Soft Tissue Surgery: Endocrine Surgery

Question 1

Describe the position of the thyroid glands in cats

What are some important nearby structures?

Answer 1

• Paired- one left, one right in dogs may communicate ventrally
• Lateral/ventral to trachea 5-8 rings
• right- tracheal rings 1-5
• left- tracheal rings 3-8

Nearby structures
* Right- carotid sheath, recurrent laryngeal nerve
* Left- oesophagus, recurrent laryngeal nerve
* Parathyroid glands

Question 2

1. What is the cranial border of the larynx
2. What is in the carotid sheath
3. What does the recurrent laryngeal nerve supply?

Answer 2

1. Cricoid cartilage
2. Common carotid artery, internal jugular, vasosympathetic trunk
3. Innervates most intrinsic muscles of the larynx

Question 3

1. What is the blood supply of the thyroid glands?
2. What is the venous drainage of the thyroid?
3. What is the innervation of the thyroid gland?

Answer 3

1. Cranial thyroid artery- common carotid branch, Caudal thyroid artery- brachiocephalic artery (absent in most cats)
2. Cranial thyroid vein, Caudal thyroid vein
3. Innervation- thyroid nerve

Question 4

Where is ectopic thyroid tissue commonly found?

Answer 4

• Along the trachea
• Thoracic inlet
• Mediastinum
• Thoracic descending aorta

Question 5

Where are the parathyroid glands found?

Answer 5

Two pairs- location varies
* External- near the cranial pole of each thyroid gland
* Internal- embedded within the caudal pole of each thyroid gland

Question 6

What are the functions of thyroid?
What are the clinical signs of hyperthroidism?

Answer 6

Functions
* Increase metabolic rate
* Increase catabolism of fat and muscle
* Increase body temperature
* Increase sympathetic drive
* Direct action on emetic centre and cardiac muscle
* Some impact on every tissue/organ in the body

Clinical signs
* Weight loss despite polyphagia
* Behavioural changes- hyperactivity
* PUPD
* GI signs- vomiting/diarrhoea
* Respiratory signs

Question 7

What are common clinical exam findings of hyperthyroid cases?

Answer 7

• Poor BCS
• May be restless and/or vocal
• Thin/roughened hair coat
• Cardiac disease- tachycardia, gallop rhythm, murmurs
• Hypertension
• Palpable, mobile cervical mass

Question 8

How can hyperthyroid disease be diagnosed?

Answer 8

• Haemtology- no specific findings
• Serum biochem- increased liver enzymes, decreased creatinine, decreased K+, increased phosphate
• Increased total T4
• Scintigraphy

Question 9

What are the advantages and diadvantges of anti-thyroid medications?

Answer 9

Advantages
* Readily available
* Reversible in the event of side effects
* Initially cheaper

Disadvantages
* More expensive in the long term
* Side effects
* Patient and owner compliance

Question 10

What are the advantages and disadvantages of radioactive iodine?

Answer 10

Advantages
* Curative
* Minimal side effects
* Cheaper long term
* Minimal cat/owner compliance

Disadvantages
* requires hospitalisation for 4-14 days
* High initial exposure
* Specialist procedure

Question 11

How is a thyroidectomy preoperatively managed?

Answer 11

• Euthyroid state- antithyroid drugs 6-12 weeks
• Check for unmasking significant renal disease
• Cardiac assessment if persistent tachycardia/murmur- B-blocker
• Treat hypertension
• Ensure normokalaemia

Question 12

1. What are the considerations for thyroidectomy?
2. What position is best?
3. Describe the surgical approach?

Answer 12

1. Delicate surgery, careful homeostasis, preserve parathyroid
2. Dorsal recumbancy- towel under neck, thoracic limbs pulled and secured
3. Incision from larync to manubrium, sternohyoid and sternohyoid mm bluntly separated to reveal trachea, paratracheal fascia bluntly dissected to expose thyroid glands

Question 13

How is the parathyroid identified?
Why does care need to be taken?

