats developed postoperative immunohistochemistry; follicular tumors are more common. 208
hypoadrenocorticism. In a series of 10 cats undergoing unilateral It has been suggested that medullary carcinomas may have a less
adrenalectomy for management of aldosterone-secreting tumors, aggressive behavior, 208,209 although this distinction rarely is used
eight cats survived to discharge and the overall MST was 1297 clinically. This tumor often is detected as an incidental finding
days, with none of the cats requiring further medical therapy. 167 by the owner or primary care veterinarian, which highlights the
Laparoscopic adrenalectomy for unilateral adrenal tumors also has importance of careful neck palpation on every physical examina-
been described in cats, but 4 of the 11 reported cases required con- tion. It should be noted that palpation of the mass is not sensitive
version to laparotomy. Ten of the 11 cats survived to discharge, or specific for determining histopathologic invasion 210,211 ; there-
and the MST was 803 days. 200 fore incidentally detected cervical masses always should be investi-
gated further. With the increasing adoption of advanced imaging
Incidental Adrenal Masses techniques, incidental thyroid masses also have been identified on
CT scans 212 and cervical ultrasound studies. 213 In one study of
Advances in abdominal imaging have led to the diagnostic dogs that had a cervical CT scan for an unrelated reason, the over-
dilemma of the incidental adrenal mass (“incidentaloma”) in both all incidence of a thyroid mass identified as an incidental finding
human and veterinary medicine. In a published study of dogs was 0.76%. 212 If dogs present with clinical signs, these generally
undergoing abdominal ultrasound examination, 4% were found are due either to a mass effect or to invasion of the thyroid tumor
to have an incidental adrenal gland lesion, with affected dogs into adjacent tissue; such signs include dysphagia, voice change,
being older than a control population with no adrenal lesions. 201 laryngeal paralysis, Horner’s syndrome, and dyspnea. 214–216
Twenty of these dogs underwent surgery or necropsy; six were Potential causes of thyroid carcinoma in humans include expo-
determined to have malignant tumors, all of which had a maxi- sure to radiation, persistently elevated thyroid-stimulating hor-
mum dimension greater than 20 mm. In another study of 20 dogs mone (TSH), and dietary and genetic factors. 207 In dogs, breed
with non–cortisol-secreting adrenal tumors that did not undergo predisposition suggests a genetic factor. Persistently elevated TSH
surgery, the MST was 17.8 months 202 ; however, not all the tumors also has been suggested as a potential risk factor. 207,217 Most dogs
in those cases were truly incidental findings. Adrenal masses may with thyroid carcinoma are euthyroid, with some hypothyroid
also be incidentally found on abdominal CT studies. In a series and some hyperthyroid dogs. 207,218 The serum concentrations
of 270 dogs undergoing abdominal CT for reasons unrelated to of thyroid hormone and TSH should be assessed preoperatively
adrenal disease, 25 (9.3%) had adrenal gland masses; as with the because some patients require postoperative monitoring and treat-
ultrasound findings, these incidental masses were more likely in ment. The term “functional thyroid carcinoma” in dogs generally
older dogs. 203 refers to the production of thyroid hormone and a hyperthyroid
When an incidental adrenal mass is identified in a dog or cat, a patient. Functional thyroid carcinoma in human patients generally
thorough history and physical examination, including blood pres- refers to the ability of thyroid carcinoma cells to trap and organ-
sure measurement and fundic examination, are indicated. Endo- ify iodine. This is more clinically important in human patients
crine testing should be pursued to rule out a functional tumor. because radioactive iodine therapy is a routine part of treatment.
Given the high incidence of metastasis to the adrenal glands in The workup of a suspect thyroid tumor involves confirmation
cats and dogs, imaging of the thorax and abdomen should be of the tumor type and clinical staging. Ultrasound examination