Principle of Thyroid Surgery

Introduction

The father of Thyroid surgery is THEODOR KOCHER. Thyroid surgery is mainly divided into preoperative, intra and post-operative preparation. The main principle of preoperative preparation for a patient is to be Euthyroid. This is achieved by giving antithyroid drugs like carbimazole 4-6 weeks before surgery. The patients can also be given non-selective beta blockers to decrease the effects of thyroid hormones.

The Last dose of ATD must be in the evening before surgery and for beta blockers is morning before surgery and continued 7 days after surgery. We can also give Lugol’s iodine which is 5% potassium iodide in 10% iodine solution. This solution helps in decreasing the vascularity of glands makes easy for patients and surgeons. During preoperative preparation surgeons do assessment of the vocal cord function and non-invasive physical examination like laryngoscopy. Laryngoscopy is done if the patient has preoperative voice problem, there is a redo surgery, the patient has thyroid cancer, and there is retrosternal goitre to the patient.

Three Most Important Aspects For Thyroid Surgery Are:

1. Position: the neck of the patient is kept extended Head end elevated by 30 degree to decrease the venous congestion known as Rose Position.
2. Incision: the incision  done is the collar insicion,  transverse incision 2 cm above the sternal notch or 1 cm below cricoid cartilage.
3. Flaps:  sub platysmal flaps are raised and   the strap muscles are divided , these muscles are divided  higher up,  to protect the nerve supply from ANSA cervicalis.

• The first vessel to be ligated during surgery is the Middle thyroid vein. Superior thyroid vessels are ligated next  and are dissected  in avascular plane  space of Reeves (lies between the medial aspect of the superior pole of the thyroid gland   and cricothyroid muscle) .Superior thyroid vessels are ligated as close to the gland as possible.

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Inferior thyroid artery not only gives the supply to thyroid gland but also to the Parathyroid gland. Main trunk of the artery is not ligated, only the individual branches of the artery are ligated as close to the gland as possible so that we do not injure RLN.

Structure To Save During The Surgery:

RLN (Recurrent Laryngeal nerve): It is identified at level of  Cricoid Cartilage. Beahr’s Triangle- It is a triangle which Is very important in identification of   RLN . Boundaries are- Common carotid artery, Inferior thyroid artery, Recurrent laryngeal nerve.

Parathyroids Identification

They are generally present within 1 cm of where RLN crosses the inferior thyroid artery. These are generally  golden yellow in colour and are lie in  halo of fat (Sentinel Pad of fat). If this halo of fat sinks in saline solution they are characterized as parathyroids and if floats are fat molecules.

Post Operative Complications

1. Hematoma: It is also known as Tension hematoma of neck. Incident is 0.1-1% of patients. It occurs when there is bleeding due to slippage of ligatures over Superior Thyroid Artery. There can be bleeding from muscular branches also . It can  cause respiratory distress due to pressure building up over trachea. The primary management step is opening of the sutures and evacuation of hematoma so that pressure can be relieved. 
2. Respiratory Distress: The most common cause of respiratory distress is Laryngeal Edema. Tracheo Malacia can also occur- if prior to surgery it is suspected , patient is electively  intubated for 1-2 days after the surgery. 
3. EBSLN (External Branch of Superior Laryngeal Nerve): It is the most common nerve injury accounting 20-22% incident cases. It is identified through loss of pitch, voice fatigue and unable to take high notes by the patient.
4. RLN damage: It occurs temporarily for 4- 10% incident cases of the patient and 0.5-2% permanently in the patients.

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Potential Sites For Recurrent Laryngeal Nerve Can Get Injured

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• Ligament of Berry: It is the most common site for damage. In relation to the Inferior Thyroid artery and branches. In the thoracic inlet at the tracheoesophageal groove. The Nerve damaged supplies to the intrinsic Muscles of the larynx and sensory supply below the vocal cords. This creates mix pathology in the larynx. Most common manifestation for the damage is paralysis of the vocal cord on affected side.

Rln Injury Can Be Unilateral As Well As Bilateral

• Unilateral RLN injury: If the cord is paralysed  at midline or paramedian position , then there can be some approximation by the contralateral cord  leading  to weak voice or nearly normal voice. OR if the cord is paralysed in a  abducted position , the opposite cord will not be able to approximate and  this leads to severely impaired voice, Poor cough reflex and high chances of  aspirations.
• Bilateral RLN injury: If both the cords are paralysed at midline or paramedian position then it leads to loss of voice, severe airway obstruction which needs urgent airway. OR If both the cords are paralysed at abducted  position ,which increases the aspirations chances  and can lead to respiratory tract infection.

Other Complications 

• Hypoparathyroidism:  It is the most common complication. It occurs due to devascularisation of parathyroid’s or accidental removal during surgery. It generally also leads to hypocalcaemia. It is mostly temporary (5-15%) i.e  occurring for  less than 6 months after surgery and (2-3%) permanent i.e  occurring for more than 6 months after surgery. It is most commonly presented after 2-5 days after surgery. The  earliest symptoms seen is circumoral perioral tingling.
• Trousseau Sign:   If  we inflate the BP cuff above SBP for 3 minutes there  can be  carpopedal spasm.
• Chvostek’s Sign:  if we tap the area over the Facial nerve it leads to  Facial Spasm.

Treatment

If the Serum calcium levels are less than 8 mg/dl then IV calcium gluconate is given to the patients.  If the symptoms are mild and  patient has serum  Calcium more than 8 mg/dl oral Ca and Vit . D  are given.

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Auto Transplantation

It is done for Parathyroid glands. The most common place for auto transplantation is Sternocleidomastoid muscle, but the only exception is  in case of  total thyroidectomy for medullary thyroid cancer MEN 2A syndrome then site for auto transplantation is Brachioradialis muscle non dominant forearm. 

Thyroid Storm

It is also known as thyroid crisis. It can occur pre operation, intra operation and post operation. The most common presentation is during intra operative. The most common cause for its occurrence is inadequate preparation and rough handling of the patient. It can occur also  due to rough handling of the patient,  Upper respiratory tract infection, trauma, Radioactive I_2, amiadrone. Clinical features include: arrhythmia (MCC of mortality), hyperpyrexia, dehydration, vomiting, confusion , agitation , Adrenergic overstimulation -  coma

Treatment includes

• Coding with Ice packs
• Anti thyroid drugs (PTU, Carbimazole)
• I.V fluids
• Oxygen supply
• Beta blockers
• Iodine and IV steroids
• The last try is of Plasmapheresis, Plasma Exchange of the patient.

Newer Advances in the Surgery

• Role of IONM (Intra Operative nerve monitoring): It can be achieved through continuous endotracheal tube electrodes   or intermittent with periodic stimulation .
• Novel technologies for parathyroid identification:  It can be achieved through- Near Infra-Red Autofluorescence, Indocyanine Fluorescence angiography: Indocyanine green dye is used.
• Minimally Invasive Video Assisted Thyroid Surgery (MIVAT): It is also known as endoscopic or videoscopic thyroid surgery.

Indications includes: Benign thyroid swellings (<3 cm), Papillary carcinomas (T1)

Approaches

• Most common approach is Trans Axillary.
• Anterior chest includes the nipple areola complex,
• Trans oral
• Retro auricular (Face lift)
• Contra indications to these methods are Prior neck surgery, Lymph node metastases, Large swellings, Thyroiditis

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