Answer 13

Normal thyroids- pale tan and flat
Parathyroid- typically paler then thyroid tissue

Parathyroid must be differentiated from fat deposits on the thyroid capsule
PT glands have a fine blood vessel that bifurcates and surround the gland

Question 14

Whats the advantages/disadvantages of bilateral/staged bilateral thyroidectomy?

Answer 14

Bilateral
* Adv- single anaesthetic episode
* Dis- greater risk hypoparathyroidism

Stages bilateral- largest gland removed, second upto 6 months later
* Adv- less risk of hypoparathyroidism
* Dis- two anaesthetics

Question 15

What are the four surgical techniques for thyroidectomy?

Answer 15

1. Intracapsular technique- incision into thyroid capsule- blunt dissection of parenchyma, external parathyroid preserved, high recurrence rate
2. Extracapsular technique- thyroid removed within its capsule along with parathyroid- high rate hypoparathyroidism, low recurrence rate
3. Modified intracapsular
4. Modified extracapsular

Modified technique preferred

Question 16

1. Describe the modified intracapsular technique?
2. Describe the modified extracapsular technique

Answer 16

1. Initially same approach as for intracapsular technique- incise capsule and blunt dissect gland parenchyma free. Most of remaining capsule then excised- small cuff of capsule left around the external parathyroid
2. Incision of the capsule around the external parathyroid- preserving its blood supply. Remainder of the capsule and thyroid gland dissected free

Question 17

When is a parathyroid autotransplantation indicated?
Describe the process

Answer 17

Performed when external parathyroid is inadvertently removed or blood supply disrupted

• Small pocket made in the sternohyoid or sternohyoid m
• Dissected parathyroid gland inserted into this pocket which is sutured closed
• Vital to avoid concurrent transplant of thyroid cells
• Takes 7-21 days for transplant to begin functioning- acute hypocalcaemia not prevented

Question 18

What are the potential complications of thyroidectomy?

Answer 18

• Haemorrhage
• Dyspnoea
• Laryngeal paralysis
• Horner’s syndrome- vagosympathetic trunk damage/inflammation
• Hypothyroidism
• Hypoparathyroidism
• Recurrence

Question 19

1. What does iatrogenic hypoparathyroisism cause?
2. How is it treated?

Answer 19

1. Mild transient disease in serum calcium- restlessness, face twitching, tetany, weakness, anorexia, panting, seizures
2. Acute, clinical hypocalcaemia- slow IV calcium gluconate- monitor ECG
   Subclinical hypocalcaemia- oral vitamin D and calcium- 3 weeks

Question 19

1. What does iatrogenic hypoparathyroisism cause?
2. How is it treated?

Answer 19

1. Mild transient disease in serum calcium- restlessness, face twitching, tetany, weakness, anorexia, panting, seizures
2. Acute, clinical hypocalcaemia- slow IV calcium gluconate- monitor ECG
   Subclinical hypocalcaemia- oral vitamin D and calcium- 3 weeks

Question 20

How are canine thyroid tumours diagnosed?

Answer 20

Ultrasound- origin, invasivness and vascularity
CT- invasiveness, vascularity, staging
Cytology- confirm thyroid origin
Biopsy contraindicated- high risk of severe haemorrhage

Question 21

What is the preoperative managment for thyroidecotmy in dogs?

Answer 21

• Euthyroid state- not necessary like in cats
• Treatment of severe tachcardia, arrythmias and hypertension
• Coagulation panel
• Blood typing and cross-matching

Question 22

1. How are canine thyroids removed?
2. What are the complications?
3. What is the mean survival time?

Answer 22

1. Mobile tumours most amenable, invasive highly vascular- similar to feline thyroidectomy
2. Haemorrhage, hypothyroidism, hypoparathyroidism, laryngeal paralysis, megaoesohpagus, aspiration pneumonia
3. Mobile tumours- 3 years, Invasive tumours- 6-12 months

Question 22

1. How are canine thyroids removed?
2. What are the complications?
3. What is the mean survival time?

Answer 22

1. Mobile tumours most amenable, invasive highly vascular- similar to feline thyroidectomy
2. Haemorrhage, hypothyroidism, hypoparathyroidism, laryngeal paralysis, megaoesohpagus, aspiration pneumonia
3. Mobile tumours- 3 years, Invasive tumours- 6-12 months

Question 23

What are the clinical signs of primary hyperparathyroidism?

