Thyroid Flashcards
Normal thyroid US appearance
- Homogeneous parenchyma
- Medium-high level echoes (hyperechoic to straps muscles)
- Thin hyperechoic capsule
- Vascular (uniformly distributed)
Thyroid location
Midline neck (infrahyoid compartment) - Level C5-T1
- Post to strap muscles
- Ant to trachea
- Inf to thyroid cartilage
- Med to CCA + IJV
Label the image
Identify each structure
Describe its US appearance + location in relation to the thyroid
- Strap muscles (anterior/ thin hypoechoic band)
- Sternocleidomastoid m. (lateral/ oval hypoechoic)
- Longus colli m.(posterolateral/ triangle)
- Trachea (posterior midline/ air shadow)
- Esophagus (posterior to left lobe/ target)
- CCA (lateral)
- IJV (lateral
An enlarged thyroid measures..
> 2cm AP
> 1cm isthmus thickness
Normal thyroid measurements + volume
- <6cm long
- 1.8 cm AP
- <6mm isthmus thickness
- <18ml women
- <25ml men
To measure: 1 caliper in long, 2 calipers in trans
What is the function of the thyroid?
Endocrine gland
Secretes hormones:
- Thyroid hormones (T3 + T4)
- Calcitonin
Regulates metabolism:
- Affects growth + development (organs, immune system, sexual development)
- Controls heart rate, energy levels, weight loss/ gain, cholesterol, memory
What are the thyroid hormones?
Where are they secreted?
What are the primary effects?
T4 (Thyroxine)
- 90% of secretions
- Contains 4 iodine atoms
- Most converts to T3
T3 (Triiodothyronine)
- 10% of secretions
- Contains 3 iodine atoms
Secreted by follicular cells
- Thyroglobulin uses iodine to make T3 + T4
Primary effects:
- Increase metabolism
- Increase basal metabolic rate (BMR)
- Stimulate growth
- Increase cardiac output
Where is calcitonin secreted?
What is its primary effect?
In what condition is calcitonin elevated?
Secreted by parafollicular cells (C-cells)
Decrease blood calcium levels (preventing hypercalcemia)
Elevated with medullary thyroid cancer
Explain normal thyroid hormone regulation
Negative feedback system:
- Low thyroid hormone (TH) concentration in blood…
- Thyrotropin-releasing hormone (TRH) released by hypothalamus
- Thyroid-stimulating hormone (TSH) released by pituitary gland
- A.k.a Thyrotropin - Thyroid hormone is released until blood-hormone level normalies
- TSH secretion ceases.
What is a pyramidal lobe?
3rd lobe
Arising from isthmus to hyoid bone
Label the thyroid arterial supply
Superior thyroid a:
- 1st branch of ECA
- Inserts inf poles
Inferior thyroid a:
- Branch of subclavian artery
- Inserts post aspect of inf poles
Thyroid ima a:
- 1-% of people
- Usually arises from brachiocephalic trunk
Label the thyroid venous drainage
Superior + middle thyroid veins drain –> IJV
Inferior thyroid veins drain –> brachiocephalic vein
Thyroid function tests (TFTs)
TSH:
FT4: free T4
FT3: free T3 (most sensitive for hyperthyroidism)
Euthyroid sick syndrome
Abnormal TFTs caused by non-thyroidal conditions:
- Pregnancy (high estrogen → high T3/T4)
- Critical illness
- Liver disease
- Renal disease
- Malnutrition
- Various medications (e.g. birth control → high T3/T4)
Thyroid hypoplasia
Abnormally enlarged thyroid (‘non-toxic goiter)
Causes:
- Iodine deficiency
- Hereditery
- Medication
- *Uniformly enlarged thyroid**
- Rounded poles
- >2cm AP
- >1cm isthmus
- *Increased volume**
- >18cc women
- >25cc men
- *Homogeneous parenchyma**
- *-** Normal vascularity
Graves disease
Hyperthyroidism (‘toxic goiter’)
- *Autoimmune disease:** immune system attacks thyroid → excess production TH → thyrotoxicosis
- Women >30
- Diagnosis
- Clinical/ lab: low TSH, high T3/T4
- US useful if asymetric enlargement
- Treatment
- TSH receptor blocker (medical)
- Thyroidectomy
Uniformly enlarged thyroid
Hypoechoic
Heterogeneous echotexture
Hypervascular (‘Thyroid inferno’)
Differential = Hashimoto’s Thyroiditis
Hashimoto’s thyroiditis (Autoimmune)
Hypothyroidism (most common thyroiditis)
- *Autoimmune disease**
1. Acute phase: immune system atacks thyroid → THs leak → circulation → temporary hyperthyroidism (thyrotoxicosis)
- Chronic phase: thyroid damged/ burns out → decrease in THs → hypothyroidism
- Chronic inflammation: functioning cells atrophy → connective tissue + immunce cells build up → gland enlarges
- Autoimmune disease
- Treatment
- TH replacement therapy (medical)
- FNA (nodules)
- Thyroidectomy (v large goiter, Ca suspicion)
Uniformly enlarged thyroid
Hypoechoic
- *Heterogeneous echotexture**
- *-** Hypoechoic micronodules
- Echogenic septations
- *Hypovascular**
- Can by hypervascular in acute phase
Differential = Graves diseas
Subacute granulomatous thyroiditis (de Quervain’s disease)
Cause = viral infection of upper respiratory tract → spreads to thyroid
- Diagnosis = clinical/ lab
- Signs of hyperthyroidism
- *-** Low TSH, high T3/T4, elevated ESR + CRP
- Tender palpable thyroid
- Treatment = self limiting
Enlarged thyroid
- *Poorly defined focal hypoechoic areas**
- Decreased vasc
Invasive fibrous thyroiditis (‘Riedel’s)
Rare
- *Autoimmune disease**
1. Immune cells attack thyroid → leads to hypothyroidism
2. Fibrous tissue replaces normal tissue → enlarged gland
3. Fibrosis extends beyond thyroid → affects trachea, muscles, nerves, blood vessels → neck structures fuse - Presents:
- Large v hard goiter
- SOB, dysphagia (pressure on trachea/ esophagus)
- Signs of hypothyroidism
- Management:
- US (assess extrathyroid ext.)
