Thyroid Thyroid diseasesdiseases

EmbryologyEmbryology• 1st of the body’s endocrine glands to

develop (28th day of gestation)• Originates as a proliferation of

endodermal epithelial cells

• As the thyroid start to descent it is still connected to the tongue via thyroglossal duct

• This tubular duct later solidifies & obliterates entirely (7-10 wk of gestation)

• Some• While the gland descent it passes

anterior to hyoid bone & then laryngeal cartilages, forming its mature shape & median isthmus

• Completes its descent 7th wk…immediately anterior to trachea

• An ectopic thyroid gland • Failure of thyroid to descend→

lingual thyroid• Incomplete descent result in

resting point of gland high in the neck or just below the hyoid bone

• Imp. Differentiate between ectopic & thyroglossal cyst → total thyroidectomy

• Hyoid bone • Sistrunk procedure

• If thyroglossal duct does not atrophy → remnant can manifest clinically as thyroglossal cyst, midline mass track anywhere from the thyroid cartilage to base of tongue (rupture)

• Pyramidal lobe of thyroid 50%.• Represents a persistence of

inferior end of thyroglossal duct that has failed to obliterate

• Parafollicular ( C cells), special subset of cells within thyroid gland→ secrete calcitonin

• Arise from the ultimobranchial body, which is infiltrated by neural crest cells→ last structure derived from pharyngeal pouches

AnatomyAnatomy• Under middle layer of deep cervical fascia,

thyroid has an inner true capsule → thin & adheres closely to gland

• Extension of the capsule →lobes & lobules. Lobules are composed of follicles (structural units of gland) → consist of a layer of simple epithelium enclosing a colloid- filled cavity, which contain iodothyroglobulin (precursor of thyroid hormone)

• Epithelial cells: 1) principal (follicular) cells →formation of colloid

2) parafollicular (C) cells →cacitonin

• Anterior suspensory ligament extends from superior-medial aspect of each thyroid lobe to cricoid & thyroid cartilage

• Posteromedial aspect of gland is attached to side of cricoid cartilage, 1st & 2nd tracheal ring by posterior suspensory (Berry) ligament

• This firm attachment to the laryngoskeleton is responsible for its movement during swallowing

• Lateral surface of the gland is covered by sternothyroid m.

• Sternohyoid & sternothyroid ms. are joined in the midline by avascular fascia that must be incised to retract the muscles laterally to access the gland during thyroidectomy

• Should…high in neck cus motor N. supply from ansa cervicalis enters these ms. inferiorly

Arterial spplyArterial spply• Superior & inferior thyroid as. & occasionally thyroid ima a. • Thyroid ima is a single artery which enter the gland from

inferior border of isthmus (imp. to consider in tracheostomy→ potential source of bleeding

• Superior thyroid a. →1st anterior branch of external carotid a.

• Superior to the superior pole the external branch of superior laryngeal N runs with superior thyroid a

• High ligation of this artery places the nerve at risk of injury

→dysphonia

• Inferior thyroid a. → arises from thyrocervical trunk

• Closely associated with recurrent laryngeal N, relationship is highly variable

• Follicular cells synthesize & secrete 2 major hormones (T3 & T4) →collectively referred to as thyroid hormone

• Thyroid hormone affect all cells within the body except those in brain, spleen, testes & uterus

• Regulated through a feedback loop hypothalamus (TRH)

↓Anterior part of pituitary (TSH)

↓Thyroid gland (T3 & T4)

90% T4 & 10% T3..in body tissues T4 →T3 greatest metabolic effect

Investigations & Investigations & TreatmentTreatment

Blood testsBlood tests• Thyroid Function Test mesure serum TSH free T4 & free T3

• Thyroid Autoantibody estimation . Antithyroid Abthyroid microsomal Ab (TMAb) 95% of

patients with Hashimoto.D

Thyroglobulin Ab (TGAb) 60% of patients with Hashimoto.D

Ab against thyroid TSH receptors (TRAbs) seen in patients with Graves . D

• Serum thyrogloublin …used in follow up of metastatic thyroid carcinoma after tyhyroidectomy

X- raysX- rays• Plain radiograph chest & thoracic inlet ….to detect retrosternal thyroid extension ,thyroid calcification

,bony or mediastinal LN & lung metastases

• CT scan……For detecting regional &distant metasasis from thyroid cancr

• MRI….diagnosis of cervical LN metastasis

AP CXR with large retrosternal

Goitere

CT scan

UltrasoundUltrasound• Used to establish the size & shape of

the gland .• May indicate if nodules are single or

multiple.• It will distinguish between cystic &

solid lesions. (intrathyroid lesion)

Radioisotpe scanRadioisotpe scan• Single or multiple nodules .• Over functioning (hot nodules) or

non-functioning (cold nodules) • 20% of cold nodules are malignant• Hot nodules ….rarely malignant

Hot nCold n

HowHow????• An injected or inhaled or ingested compound

labelled with a suitable radionuclide is concentrated in the organ under review .

• The emitted radiation is detected by the gamma camera.

• Examples of radionuclides… Technetium 99m (99mTc) iodine 131(131I) Krypton (81mKr) Gallium67

(67Ga)

FNAFNA• Should be performed in the investigation

of all thyroid nodules.

