Cytology of thymomas

Abstract

BACKGROUND Aspirates of thymomas are distinguishable from other lesions and fine‐needle aspiration (FNA) is a proven method for investigating mediastinal masses. METHODS Thirty‐four cytology specimens of thymomas from 31 patients were examined. Corresponding surgical materials were available in 32 cases. Ten cases were benign and 22 were malignant. Cytologic features of these thymomas were correlated with various histologic classification systems and with biologic behavior. Dual epithelial and lymphoid populations and irregular cohesive tissue fragments of varying proportions of lymphoid and epithelial cells were characteristic of all aspirates. RESULTS Using the Lattes‐Bernatz classification, 10 cases predominately were lymphocytic, 3 cases predominately were epithelial, 3 cases predominately were spindle, 15 cases predominately were mixed, and 1 case was a thymic carcinoma. In the Muller‐Hermelink classification, 3 cases were medullary, 12 were mixed, 8 predominately were cortical, 2 were cortical, 6 were well differentiated thymic carcinoma, and 1 was a poorly differentiated thymic carcinoma. In the majority of the cases the epithelial cells were round to oval. Spindle cells and a mixture of round to oval and spindle cells also were observed. No cytologic feature was found to correlate significantly with any classification scheme. Necrosis was present in 5 of the 32 aspirates, most frequently in malignant tumors. Thymomas showing predominately spindle cells frequently were encapsulated. Tumors with predominantly round to oval cells or a mixed population behaved more aggressively than those with spindle cells. Tumors that were well encapsulated and benign clinically tended to possess benign‐appearing nuclei. Among the 22 invasive or malignant lesions, 8 exhibited moderate to marked cytologic atypia and 14 showed little or no atypia. No atypia was observed in benign tumors. CONCLUSIONS The presence of cytologic atypia of epithelial cells may be helpful in predicting aggressiveness. However, the absence of atypia and necrosis may not imply a benign course. Correlation with clinical and radiographic findings should be sought. Cancer (Cancer Cytopathol) 2000;90:24–32. © 2000 American Cancer Society.

Multifocal Primary Intrapulmonary Thymoma: A rare subtype of ectopic thymoma

“…Although histological evaluation of the entire tumor is ideally required to make a confident diagnosis, as we suspected primary lung cancer clinically and as the lesion was not amenable to resection right in the first instance, we pursued a preoperative tissue diagnosis. The biopsy samples were not reflective of the entire tumor and lacks information on the microinvasion of tumor cells into the adjacent tissues [ 12 ].…”

“…PITs share similar histological features with mediastinal thymomas and there are a few differential diagnoses from which it need to be distinguished[ 12 ]. The lack of cellular atypia and low mitotic activity in the epitheloid component as seen in our patient does not favour the diagnosis of metastatic carcinoma or poorly differentiated carcinoma of the lungs.…”

Primary Intrapulmonary Thymoma Presenting as a Solitary Pulmonary Nodule

“…A cytologic diagnosis based on a biopsy with a small amount of the thymoma tissue is extremely challenging. This is in part attributed to the fact that epithelial cells are difficult to recognize in lymphoid-rich aspirate smears and there is an inherent sampling error in a tumor that frequently displays heterogeneous histopathology [ 6 ]. Moreover, invasion into an adjacent tissue is difficult to identify in biopsy samples.…”

Approach to Mediastinal Fine Needle Aspiration Cytology

“…32,33 Thymic carcinomas are classified into multiple histologic subtypes based on histologic characteristics, including squamous cell carcinoma (up to 80% of thymic carcinoma), basaloid carcinoma, mucoepidermoid carcinoma, lymphoepithelioma-like carcinoma, clear cell carcinoma, sarcomatoid carcinoma, adenocarcinoma, NUT carcinoma, and undifferentiated carcinoma etc. 28,34,35 Histologically, thymic carcinomas are composed of nests/sheets of or individual malignant epithelioid cells with thick fibrous cords. Each histologic subtype resembles its counterpart in other organ systems.…”

“…Thymic carcinomas are classified into multiple histologic subtypes based on histologic characteristics, including squamous cell carcinoma (up to 80% of thymic carcinoma), basaloid carcinoma, mucoepidermoid carcinoma, lymphoepithelioma-like carcinoma, clear cell carcinoma, sarcomatoid carcinoma, adenocarcinoma, NUT carcinoma, and undifferentiated carcinoma etc 28,34,35…”