Introduction on the thyroid gland
A thyroid gland is a butterfly- or H-shaped organ located in front of the center of the neck. It usually consists of 2 lobes, right and left lobes adjacent to the side of the trachea or windpipe, with the 2 lobes being connected by an isthmus. There may also be a rudimentary pyramidal lobe that usually arises from the isthmus going upwards along the midline and is usually located in front of the thyroid cartilage. Because of its small size, the pyramidal lobe is usually not detected on imaging procedures, usually only on operation.
When do we say that a thyroid gland is enlarged?
When do we say that a thyroid gland is enlarged? The question is on enlargement. There are two forms of structural pathologies of the thyroid gland – enlargement and nodule formation. The presence of abnormal enlargement can cause increase in the dimensions of the thyroid gland so does the presence of a nodule, especially it is large and multiple. The discussion here will be limited to enlargement or thyromegaly, a medical term commonly used in imaging reports.
Illustration of enlargement
Illustration of nodule
A thyroid gland can be assessed through physical examination and imaging techniques. The latter includes ultrasound of the thyroid; thyroid scan; CT scan; and MRI.
Enlargement of the thyroid gland can be assessed through physical examination and imaging techniques.
It is said that the normal thyroid gland weighs approximately 15 to 25 g. It will be difficult to assess the weight unless you have to remove the whole thyroid gland in the operation theatre or in the morgue. Thus, in the usual medical practice, weight is not used in determining thyroid enlargement or thyromegaly.
In a study using thyroid glands, the following were the findings:
“The longitudinal length of the lobes and the width of the whole gland were found to be the essential parameters in defining the size of the thyroid gland. When these 2 dimensions measure 6.5 cm. or more, the thyroid gland should be considered enlarged.”
This has been used as the basis for saying a thyroid gland is enlarged based on thyroid scan.
A commonly used imaging technique for measuring the size of the thyroid gland is the ultrasound. It may report in terms of volume or dimensional measurement.
It is reported that normal adult thyroid volume is about 10-15cc.
The normal dimensional measurements, although commonly quoted at 4 to 6 cm in length and 1.3 to 1.8 cm in thickness for each thyroid lobe and less than 4 to 5 mm in thickness for the isthmus, may vary from one radiological center to another.
For example, one center would state the following:
Each lobe is no more than 3 – 4 centimeters in height, 1 – 1.5 cm in width, and 1 centimeter in depth. The isthmus is approximately 0.5 cm in height and 2 – 3 mm in depth.
On physical examination, it is commonly taught that if the thyroid gland is palpable, then there is thyroid enlargement. If not, none.
What do we make out from the above information?
There is a range of normal dimensions or volume. There are normal variations.
My approaches are:
If there is no ultrasound or thyroid scan to evaluate or to consider, just palpate the thyroid gland. If it is not palpable, then it is not enlarged. If it is palpable, then it is enlarged. Determine the degree of enlargement as to mild, moderate, or severe. One may use the following clinical classification of goiter based on physical size – Gr. III, goiter is evident and visible even if the patient’s neck is not hyperextended; Gr. II, goiter is evident and visible only if the patient’s neck is hyperextended; and Gr. I, goiter is small and not evident even when neck is hyperextended.
If the ultrasound or thyroid scan result reported thyromegaly based on dimensions or volumes, correlate clinically. If the thyroid gland is palpable, then accept the report of thyromegaly. If not, make a clinical decision – to put on hold, to repeat the diagnostic test, or to do another test.