Follicular neoplasm describes an abnormal growth of follicular cells, the primary cell type, within the thyroid gland. This growth may or may not be cancerous, and further investigation is necessary to determine its nature. The term “neoplasm” simply means new growth, not inherently classifying it as benign or malignant.
Understanding Follicular Neoplasm
The thyroid gland, a butterfly-shaped organ at the base of the neck, is part of the endocrine system. It produces hormones like thyroxine (T4) and triiodothyronine (T3) that regulate metabolism, growth, and development. Follicular cells are the thyroid’s major cell type, organized into spherical structures called follicles that store hormones. A follicular neoplasm originates from these cells.
The Diagnostic Dilemma
Distinguishing between a benign (non-cancerous) and malignant (cancerous) follicular neoplasm is challenging. Malignancy is defined by capsular or vascular invasion, where cells break through the growth’s capsule (a thin tissue barrier) or enter blood vessels.
However, a fine needle aspiration (FNA) biopsy, a common initial diagnostic procedure, cannot reliably detect this. FNA collects only a small cell sample, which may appear similar whether benign or cancerous. Without examining the entire capsule and surrounding tissue, invasion cannot be confirmed.
Therefore, an FNA diagnosis of “follicular neoplasm” is indeterminate, meaning it cannot definitively confirm or rule out cancer. Further steps are necessary for a conclusive diagnosis, as approximately 20-30% of FNA-diagnosed follicular neoplasms are later found to be cancerous upon surgical removal.
Evaluating Follicular Neoplasm
Once a follicular neoplasm is identified through an FNA biopsy, further evaluation is necessary due to diagnostic limitations. Molecular testing, which analyzes genetic markers within the cells, can help assess the risk of malignancy. While molecular tests can provide valuable information and help stratify risk, they are not always definitive, but can guide next steps in management.
Surgery is often required to obtain enough tissue for a definitive diagnosis. During surgery, part or all of the thyroid gland containing the neoplasm is removed. A pathologist then examines the entire growth under a microscope, specifically looking for capsular or vascular invasion. This examination of the whole specimen is the only way to definitively determine if the follicular neoplasm is benign or malignant.
Management and Outlook
The management of a follicular neoplasm depends entirely on the definitive diagnosis made after surgical removal. If the growth is confirmed to be a benign follicular adenoma, no further treatment is typically required. The surgical removal of the nodule is considered curative.
If the pathology report confirms follicular carcinoma, further treatment and long-term follow-up are necessary. This may involve additional surgery to remove any remaining thyroid tissue, particularly if only a portion was initially removed. Radioactive iodine therapy might be recommended to destroy any remaining thyroid cancer cells that could not be surgically removed. Follicular carcinomas generally have a favorable prognosis, especially when identified and treated early.