Rare Presentation of Intrathyroid Thyroglossal Ductal Cyst

AUTHORS:
Daniel R. O’Neill, BS¹ • William O. Collins, MD²

AFFILIATIONS:
¹University of Florida College of Medicine, Gainesville, Florida
²Department of Otolaryngology, University of Florida College of Medicine, Gainesville, Florida

CITATION:
O’Neill DR, Collins WO. Intrathyroid thyroglossal ductal cyst. Consultant. 2021;61(11):e43-e45. doi:10.25270/con.2021.02.00009

Received September 9, 2020. Accepted December 28, 2020. Published online February 18, 2021.

DISCLOSURES:
The authors report no relevant financial relationships.

CORRESPONDENCE:
William O. Collins, MD, University of Florida College of Medicine, 1345 Center Drive, Gainesville, FL 32610 (William.collins@ent.ufl.edu)

A 14-year-old healthy boy presented to our clinic with 1-month midline swelling of the lower neck and 1-week of cervical neck pain, dysphagia, pharyngitis, fever, and difficulty speaking. He had no significant medical history.

Physical examination. The physical examination findings were significant for a fullness of his left anterolateral neck, measuring approximately 5 × 5 cm. The mass was firm, minimally tender to palpation, and had no overlying skin changes. All other findings were normal.

Diagnostic testing. Laboratory findings were significant for only a mild leukocytosis with left shift. The patient received an ultrasonography scan of the neck, results of which showed a midline complex cystic structure near the left isthmus of the thyroid, measuring 5 × 2 × 3.3 cm.

A follow-up computed tomography (CT) scan was performed. Results showed a thick-walled, septated, complex fluid collection found to the left of midline underneath the hyoid bone and extending inferiorly involving the left lobe of the thyroid near the junction of the isthmus (Figure 1). Additionally, the CT scan showed adjacent inflammation, prominent midline neck lymph nodes, and abnormal fluid density tracking from the mass ventrally to the floor of the mouth (Figure 2).

Figure 1. Axial view of initial CT scan of neck mass.                                                            

Figure 2. Axial view of initial CT scan showing fluid track.

Treatment and management. Our differential diagnosis included an infected thyroglossal duct cyst (TGDC) or an infected 3rd or 4th branchial cleft cyst (BCC). We then proceeded to treat the presenting infection with antibiotics and oral steroids and ultimately decided to surgically resect the mass. Our surgical plan was a possible hemithyroidectomy vs Sistrunk procedure with additional direct laryngoscopy and bronchoscopy.

At the start of the procedure, we used a direct laryngoscope to look for an internal piriform sinus tract opening, which is pathognomonic of a 3rd or 4th branchial cleft sinus tract. No such tract opening was identified. The left neck cyst and left thyroid lobe were found to be continuous, and the thyroid gland was dissected out (Figure 3). The capsule of the neck cyst was followed superiorly toward the hyoid bone, and a Sistrunk procedure was performed to release the middle of the hyoid bone. The mass was removed en bloc and sent for histopathological examination (Figure 4).

 Figure 3. The cystic mass with intrathyroid involvement was resected.

Figure 4. The intrathyroid thyroglossal ductal cysts were resected.

The pathology report noted that the cyst was lined with pseudostratified ciliated columnar epithelium with focal squamous epithelium involving the left thyroid lobe and excised hyoid bone. These features confirm a diagnosis of TGDC within the thyroid lobe.

Discussion. TGDCs are the most common cause of midline neck masses, with an estimated prevalence of 7% of the global population.¹ These congenital cervical developmental abnormalities arise due to an incomplete closure of the thyroglossal duct. If any aspect of the duct survives past 10 weeks of gestation, the epithelial lining of the duct can lead to secretions, inflammation, then eventual cyst development.²

Intrathyroid thyroglossal ductal cysts (ITTDCs) are the rarest form of TGDCs, with only 5 cases having been described in the pediatric population.³ ITTDCs are difficult to diagnose because they are rare, do not have any specific external physical characteristics independent from other thyroglossal ductal cysts and some brachial cleft cysts, and thyroid function tests are usually normal.⁴ Thus, in order to diagnose an ITTDC, histologic evaluation of tissue must be performed. 

On physical examination, the TGDC typically elevates while swallowing or during tongue protrusion and are often asymptomatic. They are susceptible to infection and can progress to an abscess with a draining sinus, which was consistent with the initial findings in our patient. Ultrasonography scanning is the initial diagnostic test of choice, but CT scans and/or magnetic resonance imaging (MRI) are utilized if the clinical presentation is unclear.

A well-established, unique feature of TGDCs is its relationship with the hyoid bone, which can be superior to (20%-25%), inferior to (25%-65%), or at the level of the hyoid bone (15%-20%).⁵ Atypically, TGDCs can be found in the suprasternal region (7%), within the tongue (3%), and within the thyroid gland itself (<1%), as was seen in our patient.⁶ Due to low risk of malignancy (<1%) and/or recurrent infections, the treatment of choice for a TGDC is surgical removal. The preferred surgical procedure for removal is the Sistrunk procedure, showing superior rates of nonrecurrence of the cyst (<10%) vs simple excision (40%-50%).⁷

The other cervical congenital anomaly that can involve the thyroid gland is a BCC. BCCs form due to an incomplete involution of the first through fourth pharyngeal clefts, are typically found on the lateral aspect of the neck, and are discovered once they have become symptomatic by inflammation or external fistula drainage, similar to TGDCs.⁸ In differentiating BCCs from TGDCs, BCCs have unique characteristics depending on their corresponding brachial cleft. First arch BCCs are present around the angle of the mandible/submandibular area and externalize at either the external auditory canal or the angle of the mandible.⁹ Second arch BCCs are the most common and can be found along the tonsillar fossa. An external opening would be found medial/anterior to the sternocleidomastoid muscle.⁹ Third and fourth arch BCCs are rare but can present as intrathyroidal abscesses or infections and thus can be confused with ITTDCs. Third and fourth BCCs with a sinus tract can be identified via direct laryngoscopy, which drains to the piriform sinus or hypopharynx and externally typically on the left side of the neck.¹⁰

With our patient, we were able to rule out first and second arch BCCs based on location alone. To rule out third and fourth arch BCCs, we first performed a direct laryngoscopy and did not visualize a sinus opening near the piriform or hypopharynx. Lastly, because a fourth arch BCC can present as an intrathyroidal mass, histological examination was conducted in order to make a definitive diagnosis.¹¹ On histologic examination, both the TGDC and the BCC will similarly show nonkeratinizing stratified squamous epithelium. However, a TGDC will also show alternating respiratory epithelium, where BCCs will congruently have unique subepithelial lymphoid tissue associated with it. ¹¹

Conclusions. Similar characteristics of BCCs and ITTDCs can convolute the diagnostic process. They are both more common in the pediatric population, both present as neck masses that can develop fistulas, and both have thyroid involvement. The nuance in differentiating between the 2 must be performed to obtain the proper diagnosis, specifically direct visualization of the piriformis recess and histopathological examination.

Patient outcome. At the 6-month follow-up, the patient had no evidence of cyst recurrence and was symptom free with a normal thyroid function panel.

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