Anatomy and physiology of the Thyroid gland

The thyroid gland. (Image credit: Don Bliss (Illustrator), source and license)

The thyroid gland lies in front of the larynx in the neck and is responsible for producing thyroid hormones T3 and T4. These hormones act on most cells within the body to increase their metabolic rate.

It has two lobes which are joined by an isthmus.

See more details and the surrounding structures on the image below.

Anatomical detail of the anterior thyroid. (Image credit: CFC, via Wikimedia Commons, license)

Indications for surgery

Removal of the thyroid gland (or part of it) may occur for several reasons:

1. Enlargement – a goitre may be causing swallowing or breathing difficulties.
2. Overactivity – such as in Graves’ disease
3. Diagnosis – nodules may be excised to aid diagnosis
4. Malignancy – to remove certain cancers (these tumours are usually hard and rapidly growing)

Pre-operative considerations

Pre-operative preparation occurs from the time of booking for surgery. A full set of bloods should be checked including thyroid function tests. Patients should be euthyroid (which is a state of having normal thyroid gland function) by the time of surgery, as it is safer to operate.

Assessment of the mass includes clinical assessment as well as CT to look at the extent of the spread, any retrosternal extension and any airway compromise that may make intubation difficult. The recurrent laryngeal nerve can be damaged intraoperatively, so fibreoptic nasendoscopy is useful as part of the preoperative assessment to assess if there is any impaired function of the vocal cords prior to surgery.

Below you can see an axial image of a large goitre with tracheal deviation, causing airwya obstruction. At the centre, in white, is the patient’s vertebra.

The parathyroid glands are usually left in situ. There may be a drain present.

CT of a large thyroid tumour. (Image credit: Mnahi Bin Saeedan et al, via Wikimedia Commons, license)

What does a thyroidectomy involve?

The patient will then be listed for thyroidectomy. This is an open procedure with an incision at the front of the neck, although minimally invasive and trans oral techniques have been described. Occasionally the sternum may have to be opened if there is extensive retrosternal extension.

All or part of the gland will be removed:

• Total thyroidectomy: removal of the whole gland
• Subtotal thyroidectomy: removal of most of the gland, leaving behind a small amount of functioning tissue
• Hemithyroidectomy (or lobectomy): removal of one half of the thyroid gland

Total thyroidectomy. (Image credit: Cancer Research UK, via Wikimedia Commons, license)

Postoperative care after thyroidectomy

Clinical Scenario: Ms Mathews

Ms Mathews, a 44-year-old female is handed over to you in POCU after her total thyroidectomy for Graves disease.

Handover in POCU. (Photo credit: J.D. Williamson)

She is initially settled, with normal observations, however over the next hour she becomes progressively more tachycardic, anxious and starts complaining of difficulty swallowing.

Hopefully you would have picked up that these signs are worrying, as they are signs of acute airway compromise. Close postoperative observation is essential after thyroidectomy to look for these signs.

The tool below shows the signs and symptoms to look out for in the immediate postoperative period.

If one or more of the signs below are present, you must ask for immediate senior surgical review. If unavailable, urgent anaesthetic support should be sought.

The Difficult Airway Society (DAS), British Association of Endocrine and Thyroid Surgeons (BAETS) and British Association of Otorhinolaryngology, Head and Neck Surgery (ENT-UK) post-thyroid surgery regular review. This figure forms part of the consensus guidelines for the management of haematoma after thyroid surgery and should be used in conjunction with the text. Remember to always check for updates on guidelines. (EWS, early warning score; NEWS, national early warning score). © DAS, BAETS, ENT-UK 2021. (Image source)

In this case example, we will work our way through the potential different causes of an acute airway compromise post thyroidectomy and the subsequent management.

Thyroidectomy has a number of postoperative complications you should be aware of.

These include:

• Haematoma
• Tracheomalacia
• Laryngeal oedema
• Recurrent laryngeal nerve damage
• Hypocalcaemia
• Pneumothorax

NB: Points in bold may all present with acute airway compromise.

