New upper neck mass after thyroidectomy, radioactive iodine ablation for thyroid cancer

Issue: June 2011

ByStephanie L. Lee, MD, PhD, ECNU

A 24-year-old with bilateral pain in her upper neck inferior to her ears and tachycardia was seen in the emergency department. No masses were detected on exam of her neck, but her thyroid-stimulating hormone was minimally elevated at 5.37 mIU/L. She was referred to the endocrine clinic for evaluation.

The patient denied prior head and neck radiation. Her mother had thyroid nodules that were benign based on a thyroid biopsy. On exam, this patient was euthyroid; however, her thyroid was small and firm, consistent with chronic thyroiditis, with a 2.5-cm mobile, nontender, isthmus mass and a 1-cm mass in the left lobe of the thyroid. The ultrasound characteristics of both nodules, including hypoechogenicity, intranodular hypervascularity and microcalcifications, were concerning for malignancy (Figure 1). Bilateral 1-cm to 2-cm reactive nodes were noted in the level II and level III, but no abnormal adenopathy was found.

Thyroidectomy revealed a 2.5 cm Ã— 2 cm Ã— 2 cm follicular variant of papillary thyroid carcinoma with capsular and vascular invasion in the isthmus, and a second 1-cm focus in the left lobe. No adenopathy was found. Postoperatively, with a normal TSH, her thyroglobulin was 7.1 ng/mL. Because of the risk for persistent disease, she was ablated after recombinant human TSH stimulation with 52 mCi I-131. Her 1-week post-therapy scan only showed intense uptake in the thyroid bed consistent with thyroid remnant. She did not have any complications after the therapy, including nausea, loss of taste or sialadenitis.

Figure 1. Sonography of the thyroid isthmus mass. Transverse (A) and sagittal (B) views of the isthmus mass using a 14-MHz linear probe. Although the margins are fairly well-defined, the mass has vigorous intranodular vascular flow by Doppler analysis (B) and microcalcifications. Trachea (TR).

Photo courtesy of: Stephanie L. Lee, MD, PhD

Development of a new mass

Stephanie L. Lee, MD
Stephanie L. Lee

Nine months after her radioactive iodine ablation, the patient called for 5-day history of a right neck mass. The mass was not tender and it was stable in size. She noted that eating did not make the mass larger. Three weeks before this call, at a routine clinic visit, her serum thyroglobulin level was <0.2 ng/mL; thyroglobulin antibodies <20 IU/mL; and TSH 0.84 mIU/mL. She was seen urgently in clinic, and a very firm, well-defined, mobile, non-tender, 1-cm mass was felt in right level II just below her ear (Figure 2). The mass was anterior to the anterior margin of the sternocleidomastoid muscle and posterior to the mandible. Sonography of right level II demonstrated an adjacent benign node with a well-formed hilum (Figure 2), without peripheral vascularity by Doppler analysis and no microcalcifications. The palpable mass was a 1.2-cm cystic, nonvascular structure within the tail of the parotid gland (Figure 3). There were no dilated ducts and the parotid parenchyma was homogeneous and normal. This structure did not contain any internal solid material or microcalcifications.

After informed consent, aspiration of the cystic structure was performed. A very small amount of clear fluid was removed via 25-gauge needle and the needle wash was sent for thyroglobulin assay. The level of thyroglobulin in the needle washout was <0.2 ng/mL, excluding a cystic metastatic thyroid cancer metastasis. The patient was instructed to increase her fluid intake to 8 to 10 cups of fluid each day and suck on a slide of lemon every few hours. The patient reported back that with this treatment plan, the mass resolved in 48 hours.

Figure 2. Lymph node levels of the neck. The borders of level II nodes (light green) are the digastric muscle superiorly (red arrow) and the hyoid bone inferiorly (black arrow) and the posterior edge of the sternocleidomastoid muscle posteriorly (yellow arrow). Level II nodes include upper jugular, jugulodigastric and upper posterior cervical nodes. The palpable mass is indicated by a red circle.

Image used with permission from Francesco Gaillard c/o Radiopaedia

Figure 3. Sonography with Doppler analysis of a benign level II lymph node. This node measures 0.8 cm Ã— 1.2 cm Ã— 0.9 cm on transverse (A) and sagittal (B) images. Sonographic evidence that this is a benign node includes a well-defined hyperechoic hilum (arrow) and absence of peripheral vascular flow and microcalcifications.

Photo courtesy of: Stephanie L. Lee, MD, PhD

Localized obstruction

In summary, this patient had an occlusion of one of the minor ducts of the parotid gland. It should be recognized that the tail of the parotid may extend under the jaw posterior to the angle of the mandible and inferior to the ear.

Thyroid cancer can rarely metastasize to the parotid gland. Case reports describe metastatic thyroid lesions discovered either as a masses in the parotid gland located under the malar bone (cheekbone) or, as with this patient, an isolated mass located inferior to the ear. Evidence that this is a simple cyst includes lack of solid material or vascular flow within the nodule and the enhancement of the signal posterior to the cyst (Figure 4). The absence of thyroglobulin on the needle washout after aspiration of the cystic suggested that this was not a tumor recurrence.

Figure 4. Sonography of a cystic mass in the tail of the parotid located inferior to the ear and posterior to the angle of the mandible. A purely cystic 1.2-cm mass (blue arrow) is seen in transverse (A) and sagittal (B) images within the tail of the parotid gland that extends under the angle of the mandible inferior to the ear. There are no internal echoes suggesting a solid component. No vascular flow within the cystic nodule was seen with Doppler analysis. The cystic nature of the mass was suggested by the hyperintense echoes posterior to the cyst caused by the through transmission and lack of signal scatter of the signal in liquid (yellow arrow).

Photo courtesy of: Stephanie L. Lee, MD, PhD

The resolution of the mass with increased fluid intake and sucking on sour lemons confirms it was a localized obstruction of one of the minor parotid ducts. Obstruction of the main parotid duct Stensenâ€™s duct would have led to the entire parotid gland becoming enlarged and tender, especially with eating. It is likely that the obstruction was related to narrowing of the salivary ducts that occur as a result of the radiation sialadenitis from her radioactive iodine therapy.

For more information:

Lee SL. J Natl Compr Canc Netw. 2010;8:1277-1286.

Mandel SJ. Thyroid. 2003;13:265-271.

Mathew PC. Int J Oral Maxillofac Surg. 2007;36:965-966.

Stephanie L. Lee, MD, PhD, is director of the Thyroid Health Clinic at Boston Medical Center and associate professor of medicine at Boston University School of Medicine. She is also an Endocrine Today Editorial Board member.

Disclosure: Dr. Lee reports no relevant financial disclosures.