[Chronic invasive fibrous thyroiditis (Riedel struma). Case report with special reference to preoperative diagnosis].

Chronic invasive fibrous thyroiditis (Riedel's struma) is a very rare disease of unknown aetiology mainly affecting middle-aged or old female patients. An aggressive fibrosis partly or totally replaces normal thyroid gland tissue. The gland becomes stony hard, is not displaceable and, characteristically, the fibrous tissue penetrates the capsule and infiltrates into surrounding structures such as muscles, vessels, nerves and even the trachea. Riedel's struma is often associated with fibrotic processes in other parts of the body. The preoperative differential diagnosis includes malignant tumours and fibrosing stages of Hashimoto's disease, as well as subacute thyroiditis de Quervain. This paper reports the case of a 60-year-old woman suffering from Riedel's struma and discusses differential diagnostic aspects with regard to preoperative investigation and pathohistology.