Riedel Thyroiditis

Epidemiology:

•  Extremely rare
• female predominance

Common Sites:

• thyroid
• surrounding tissues usually involved as well
• parathyroids (25%)

Gross features:

•  stony hard / woody fixed
• involves all or part of thyroid
• characteristic extension of fibrosis beyond the thyroid

Histologic features:

•  normal architecture replaced by keloid-like fibrous tissue
• lymphocytes, plasma cells
• fibrous tissue extends into muscles, nerves, fat, entraps blood vessels
• phlebitis / vasculitis
• frequent thrombosis
• associated adenoma at the centre (25%)

Immunophenotype:

Marker:	Sensitivity:	Specificity:
Lambda light chain predominance (70% of plasma cells)
IgA increased (45% of plasma cells)

Molecular features:

Other features:

•  euthyroid mostly
• may occur in association with systemic disease:
• retroperitoneal, mediastinal, or retroorbital fibrosis
• sclerosing cholangitis

References:

•  Sternberg’s Diagnostic Surgical Pathology (2004)