Thyroglossal Duct Cyst Carcinomas: A Clinicopathologic Series of 22 Cases with Staging Recommendations.

Abstract

Carcinomas arising from thyroglossal duct remnant cysts (TGDCs) are rare, without well-defined management and staging criteria. All TGDCs (n=685) diagnosed between 2005 and 2015 were retrospectively reviewed, with 22 carcinomas identified (3.2% incidence). Twenty-two patients (17 females, 5 males), aged 12-64years (mean 39.9years; median 39years) were identified. An anterior, superior midline neck mass was the presenting symptom in all patients. A cancer diagnosis [all papillary thyroid carcinoma (PTC)] was made after the Sistrunk procedure (SP), with a Bethesda Category V or VI classification preoperatively by fine needle aspiration in 5 of 12 cases tested. A SP was performed in all patients, with total thyroidectomy concurrently (n=4) or subsequently (n=12). A selected neck dissection was performed in 5 patients, with metastases found in 3. Of the patients who had a thyroidectomy, synchronous PTC was identified in 6 (thus, 6 of 22 patients had synchronous thyroid gland primaries). This supports an origin from extra-thyroidal remnants (cyst origin) rather than metastatic tumor from a thyroid gland primary. Follow-up radioactive iodine therapy was performed in 13 patients. Metastatic disease to local lymph nodes 57months after presentation was seen in 1 patient, with all others alive and disease free (mean 3.8years; range 0.4-10.8years). The TGDCs ranged from 0.8 to 5cm (mean 2.3cm), while the PTCs ranged from 0.1 to 3.8cm (mean 1.4cm). All of the tumors were classical PTC, showing a sclerotic and infiltrative pattern, with a capsule present in 11. Lymphovascular invasion was detected in 11; margins were positive in 6. Using currently defined criteria, the patients were separated into AJCC stage group I (n=21) or II (n=1). However, if extension into the adipose tissue (n=11), skeletal muscle (n=10), or perineural/perivascular tissues (n=10) were used to stage the patients, interpreted to represent the equivalent of "extrathyroidal extension" (n=13) as defined for thyroid gland primaries, there would be 15 group I and 7 group III cases. All seven group III patients were ≥45years. Three of four patients with lymph node metastasis also showed soft tissue extension. In conclusion, TGDC carcinomas (TGDCCa) are uncommon, with all classical PTC. For "microcarcinomas" (≤1cm), conservative management can be used for patients <45years (i.e., Sistrunk procedure only); for >1cm tumors, and due to the high incidence of concurrent papillary carcinoma and higher stage at presentation in older patients, completion thyroidectomy is recommended for patients ≥45years. Thus, even though a good prognosis can be expected for PTC developing in TGDCs, staging is advocated to more appropriately match therapeutic interventions.