An Unusual Case of a Papillary Thyroid Carcinoma Arising in a Branchial Cyst

Significance Statement

Papillary thyroid carcinoma arising from a branchial cyst is a rare finding and a diagnostic challenge. As branchial cleft cysts are common lesions in the lateral neck, the possibility of a papillary thyroid carcinoma bears significant importance. We present a case of a lateral neck mass for which postoperative histology indicated papillary thyroid carcinoma that arose in ectopic thyroid tissue within a branchial cyst. Subsequently, thyroidectomy was performed, and final histopathology was positive for papillary carcinoma.

Cervical cystic masses usually derive from an embryological maldevelopment under an unclear underlaying mechanism. ¹ Ontogenesis of the human thyroid gland is the basis of the identification on several diagnostic challenges due to anatomical abnormalities in the migration route of the thyroid gland from the primitive pharynx to its final position. ² Despite the fact that most cervical cystic masses are branchial cysts, one should remain vigilant for potential malignancies, ³ which may constitute an incidental finding following surgical resection. ⁴ A primary malignancy of papillary thyroid carcinoma can be a far-fetched possibility, as ectopic thyroid tissue can rarely be found within branchial cysts.

A 42-year-old nonsmoker male with no notable past medical history arrived at our department complaining about an enlarging left neck lesion. Typical head and neck physical examination did not yield abnormalities apart from an easily palpable, painless and nontender left neck mass.

A contrast-enhanced computed tomography (CT) was conducted, which depicted a single cystic mass of 3 cm × 3 cm × 3.5 cm on the lower lateral neck, posterior/deep to the left sternocleidomastoid (Figure 1(a)). On magnetic resonance imaging, the cystic mass showed low signal intensity on T1 and high on T2 sequence, compatible with a branchial cleft cyst (Figure 1b).

Figure 1.

(a) Cystic mass of 3 cm × 3 cm × 3.5 cm on the lower lateral neck, posterior/deep to the left sternocleidomastoid on computed tomography scan. (b) High signal intensity on T2-weighted magnetic resonance imaging. (c) Dark brown fluid mass excised.

The age of the patient and the surrounding structures of the cystic mass can give us important information. ⁵ A thyroglossal duct cyst on CT scan most of the time is closely related to the hyoid bone and appears as a low-density, well-circumscribed cystic lesion in the midline. ⁶ On the other hand a branchial cyst on a CT scan is a well-circumscribed, non-enhancing mass at the lateral aspect of the neck. ⁷

The patient underwent excision of the mass under general anesthesia. Intraoperative findings included a 3 × 3 × 4 cm-sized dark brown fluid mass lateral and in close contact with the internal jugular vein (Figure 1c). Histopathological examination depicted findings compatible with a typical cystic lesion, yet there was also lymphocytic infiltration. Representative area of the cyst showed a neoplasm with a complex papillary appearance, consisting of fibrovascular cores lined by neoplastic epithelium. The immunohistochemical test was positive for CKAE1/AE3, TTF-1, and thyroxine binding globulin (TGB). The tumor cells exhibited cytological and nuclear features of papillary carcinoma (Figures 2 and 3).

Figure 2.

Histological sections of branchial cyst (BCC) wall with papillary thyroid carcinoma growth: BCC with a wall surrounded by fibrous tissue, having intra-cystic papillary structures such as true papillae with multiple branching, stromal stalk with microvessels, and optically clear (empty, ground-glass) nuclei with thick nuclear membrane (H&E, high power ×400).

Figure 3.

Immunohistochemically positive staining for CKAE1/AE3 and TTF1 in papillary carcinoma. Intense cytoplasmic and membrane expression of CKAEI/AE3 (×100). Intense nuclear expression of TTF1 (×40). The neoplastic cells were stained positive for TTF1, CKAEI/AE3, CK19, and thyroxine binding globulin (TGB), confirming the thyroid origin.

Considering the remarkable histological findings, an ultrasound scan of the thyroid gland was postoperatively decided which showed two nodules, one on the right lobule about 1.4 cm in size (TIRADS 4) and one on the left lobule about 1.1 cm in size (TIRADS 4). Reasonably, a US-guided fine needle aspiration biopsy (FNA) was conducted, which revealed suspicious findings for papillary carcinoma of the thyroid gland (Bethesda grade V). On these grounds a total thyroidectomy was performed, and final histology confirmed the presence of a papillary carcinoma.

Most cystic masses laterally in the neck develop from branchial remnants, yet as the thyroid gland originates from the migration of the thyroid anlagen, ectopic thyroid tissue can be found from the base of the tongue until its final position, and extremely rarely in other areas of the neck. ⁸ Thyroid carcinomas arising from ectopic thyroid tissue are also very rare and are typically seen in thyroglossal ducts. Only few cases of primary papillary thyroid cancer in branchial cysts have been reported in literature.

It is questionable whether such cases of otherwise benign looking lateral neck masses should be either just followed up, scheduled to be excised in a planned manner at some future point, or whether it is advisable to excise them promptly, to avoid rare postoperative findings, such as ectopic papillary thyroid carcinoma.

Concerning follow-up therapeutic approach, it is debatable whether it should include solely a wait-and-see approach with careful follow-up or total thyroidectomy. In our case, such a decision was evidently dictated by a positive thyroid FNA for papillary carcinoma, yet in cases where the thyroid gland appears disease-free, pros and cons are to be weighted for both of the aforementioned options.

In any case, optimum overall management requires a high index of clinical suspicion and a multidisciplinary approach.