Definition/General

Introduction:
-Thyroid FNAC follicular lesions represent a spectrum of follicular-patterned thyroid nodules
-These include follicular adenoma, follicular carcinoma, and follicular variant of papillary carcinoma
-Cytological distinction is challenging due to morphological overlap
-Bethesda Category IV (Follicular Neoplasm/Suspicious for Follicular Neoplasm).
Origin:
-Arise from thyroid follicular epithelial cells
-Show follicular architecture with varying degrees of atypia
-May demonstrate Hürthle cell changes
-Can progress from hyperplasia to neoplasia
-Genetic alterations include RAS mutations and PAX8-PPARG rearrangements.
Classification:
-Classified according to Bethesda System for thyroid cytopathology
-Category III: Atypia of Undetermined Significance (AUS)
-Category IV: Follicular Neoplasm/Suspicious for Follicular Neoplasm (FN/SFN)
-Category V: Suspicious for Malignancy.
Epidemiology:
-Follicular lesions comprise 15-25% of thyroid FNAC cases
-Peak incidence in 4th-6th decades
-Female predominance (3-4:1)
-Iodine deficiency increases incidence
-Risk of malignancy: AUS 5-15%, FN/SFN 15-30%.

Clinical Features

Presentation:
-Solitary thyroid nodule (most common)
-Multiple nodules in multinodular goiter
-Cold nodule on scintigraphy
-Solid or predominantly solid on ultrasound
-Size usually >1 cm for FNAC indication.
Symptoms:
-Usually asymptomatic
-Neck discomfort or pressure
-Dysphagia (large nodules)
-Voice changes (recurrent laryngeal nerve involvement)
-Hyperthyroidism (toxic adenoma)
-Rapid growth (suspicious for malignancy).
Risk Factors:
-Iodine deficiency
-Radiation exposure
-Family history of thyroid cancer
-Previous benign thyroid disease
-Female gender
-Age >40 years
-Genetic syndromes (Cowden, Carney complex).

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Gross Description

Microscopic Description

Immunohistochemistry

Molecular/Genetic

Differential Diagnosis

Sample Pathology Report

Template Format

Sample Pathology Report

Complete Report: This is an example of how the final pathology report should be structured for this condition.

Specimen Information

Thyroid FNAC, [location], [ultrasound guided], [number] passes

Adequacy

Specimen is [adequate/inadequate] for evaluation

Cellularity

Cellularity: [high/moderate/low], [number] cell groups present

Morphological Features

Shows [microfollicular/trabecular] pattern with [nuclear features]

Nuclear Features

Nuclear size: [enlarged/normal], pleomorphism: [mild/moderate], chromatin: [fine/coarse]

Colloid

Colloid: [abundant/scanty/absent]

Background

Background shows [blood/inflammatory cells/proteinaceous material]

Bethesda Category

Bethesda Category [III/IV/V]: [specific category name]

Risk of Malignancy

Risk of malignancy: [percentage]%

Recommendations

Clinical correlation, [molecular testing/surgical consultation] recommended

Final Diagnosis

Final diagnosis: [specific diagnosis], Bethesda Category [X]