A very rare benign entity wherein thyroid tissue is replaced by fibrous tissue which interestingly infiltrates thecapsuleinto surrounding muscles, paratracheal tissues, carotid sheath. ('Woody Thyroiditis', 'Ligneous Thyroiditis).

Pathophysiology

It is often associated with retroperitoneal and mediastinal fibrosis and sclerosing cholangitis.
There is both intrathyroidal as well as extrathyroidal fibrosis. It also encroaches parathyroids and recurrent laryngeal nerves.
It may be unilateral or bilateral.

Clinical features

Swelling with irregular surface, stony hard consistency, 
strider, with positive Berry'ssign (absence/impalpablecarotid pulsation); small goitre; common in males.

Differential diagnosis:

Anaplastic carcinoma of thyroid.

Investigations: 

• T3, T4 may be low due to hypothyroidism. 
• Radioisotope scan will not show any uptake. 
• FNAC to rule out carcinoma.

Treatment:

lsthmectomy is done to relieve compression on the airway.They require L-thyroxine replacement later, as hypothyroidism is common.

High dose of steroid often used.

Thyroidectomy is not necessary. 

Resource: SRB's Manual of Surgery,6th Edition