Cytologic diagnosis of metastatic alveolar rhabdomyosarcoma to the thyroid gland by fine-needle aspiration

Primary thyroid rhabdomyosarcoma in an adult: A challenging case with histomolecular diagnosis and literature review

INTRODUCTION AND IMPORTANCE

Primary thyroid sarcomas are very rare tumours, accounting for less than 1 % of all thyroid malignancies. We present the fifth case in the literature of primary thyroid rhabdomyosarcoma and the third in adults with, for the first time, an extensive molecular analysis.

CASE PRESENTATION

A 61-year-old woman presented with a rapidly progressive neck mass with extensive local invasion of the tumour.

CLINICAL DISCUSSION

Histologically, the neoplasm was composed of sheets of pleomorphic or spindle-shaped cells with eosinophilic cytoplasm and few large and very pleomorphic cells admixed with the spindle cell proliferation, without any thyroid epithelial component. Immunohistochemically, the tumour cells were positive for muscular markers and negative for epithelial and thyroid differentiation markers. Molecular tests revealed the presence of NF1, PTEN and TERT pathogenic mutations. Classifying undifferentiated neoplasm with muscular differentiation into the thyroid is challenging as many more common differential diagnoses could be favoured including anaplastic thyroid carcinoma with rhabdoid phenotype, leiomyosarcoma, and other rare sarcomas.

CONCLUSION

Primary thyroid rhabdomyosarcoma is extremely rare and can be diagnostically challenging. We emphasize the histological, immunohistochemical and molecular criteria in order to make an accurate diagnosis.

From Malignant Thyroid Teratoma to Thyroblastoma: Evolution of a Newly-recognized DICER1 -associated Malignancy

Thyroblastoma is a novel thyroid malignancy included in the 5th Edition WHO Classification of Endocrine and Neuroendocrine Tumours. The majority of tumors now classified as thyroblastoma were originally regarded to be malignant thyroid teratomas. However, these neoplasms were recently recognized as a separate entity based on a distinctive constellation of primitive multilineage elements, including immature thyroid epithelium, undifferentiated or rhabdomyoblastic spindle cell proliferations, and neuroepithelial blastema, as well as recurrent DICER1 hotspot mutations. Thyroblastoma is an aggressive tumor that leads to death from disease in ~50% of patients, making it essential to differentiate this entity from a wide range of other thyroid tumors that show overlapping histologic features or DICER1 mutations. This review aims to provide a practical overview of the background, clinicopathologic features, molecular underpinnings, and differential diagnosis of this recently-described and molecularly-defined entity.

Primary rhabdomyosarcoma of the thyroid in an adult with auricular thrombosis

INTRODUCTION

Rhabdomyoscarcoma (RMS) is the most common soft-part tumour in children, however, it is infrequent in adults. Thyroid involvement is exceptional and only four cases have been reported: two primary RMS in children and another two cases in young adults with RMS metastasis to the thyroid. We report the first case in the literature of a primary adult RMS with thyroid involvement and superior vena cava syndrome.

CASE PRESENTATION

A 67-year-old male was admitted for an oedema of the arm extending to the laterocervical region. Computed tomography showed a 6cm mass in the hemithyroid with venous thrombosis to the auricle. Fine-needle aspiration was compatible with Bethesda category III. Surgery revealed a stone-hard consistency thyroid. An intraoperative biopsy showed an undifferentiated neoplasia, and no additional surgical intervention was undertaken. The patient died 48hours later. Definitive histology showed a RMS.

DISCUSSION

Venous thrombosis due to a thyroid tumour is infrequent. The scarce information in the literature recommends that thyroid carcinomas with auricular thrombosis be resected as soon as they are diagnosed. However, in cases of anaplastic or poorly differentiated carcinomas is controversial. Had there been a preoperative diagnosis in the histology in our case, surgery would not have been indicated.

Secondary tumors involving the thyroid gland: A multi-institutional analysis of 28 cases diagnosed on fine-needle aspiration

BACKGROUND

Fine-needle aspiration (FNA) is routinely used to evaluate primary thyroid lesions (PTLs), however, its role in diagnosing secondary thyroid neoplasms (STNs) has not been extensively studied. The goal was to examine the clinical and cytopathologic features of STNs diagnosed on FNA.

METHODS

The clinico-pathologic features of 28 STNs were analyzed. All PTLs, lymphomas, and locally invasive tumors were excluded.

RESULTS

There were 28 STNs (0.18% incidence) out of 15,800 thyroid FNAs (12 males, 16 females, 32 - 85 years), all occurring metachronously (3 weeks-20 years, average 78.3 months) comprising 24 (85.7%) metastatic carcinomas (14 [50%] renal; 4 [14.3%] head and neck squamous cell carcinomas, 3 [10.7%] breast, and 1 [3.6%] colorectal, uterine serous carcinoma, and lung adenosquamous carcinoma, respectively), 3 sarcomas (10.7%) and 1 melanoma (3.6%).

CONCLUSIONS

STNs are rare and diverse tumors which may occur decades after primary malignancy. Renal carcinomas are the most common. Prior history of malignancy, high index of suspicion, and attention to key distinguishing cytologic clues are critical for accurate diagnosis.