Lecture 23: Thyroid surgery

• What kind of tumors are seen in canine tumors?

  Epithelial tumors (follicular carcinoma and solid carcinoma)
• Do thyroid tumors tend to be benign or malignant?

  Tend to be malignant
• Where do thyroid tumors like to metasize to?

  Lungs, region LN (not as common as lungs) are the most common. Also jugular vein, adrenal, kidney, brain
• At what tumor size to tumors tend to have a 100% metastasis?

  >100 cm
• Hyperthyroidism in dogs is <____% of thyroid tumors in dogs

  20%
• CS of hyperthryoidism in dogs

  PU/PD, WL, polyphasia, ventral cervical mass
• Resectable thyroid tumor


  -Well encapsulated and well circumscribed

  
• Non-resectable thyroid tumor

  -Surrounding nearby structure

  -Irregularly shaped

  -DON'T try to debunk because they will hemorrhage

  
• Medical treatment of hyperthyroidism

  -Chemotherapy

  -I131

  -Radiation therapy
• Why do you not want to do a biopsy on a thyroid tumor?

  Very vascular, will bleed a lot
• Principles of thyroidectomy


  -Ventral cervical approach

  -Meticulous hemostasis

  -Avoid the laryngeal n.

  -Preserve parathyroids
• Important thyroid anataomy

  -Sternhyoideus

  -Trachea

  -Blood supply

  -Recurrent laryngeal n.
• What should you always do with metastatic tumors?

  Take chest films!!
• Thyroidectomy techinique


  1. Dorsal recumbency, neck over a roll

  2. Ventral midline cervical approach

  3. Divide the paired sternohyoideus muscles

  4. Place Gelpi retractors

  5. Identify recurrent laryngeal nerves

  6. Examine opposite thyroid gland

  7. Work from caudal to cranial

  8. Meticulous hemostasis
• How common is hyperthryoidism secondary to thyroid tumor?

  Not very common at all
• The _____ thyroid tumor the more likely it is to metasize

  Bigger
• What is more likely to be metastatic, a large or small spleen tumor?

  Small spleen tumor
• Invasive carcinoma

  
• Most common presentation of thyroid tumors?

  Owner or groomer feels the lumps around the neck
• Bilateral thyroidectomy

  
• Complications for bilateral thyroidectomy

  Hypocalcemia, chronic calcitriol administration
• Three layers of closure

  1. Sternohyodeus muscles

  2. Subcutaneous tissue

  3. Skin
• Complications of thyroidectomy


  -Hemorrhage

  -Seroma

  -Laryngeal paralysis

  -Hypoparathyroidism

  -Recurrence (incomplete resection)
• Most common endocrinopathy of older cats

  Hyperthyroidism
• Hyperthyroidism in cats is a ______ metabolic disorder

  Multisystemic
• What hormone is elevated with hyperthyroidism?

  Thyroxine
• Who has a better outcome, a dog with a resectable thyroid tumor or a dog with nonresectable thyroid tumor on medical therapy?

  Surgically respectable tumor
• What do we place under a dog for thyroidectomy?

  A roll to make the structures pop off
• CS of hyperthyroidism in cats

  -Weight loss

  -Hyperactivity

  -Polyphagia (Always hungry!!!)

  -Tachycardia

  -V/D
• What is the way to tell of a thyroid tumor is able to resected with just PE?

  If it is freely movable it can be resected easily
• Which of the following is a characteristic of Epithelial tumors found in dogs' thyroid glands?

  
  

  a. Follicular carcinoma

  b. Ventral cervical mass

  c. Hypocalcemia

  d. Renal function improvement

  a. Follicular carcinoma
• Major blood supply to the thyroid and parathyroid


  from the paired cranial thyroid artery and vein
• What is the presentation in 5% of hyperthyroid cats that present as depressed, lethargic, anorexia, weakness?

  Apathetic hyperthyroidism

  
• Diagnosis of hyperthyroidism in cats?

  -Total T4

  -Free thyroxine by dialysis

  -Provactive tests (TRH stimulation and T3 suppression0

  -Radionuclide thyroid scan
• Why do you start caudal in thyroidectomy?

  Usually doesn't have as rich of a blood supply
• Preoperative considerations for hyperthyroid cats

  -Tachycardia/heart disease

  -Cachexia

  -Renal issues
• What can happen to kidney function after thyroidectomy?

  May get worse, T4 helps with blood flow to kidneys
• Metastasis of carcinomas to the brain is observed most often in which region?

  
  

  a. Lungs

  b. Regional lymph nodes

  c. Jugular vein

  d. Brain

  a. Lungs
• What are the most common clinical signs of Hyperthyroidism in dogs?

  Select all that apply.

  
  

  a. Weight loss

  b. Hyperactivity

  c. Tachycardia

  d. Vomiting

  e. All of the above


  e. All of the above
• What is a crucial principle to follow during Thyroidectomy?

  
  

  a. Ventral cervical approach

  b. Division of the paired sternohyoideus muscles

  c. Cut the recurrent laryngeal nerves

  d. Remove the parathyroids

  a. Ventral cervical approach