A thyroid nodule is an unusual growth of cells that forms a lump within the thyroid gland, a gland at the base of the neck. These nodules are common, found in up to 65% of adults, and their prevalence increases with age. While most thyroid nodules are non-cancerous, a small percentage can be malignant, requiring further evaluation.
Understanding Suspicion Levels
Medical professionals classify thyroid nodules based on ultrasound characteristics to assess their likelihood of being cancerous. This classification uses a standardized system, such as the Thyroid Imaging Reporting and Data System (TIRADS), which assigns categories from low to high suspicion. Each category has specific ultrasound features and an associated probability of malignancy.
A “moderately suspicious” thyroid nodule typically corresponds to a TIRADS 4 classification. Nodules in this category exhibit features that raise concern, but are not definitive for cancer. Characteristics include slight irregularity of margins, hypoechogenicity (appearing darker than surrounding thyroid tissue), or a taller-than-wide shape.
These features suggest a moderate probability of malignancy, generally ranging from 10% to 30%. A “moderately suspicious” classification does not confirm cancer; it indicates a higher chance of malignancy compared to “low suspicion” or “benign” nodules, necessitating further investigation.
Diagnostic Pathway for Moderately Suspicious Nodules
Once a thyroid nodule is identified as moderately suspicious by ultrasound, the next step is a Fine Needle Aspiration (FNA) biopsy. This procedure collects cells from the nodule for microscopic examination. FNA biopsy is a common and accurate method for evaluating thyroid nodules.
During an FNA biopsy, a thin, hollow needle is inserted into the thyroid nodule. The procedure is guided by ultrasound to ensure precise needle placement within the nodule.
The doctor aspirates cells and sometimes fluid into a syringe. Multiple samples are typically obtained from different parts of the nodule to increase the chance of collecting a representative sample. The procedure usually takes less than 30 minutes and is often performed in an outpatient setting, sometimes with a local anesthetic.
Interpreting Biopsy Results and What’s Next
After a Fine Needle Aspiration (FNA) biopsy, the collected cells are sent to a pathology laboratory. Results are classified using a standardized system, the Bethesda System for Reporting Thyroid Cytopathology, which categorizes outcomes into six groups. These categories help guide management decisions.
Results range from benign (less than 3% risk of cancer) to malignant (97-99% chance of being cancerous). Indeterminate categories include “Atypia of Undetermined Significance (AUS)/Follicular Lesion of Undetermined Significance (FLUS)” (5-15% risk of malignancy) or “Follicular Neoplasm/Suspicious for Follicular Neoplasm” (15-30% risk). “Suspicious for Malignancy” suggests a 60-75% chance of cancer, with worrisome features present but not definitive for a malignant diagnosis. “Moderately suspicious” is an initial imaging classification, and the biopsy provides a more definitive cellular diagnosis.
Management and Ongoing Care
The management plan for a thyroid nodule is determined by the biopsy results. If the biopsy indicates a benign nodule, watchful waiting is often recommended, involving periodic follow-up ultrasounds and physical examinations to monitor for any changes.
For indeterminate results, additional steps may be necessary. This could include a repeat FNA biopsy, molecular testing of the nodule cells to assess specific genetic mutations, or in some cases, surgical removal of part of the thyroid for a definitive diagnosis. Molecular tests can help predict whether an indeterminate nodule is benign or cancerous, potentially avoiding unnecessary surgery.
If the biopsy results are suspicious for malignancy or frankly malignant, surgery is typically the primary treatment. The extent of surgery depends on the type and size of the cancer, potentially involving removal of half or all of the thyroid gland. In some cases, radioactive iodine therapy may follow surgery for certain types of thyroid cancer. Long-term follow-up is important for all patients, especially those with cancerous nodules, to monitor for recurrence and manage thyroid hormone levels.