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Neuroradiology Case of the Week

Case 112

Clinical Presentation: The patient is a 19-year-old female who presented with a 2-week history of sore throat, diagnosed by her PCP as a Strep infection, and a 2-day history of left-sided neck pain.  The morning of her presentation to the ED, she awoke with left-sided neck swelling and was febrile.

Radiological Findings: CT of the neck shows an ill-defined hypodense lesion of the left side of the thyroid gland with surrounding soft tissue swelling and stranding of the subcutaneous fat.  The carotid arteries and veins of the left side are deviated to the posterolateral side, and the trachea and thyroid cartilage are deviated to the right side.  Low dense areas are noted in the oropharynx, especially on the left side and inferiorly to the thoracic inlet.  Bilateral lymphadenopathy is also noted.  The right side of thyroid gland is normal. 
     Ultrasound of the neck shows a complex, septated, heterogeneous structure, measuring 4.1 x 3.8 x 2.3 cm and arising from the left lobe of the thyroid.  There are multiple small hypoechoic components and hypervascular margins.
      Esophagram shows a blind pouch coming from the inferior end of the left piriform sinus.  The pouch does not communicate with the thyroid, thus excluding the presence of a piriform sinus fistula.

Hospital Course: On admission, the patient was found to be hyperthyroid. She received FNA, ultrasound-guided aspiration, and surgical incision and drainage of the lesion. Microbiology found the sample to be positive for Streptococcus.

Diagnosis: Acute suppurative thyroiditis with abscess of the left hemithyroid.

Discussion: Acute suppurative thyroiditis (AST) is a rare cause of inflammation of the thyroid in which there is invasion of the thyroid by bacteria, fungus, or other organism. The most significant causal organisms are Staphylococcus and Pneumococcus, but infection occurs from Salmonella, Mycobacteriumtuberculosis, Pneumocystic carinii, and other fungi as well. If left untreated, AST can lead to thyroid abscess formation.
     AST is most often seen in patients who are immunocompromised or otherwise debilitated.  However, in children, the etiology may be due to the presence of a piriform sinus fistula, extending to, or adjacent to, the thyroid. Most commonly, the sinus extends to the left lobe of the thyroid. While the embryologic origin is debated, the leading belief is that the piriform sinus malformation is a derivative of the third and fourth branchial apparatus.
     As mentioned above, AST and thyroid abscess are rare entities, accounting for only 0.1-0.7% of surgically treated thyroid pathologies. The thyroid gland is remarkably resistant to infection as it has a prosperous lymphatic and vascular supply, a well-developed capsule, and high iodine content.
     Radiographic imaging of AST reveals an enlarged lobe and/or isthmus with heterogeneous CT density and MR signal intensity. If thyroid abscess forms, adjacent soft tissue in the neck may be obliterated due to cellulitis and myositis.
     The clinical presentation of AST includes a swollen and tender affected lobe, dysphagia, odynophagia, referred pain to the pharynx and/or ear, and fever and chills. The patient often has recently had an upper respiratory infection. Physical examination of the thyroid will almost always reveal a painful thyroid swelling with probable erythema of the overlying skin. Laboratory features include elevated ESR and possibly an elevated WBC. The patient may or may not be hyperthyroid. Treatment includes drainage of the affected lobe, usually by surgical incision and drainage, antibiotics or antifungals, and removal of a piriform sinus fistula, if present. Prognosis is very good, with maintenance of thyroid function.

References:

1. Som and Curtin: Head and Neck Imaging, 4th ed., Volume Two. 2003 Mosby: 2147.
2. Rohondia OS, Koti RS, Majumdar PP, Vijaykumar T, Bapat RD. Thyroid abscess. Journal of Postgraduate Medicine 1995; 41(2):52-54. [Medline]
3. Goldman: Cecil Textbook of Medicine, 21st ed., 2000, W.B. Saunders Company: 1244.
4. Larsen: Williams Textbook of Endocrinology, 10th ed., 2003 Elsevier: 447-449.
5. Astl J, Kuchynkova Z, Taudy M, Betka J. Thyroid abscess at an adolescent age. International Journal of Pediatric Otorhinolaryngology 2003; 67:1375-1378. [Medline]
6. Franciosi JP, Sell LL, Conley SF, Bolender DL. Piriform sinus malformations: a cadaveric representation. Journal of Pediatric Surgery 2002; 37(3):533-538. [Medline]