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 Scan plane transverse
Transverse view of a normal thyroid.
Isthmus scan plane-longitudinal view
The isthmus should be less than 10mm. It can be almost imperceptably thin.
Scan plane for longitudinal view Right lobe.
Normal Thyroid Lobe - longitudinal view of left lobe
- 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.
|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.
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
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
- 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)
The inferior most aspect of an enlarged thyroid with marked retrosternal extension will not always be visible on ultrasound.
- 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.
- 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.
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
Macro v's microcalcification
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
Importantly, a diagnosis of malignancy cannot be made without biopsy.
Again, keep in mind that the vast majority of thyroid nodules are benign.
- 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.