A Misleading Neck Mass: Branchial Cleft Cyst Mimicking Anaplastic Thyroid Carcinoma

Abstract

A 33-year-old female individual had a history of a lymph node excision positive for metastatic papillary thyroid carcinoma (PTC) in 2016. She was treated with a total thyroidectomy and central neck dissection showing 0.2-cm micro-PTC without paratracheal lymph node involvement, followed by adjuvant radioactive iodine treatment with 104 mCi of iodine-131. After 9 years without evidence of disease, she presented with a mildly tender, firm, left neck level II mass rapidly enlarging over 3 weeks. Neck ultrasound revealed a 3.5 cm irregular hypoechoic mass with internal vascularity and punctate echogenic foci. A fine needle biopsy showed inflammatory and mature squamous cells with elevated thyroglobulin but no definitive evidence of malignancy. The patient was scheduled for urgent neck dissection; however, just a left lymph node excision was performed as intraoperative frozen pathology showed no cancer. Surgical histopathology showed branchial cleft cyst tissue. The most concerning diagnosis for a rapidly enlarging neck mass in an adult with a history of metastatic PTC is anaplastic thyroid carcinoma. However, other diagnoses such as branchial cleft anomalies, lymphoma, or non-thyroid metastatic malignancies should be considered. Intraoperative frozen section pathology is crucial to direct surgical management of an unknown neck mass concerning for anaplastic thyroid cancer.

Keywords: anaplastic thyroid cancer; branchial cleft cyst; lymph node dissection; neck mass.

Figure 1.

Ultrasound transverse (A) and color Doppler (B) view of the left level II nodule in a young female patient with a history of papillary thyroid cancer without evidence of disease for about 9 years who presented with a rapidly enlarging left neck mass over a 3-week timespan.

Figure 2.

Computed tomography (CT) of the neck with contrast in axial (Photo A), coronal (Photo B), and sagittal (Photo C) plane images of the left level II neck mass in a young female with a history of papillary thyroid cancer who presented with a rapidly enlarging left neck mass. The radiology report showed “left cervical adenopathy with dominant 18 × 18 × 28 mm necrotic zone 2 node with irregular borders. Multiple adjacent smaller nodes. Differential is metastatic adenopathy. Infected reactive adenopathy considered less likely given morphology.”

Figure 3.

Photos A–C: Photo A and B, Low-power views of the excision specimen show a unilocular cyst lined by stratified squamous epithelium with prominent lymphoid tissue in the cyst wall after surgical resection of the left neck mass from a young female patient with a rapidly enlarging left neck mass with a history of papillary thyroid cancer (Photo A: hematoxylin and eosin, 40× magnification. Photo B: hematoxylin and eosin stain, 20× magnification.). Photo C, Histopathological section in a high-power view of the excised specimen shows intraepithelial and intramural acute inflammation after surgical resection of the left neck mass. No evidence of malignancy was seen. The histomorphologic findings are consistent with an inflamed/ruptured branchial cleft cyst. (hematoxylin and eosin stain, 200× magnification).