Everything you need to know about Thyroid-related disorders

The thyroid is a small, butterfly-shaped gland located at the base of the neck but plays a huge role in how our bodies use energy. The two hormones released by this thyroid gland affect each and every cell in the body. Despite its small size, it has enormous importance in the human body. Let’s learn everything about this little endocrine gland and its related disorders.  

Thyroid is an important topic of Surgery subject for NEET PG preparation. The contents of this blog have been prepared according to the exam pattern of NEET PG Surgery and will help you ace your preparation.

Thyroid is the storage site of iodine. Normal weight of thyroid is 20-25gms. 90% of the body's iodine is stored in thyroid. Normal Iodine requirement is 100-150 ug/ day. Father of thyroid surgery is Theodor Kocher. The patients who are having iodine deficiency, will develop goitre. Weight of thyroid is inversely proportional to iodine intake. Isthmus is related to 3^rd tracheal ring

Wolff Chaikoff effect

It is iodine induced hypothyroidism. 

Jod Basedow effect

It is iodine induced hyperthyroidism.

Pendred Syndrome

Characterized by congenital sensorineural hearing loss + goitre. The gene for this syndrome is located in 7q (long arm)

Refetoff Syndrome

End organ resistance to T4

Disorders of Thyroid

Thyroglossal Cyst

It is a  congenital condition, but despite being a congenital condition, the age of the presentation is 15-30 years. The most common location of the thyroglossal cyst is subhyoid or  infrahyoid, near foramen cecum, in the floor of the mouth. This cyst moves with deglutition. Patient presents with midline swelling in the anterior part of the neck. Since it is connected to the tongue, when patients protrude the tongue, the swelling moves up. 

Complications

1. Infection- if there is abscess formation and incision , drainage done, the thyroglossal cyst will convert into fistula. This thyroglossal fistula is an acquired condition. 
2. Long standing thyroglossal cyst can lead to papillary carcinoma of the thyroid.

Management

If the part of the cyst is passing through the central part or body of the hyoid bone. Treatment of choice is Sistrunk operation.

Sistrunk operation is in block excision of cyst along with central part or body of the hyoid bone

17. What is the endemic goitre?

When >5% of the people in population is having endemic goitre 

Retrosternal Goitre

When > 50% of the thyroid tissue is located below the opening of the thoracic cage. In the majority of cases the goitre is small , so it's asymptomatic. If it is asymptomatic, it is diagnosed incidentally on radiological investigation. Whenever there is a large thyroid, it is going to compress midline structures. The most common symptom is dyspnea (which is common at night), dysphagia, hoarseness of voice (because of compression of recurrent laryngeal nerve). Dilated veins over the anterior chest wall because of development of collaterals due to  compression of venous drainage of face. Pemberton sign positive (on elevation of upper limb above forehead, there is facial congestion, facial puffiness)

Management

Thyroidectomy ( Cervical incision is preferred )

Radio Isotopes used in Thyroid

Commonly used are I¹²³ (half life 13 hours) and I¹³¹ (half life 8 days)

I¹²³- It is mainly used for diagnostic purpose, used in radioactive Iodine scan

I^131- It is mainly used for therapeutic purpose,  used in radioactive iodine ablation

Why do we use I¹³¹ in radioactive ablation?

I¹³¹- emit beta (90%) and gamma rays (10%). Beta rays are responsible for therapeutic effects. Depth of penetration of beta rays is 0.5 mm. It will going to ablate only thyroid even parathyroid glands are safe

Gamma rays are used in tracer studies. They are responsible for side effects. 

2 absolute contraindications of radioactive ablation:

1. Pregnancy
2. Lactation

Because there is direct exposure on the fetus. 

Radioactive Iodine uptake

Uptake of radioactive Iodine by thyroid in stimulated period of time (6-24hrs)

Radioactive Iodine Scan

It is the scanning of cervical region with gamma probe also known as thyroid scan

Perform to see the appearance of normal thyroid, hot nodule and cold nodule. In hot nodules- there is increased uptake in one nodule as compared to surrounding thyroid tissue. In cold nodules- there is decreased uptake as compared to surrounding thyroid tissue. 

