Fine needle aspiration of mediastinal germ cell tumors

The Utility of Fine Needle Aspiration (FNA) Biopsy in the Diagnosis of Mediastinal Lesions

Fine needle aspiration is a minimally invasive, low-morbidity, and cost-efficient technique for the sampling of mediastinal lesions. Additionally, ancillary testing on FNA samples can be used for the refinement of diagnoses and for treatment-related purposes (flow cytometry, cytogenetics, immunohistochemistry, and molecular diagnostics). Mediastinal lesions, however, can show a variety of lineages and morphologic features, giving rise to diagnostic dilemmas. As a result, the differential diagnosis can vary widely and becomes especially challenging due to the smaller sample size on FNA and the variability in component sampling. For appropriate patient management and to determine the correct treatment strategies, accurate pathologic diagnoses are paramount. In this review, we present the cytomorphologic features together with the immunophenotypic findings of mediastinal lesions, with emphasis on the diagnostic challenges and pitfalls in FNA cytology samples, including smears and cell block sections.

B3 thymoma mimicking poorly differentiated thyroid carcinoma: Diagnostic pitfalls of anterior mediastinal mass fine needle aspiration

B3 thymoma is a rare malignant type of thymic epithelial neoplasm found in the anterior mediastinum. Diagnosis of thymoma from fine needle aspiration (FNA) can be challenging due to the infrequency of sampling and its morphologic overlap with other entities such as squamous cell carcinoma, lymphoma or thyroid carcinoma. We report a case of B3 thymoma mimicking poorly differentiated thyroid carcinoma. We present its diagnostic pitfalls on cytology specimens, especially where it concerns identifying the correct location of the lesion, discuss the differential diagnosis, and correlation with the corresponding surgical resection specimen. A neck computed tomography angiogram (CTA) revealed a partially calcified 2.1 cm mass inferior to the left thyroid lobe in a 51 yr old woman being evaluated for stroke/TIA symptoms. She was referred for evaluation of the lesion. On the initial FNA and core needle biopsy, the lesion showed high-grade epithelioid cells with abundant lymphocytic infiltration and occasional necrosis, and was diagnosed as a high-grade carcinoma, favored to represent a poorly differentiated thyroid carcinoma considering the location on imaging. The patient subsequently underwent total thyroidectomy, central neck dissection, and thymectomy. Final surgical pathologic diagnosis indicated a type B3 thymoma. Due to the infrequency of sampling, thymoma poses a diagnostic challenge on preoperative FNA or core needle biopsy. Herein, we present a case of B3 thymoma with a preoperative cytologic specimen that consisted of hyperchromatic sheets of epithelioid tumor cells with a background of lymphocytes without definitive follicular cells or colloid. The core needle biopsy and cell block material showed abundant necrosis, intermixed lymphocytes and neoplastic epithelial cells with strong positive staining for pan-keratin and p40. The cytology and core needle biopsy material were interpreted as representing a probable thyroid neoplasm and raised a broad differential including anaplastic thyroid carcinoma, poorly differentiated thyroid carcinoma with squamous features, metastatic squamous carcinoma, and metastatic carcinoma to a lymph node. The final surgical resection specimen showed a B3 type-thymoma.

Approach to Mediastinal Fine Needle Aspiration Cytology

Mediastinal fine needle aspirations are routinely encountered in cytopathology practice. Mediastinal lesions may pose diagnostic challenges owing to their rarity and locations associated with the complexity of the mediastinal anatomic structures in the thoracic cavity. Diagnosing mediastinal lesions and guiding patient management usually require correlating with clinical and radiologic findings, being familiar with cytomorphologic features and appropriately triaging the diagnostic material for ancillary testing. This review proposes a practical approach to interpret mediastinal fine needle aspirations and emphasizes potential diagnostic pitfalls for mediastinal lesions including benign cysts, thymic neoplasms, lymphoproliferative disorders, germ cell tumors, mesenchymal tumors, and metastatic tumors.

Diagnostic Challenges in the Cytology of Thymic Epithelial Neoplasms

Simple Summary

Thymic epithelial neoplasms, including thymoma, thymic carcinoma, and thymic neuroendocrine neoplasms, constitute the majority of anterior mediastinal masses. Fine needle aspirations (FNA) of mediastinal masses are infrequently encountered and are highly challenging to interpret. Thymic neoplasms display a significant degree of histologic diversity and have overlapping morphologic features with tumors from other sites. However, when properly interpreted alongside ancillary studies and radiologic findings, FNAs can yield clinically actionable results. This review aims to illustrate the usefulness and diagnostic pitfalls of thymic FNAs to assist pathologists in analyzing these specimens.

Abstract

Thymic epithelial neoplasms are rare tumors that constitute the majority of anterior mediastinal masses. They are classified as thymomas, thymic carcinomas, and thymic neuroendocrine neoplasms. Biopsy diagnosis is not common, and most tumors are surgically resected. Biopsy, including cytology, is indicated when a non-surgical entity is suspected or in cases of locally advanced disease. Smears of thymomas consist of round or spindle epithelial cells admixed with varying amounts of lymphocytes depending on the type of thymoma. Smears of thymic carcinoma and thymic neuroendocrine neoplasms are often indistinguishable from corresponding tumor types from other organs. Accurate cytological diagnosis can be difficult due to the histological diversity of thymomas, as well as the morphological features that certain thymic tumors share with similar tumors from other organs. However, fine needle aspiration (FNA) of anterior mediastinal masses can provide clinically actionable information and can be used to determine whether lesions require surgical, systemic, or local noninvasive treatments. Ancillary studies, namely, immunocytochemical stains, flow cytometry, and radiology, are important tools in the evaluation of thymic aspirates. This review discusses the utility and limitations of thymic FNAs and illustrates the diagnostic features and pitfalls of these specimens.

Diagnostic Challenges in Fine-Needle Aspiration Cytology of Mediastinal Tumors and Lesions

CONTEXT.—

Mediastinal tumors/lesions are frequently encountered in daily cytopathology practice. These lesions are accessible through endoscopic/endobronchial ultrasound-guided or computed tomography-guided fine-needle aspiration cytology and represent a wide range of primary and metastatic tumors. This often poses diagnostic challenges because of the complexity of the mediastinal anatomic structures. Tumors metastatic to mediastinal lymph nodes represent the most common mediastinal lesions and must be differentiated from primary lesions.

OBJECTIVE.—

To provide an updated review on the fine-needle aspiration cytology of mediastinal tumors/lesions, with an emphasis on diagnostic challenges. This review encompasses thymic epithelial neoplasms, mediastinal lymphoproliferative disorders, germ cell tumors, neuroendocrine tumors, soft tissue tumors, and metastatic tumors. Differential diagnoses; useful ancillary studies, including targeted immunohistochemical panels; and diagnostic pitfalls are discussed.

DATA SOURCES.—

Data were gathered from a PubMed search of peer-reviewed literature on mediastinal tumors. Data were also collected from the authors' own practices.

CONCLUSIONS.—

Fine-needle aspiration cytology plays a vital role in evaluation of mediastinal lesions. Being familiar with the clinical and cytomorphologic features of these lesions, appropriately triaging the diagnostic material for ancillary testing, and correlating with radiologic findings are important in arriving at correct diagnoses and guiding management.