The parathyroid glands are small endocrine glands, typically four in number, situated in the neck, usually behind the thyroid gland. These glands play a fundamental role in regulating the body’s calcium levels by producing parathyroid hormone (PTH). Maintaining proper calcium balance is important for nerve and muscle function, as well as bone health. Due to their small size and specific location, imaging these glands with ultrasound can present challenges, though it remains a common approach when parathyroid issues are suspected.
Why Parathyroid Glands Are Hard to See
Normal parathyroid glands are difficult to visualize with ultrasound due to their anatomical and physical characteristics. They are very small, often described as being the size of a grain of rice. Their small dimensions make them challenging to distinguish from surrounding tissues.
Their location also contributes to imaging difficulty. While most individuals have four glands behind the thyroid, their exact position can vary significantly. Some parathyroid glands can be in less common, or “ectopic,” locations, such as along the esophagus, within the thyroid gland, or even in the chest (mediastinum). Additionally, the echogenicity, or how they appear on ultrasound, of normal parathyroid glands can be similar to adjacent structures like the thyroid or fat tissue, causing them to blend in. Normal glands typically lack distinct features that would make them stand out on an ultrasound scan.
When Ultrasound Can Detect Parathyroid Glands
While normal parathyroid glands are rarely seen on ultrasound, their visibility increases when they become abnormal, particularly when enlarged due to conditions such as hyperparathyroidism. The most common cause of primary hyperparathyroidism is a single enlarged gland, known as an adenoma. As a parathyroid gland grows, it becomes easier for the sonographer to identify and differentiate it from the surrounding neck tissues.
An enlarged parathyroid gland, such as an adenoma, typically appears as a discrete, oval, or bean-shaped mass that is homogeneously hypoechoic, meaning it looks darker than the adjacent thyroid gland. These abnormal glands may also show changes in their shape, becoming lobulated, or exhibiting internal features like cystic areas or calcifications. The presence of an enlarged gland suggests a pathological condition.
Optimizing Ultrasound Detection
Detecting abnormal parathyroid glands with ultrasound relies on specialized equipment and the expertise of the medical professional. High-resolution ultrasound equipment with high-frequency transducers is important, as these provide better detail of the small structures in the neck. These advanced transducers can detect structures as small as 2 mm. The skill and experience of the sonographer are also important, as they must meticulously scan the neck and recognize subtle signs of an enlarged gland.
Specific scanning protocols improve detection. This includes careful positioning of the patient with the neck extended and scanning from the carotid arteries to the midline, from the jawline down to the chest. Color Doppler ultrasound is a valuable technique, as parathyroid adenomas tend to be highly vascular. This can help identify a characteristic polar feeding vessel entering the gland, which distinguishes it from other neck structures like lymph nodes that have different vascular patterns.
Ultrasound’s Place in Diagnosing Parathyroid Conditions
Ultrasound is a common initial imaging test for parathyroid disorders. Its non-invasive nature and wide availability make it a practical choice for localizing an enlarged parathyroid gland before surgery. The technique is also useful in depicting potential co-occurring thyroid disease, which is found in a substantial percentage of patients with parathyroid conditions.
However, ultrasound has limitations. It may struggle to detect very small adenomas, with sensitivity decreasing for glands under 1 cm. It also has reduced sensitivity in identifying glands in ectopic locations, particularly those deep in the neck or within the chest, or when multiple glands are affected (multiglandular disease). If ultrasound findings are inconclusive or negative, other imaging modalities, such as Sestamibi scans or 4D CT scans, may be utilized to further localize the abnormal gland. Combining ultrasound with other tests can improve accuracy in localizing parathyroid issues.