ULTRASOUND OF THE THYROID - Normal

  • It is a superficial gland which should be homogeneous in it's echotexture. There are 2 sides of the gland with an isthmus joining the left and right sides.
Thyroid function tests explained

 

Thyroid Normal Scan plane Thyroid- Normal Image

Thyroid Scan plane transverse

Transverse view of a normal thyroid.

thyroid-scan-plane-isthmus.jpg Isthmus - longitudinal view

Isthmus scan plane-longitudinal view

The isthmus should be less than 10mm. It can be almost imperceptably thin.

Longitudinal View of Right lobe Thyroid- Normal longitudinal view

Scan plane for longitudinal view Right lobe.

Normal Thyroid Lobe - longitudinal view of left lobe

 

THYMUS

  • The thymus is an important gland in the development/education of our T-cells (T lymphocytes) from the neonatal period to puberty when it atrophies.
  • The thymus lies superior to the heart and can easily be seen inferior to the left thyroid prior to puberty. It may still occassionally be seen in adulthood.
  • Pathology is rare. Lymphoma or a thymoma are the two most likely pathologies.
 

Greys anatomy thymus diagram

Ultrasound of a normal thymus gland.
Anatomical diagram of the thymus gland in a neonate.

Normal thymus in a 12 year old girl.

Use of a curvilinear probe readily demonstrates the normal thymus inferior to the left lobe of the thyroid.

 

Ultrasound of a pediatric thymus gland

Ultrasound transverse view of a normal thymus

Longitudinal view of the thymus gland in a child.

Power doppler shows the normal flow.

Transverse view of the thymus gland in a child.

ULTRASOUND OF THE THYROID PROTOCOL

ROLE OF ULTRASOUND

Ultrasound is a valuable diagnostic tool in assessing the following indications;

  • Classification of a palpated lump. eg solid, cystic, mixed
  • Evaluate adjacent structures
  • Determining the location of a palpable lump (within or outside of the thyroid)
  • Identifying a cause for Hyperthyroidism
  • Identifying a cause for Hypothyroidism
  • Post surgical complications eg abscess, oedema
  • Multi Nodular Goiter (MNG): Follow up nodules
  • Guidance of injection, aspiration or biopsy
  • Relationship of normal anatomy and pathology to each other

DIFFERENTIAL DIAGNOSES

If the patient presents with a neck lump/swelling for investigation, common possible diagnoses other than the thyroid are:

  • Fat roll at the base of the neck
  • Lymphadenopathy
  • Branchial cleft cyst (supero-lateral to the thyroid. May be transient)
  • Thyroglossal duct cyst (midline superior to the thyroid)
  • Parathyroid gland mass (Usually small and inferior on the thyroid)

LIMITATIONS

The inferior most aspect of an enlarged thyroid with marked retrosternal extension will not always be visible on ultrasound.

PREPARATION

  • Low collared shirt
  • Remove jewellery around the neck
  • Towel across the shoulders/chest
  • Lie the patient so their head is at the top of pillow and tipped right back.
  • A pillow or towel can be placed under the shoulders

EQUIPMENT SELECTION AND TECHNIQUE

  • A 7-14mHz linear transducer
  • Deep seated tumours, retrosternal thyroids or large patients may require a curvi-linear array transducer of 3.5MHz
  • Good colour / power / Doppler capabilities when assessing vessels or vascularity of a structure.

SCANNING TECHNIQUE

  • Begin with a survey scan in transverse down the midline to assess for tracheal deviation and obvious pathology.
  • Tilt the patients head slightly to the contralateral side and scan down in transverse.
  • Rotate into longitudinal and scan from medial to lateral.
  • Repeat this for the other side with the head tilted the other way.
  • With the patients head/neck straight, scan the isthmus in longitudinal and transverse.
  • Scan down each side of the neck in transverse for alternative pathology.

PATHOLOGY

Thyroid Nodules

Usually is a MULTINODULAR GOITRE (MNG) but....

Malignant V's Benign

There is no single ultrasonographic feature to distinguish between the two. Features to assist in differentiating include:

Cystic v's solid

Single v's multinodularity

Hypoechoic v's

Halo

Macro v's microcalcification

Vascularity

THYROID MALIGNANCIES

Malignancy occurs in approximately 1% of thyroid nodules.
Papillary and/or mixed papillary/follicular carcinomas are by far the most common malignancy.
The incidence is dramatically increased in post head/neck radiotherapy patients.

  • Papillary Carcinoma 78%
  • Follicular Lesion Carcinoma 17%
  • Medullary Carcinoma 4%
  • Anaplastic Carcinoma 1%
  • Thyroid lymphoma - rare
  • Thyroid metastases - rare

A 'cold nodule' on nuclear medicine increases the suspicion of malignancy however the likelihood is still low. Sonographic signs increasing the suspicion of malignancy:

  • Solitary nodule
  • Punctate calcification (rather than large or peripheral calcifications)
  • Irregular surrounding halo
  • Solid

Importantly, a diagnosis of malignancy cannot be made without biopsy.
Again, keep in mind that the vast majority of thyroid nodules are benign.

THYROIDITIS

  • Hashimoto's Thyroiditis
  • Graves disease
  • De Quervain's subacute thyroiditis
  • Acute suppurative thyroiditis
FOR DETAILED DESCRIPTIONS AND IMAGES OF THYROID         PATHOLOGY

 

BASIC HARD COPY IMAGING

A thyroid series should include the following minimum images:

  • Transverse images of the gland from superior to inferior.
  • Longitudinal images of the gland with a length measurement.
  • Measure the glands volume: Normal=7-11cc/lobe
    (or at least the maximum length, thickness and width)
  • Isthmus, trans and long with a maximum AP diameter.
  • Left neck.
  • Right neck.
  • Assess the paracervical lymph nodes, carotid artery and jugular vein.
  • Document the normal anatomy. Any pathology found in 2 planes, including measurements and any vascularity.
 
 

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