Q. What's the risk of malignancy in hot nodules?

• 1-3%

Q. What is the risk of malignancy in cold nodules?

• 17-20%

In Graves Disease ( Diffuse toxic goitre), there is increased uptake diffusely in the whole thyroid gland. In toxic multi nodular goitre, there are multiple nodules that are hot and some of them are cold.In Thyroiditis, there is significantly decrease in radioactive thyroid iodine (hardly < 5% of radioactive iodine is there. 

Thyroidectomy

Removal of all visible thyroid tissue is called total thyroidectomy. Removal of one lobe with Isthmus is called hemithyroidectomy. Leaving 3-4 gms of thyroid in each lobe with removal of the rest of the thyroid is called subtotal thyroidectomy. Leaving 4-6 gms of thyroid in one lobe with removal of rest of the thyroid is a modification of subtotal thyroidectomy called Hartley Dunhill procedure also known as Dunhill procedure. When leaving <1gm of thyroid tissue adjacent to recurrent laryngeal nerve near ligament of the berry with removal of the rest of the thyroid gland is called near total thyroidectomy. 

Which type of thyroidectomy should be performed in which particular condition ? 

Hemithyroidectomy- done for benign disorder involving one lobe only. Total thyroidectomy- performed in thyroid malignancy or benign disorder involving both lobes. 

Incase of multi nodular goitre, perform total thyroidectomy and give Levothyroxine lifelong. 

Single indication for subtotal thyroidectomy 

 Multinodular goitre in elderly, because of shorter life span, no chance of recurrence after 20-30 years. 

Solitary Thyroid Nodule

Colloid goitre is the most common, followed by follicular adenoma.

 Ist investigation done is a thyroid function test. Components of TFT are T3, T4 and TSH and most informative is TSH because of its ultra sensitivity. Because of ultrasensitivity subclinical hypo or hyperthyroidism can be detected. If TSH starts increasing , its subclinical hypothyroidism and if TSH starts decreasing , its subclinical hyperthyroidism. 

Investigation of choice- FNAC ( Fine needle aspiration cytology).

Certain limitations of FNAC

• Follicular Neoplasia- It cannot differentiate follicular adenoma from follicular carcinoma, because the diagnosis of follicular carcinoma is based on vascular and capsular invasion. These vascular and capsular invasion is visible in biopsy, so they are diagnosed in biopsy.
• Riedel's Thyroiditis (also known as invasive fibrous thyroiditis)- In Riedel's thyroiditis, there is complete replacement of thyroid and parathyroid by fibrous tissue. If FNAC is performed, there will be very poor or no yield. 
• Thyroid Lymphoma- The investigation of choice in lymphoma is biopsy, because  adequate amount of tissue is required for putting the  markers, which is not there in FNAC

Because of all these limitations , generally biopsy is preferred

IMPORTANT INFORMATION

• All thyroid related disorders are more common in females
• Investigation of choice- FNAC

Also Read: Symptoms of Hyperthyroidism

Management

IF FNAC shows inconclusive- repeat FNAC. In the case of benign lesions, it can be cystic or solid. If it is cystic,go far aspiration. There is recurrence after aspiration , so respiration should be done 3 times. If after respiration there is again recurrence, then go for hemithyroidectomy. In solid benign lesions thyroxine is given in the beginning but if there is no improvement or having compression symptoms, go for hemithyroidectomy. In suspicious lesions, RAI scan is performed. Can we have 2 possibilities, hot or cold nodule.In cold nodule, there is decrease in RAI uptake, so RAI ablation cannot be used. Only option left is hemithyroidectomy.  For hot nodules, there are 2 options, either hemithyroidectomy or RAI ablation. In thyroid malignancy, the treatment is total thyroidectomy

The Bethesda system reporting for Thyroid Cytopathology

Known as TBSRTC . 

THY1- Non diagnostic

THY 1C- Non diagnostic cystic

THY2- Non neoplastic

THY3- Follicular neoplasm

THY4- Suspicious for malignancy

THY5- Malignant lesion.

And that is everything you need to know about thyroid related disorders. Keep following this blog for more informative and useful articles like this. For more informative articles, download the PrepLadder App now.