The most likely diagnosis is b) thyroglossal duct cyst.

Thyroglossal duct cysts (TDCs) represent focal cystic dilations of the epithelial remnants of the thyroglossal duct tract, formed during the migration of thyroid tissue from the lingual region into the thyroid bed in the lower anterior neck, during embryogenesis. These masses represent the most common congenital cysts in the neck and are typically midline (along the tract line), around the level of the hyoid bone or just inferior. They can, however, develop anywhere along the course of the tract. On physical exam, these masses characteristically glide superior and inferior on swallowing motions, just like normal thyroid tissue does, due to the congenital thyro-lingual tract connection. Most patients present as children, although they can present at any age. Men and women are equally affected. Most TDCs are asymptomatic but can become infected and form local abscesses, creating “draining cystulas” requiring drainage and/or surgical excision.

When your patient presents with a palpable anterior midline neck mass and you suspect a TDC, the next step can either be neck ultrasound, or enhanced CT scan. Ultrasound will differentiate between cystic and solid masses and is the imaging modality of choice in children and young adults, due to the lack of ionizing radiation involved. CT will best delineate the relationship of the mass lesion to the surrounding anatomical structures and provide accurate information regarding mass size and extent. On the CT scan, as shown, the discrete margins of the anterior midline mass lesion, the homogeneous hypodense appearance and, most important, the CT density in the fluid range are all in keeping with a cystic mass lesion. Unenhanced neck MRI can also be utilized in cases where patients are allergic to CT contrast, and the neck ultrasound exam is equivocal.

Once the diagnosis is made, or highly suspected, the next step is referral to an ENT specialist for pre-operative evaluation.

In the pre-operative assessment, it’s extremely important to ensure that the patient has a normal functioning thyroid gland in normal orthotopic position, as the differential diagnosis of an anterior neck mass is ectopic thyroid tissue. Such a mass lesion would also glide up and down during swallowing on physical exam, potentially confusing the examiner. Among ectopic thyroid glands, 90% are lingual and 10% are sublingual. Although demonstration of a normal appearing thyroid gland in normal position on ultrasound is pretty convincing evidence, it may still be prudent to perform a nuclear medicine thyroid scan pre-operatively to rule out the presence of ectopic thyroid tissue more superior.

In the case presented, ectopic thyroid tissue is a much less likely diagnosis due to the cystic appearance of the mass. Similarly, adenopathy related to lymphoma, or any other cause, would also reveal an enhancing solid appearing mass lesion, not a uniformly cystic mass. Lymphoma can present as a solitary enlarged node, although usually many regional or systemic nodes are involved. This would be a highly unlikely cause of the presenting mass lesion. A Zenker’s diverticulum is an outpouching of the pharyngoesophageal mucosa that develops at the junction of the hypopharynx and the esophagus, just proximal to the cricopharyngeus muscle. The diverticulum extends posterior or posterolaterally and, as such, would not be a consideration in this case. A retropharyngeal abscess, by definition, is of course behind the pharynx, in the prevertebral space, not in front, and would also not be considered in the case presented.

References

1. Sung YM et al. Am J Roentgenol 2008;190:W161-3.
2. Wong KT et al. Am J Roentgenol 2005;185:1355-7.
3. Ducic Y. Am J Otolaryngol 2002;23:17-9.
4. Organ GM, Organ CH Jr. World J Surg 2000;111:119-23.