A 47-year-old man underwent ultrasonography of the thyroid for a neck mass. He had undergone right thyroidectomy and isthmusectomy 10 years earlier for a progressively enlarging thyroid gland. Multiple biopsies from this procedure were negative for malignancy. Preoperatively, thyroid antibodies were negative and, despite levothyroxine sodium therapy (Synthroid, Abbott Laboratories, Abbott Park, IL), thyromegaly progressed.
A 47-year-old man underwent ultrasonography of the thyroid for a
neck mass. He had undergone right thyroidectomy and isthmusectomy
10 years earlier for a progressively enlarging thyroid gland.
Multiple biopsies from this procedure were negative for malignancy.
Preoperatively, thyroid antibodies were negative and, despite
levothyroxine sodium therapy (Synthroid, Abbott Laboratories,
Abbott Park, IL), thyromegaly progressed. The patient reported
difficulty swallowing solid foods but no other compressive
symptoms. Pathologic findings were consistent with Riedel's struma,
displaying inflammatory fibrosclerosis with hyaline bands of coarse
fibrosis. The left thyroid lobe was not explored. Following
surgery, the patient noted an improvement in swallowing.
The patient underwent ultrasonography of the neck, which showed
a 3-cm hypoechoic mass with posterior shadowing within the lateral
aspect of the remaining left thyroid lobe (Figure 1). There was
minimal normal thyroid tissue medially. One month later, an I
thyroid scan was performed at an outside institution that revealed
absent uptake on delayed images (not shown). Three months later,
magnetic resonance (MR) imaging of the neck was performed (Figure
2). Low signal intensity was present throughout the left lobe on
T1-weighted images, with further decreased signal intensity on
T2-weighted images. Mild extrinsic impression on the esophagus and
tracheal deviation to the right was also found.
Riedel's thyroiditis is a rare entity in which fibrous tissue
replaces the thyroid gland and tends to extend into the surrounding
It was first described in 1883 by Bernard Riedel.
In 1957, a study by Beahrs et al
found Riedel's thyroiditis in 20 of 40,000 thyroidectomies over a
period of 36 years, attesting to the rarity of the disease. Hay et
found that the overall incidence in the ambulatory setting is 1.06
in 100,000 individuals.
Pathologically, Riedel's thyroiditis is characterized by
replacement of normal thyroid tissue by fibrotic connective tissue,
with obliteration of normal thyroid architecture and involvement of
adjacent tissues following extension through the thyroid capsule.
Diffuse or partial involvement of the gland may occur. There is
absence of skin and lymph node involvement.
Clinically, the thyroid gland is enlarged and hard but nontender
and frequently involves a previously existing goiter.
Direct extension causes compression of the trachea and the
esophagus, resulting in dyspnea and dys-phagia.
An association exists between Riedel's thyroiditis and multifocal
idiopathic fibro-sclerosis, which includes retroperitoneal
fibrosis, pseudo-tumor of the orbit, sclerosing cholangitis, and
The exact etiology is still unknown.
Although it was previously thought to represent the later stages of
Hashimoto's thyroiditis, Riedel's thyroiditis is now recognized as
a unique disease process.
Early lesions show inflammatory cell infiltration with destruction
of normal thyroid architecture. Ensuing fibrosis replaces normal
thyroid tissue and is not confined to the thyroid gland.
Thyroid function is typically preserved until later stages when
patients exhibit hypothyroidism, which can also occur from fibrotic
infiltration of the parathyroid glands.
In a review of cases of Riedel's thyroiditis reported in the
literature, Schwaegerle et al
found that the majority of patients were euthyroid, predominantly
female, and had a wide age range of 23 to 77 years. Wedge resection
is required for tissue diagnosis; fine needle aspiration does not
provide adequate tissue.
Our patient was described to have had multiple biopsies before
thyroidectomy, showing neither evidence of malignancy nor evidence
of Riedel's thyroiditis. The natural history of Riedel's
thyroiditis is most likely self-limiting; however, treatment can
include steroids, as well as surgical excision of all or part of
the gland to alleviate compressive symptoms.
Ultrasound can demonstrate a hypoechoic, hypodense mass
replacing normal thyroid tissue with extension into adjacent
Scintigraphic findings in Riedel's thyroiditis indicate an
irregular thyroid gland with low radioiodine uptake, specifically
with later stages of the dis-ease.
The patient's I
scan performed after right thyroid lobectomy and isthmusectomy
revealed no activity on delayed images. MR findings are those
characteristic of fibrosis: hypointense signal intensity on T1- and
T2-weighted images. There can be contrast enhancement with
gadolinium. This is contrasted with most other conditions,
including thyroid carcinoma, lymphoma, and Hashimoto's thyroiditis,
where there is increased signal intensity on T2-weighted images.
Riedel's thyroiditis is a rare fibrotic process involving the
thyroid gland and surrounding soft tissues. The imaging appearance,
as typified by this case, reflects the fibrosis. The lesion can be
expected to be hypoechoic, with poor through transmission, on
ultrasonography and to have low uptake on scintigraphy and low
signal on T1- and T2-weighted MR sequences.