Aspiration Cytopathology of Metastatic Mucinous Papillary Thyroid Carcinoma

Abstract

The light microscopic histopathology and cytopathology of papillary thyroid carcinoma (PTC) and its variants is amply depicted in reviews, books, and book chapters. One of the changes in PTC, however, that is infrequently discussed or illustrated in the literature is that of mucinous metaplasia. In the aspiration cytopathology literature, we are aware of only a rare report of PTC exhibiting extensive mucinous metaplasia. We present an example correlating the histopathology and fine needle aspiration cytopathology of a PTC that had metastasized on several separate occasions to cervical lymph nodes, and in the process demonstrated mucinous trans- The presence of mucin in endocrine neoplasms is an unexpected finding in contrast to its frequent production in non-endocrine epithelial tumors. This can assume diagnostic importance if the pathologist is asked to determine the site of a mucin-producing metastatic carcinoma in a patient with either an unknown primary or a remote history of cancer. Almost four decades ago, in a large study of the surgical pathology of various metastatic neoplasms (including 93 examples of thyroid cancer), Foster et al. concluded that "the thyroid is the only site studied that can be ruled out with great assurance when one is dealing with a mucicarmine positive metastasis" (1). Although reports to the contrary have been published (2-4), our impression is that many pathologists remain under the misconception that carcinomas of the thyroid are nearly all mucin-negative. This assumption from histopathology has been transferred to fine needle aspiration (FNA) cytopathology of thyroid carcinoma, where only rare descriptions or illustrations of extracellular mucin or mucin-filled vacuoles exist (5, 6). The aim of this article is to illustrate and describe the FNA cytopathology (and corresponding histopathology) of a mucinous papillary thyroid carcinoma (PTC) and to discuss the potential pitfalls related to this phenomenon. CASE REPORTA 66-year-old man had undergone complete thyroidectomy at an outside hospital for PTC 10 years earlier after an initial right cervical lymph node biopsy revealed metastatic disease. Over the past decade, he has received three courses of radioactive iodine therapy and has had two separate surgical procedures to excise repeatedly enlarged right neck lymph nodes. On each occasion these nodes contained metastatic PTC both within the node proper and in extranodal soft tissue. No metastasis beyond the right cervical lymph node group has ever been detected.He presented to our medical center because of a third recurrence of right cervical lymphadenopathy since his initial thyroidectomy. FNA biopsy of an enlarged right cervical lymph node was performed and revealed metastatic carcinoma. Subsequent surgical resection of the aspirated node and surrounding soft tissue was performed 2 weeks after FNA confirmed that diagnosis. One year after the FNA, he presented with a fourth recurrence of a right neck mass. This was excised without performing another prior FNA, and again it reve...

FNA of misclassified primary malignant neoplasms of the thyroid: Impact on clinical management

“…Mucinous metaplasia of papillary thyroid carcinoma, as seen in case 11, is extremely uncommon but a potential pitfall in the cytopathology of aspiration smears. [ 23 24 ] Similarly, our case 13 of papillary carcinoma, with nodular fasciitis like stroma (case 12), also posed difficulty on FNA, due to sampling areas being limited to areas of nodular fascitis like stroma, which was misinterpreted as myxoid sarcoma. [ 8 ] Although sampling different areas of lesion may yield better cytologic sample, sampling limitation in fine needle aspiration can be a source of misinterpretation, as noted in our cases.…”

Follicular Adenoma with Extensive Extracellular Mucin Deposition: Report on Two Cases

“…8,12,17,18 Mucin-producing medullary carcinoma can be distinguished from the present two cases based on the absence of amyloid, the positivity for thyroglobulin, and negativity for CEA and calcitonin. However, the cytological overlapping features such as abundant mucin, frequent nuclear inclusions, and intravacuolar globules with violaceous-colored magenta bodies of the target-like cytoplasmic vacuoles under Diff-Quik stain, prompted a differential diagnosis with mucin-producing papillary carcinoma 2,19,20. Intranuclear inclusion is usually considered the most important feature and is a characteristic but not a specific cytologic finding of papillary carcinoma in up to 90% of cases.…”

“…Mucin can be seen in a wide spectrum of primary thyroid tumors including follicular neoplasms, medullary carcinoma, poorly differentiated carcinoma, papillary and undifferentiated carcinomas, and mucoepidermoid and primary mucinous carcinomas 1–16,19,25,26. A mucin-containing thyroglossal duct cyst in the thyroid has also been described in the literature 27.…”

“…However, the cytological overlapping features such as abundant mucin, frequent nuclear inclusions, and intravacuolar globules with violaceous-colored magenta bodies of the target-like cytoplasmic vacuoles under Diff-Quik stain, prompted a differential diagnosis with mucinproducing papillary carcinoma. 2,19,20 Intranuclear inclusion is usually considered the most important feature and is a characteristic but not a specific cytologic finding of papillary carcinoma in up to 90% of cases. It can be observed in a variety of thyroid lesions such as follicular adenoma, hyalinizing trabecular adenoma, and even colloid goiter, as well as lesions mentioned above.…”

Fine needle aspiration of a metastatic mucinous tumour of the thyroid gland from ovarian adenocarcinoma: a potential pitfall in the differential diagnosis of thyroid neoplasms

“…Mucinous change in the thyroid gland is an unusual event, but can occur in a wide variety of thyroid lesions (follicular neoplasm, papillary carcinoma, anaplastic and medullary carcinomas) 1–5 . Another variant of thyroid tumour with features of mucinous adenocarcinoma, which should be considered in the differential diagnosis is that of thyroid involvement as part of systemic metastases of a malignant neoplasm.…”