Riedel's invasive fibrous thyroiditis is a very rare form of thyroiditis in which the inflammation of the thyroid gland causes it to merge with surrounding structures such as muscle and trachea (windpipe). In fact, many physicians think that this disease is not a form of thyroiditis at all, but rather a rare form of low-grade tumor that happens to involve the fascia (or envelope) of tissue that surrounds the thyroid gland.
The thyroid gland itself becomes quite hard, like a rock and it may be very difficult to tell if this rock-hard thyroid is a result of inflammation or cancer. Blood tests for thyroid function are usually normal except in the extreme cases where the inflammation is so invasive that the thyroid can no longer function properly. In this situation, you may become hypothyroid. A biopsy is necessary in order to distinguish this benign disease from cancer. However, since the thyroid gland in this illness is so hard, a fine needle aspiration biopsy may not be possible. Instead, a biopsy done in the operating room may be necessary.
In the most severe forms of this disease, the thyroid gland becomes so tight and solid that it may squeeze the trachea or breathing tube. In this instance, an operation may be necessary to remove the middle portion of the thyroid and remove this constricting ring. A complete removal of the thyroid gland can not be performed because the thyroid blends with normal muscles and other tissues, making more extensive surgery quite dangerous. Once this little middle portion of the thyroid is removed, the windpipe is no longer constricted and breathing is facilitated.