Uses

• Excision of functional thyroid adenomatous hyperplasia and treatment of associated hyperthyroidism Hyperthyroidism.
• Excision of functional thyroid carcinomas Thyroid gland: neoplasia (rare).
• Excision of functional parathyroid adenoma of the caudal internal parathyroid (rare).

Advantages

• Definitive removal of abnormal tissue and allowing histopathology.
• Preferable in cats that are difficult to medicate or do not tolerate side effects of medication.
• Relatively cheap treatment options which is widely available without the need for specialist facilities.

Disadvantages

• Ectopic thyroid tissue (thoracic inlet, mediastinum) can result in recurrence of hyperthyroidism (5% of cases).
• Recurrence of hyperthyroidism due to residual nests of cells left behind with cranial capsules or tissue is a risk especially with intracapsular techniques.
• Requires general anesthesia General anesthesia: overview and in some cats, especially with comorbidities, this may be poorly tolerated.

Alternative techniques

Antithyroid drug therapy (Methimazole or Carbimazole)

• Pros  →   no surgery/anesthesia, least expensive method: best option for very old animals.
• Cons  →   abnormal tissue persists, life-long medication, possible side-effects from drugs, possible difficult administration/client compliance.

Radioactive iodine isotope therapy (Iodine 131)

• Pros  →   no surgery/anesthesia, normal atrophic tissue preserved   →   often seen as the treatment of choice in hyperthyroidism associated with abnormal thyroid tissue. Treats functional ectopic thyroid tissue as well. Single subcutaneous injection results in a euthyroid state in 95% of cats.
• Cons  →   costs, hospitalization necessary, limited regional availability.

Decision taking

Criteria for choosing test

Options of surgical technique

• Four surgical techniques are described:
  • Extracapsular
  • Intracapsular
  • Modified extracapsular
  • Modified intracapsular
• The techniques vary predominantly with regards to the preservation or sacrifice of the parathyroid glands and how this is achieved.
• All four techniques sacrifice the caudal internal parathyroid gland. The extracapsular technique sacrifices both parathyroid glands.
• The intracapsular techniques removes glandular tissue from within the capsule. The modified intracapsular technique subsequently removes the capsule remnant, other then the small area surrounding the cranial external parathyroid. Disadvantage: residual nests of tissue may remain leading to a higher risk of recurrence.
• The author favors the modified extracapsular technique due to optimising removal of functional tissue and preservation of the cranial external parathyroid gland. This technique will be described in detail.

Parathyroid autotransplantation

• For parathyroid tissue that has been inadvertently removed or has lost its blood supply neovascularization can be established.
• Morcelizing the excised gland and suturing into a pocket created in the cervical musculature is described.

Unilateral versus bilateral

• Bilateral disease is present in 70-90% of cats. Bilateral surgery generally recommended.
• If unilateral disease has been demonstrated on scintigraphy Scintigraphy: overview, perform a unilateral procedure as chance of recurrence is low.
• Consider staging bilateral procedures by 2-3 weeks to reduce the risk of post-operative hypocalcemia.
• Bilateral procedures in one surgery are typically safe when performed by an experience surgeon. Perform post-operative monitoring.

Risk assessment

• Assessment of heart status important   →   cardiomyopathy/congestive heart failure   →   anesthetic risk Heart: congestive heart failure     .
• Full blood work-up   →   liver function tests, renal assessment.
• Determine T3/T4 Thyroxine assay.
• Establish euthyroidism prior to surgery - unless very mild case.