A Hurthle cell adenoma is a benign growth, or adenoma, that forms within the thyroid gland. This growth is composed of specialized cells known as Hurthle cells, sometimes referred to as oxyphilic cells or oncocytes. The thyroid gland, located at the base of the neck, produces hormones that regulate the body’s metabolism. Understanding the specific nature of a Hurthle cell adenoma is the first step in the diagnostic process.
What Exactly Is a Hurthle Cell Adenoma?
Hurthle cell adenomas are defined by the specific cells that make up the tumor. Hurthle cells are a variant of follicular cells lining the thyroid gland’s follicles. These cells are distinct because they contain an abnormally high number of mitochondria, the energy-producing powerhouses of the cell. This abundance causes the cells to appear granular and eosinophilic (pink) when stained and viewed under a microscope.
A lesion is classified as an adenoma because it is a non-cancerous growth completely encapsulated and confined within the thyroid gland. The tumor is typically solitary, well-circumscribed, and surrounded by a thick, fibrous capsule. This encapsulation differentiates a benign adenoma from its malignant counterpart, Hurthle cell carcinoma. The tumor is considered a Hurthle cell neoplasm when at least 75% of the cells exhibit this characteristic oncocytic appearance.
Identifying the Tumor: Symptoms and Initial Presentation
The presence of a Hurthle cell adenoma is often first noticed as a physical change in the neck area. The most common presentation is a painless, solitary nodule within the thyroid gland that can be felt (palpated) during a physical examination. Many patients are asymptomatic, and the nodule is discovered incidentally. Incidental discovery frequently occurs during imaging studies, such as an ultrasound or CT scan, ordered for an unrelated medical reason.
If the nodule grows large enough, it can begin to press on surrounding structures in the neck, causing compression symptoms. These symptoms can include difficulty swallowing (dysphagia), or a feeling that food or pills are getting “stuck.” A large nodule may also cause hoarseness or other changes in the voice, as well as shortness of breath, particularly when lying flat.
Diagnostic Challenges and Procedures
The initial step in evaluating a thyroid nodule involves an ultrasound, which characterizes the nodule’s size, borders, and internal features. This imaging is often followed by Fine Needle Aspiration (FNA), where a small, thin needle collects cells directly from the nodule. The collected cells are then examined by a cytopathologist to determine their nature.
FNA presents a significant diagnostic challenge for Hurthle cell neoplasms. The problem arises because the cells of a benign Hurthle cell adenoma look microscopically identical to those of a malignant Hurthle cell carcinoma. Both lesions are composed of the same large, mitochondria-rich Hurthle cells. Consequently, the FNA cytology often yields an indeterminate or suspicious result, frequently categorized as Bethesda Category III or IV.
The definitive distinction between an adenoma (benign) and a carcinoma (malignant) is based on invasion into the surrounding structures. A pathologist must confirm whether the Hurthle cells have invaded the tumor’s capsule or the surrounding blood vessels. Since FNA only collects a small sample of cells, it cannot provide the pathologist with the intact capsule and surrounding tissue necessary to assess for capsular or vascular invasion. This limitation means that surgical removal of the entire nodule is required to obtain the tissue needed for a definitive diagnosis.
Treatment and Post-Surgical Follow-up
Surgical resection is the standard treatment for a suspected Hurthle cell neoplasm. The primary goal is to remove the tumor and secure the entire specimen for final pathological analysis, which is the only way to confirm if the lesion is an adenoma or a carcinoma. The procedure performed is typically a lobectomy, which removes only the half of the thyroid containing the nodule. A total thyroidectomy (removal of the entire gland) may be considered if the tumor is large, highly suspicious for malignancy, or involves both sides of the thyroid.
Following surgery, the removed tissue is sent for detailed histological examination. This post-surgical pathology report provides the final diagnosis, confirming whether the lesion is a benign Hurthle cell adenoma or a malignant carcinoma based on capsular or vascular invasion. If the diagnosis confirms a benign Hurthle cell adenoma, the surgical removal is considered curative, and no further treatment is required.
Long-term care involves monitoring the patient, which may include regular physical exams and neck ultrasounds to check for new nodules. If a total thyroidectomy was performed, the patient will require lifelong thyroid hormone replacement therapy to compensate for the loss of hormone production. The prognosis for confirmed Hurthle cell adenomas is excellent, as the tumor is fully removed and does not carry a risk of metastasis.