Unilateral Hypopharyngitis, Cellulitis, and a Multinodular Goiter: A Triad of Findings Suggestive of Acute Suppurative Thyroiditis

Discussion

In general, the thyroid gland has a relatively high resistance to infection. Multiple factors contribute to this resistance, including the protective fibrous capsule of the thyroid, an extensive venous and lymphatic drainage, and a high concentration of iodine.^5,6 On the other hand, the highly vascularized nature of the thyroid gland can lead to its seeding from hematogenous sources.

Despite this potential hematogenous spread of infection, AST remains a relatively uncommon disorder. Although it is often secondary to a pyogenic bacterial infection, it can rarely be secondary to a fungal, parasitic, or viral infection or can be caused by Pneumocystis carinii, especially in immunosuppressed or immunocompromised patients.^3,6–8 A study from Nigeria of 84 women with endemic goiters demonstrated that acute thyroiditis occurred in 10.7% of the patients. In this study, the most common causative agent was Staphylococcus aureus. Less often Streptococcus pyogenes and Pseudomonas organisms were the offending agents.¹

The most common route of spread is very likely hematogenous from a pharyngitis. However, a few cases have been reported with a congenital fistula to the thyroid gland from the apex of the pyriform sinus. When this occurs, the fistula likely represents a rare fourth branchial anomaly, and these reported cases share certain findings in common, including onset in infancy or childhood, left thyroid lobe involvement, and frequent recurrences unless surgery is performed.⁴ Because our patient developed her thyroiditis as an adult, had no prior history of such episodes, and has had no subsequent episodes, it is unlikely that she had such a rare fistula. Furthermore, no fistula was identified on CT, sonography, barium swallow, or at surgery.

As mentioned, in most cases of AST, the patient has an underlying thyroid condition, such as a multinodular goiter. However, chronic thyroiditis, an adenoma, a carcinoma, or a history of direct thyroid trauma has also been reported.⁶

The typical clinical presentation of AST is swelling and tenderness in the anterior neck, which may be accompanied by fever, dysphagia, hoarseness, or coexisting pharyngitis.^9,10 Laboratory findings characteristically include an elevated erythrocyte sedimentation rate and leukocytosis. Results of thyroid function tests are generally normal.^6,8–10

Thyroid sonography usually demonstrates a thyroid gland with diffusely decreased echogenicity intermixed with hyperechoic trabeculae. Sonography is useful for detecting a local abscess, performing drainage of the abscess, and obtaining a specimen to identify the causative pathogen. Contrast-enhanced CT also provides excellent assessment of the thyroid gland, the pharynx, and adjacent soft tissues as well as the presence of an abscess.^6,11 MR imaging, although not performed in our patient, can also be useful for depicting an abscess; it would typically demonstrate restricted diffusion on diffusion-weighted imaging.¹² Antibiotic therapy is typically curative. Although in almost all adult cases, a fistula is not identified, if a fistula is present, surgical resection is suggested. If an abscess is present, surgical incision and drainage may be necessary.¹

This case demonstrates that when the triad of a multinodular goiter and a unilateral hypopharyngitis with a surrounding cellulitis is present, the diagnosis of acute thyroiditis should be considered by the radiologist, because this diagnosis may not be initially considered purely on the basis of the clinical presentation. Although in children AST may be associated with a fistula, in adults such a fistula is rarely reported, and the spread of infection from the pharynx to the thyroid is believed to be via a hematogenous route.