Thyroid surgery Flashcards
Anatomy of the thyroid gland
Paired
Light brown in dogs, tan in cats
Flat and long
Supplied by cranial and caudal thyroid arteries and veins
Lymphatic drainage in cranial direction
Four parathyroid glands are closely associated
Recurrent laryngeal nerves are closely associated
Ectopic thyroid tissue is commonly present
Causes of feline thyroid masses
Functional adenomas (98%) - secrete T4 (goitre)
Carcinomas (1-2%), also predominantly functional. Larger and more invasive.
Radioactive iodine for the treatment of feline thyroid masses
Can treat unilateral/bilateral or ectopic disease
No risk of injury to adjacent structures during treatment
Generally offers excellent long-term control of thyroid function and avoids long-term medication
Has limited availability/locations
Requires prolonged hospitalisation + associated risks
More costly as an initial lump sum
Surgery for the treatment of feline thyroid masses
Can treat unilateral/bilateral disease, BUT not ectopic disease usually
Is readily available as a treatment option in general practice.
Generally offers excellent medium-long term control of thyroid function and avoids ongoing medication
Has associated surgical and anaesthesia risks
More costly as an initial lump sum (but less than radioactive iodine)
Pro-operative assessment for feline thyroidectomy
- Is cardiac disease present?
- Is renal disease present?
- Can I feel a goitre?
Pre-operative preparation for feline thyroidectomy
Dorsal recumbency
Thoracic limbs pulled away from surgical site
Entire ventral neck is clipped and aseptically prepared
Ventral midline approach
Identification of both external parathyroid glands is attempted
Four surgical techniques for feline thyroidectomy
Intracapsular (higher recurrence rate)
Extracapsular (no attempt to preserve the external parathyroid - derailment of calcium homeostasis)
Modified intracapsular (small cuff around parathyroid, low recurrence rate)
Modified extracapsular (incised around the parathyroid, low recurrence rate)
Parathyroid autotransplantation
Parathyroid tissue can be reimplanted in cases of accidental extraction, placed in muscle pocket
Post operative care of feline thyroidectomy
IV fluids
Analgesia
Calcium monitoring
Potential complications of feline thyroidectomy
Anaesthesia related
Haemorrhage
Larygeal paralysis
Hypocalcaemia
Renal function deterioration
Recurrence of hyperthyroidism
Canine thyroid carcinoma
Uncommon
Usually non-functional
Older dogs (usually 9-11)
Up to 60% have bilateral involvement
Cervical mass, usually firm but non-painful, can be mobile or fixed and invasive.
Systemic disease is rare.
Diagnosis of thyroid carcinoma
US - to assess invasiveness
MRI or CT - surgical planning aids
FNA - under US guidance, not usually very helpful
Incisional biopsy - usually not indicated due to profuse haemorrhage
Excisional biopsy - more appropriate
Staging of thyroid carcinoma
Usually a slowly progressive disease
Surgery still recommended in the face of metastatic disease
Local LNs assessed by palpation and US
Thoracic radiographs to assess forpulmonary metastases
Surgery for canine carcinoma
Surgical excision - only if mobile or limited invasion.
Approached by ventral midline cervical incision.
Ligaiton of vessels and careful blunt/sharp dissection, without entering the capsule.
Complications include haemorrhage and laryngeal paralysis.
Other treatment ooptions for hyroid carcinoma
External beam radiation - if large or invasive
Radioactive iodine - only useful for functional tumours
Chemotherapy - no proven efficacy