Answer 23

Fibrous oestodystrophy PUPD Urolithiasis and UTI- stanguria, pollakuria, haematuria

Question 24

How is primary hyperparathyroidism diagnosed?

Answer 24

Serum biochemistry * Increased ionised calcium * Normal renal values * Normal to increased PTH * Decreased PTH-rp Ultrasonography

Question 25

How is a parathyroid removed from a dog?

Answer 25

* Same positioning and approach as for thyroidectomy * Identifying abnormal glands can be difficult- slightly enlarged and firm, external parathyroid glands visually assessed, internal parathyroid usually palpable * External parathyroidectomy- sharp incision between parathyroid and thyroid capsules, partial thyroidectomy if incomplete excision * Internal parathyroid ectomy- partial thyroidectomy- remove the caudal pole of the thyroid containing the affected gland

Question 25

How is a parathyroid removed from a dog?

Answer 25

* Same positioning and approach as for thyroidectomy * Identifying abnormal glands can be difficult- slightly enlarged and firm, external parathyroid glands visually assessed, internal parathyroid usually palpable * External parathyroidectomy- sharp incision between parathyroid and thyroid capsules, partial thyroidectomy if incomplete excision * Internal parathyroid ectomy- partial thyroidectomy- remove the caudal pole of the thyroid containing the affected gland

Question 26

How is parathyroidectomy post operatively managed in dogs?

Answer 26

* Monitor Ca concentration for 5-7 days * Keep calm- cats indoors for 14 days * Treatment of hypocalcaemia as previously described * Recurrence rate

Question 27

1. Where are the adrenal glands located? 2. Describe the inner composition of adrenal glands?

Answer 27

Located medial to cranial poles of each kidney * Left- adjacent to the aorta * Right- adhered to the caudal vena cava Outer cortex and internal medulla Cortex- zona glomerulus (aldosterone), zona fasiculata (glucocorticoids), reticularis (sex hormones) Medulla- catecholamines- adrenaline

Question 28

What is the difference btween an adenoma or phaeochromocytoma with adrenal tumours? How are they diagnosed?

Answer 28

Adenoma- cortisol-secreting tumours Phaeochromocytoma- catecholamine-secreting tumours Diagnosis * Haematology and biochemistry * Urinalysis ± urine metanephrine * LDDST * Imaging: ultrasound, CT

Question 29

What are hyperadrenocorticism clinical signs?

Answer 29

* PUPD * PP * Panting * Abdominal enlargment * Alopecia * Muscle weakness * Lethargy

Question 30

What is the preoperative managment for adrenalectomy?

Answer 30

Cortisol-secreting tumours: * Trilostane for 3-4 weeks- reduce immunosupression, hypertension, hypercoagulability, pancreatitis, wound healing complications Phaechromocytomas * alpha blocker- 2-3 weeks- limit inoperative hypertension * B-blocker may also be required- limit persistent tachycardia Very difficult anaesthetics

Question 31

Describe the process of an adrenalectomy?

Answer 31

* Ventral midline coeliotomy * Exposure of the right adrenal gland is more complicated- left- colonic manouvre Right- transection of hepatorenal ligament, retraction of the right lateral and caudal hepatic lobes cranially * Incise peritoneum at lateral aspect of the gland- avoiding aorta, vena cava and renal vasculature * Gland meticulously dissected free While minimizing manipulation as much possible, more difficult for invasive masses, concurrent unilateral nephrectomy may be required

Question 32

What are the potential complications of adrenalectomy?

Answer 32

* Haemorrhage * Pulmonary thromboembolism * Hypoadrenocorticism * Wound complications