Let’s look at each of these in turn

Haematoma

Haematoma after thyroid surgery occurs in 0.45-4.2% of patients. Even a small amount of bleeding can cause life threatening airway obstruction. The mechanism of this is through accumulation of blood causing external compression of the trachea.

The Difficult Airway Society, ENTUK and BAETS recently developed a consensus guideline for postoperative management of haematoma after thyroid surgery, which can be found below.

Open access here

The recommendations are to keep a Post-Thyroid Surgery Emergency Box at the bedside of the patient, a similar concept to a tracheostomy box.

The box should include:

Management

If a haematoma is suspected and there is acute airway compromise, then the management is to open the surgical incision to evacuate the haematoma. This will release the external pressure on the airway, relieving the life-threatening airway obstruction.

**Please familiarise yourself with the images and posters within the consensus guideline including the protocol for the management of a suspected haematoma and SCOOP guideline.

Tracheomalacia

This is where the cartilage of the trachea becomes soft and can collapse causing airway obstruction. This is often associated with longstanding tumours that have caused the cartilage to become soft over time.

Tracheomalacia is usually assessed for at the end of surgery by direct assessment of the trachea and gradual withdrawal of the endotracheal tube. Acute presentation in recovery is rare in the western world, however if it does occur prompt reintubation will be required with possible need for front of neck access.

Laryngeal oedema

Again, this may present with signs of acute airway obstruction. Dexamethasone is usually given intra-operatively to reduce airway oedema and may be continued for a period of time, postoperatively.

Nursing head and neck patients postoperatively in the 45 degree head up position reduces oedema and aids venous drainage.

Recurrent laryngeal nerve damage

Vocal cord paralysis. (Image credit: Prejun, via Wikimedia Commons, license)

Complete transection of the nerve results in a relaxed vocal cord, part way between abduction and adduction, however partial injury to the recurrent laryngeal nerve results in complete adduction (closure). If this occurs bilaterally you can have complete airway obstruction.

Bilateral damage is rare, however unilateral paralysis can occur in up to 3.5% of patients. This has longer term consequences of increasing their chance of aspiration pneumonia, and lead to a hoarse voice and increased vocal effort.

Recurrent laryngeal nerve palsy is often checked for after the procedure by examining the vocal cords with laryngoscopy.

Hypocalcaemia

This is the most common complication after a thyroidectomy. Calcium levels in the blood are controlled by the parathyroid hormone. This is secreted by the parathyroid glands which are in very close proximity to the thyroid gland. Whilst every effort is made to spare these during thyroidectomy, they can be damaged or temporarily not function properly postoperatively.

Corrected calcium should be checked within 12 hours of surgery and replaced if low. There are national guidelines on this BAETS 2017, and some hospitals will have local guidelines (see just under).

BAETS guideline for calcium supplementation in patients undergoing thyroidectomy. (Image source)

You may know the patient is hypocalcaemic before the blood results are back. Acute hypocalcaemia causes increased neuromuscular irritability so please be on the watch for these signs and symptoms of acute hypocalcaemia:

• Tingling (often in lips, tongue, fingers and feet)
• Muscle aches
• Spasm of the muscles in the throat (leading to difficulty in breathing)
• Tetany (stiffening and spasms of muscles)
• Abnormal heart rhythms
• Seizures

If your patient does have any of these features, prompt escalation for management by the doctors looking after the patient is required.

Other postoperative considerations to be aware of….

• Occasionally the pleura can be damaged intra-operatively and the patient can develop a pneumothorax.
• There is an increased risk of intra-operative eye damage during head and neck surgery. Eyes are well taped and padded but damage will often only become apparent in recovery once the patient is awake, where they may complain of eye pain or red eye. In this case, the doctor should be informed and the hospital ophthalmologist may review the patient as an inpatient.