Fine-Needle Aspiration Cytology of Follicular Dendritic Cell Sarcoma of Cervical Lymph Node: A Challenging Diagnosis.

Follicular dendritic cell sarcoma (FDCS) is a rare malignant tumor that could arise in both nodal and extranodal sites, with only nine previously reported cases demonstrating cytologic features. In this report, we describe a case of FDCS in a 60-year-old female who presented with neck mass. Fine-needle aspiration cytology and subsequent core biopsy were suggestive of metastatic carcinoma. The cytologic features were epithelioid-to-spindle cell morphology, vesicular nuclei, prominent nucleoli, intranuclear inclusions, and occasional binucleated and multinucleated forms. However, absence of cytokeratin expression was against the diagnosis of metastatic carcinoma. The definitive diagnosis was reached by the demonstration of CD21 and CD23 expression. The pathologist should be aware of this rare malignant tumor, especially its cytologic features in aspirated material. The differential diagnosis in the above case was metastatic carcinoma, melanoma, and malignant granular cell tumor. The demonstration of expression of one or more dendritic cell marker is the clue for the diagnosis, which could be applied on cytological preparations with sufficient material.

Evaluation of the diagnostic value of emerin and CD56 in papillary thyroid carcinoma - an immunohistochemical study.

Papillary thyroid carcinoma (PTC) is diagnosed in both cytological and histological specimens on the basis of distinct nuclear morphology. These features may not be prominent in some PTC variants and may be seen in some benign conditions. It is necessary to differentiate PTC from other neoplastic and nonneoplastic lesions since it affects treatment strategy and patients' fate. Emerin is a type II integral membrane protein of the inner nuclear membrane that has a characteristic staining pattern in PTC. CD56 is a homophilic membrane glycoprotein that is expressed in thyroid follicular epithelial cells and adrenal glands. The aim of this study was to evaluate the diagnostic value of emerin (positivity, percentage, and highlighting nuclear features) and CD56 (positive versus negative) both singly and in combination for differentiation of PTC from other neoplastic and nonneoplastic mimics. This study was performed on 50 cases of PTC, 9 cases of follicular adenoma (FA), and 12 cases of nonneoplastic thyroid lesions using immunohistochemistry for detection of emerin and CD56. Positive emerin expression was seen in 82% of PTC and in 16.7% of nonneoplastic cases with an absence of expression in FA. CD56 was expressed in 88.9% of FA, 91.7% of nonneoplastic cases and in a minority of PTC cases (6%). Positive emerin revealed 82% sensitivity and 90% specificity, while emerin-highlighted nuclear changes was more specific (95%). Negative CD56 expression revealed 84% sensitivity and 90% specificity. Combined positive emerin (including highlighting nuclear changes) and negative CD56 showed 72% sensitivity and 100% specificity. Positive emerin expression (moderate/strong) and its highlighting nuclear changes combined with negative CD56 could be a very helpful procedure in difficult and overlapping cases with high diagnostic validity (high specificity and positive predictive value).