Neuroradiology Case of the Week

Case 45

Karin Westesson, Kha Nguyen, and P-L Westesson, MD, PhD, DDS

Clinical Presentation: A 41-year-old female presented with right neck swelling. Clinically an abscess was suspected and a CT scan of the neck was requested.

Radiological Findings: The neck CT scan showed heterogeneous enlargement of the thyroid gland with an ill-defined hypodensity within the left thyroid lobe. The findings are characteristic for a multinodular goiter (Figs. 1,2). The enlarged thyroid gland extended from the level of the piriform sinuses superiorly to the sternal notch inferiorly. The trachea was deviated toward the right side, but no compression is evident.
   A nuclear scan was obtained six weeks later and showed multiple nodules with a dominant hypo functioning nodule in the inferior pole of the left lobe (Fig. 3).

Figure 1: Increase size of the thyroid gland bilaterally (arrows) with a prominent pyramidal lobe (arrowhead).

Figure 2: Hypodense area in the left lobe of the thyroid gland (arrows) suggestive of cystic degeneration.

Figure 3: Enlarged thyroid gland (arrowheads) and the hypo functioning nodules on the left (arrows).

Diagnosis: Multinodular goiter, caused by hyperthyroidism

Discussion:  Goiter is a general term to meaning any clinical enlargement of the thyroid gland. When the thyroid gland is required to compensate for a lack of thyroid hormone there is hypersecretion of thyroid stimulating hormone, which causes hypertrophy of the follicular epithelium resulting in an increase of the thyroid gland. Because both the mass and the functional activity of the gland are both increased the patient will have a goiter, but will be eumetabolic [2]. Over time some patients may develop hypothyroidism and others hyperthyroidism [1]. Simple sporadic (nontoxic) goiters, such as this one, predominate in older females [4] and generally evolve into multinodular goiters. Multinodular goiters often have focal hemorrhaging, focal calcification which will show on the CT as high-density areas. They will also have cyst formation and scarring that will show on the CT scan as low-density areas [1] within the enlarged nodular thyroid [4]. Multinodular goiters can also be identified with nuclear scintigraphy using radioactive iodine or Tc-99m pertechnetate. It will show the location of hot and cold nodules [1].
   Patients with multinodular goiters have a low risk of carcinoma (<3%), but with increase size of the goiter patients are exposed to other risks [4]. The goiter may extend substernally into the anterior mediastinum [1] where it will contact the clavicles and sternum. Since the bone matter will not constrict, the goiter will start to compress soft tissue such as trachea, lungs, esophagus and blood vessels [3] with increased growth.
   Patients with small, asymptomatic goiters need only be monitored clinically and periodically evaluated with imaging. In patients with larger goiters that pose the risks noted above, radioactive iodine therapy is used. In most patients, it reduced the size of the goiter by 39% one year later and by 46% two years later. However, in 22% of the case there was a recurrence of increased growth [2].
   In a patient with hyperthyroidism, the TSH levels will be decreased. Normal levels are 0.5 - 0.6 µU/ml [3]. A TSH test will show lower levels when the thyroid is overactive. This patient had a TSH of 0.16 and was hyperthyroid. An iodine thyroid scan will show if a single nodule or the whole gland is causing the increased thyroid activity.

References:

1. Loevner, Laurie A. In: Som, Peter M., Curtin, Hugh D, eds. Head and Neck Imaging, 4th Ed. St. Louis: Mosby; 2003: 2147-2150.
2. Schlumberger, Martin-Jean, Filetti, Sebastiano, Hay, Ian D. “Non-Toxic Goiter and Thyroid Neoplasia.” In: Larsen, P Reed, Kronenberg, Henry M, Melmed, Shlomo, Polonsky, Kenneth S, eds. Williams Text of Endocrinology, 10th ed. Philadelphia: Saunders; 2003: 457-464.
3. Thyroid Gland Diseases: Hormones, Cancer, Doctors, Drugs, Surgery. 2003. Norman Endocrine Surgery Clinic. 1 July 2003. <http://www.endocrineweb.com/thyroid.html>
4. Yousem, David M, Scheff, Alice M. In: Som, Peter M., Curtin, Hugh D, eds. Head and Neck Imaging, 3rd Ed. St. Louis: Mosby; 1996:959-967.