The thyroid gland is a small, butterfly-shaped organ at the front of your neck that controls the body’s metabolism by producing and releasing hormones. When the thyroid isn’t working correctly, it can impact the entire body. Thyroid asymmetry refers to a difference in the size, shape, or texture between the gland’s two lobes.
Understanding Thyroid Gland Variations
Perfect symmetry is rare in biological structures, and the thyroid gland is no exception. A minor degree of asymmetry is a normal anatomical variation, and studies show it is common for the right lobe to be slightly larger than the left.
Discovering a size difference between the two thyroid lobes is not automatically a sign of disease. The gland’s structure can vary significantly from one person to another without impacting its function.
The distinction lies between a slight, stable asymmetry and a significant or changing imbalance that warrants investigation. A healthy thyroid is not visible or easily felt by pressing on the neck. An enlargement that becomes noticeable may indicate an underlying issue that has disrupted the gland’s normal size and shape.
Underlying Reasons for Thyroid Asymmetry
Several conditions can cause noticeable thyroid asymmetry. The most frequent causes are benign growths like thyroid nodules, which are solid or fluid-filled lumps, and goiters, which are a general enlargement of the gland. A goiter can be caused by multiple nodules, making the gland lumpy and uneven, and the vast majority of nodules are not cancerous.
Inflammation of the thyroid, or thyroiditis, is another common cause. Hashimoto’s thyroiditis, an autoimmune condition, can cause uneven swelling, while subacute thyroiditis may cause rapid and painful inflammation in one part of the gland. Fluid-filled sacs called thyroid cysts can also develop, creating localized swelling on one side.
Less common causes include thyroid hemiagenesis, a rare condition where one lobe fails to form. While most causes of asymmetry are benign, a malignant tumor is another possibility. A cancerous growth on one lobe can cause it to enlarge, but cancer accounts for only a small percentage of thyroid nodules.
Methods for Evaluating Thyroid Asymmetry
Evaluation begins with a physical examination, where a doctor palpates, or feels, the neck. This assessment allows the doctor to check the thyroid gland’s size, consistency, and symmetry, and to identify any distinct masses.
A primary tool for visualizing the gland is a thyroid ultrasound, a non-invasive test that uses sound waves to create detailed pictures of its structure. An ultrasound can measure the dimensions of each lobe, identify nodules too small to be felt, and characterize their features, such as whether they are solid or cystic.
Blood tests are performed to assess thyroid function by measuring levels of TSH, T4, and T3 hormones. This determines if the gland is overactive (hyperthyroidism) or underactive (hypothyroidism). If an ultrasound identifies a suspicious nodule, a Fine-Needle Aspiration (FNA) biopsy may be recommended. During an FNA, a thin needle is used to collect cells from the nodule for examination to determine if it is benign or malignant.
Interpreting Asymmetry and Next Steps
The significance of thyroid asymmetry is determined by combining findings from the physical exam, imaging, and lab tests. Asymmetry becomes a concern when associated with certain features, including:
- Rapid growth of a nodule
- A particularly large size
- Symptoms like difficulty swallowing, shortness of breath, or voice hoarseness
- Suspicious characteristics on an ultrasound, such as irregular margins or microcalcifications
Based on the diagnosis, the management approach varies. If asymmetry is caused by small, benign nodules with no concerning features or symptoms, the recommended course is often active surveillance. This involves periodic monitoring with follow-up ultrasounds to ensure the nodules are not growing or changing.
If the evaluation reveals an underlying issue, treatment may be necessary. For abnormal thyroid function, medications like levothyroxine can manage hypothyroidism. If a goiter causes compressive symptoms or a biopsy confirms cancer, a specialist may discuss treatments like surgery to remove part or all of the thyroid gland.