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X-ray anatomy of the thyroid gland
Last reviewed: 04.07.2025
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The thyroid gland is located in the anterior region of the neck in front of the trachea. It is horseshoe-shaped with a concavity facing backwards and consists of two unequal lobes connected by an isthmus. Sometimes there are additional thyroid glands (on the neck, in the area of the root of the tongue, in the chest cavity), which can be detected using radiological methods, especially scintigraphy.
Conventional radiographs do not produce a clear image of the thyroid gland due to its small size and minor differences in density compared to surrounding tissues. On computer and magnetic resonance tomograms, the gland is quite clearly visible: its lobes and isthmus are visible, having smooth rounded contours. The tissue of the gland is homogeneous, its density, determined by densitometry, reaches approximately 100 HU. The relationship of the gland to the trachea and blood vessels of the neck is clearly visible.
The main methods of visualizing the thyroid gland are ultrasound scanning and scintigraphy.
No special preparation is required to conduct an ultrasound examination, it can be performed repeatedly, the examination has no contraindications and is not accompanied by complications. It is carried out on devices operating in real time, with special sensors with an ultrasound frequency of about 5-7 MHz.
For the purpose of a comprehensive examination, a series of longitudinal and transverse sonograms are produced. Normally, the thyroid gland is distinguished as a formation with a homogeneous fine-grained structure. Its natural markers are the trachea and the common carotid arteries. On a longitudinal sonogram, both lobes of the gland and the isthmus between them up to 0.8 cm thick are visible. Each lobe has the shape of an oval. The skin and subcutaneous fat are visible in front of it, and the common carotid artery or thyroid cartilage is visible behind. During transverse scanning, the gland is defined as a formation symmetrically located relative to the midline, each lobe of which forms an oval. Linear echostructures are visible between the lobes - a reflection of the laryngeal cartilages. On transverse scanograms, the thyroid cartilage is also clearly visible, causing two linear structures that form an obtuse angle. Behind and slightly to the side of each thyroid lobe are rounded echo-negative figures corresponding to the common carotid artery and laterally to the jugular vein. Anteriorly and to the side of the gland lobes one can see oval fine-mesh structures of the sternocleidomastoid muscles.
Radionuclide examination of the thyroid gland is performed after preliminary preparation of the patient. Preparation consists of excluding substances that block the gland (food products and drugs containing iodine and bromine). In addition, the patient must come to the radionuclide laboratory on an empty stomach. The image of the gland is obtained by intravenous administration of 80-100 MBq 99mTc-pertechnetate.
Normally, the scintigram shows the outlines of the entire thyroid gland in the shape of a butterfly. The right and left lobes and the isthmus are visible. The size of the right lobe is usually somewhat larger than the left: 3-6 cm in length and 2-3 cm in width. The outer contours of the gland are convex. The density of the image is higher in the central parts of the lobes, since there is more glandular tissue there, and it decreases towards the periphery. There are numerous variations in the size of the lobes of the gland and in the display of the isthmus. The pyramidal lobe, extending upward from the isthmus, is rarely detected.