Multifocal fibrosing thyroiditis

Multifocal fibrosing thyroiditis is a benign pathology of the thyroid that can mimic papillary thyroid carcinoma.

It is also known as multifocal sclerosing thyroiditis.

General

• Uncommon - though may be under-recognized.
• Female predominant in largest series (93% of cases versus 7% of cases).

Microscopic

Features:

• Fibrotic foci - two foci required - key feature.
  • May be: (1) sharply demarcated from the surround parenchyma (stellate or triangular) or (2) band-like.

Note:

• MFT on average has 16 foci of fibrosis. These foci range in size from approximately 0.35 to 15 mm.
• Should not have have nuclear pseudoinclusions or psammoma bodies.

DDx:

• Hashimoto thyroiditis.
• Adenomatoid hyperplasia of thyroid.
• Papillary thyroid carcinoma.
• Riedel thyroiditis.
• Changes due to fine needle aspiration - should have hemosiderin, not multifocal.

See also

• Riedel thyroiditis.
• IgG4-related systemic diseases.