Hürthle Cell Thyroid Carcinoma: Key Characteristics
Hürthle cell carcinoma (HCC) often metastasizes to cervical lymph nodes and requires total thyroidectomy for adequate treatment. Based on the most recent guidelines, HCC is now recognized as a distinct entity with unique clinical, biological, and genetic features that differentiate it from conventional follicular thyroid carcinoma 1.
Classification and Pathology
- Hürthle cell carcinoma is now classified as a distinct type of differentiated thyroid cancer by the WHO, rather than being considered a variant of follicular thyroid carcinoma 1
- HCC is characterized by large cells with abundant eosinophilic, granular cytoplasm due to numerous mitochondria 2
- Some experts consider HCC a more aggressive form of differentiated thyroid cancer, particularly when associated with extensive vascular and/or capsular invasion 1
Metastatic Pattern and Behavior
- HCC often metastasizes to cervical lymph nodes, making it different from conventional follicular thyroid carcinoma 2, 3
- The risk of recurrence is classified as high (>20%) when HCC is associated with extensive vascular invasion (>4 foci) 1
- When compared to conventional follicular carcinoma, HCC has a higher propensity for lymph node involvement 3, 4
Surgical Management
- Total thyroidectomy is the recommended treatment for Hürthle cell carcinoma, particularly for tumors larger than 4 cm 2, 3
- Thyroid lobectomy alone is only sufficient for small, unifocal, intrathyroidal carcinomas without clinically detectable cervical nodal metastases 2
- Neck dissection should be performed when there is lymph node involvement 5, 3
Risk Stratification and Prognosis
- HCC with extensive vascular and/or capsular invasion has a recurrence risk classified as high (30-55%) 1
- For minimally invasive HCC, robust data are lacking on the true risk of recurrence 1
- Factors associated with worse prognosis include age over 45 years, distant metastases, and advanced T-stage 4
Bilateral Occurrence
- HCC is seldom bilateral, typically presenting as a unifocal disease 6, 3
- This contrasts with papillary thyroid carcinoma, which more commonly presents as multifocal disease 6
Relationship to Radiation Exposure
- Unlike some other thyroid cancers, HCC is not strongly associated with previous neck radiation 5
- Only rare cases report a history of low-dose external radiation to the head and neck in childhood 5
Radioactive Iodine Therapy
- The effectiveness of radioactive iodine therapy for HCC remains controversial 2, 3
- Despite the debate, radioactive iodine is frequently used in the treatment of HCC (reported in approximately 55% of cases) 3, 4
Diagnostic Challenges
- Preoperative diagnosis of HCC is challenging using fine-needle aspiration cytology alone 2, 7
- Definitive diagnosis requires histological evidence of capsular and/or vascular invasion, which can only be determined after surgical excision 6, 7
In conclusion, Hürthle cell carcinoma is a distinct entity with unique characteristics including frequent cervical lymph node metastases, rare bilateral occurrence, and limited association with prior radiation exposure. Total thyroidectomy is generally required for adequate treatment, particularly for larger tumors.