- CT/MRI (assess involved structures)
- FNA (fibrous tissue)
- Treatment
- Corticosteroids (suppress immune system)
- TH replacement therapy
- *Enlarged gland**
- Poorly defined marigns
Heterogeneous
- *Extrathyroid extension**
- Encasement of CCA/ IJV
Differential = anaplastic thyroid ca
Acute thyroiditis
Rare
- *Bacterial infection**
1. Starts in perithyroidal soft tissue (tonsilitis, abscess, pneumonia)
2. Hematogenous spread - Presents:
- Painful goiter
- Treatment:
- Antibiotics
- *Abscess**
- Hypoechoic mass
- Poorly defined
- Internal debris
- Peripheral vasc.
Local inflammatory lymph nodes
Colloid cyst
- Benign
- TIRADS 1
Anechoic cyst containing echogenic foci with comet tail artefact
Avascular
Differential = cystic papillary thyroid cancer
Hemorrhagic cyst
Occurs with degenerating nodules
Presents:
- Acute painful neck mass
- Obstructive symptoms (SOB, dysphagia)
Management:
- FNA
- Surgical resection
Large cyst with low-level internal echoes/ echogenic septations
Avascular
Solid colloid nodule
Spongiform
- Benign
- TIRADS 1
Predominantly (>50%) small cystic spaces, with hyperechoic spots
Adenoma
Adenoma
- Benign
- ‘Cold nodule’ on nuclear medicine (don’t produce hormones)
- TIRADS 3 or 4
- Multiple = multinodular goiter
Well-defined solid mass
Homogeneous
Isoechoic/hyperechoic with hypoechic halo
Hypervascular (peripheral → centre)
Differential = follicular cancer (cannot differentiate with US)
Papillary thyroid cancer
- Most common (75-90%)
- Arise from follicular cells
- Good prognosis (90% 20yr survival)
- Early cervical lymph nodes metastases (doesn’t worsen prognosis)
Presents:
- Enlarged cervical nodes
- Solitary palpable mass
- Women (30’s + 70’s)
Management:
- FNA
- CT
- Surgical resection/ lobectomy
- Radiation (lymph nodes mets)
- *Very hypoechoic mass**
- Irreg shape
- Ill defined borders
- Often subscapsular
- *Punctate calcifications**
- +/- shadowing
Disorganised hypervacularity
- *Cervical node mets**
- Cystic degeneration
Differntial = follicular thyroid cancer
Follicular thyroid cancer
- 2nd most common (5-15%)
- Arise from follicular cells
- Prognosis = not as good as pap. (90% 10yr survival)
- Early distant metastases via blood (bone, lung, brain, liver)
Management:
- Staging CT (distant mets)
- Surgical resection/ lobectomy
- Radiation
- FNA cannot differentiate adenoma + follicular ca
Well defined solid mass
Homogeneous
Isoechoic with hypoechic halo
Disorganised hypervascularity
Differential = adenoma
Medullary thyroid cancer
- Rare (5%)
- Arises from parafollicular cells (c-cells)
- Secretes calcitonin
- Compenent of MEN II (multiple endocrine neoplasia)
- Poor prognosis
- High incidenence of mets at presentation (50%)
Presents:
- Elevated calcitonin
- Pts with family history (20%)
Management:
- Labs (high levels calcitonin → aggressive)
- Staging CT (distant mets)
- Surgery (thyroidectomy)
Hypoechoic solid mass
- *Coarse calcifications**
- +/- shadowing
Disorganised hypervacularity
Differnential = papillary thyroid cancer
Anaplastic thyroid cancer
- Rare (<2%
- Worst prognosis (~5% 5yr survival)
- Highly agressive
- Metastasise via local invasion (muscle + vessels)
Presents:
- Rapidly enlarging mass
- Obstructive symptoms (SOB, dysphagia)
- Hoarse voice
- Elderly women
Management:
- CT/ MRI (often to large to assess with US)
- Surgery (often inoperable at presentation)
- *Large hypoechoic solid mass**
- May have microcalcs
- *Infiltrative**
- Invades adjacent muscles + vessels
Lymphoma
- Rare
- Usually non-hodgkin
- 70-80% arise from Hashimoto’s
- Poor prognosis
Presents:
- Rapidly enlarging mass
- Obstructive symptoms (SOB, dysphagia)
- Hoarse voice
- Cervical lymphadenopathy
Management:
- CT/ MRI (extent of invasion)
- Surgery (often inoperable at presentation)
- Chemo + radiation
- *Large very hypoechoic mass/ diffuse parenchyma**
- Encasement of neck vessels
- Areas of cystic necrosis
Hypovascular
Differential= Anaplastic thyroid cancer