• Distinguish between a solid lesion & a cyst • If the lesion is solid….cells are sent for

cytological examination• If the lesion is a cyst ….then the fluid can

be removed

HowHow????• A 21 G needle attached to a syringe ,flushed with

saline.

• is passed several times through the nodule while suction is maintained on the syringe.

• The aspirated cells are then smeared onto slide & wet &/or dry fixed.

• Results of cytology show benign cells, suspicious cells , malignant cells or the specimen is inadequate & consists of red cells only.

Thyroid DisordersThyroid Disorders

HypothyroidismHypothyroidism• Usually due to autoimmune disorder

(Hashimoto thyroiditis).

• Investigations.. TSH

free T4 &/or T3 Ab : TPO (thyroid peroxidase

enzyme)

antithyroglobulin

• Treatment… thyroxine to render the patient euthyroid normal dose 75-150 ug TSH cheacked every 12-18 months liothyronine(T3) is an alternative

elderly patient with ischemic heart disease

starting at 25ug & dose every fortnight (to avoid tachyarrhythmias & cardiac

failure)

HyperthyroidismHyperthyroidism• It may be caused by … Grave’s disease (autoimmune

thyrotoxicosis)

Toxic multinodular goiter

solitary toxic adenoma

Graves’ DiseaseGraves’ Disease• Investigations… TSH free T4 &/or T3 90% of patients will have arised

TRAb 70% of patients will have arised TPO

• Treatment… Initial treatment.. thyroid uptake blocking drugs eg…carbimazole & propylthyouracil SE…neutropenia (sore throat) profuse diarrhea hepatocellular failure

B-blockers (propanolol) if the patient is symptomatic with sweating ,termor

or tachycardia • Note.. Control of thyrotoxicosis usually takes 6 weeks. But maintenance is required for 18 months

• Defenitive treatment.. Radioactive iodine SE: long-term hypothyroidism

if inappropriate (young children at home) surgery

Sugery previously…subtotal thyroidectomy

but…10% recurrent thyrotoxicosis 70% hypothyroidism in long term

current surgical tratment of choice….. total thyroidectomy & long term thyroxine

postoperatively

Multinodular goitreMultinodular goitre • Two types..

non-toxic

toxic (plummer’s disease)

Investigations… TSH (if toxic MNG)

FNA…of the dominant nodule if present Ultrasound…may confirm multiple nodules X-ray of thoracic inlet & CT… extent of retrosternal extension & the

degree of tracheal deviation & compression .

• Treatment… non-toxic goitre ….total

thyoidoectomy if there is …rterosternal extension tracheal compression cosmetically

unacceptable

toxic MNG.. initially…carbimazole then ….total thyroidectomy or radioiodine

Solitary toxic adenomaSolitary toxic adenoma• Investigations… TSH 99mTcO4 thyroid isotope solitary hot

nodule

• Treatment.. initially…carbimazole then……thyroid lobectomy or

radioactive iodine

Solitary toxic noduleSolitary toxic nodule• Investigations… exclude solitary toxic adenoma (TSH) FNA…..to exclude malignancy

other investigations (not routinely required for the majority of STNs)

ultrasound …discriminate between solid & cysts 99mTcO4 thyroid isotope scan….function of nodule

• Treatment…

FNA

benign

ObserveRepeat FNAAfter 6-12months

suspicious

surgery

malignant

surgery

inadequate

Repeat FNAThyroid lobectomy

Mangement of thyroid malignancyMangement of thyroid malignancy

• Differentiated thyroid carcinoma… which include…

papillary thyroid carcinoma follicular thyroid carcinoma

• Treatment….according to the Grading system

Good prognosis

Poor prognosis

• Good prognosis

• Female < 45yrs old• Male < 40 yrs old• Tumor < 5cm• Minimally invasive follicular

carcinoma

Treatment• Thyroid lobectomy with subsequent

TSH suppression

• Poor prognosis

•Female > 45 yrs old•Male > 40 yrs old•Tumor >5 cm•Any patient with distant metastsis•Extrathyroidal invasion

Treatment•Total thyroidectomy •subsequent radioiodine (131I)•& TSH suppression with thyroxine

• Undifferentiated thyroid carcinoma (anaplastic)

Treatment…• Surgery …limited role …… (releive airway

obstruction)

• External beam radiotherapy &/or chemotherapy (mostly palliative)

the vast majority of patients die within 12 months

Medullary thyroid carcinomaMedullary thyroid carcinoma

Treatment• Total thyroidectomy with central lymph

node clearance

• Postoperatively …thyroxine replacement (but not TSH suppression)

• Postoperative calcitonin measurement is auseful tumor cell marker (follow up)

Thyroid lymphomaThyroid lymphoma

• Diagnosed by FNA or trucut biopsy• Should be staged with a bone marrow

aspirate & CT scan of chest & abdomenTreatment• If confined to the thyroid alone… thyroid lobectomy with subsequent adjuvant

radiotherapy & chemotherapy• Otherwise ….chemoradiation alone

Complication of thyroid Complication of thyroid surgerysurgery

• Damage to recurrent laryngeal nerve ….. leading to palsy & causing hoarseness.

• Damage to external branch of superior laryngeal nerve … leading to palsy & hoarseness

• Hypocalcaemia …caused by damage to parathyroids

• Haemorrhage…causing laryngeal oedema & respiratory compromise.