Follicular Adenoma

A benign encapsulated tumour of the thyroid gland that is surrounded by a thin fibrous capsule

Aetiology

  • More commonly found in women
  • Increases in incidence with increasing age
  • Increased incidence in regions of iodine deficiency
Genetic factors
  • <20% have a mutant ras or PIK3CA
  • Functional adenomas have an activating mutation in the TSHR signalling pathway → increased cAMP
  • N-ras and K-ras mutations have been implicated in the evolution of follicular adenoma to follicular carcinoma

Pathophysiology

  • Usually non-functional
  • Around 1% develop into a toxic adenoma - produces thyroid hormone autonomously
  • FA histology shows neoplastic thyroid follicles encapsulated by a surrounding collagen cuff

Clinical presentation

  • Discrete solitary mass in anotherwise normal thyroid gland
  • May be incidental finding
  • Patients with larger tumours may present with local symptoms e.g. dysphagia

Investigations

  • US scan
  • FNA - cannot distinguish between follicular adenoma and follicular carcinoma
  • Serum TSH

Management

  • Lobectomy with biopsy is required for treatment and definitive diagnosis as FNA cannot distinguish between follicular adenoma and follicular carcinoma