Aliens in the thyroid gland: The secondary lesions

A secondary lesion in the thyroid gland is a rare clinical scenario diagnosed preoperatively during the evaluation of a neck mass, postoperatively in a thyroidectomy specimen or in autopsy studies. Even though the thyroid gland is highly vascular, secondary malignant lesions are rare accounting for 0.2% of all thyroid malignancies. Thyroid gland secondary lesions are often metachronous in presentation as they are seldom evaluated in the initial diagnostic workup of the primary lesion. Fine-needle aspiration cytology (FNAC) is a useful modality for the diagnosis of secondary thyroid lesions.

A 6-year retrospective review (2016-2021) was carried out to assess the secondary lesions in the thyroid gland. Papanicolaou and field-stained FNAC smears of secondary thyroid lesions were reviewed. Ancillary techniques were performed on the cell block for differentiating from the primary thyroid gland lesions.

There were 383 patients in our archives. There were only 18 cases (4.7%) that presented with secondary neoplastic lesions in the thyroid gland either by direct extension, metastases or as a hematolymphoid malignancy. There were 14 (77.7%) cases that presented with non-hematolymphoid secondary lesions while 4 (22.3%) cases presented with hematolymphoid malignancies. Thyroid secondaries were predominantly seen in female patients (female: male ratio of 1.5:1). Most of the cases presented with a synchronous secondary lesion (n = 14, 77.7%) and few metachronous secondary lesions were also noted (n = 4, 22.3%).

Although exceedingly rare, the detection of secondary thyroid gland lesions is important for staging and planning treatment.