Solitary fibrous tumour of the thyroid gland.

Solitary fibrous tumours of the thyroid gland are rare; only five cases have been reported in the literature. Clinically, they present as a long-standing firm mass in the thyroid. Histologically, they show a range of appearances including so-called 'patternless growth pattern', spindle-cell morphology, alternating hypo- and hyper-cellular areas, keloid-like hyalinization and a prominent haemangiopericytoma - like architecture. The behaviour of extrathoracic solitary fibrous tumours is unpredictable and requires careful, long-term follow-up.