Aspiration cytology of an ectopic cervical thymoma misinterpreted as a lymphoproliferative lesion of the thyroid: A case report

Abstract

Ectopic cervical thymoma is a rare tumor that originates from ectopic thymic tissue trapped during the migration of the embryonic thymus. To the best of our knowledge, only 14 cases of ectopic cervical thymoma, which include descriptions of the cytological features based on fine-needle aspiration (FNA), have been reported thus far. The current study describes the case of a 52-year-old male presenting with an enlarging anterior neck mass that been apparent for a number of years and was now accompanied by shortness of breath. FNA cytology revealed large numbers of small lymphocytes admixed with rare groups of large, polygonal cells that were interpreted to be reactive lymphocytes or possible follicular dendritic cells. However, no definite follicular or Hürthle cells were identified. Therefore, the overall cytological features were misinterpreted as a lymphoproliferative lesion. However, subsequent histological analysis of the resected left total lobectomy specimen determined a diagnosis of thymoma, type B1. Thus, awareness of this entity combined with a careful search for thymic epithelial cells may aid in determining a correct diagnosis when FNA is performed for the evaluation of a neck mass.

Keywords: ectopic cervical thymoma; fine-needle aspiration; neck.

Figure 1.

(A) T1-weighted magnetic resonance imaging, revealing a 6.4×4.8×4.4-cm tumor with heterogenous contrast enhancement in the left thytroid, causing tracheal deviation. (B) Fine-needle aspiration smear demonstrating multiple clusters of small lymphocytes admixed with scant groups of larger cells displaying round to oval nuclei and inconspicuous nucleoli with marginally more abundant cytoplasm (Papanicolaou staining); magnification, x1,000. (C) The resected tumor, exhibiting a lobulated and gray-white cut surface with an irregular border. Discernible connective tissue septa were observed and the mass was located externally, but attached to the outer surface of the lower left pole of the thyroid gland.

Figure 2.

(A–C) Microscopic analysis of the resected tumor using hematoxylin and eosin staining. (A) Low-power view demonstrating a nodular growth pattern separated by fibrous septa; magnification, x40. (B) High-power view indicating numerous small- to medium-sized lymphocytes admixed with scattered large, polygonal epithelial cells characterized by round, vesicular nuclei and occasionally prominent nucleoli; magnification, x400. (C) Residual ectopic thymic tissue with microcystic changes present in the subcapsular area; magnification, x40. (D–F) Immunohistochemical analysis of the tumor using immunoperoxidase staining. (D) Lace-like pattern of epithelial cells exhibiting AE1/AE3 expression; magnification, x400. (E) Background lymphocytes expressing cluster of differentiation 1a; magnification, x400. (F) Large cells from the fine-needle aspiration smear expressing AE1/AE3; magnification, x1,000.