Follicular patterned lesions of the thyroid gland: a practical algorithmic approach

Area of Science:

• Pathology
• Endocrinology
• Oncology

Background:

• Follicular patterned thyroid lesions pose diagnostic challenges due to subjective interpretation.
• Sporadic encounters with these lesions can lead to uncertainty among pathologists.

Purpose of the Study:

• To emphasize diligent sampling of encapsulated thyroid lesions.
• To highlight the significance of assessing capsular and vascular invasion.
• To review nuclear changes pathognomonic of papillary thyroid carcinoma (PTC).

Main Methods:

• Review of established criteria for thyroid lesion interpretation.
• Development of an algorithmic approach for diagnosis.
• Focus on unequivocal nuclear features versus inconclusive findings.

Main Results:

• Encapsulated lesions lacking definitive PTC nuclear features but showing concerning changes may be termed 'uncertain malignant potential or behaviour, most likely benign'.
• Indubitable classical PTC nuclei are diagnostic of PTC, including follicular variants.
• Capsular and vascular invasion are the sole reliable predictors of patient outcome.

Conclusions:

• Accurate diagnosis of follicular patterned thyroid lesions requires meticulous sampling and evaluation of specific features.
• Distinguishing between benign, uncertain, and malignant potential is crucial for patient management.
• Non-invasive follicular variant PTC, even with nuclear changes, typically exhibits indolent behavior.