Recurrent Desmoid Fibromatosis of the Thyroid Gland: A Diagnostic Challenge

A 31-year-old Indian female with a history of near-total thyroidectomy 2.5 years prior presented with recurrent neck swelling. Magnetic resonance imaging (MRI) of the neck revealed an infiltrating mass involving the thyroid bed. Biopsy from the mass and review of slides from the previous thyroidectomy revealed a spindle cell tumour with interspersed areas of fibrosis and infiltrative edges entrapping thyroid follicles. Beta-catenin immunopositivity and CTNNB1 mutation confirmed the diagnosis of fibromatosis. The case is being reported for its rarity and the discussion of its differential diagnoses.