Colloid Goitre
Colloid goitre is a benign thyroid enlargement characterized by follicles distended with colloid material (thyroglobulin), representing the most common form of thyroid enlargement worldwide, particularly in iodine-deficient regions.
Pathophysiology and Definition
Colloid goitre develops when thyroid follicles accumulate excessive amounts of colloid—a proteinaceous substance primarily composed of thyroglobulin—leading to follicular distension and gland enlargement 1. This process can occur:
- With adequate iodine: Contrary to traditional teaching, colloid accumulation can occur even during TSH stimulation when sufficient iodine is available for organification 2
- Without prior hyperplasia: Many colloid goitres are colloid-rich from onset, not necessarily progressing through a hyperplastic phase 2
- Through gradual expansion: The enlargement typically develops over many years, most commonly affecting women in their fifth and sixth decades 3
Clinical Presentation
Morphologic Patterns
Colloid goitre can manifest as 1, 3:
- Nodular colloid goitre (NCG): The most prevalent form, accounting for approximately 77% of thyroid diseases in some series 4
- Diffuse symmetric enlargement: Involving the entire gland uniformly
- Asymmetric involvement: Predominantly affecting one lobe 5, 3
Symptomatic Features
When goitres become large (>100g), patients may experience 6:
- Respiratory difficulty (42% of cases)
- Dysphagia (22% of cases)
- Venous distension of neck or anterior chest wall (22%)
- Tracheal deviation (70% on radiography)
- Tracheal compression (42% on radiography)
Diagnostic Characteristics
Histopathology
Microscopic examination reveals 1:
- Variably sized follicles arranged in a follicular pattern
- Colloid-like material filling the follicular lumina
- Single layer of cuboidal or low columnar epithelium lining the follicles
- Periodic acid Schiff-positive bodies may be present in the colloid 7
Thyroid Function
Colloid goitre typically occurs in euthyroid patients 1. The structural enlargement is independent of thyroid hormone status, though some nodules may become functional over time, potentially leading to toxic multinodular goitre 3.
Differential Diagnosis
Critical Distinctions
When evaluating thyroid enlargement with follicular architecture and colloid, exclude 1:
- Thyroid-like follicular renal cell carcinoma: Distinguished by negative TTF1 and thyroglobulin staining (these are positive in true thyroid tissue) 1
- Metastatic thyroid follicular carcinoma: Requires positive TTF1 and thyroglobulin 1
- Toxic multinodular goitre: Functional nodules causing hyperthyroidism 3
- Malignancy: Particularly papillary carcinoma, which is not uncommon even in endemic goitre regions 4
Diagnostic Workup
For any thyroid nodule or enlargement 1:
- Ultrasound: First-line imaging to characterize morphology 3
- FNA with cytology: For nodules >1 cm or those with suspicious features
- TSH measurement: To assess functional status
- Calcitonin measurement: Controversial but may identify medullary thyroid carcinoma 1
Etiology and Pathogenesis
Primary Cause
Iodine deficiency remains the predominant cause globally 4. In endemic regions:
Experimental Models
Research demonstrates that colloid goitres can form through 7, 2:
- Increased fecal thyroid hormone loss with compensatory TSH elevation
- Impaired T4 to T3 conversion leading to sustained TSH stimulation
- Refractory endocytosis during continuous TSH stimulation when minimal iodine is available for organification 2
Management Implications
Surgical Considerations
For large multinodular colloid goitres (>100g), total thyroidectomy is advocated to prevent recurrence 6. Complications include:
- Permanent vocal cord paralysis: 1.7% of nerves at risk 6
- Permanent hypoparathyroidism: 3.1% 6
- No perioperative mortality in reported series 6
Prevention
Iodine supplementation is the primary preventive measure in endemic regions to reduce the medical and social burden of nodular colloid goitre 4.