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Neuroradiology Case of the Week

Case 230

Ashwani K. Sharma, MD and P-L Westesson, MD, PhD, DDS

Clinical Presentation: Patient is a 70-year-old male with status post-radiation therapy for peripheral T-cell lymphoma of lateral chest wall. On his follow-up he noticed, a small midline neck swelling.

Imaging Findings: There is a well-defined, low-density lesion located inferior to the hyoid bone in relation to the thyroid cartilage on the right side. The cystic lesion seems to be encased in the strap muscles.

Diagnosis: Thyroglossal cyst

Discussion: Cervical lesions are commonly encountered in the population. There are three basic classifications: congenital, inflammatory and neoplastic lesions. In children, in contrast to adults, most cervical lesions are benign. On a review of 445 cases, 55% of all cases were found to be of congenital origin, 27% of inflammatory origin, and 14% due to neoplasia [1]. Congenital lesions include thyroglossal duct cysts, cystic hygromas, branchial cleft anomalies, epidermoid/dermoid cysts and haemangiomas. In their series review of 102 cases Nicollas et al. reported an incidence of 53.4% for thyroglossal cysts and 11% for dermoid cysts as the most common midline cervical abnormalities [2]. Inflammatory lesions are nodal in origin and malignant lesions include lymphomas, thyroid carcinoma, rhabdomyosarcoma and neuroblastoma.

Thyroglossal Duct Cyst: During embryogenesis, the thyroglossal duct passes from the foramen cecum in the midline through the tongue musculature, anterior to the hyoid bone, loops around the inferior border of the hyoid bone posteriorly, resuming inferior course anterior to the thyrohyoid membrane and strap muscles [3]. Ultimately, the duct terminates at the level of the thyroid gland isthmus. The thyroglossal duct is lined with secretory epithelium, and cysts form anywhere along its course if involution is incomplete [3]. Remnants of thyroid tissue may occasionally be found within these cysts, and migration of the thyroid gland itself can be arrested anywhere along the course of the thyroglossal duct [3]. Only 20% of the thyroglossal duct cysts are within the suprahyoid neck, with 15% at the level of the hyoid bone and 65% below [4].
     In the oral cavity, thyroglossal duct cysts are most often located in the midline. On CT or MRI, a midline or paramedian cystic mass with or without rim enhancement is typically seen. The capsule of the cyst shows a uniformly thin enhancement or in the case of an infected cyst - a uniformly thick enhancement, and the cyst may contain debris. The infrahyoid thyroglossal duct cyst is typically seen anterior to the larynx within or beneath the strap muscles. It is located in the midline or slightly off the midline. The location of the of the thyroglossal duct cyst within the strap muscles is the key feature that allows differentiation from other adult neck masses that may have a similar CT and MR . Occasionally, the cyst can bulge over the notch of the thyroid cartilage into the preepiglottic fat space. The paraglottic space is spared, as opposed to the case with laryngoceles, which usually extend into the paraglottic space appearance, i.e., necrotic anterior cervical nodes and thrombosed anterior jugular veins. The latter, however, are located superficial to the strap muscles.

References:

1. Torsiglieri AJ Jr, Tom LW, Ross AJ 3rd, Wetmore RF, Handler SD, Potsic WP. Pediatric neck masses: guidelines for evaluation. Int J Pediatr Otorhinolaryngol. 1988 Dec;16(3):199-210. [Medline]
2. Nicollas R, Guelfucci B, Roman S, Triglia JM. Congenital cysts and fistulas of the neck. Int J Pediatr Otorhinolaryngol. 2000 Sep 29;55(2):117-24. [Medline]
3. Reede DL, Bergeron RT, Som PM. CT of thyroglossal duct cysts. Radiology. 1985 Oct;157(1):121-5. [Medline]
4. Miller MB, Rao VM, Tom BM. Cystic masses of the head and neck: pitfalls in CT and MR interpretation. AJR Am J Roentgenol. 1992 Sep;159(3):601-7. [Medline]