Multilocular Thymic Cyst in a Young, Otherwise Healthy Woman: A Case Report

Abstract

Thymic cysts are rare lesions, accounting approximately for 1% of all mediastinal masses. We report a case of a 36-year old woman who presented preoperatively with a calcified mass shadow found on a routine chest radiograph X-ray. After further investigation with chest computed tomography (CT), magnetic resonance imaging (MRI), and tests for Myasthenia gravis, a benign mediastinal cyst was diagnosed and the patient underwent median sternotomy and complete surgical excision of the lesion. The histological examination described a multilocular thymic cyst. Thymic cysts are usually associated with thymic epithelial tumors, such as thymomas, or multisystemic morbid conditions such as human immunodeficiency virus (HIV) infection, rheumatologic disease, and Myasthenia gravis. At all follow-up examinations to date, the patient remains healthy.

Keywords: cyst; mediastinal; multilocular; thymic.

Figure 1. Chest X-ray, computed tomography, and magnetic resonance imaging

A, B: Chest radiograph X-ray showing a calcified mass shadow; C: chest computed tomography showing an ellipsoid, well-defined, encapsulated cyst with low attenuation and rim calcification located in the anterior mediastinum; D: Magnetic resonance imaging showing a well-circumscribed cystic lesion with fluid content of low intensity on T1-weighted images and with no adhesion to the surrounding tissues

Figure 2. Median sternotomy, surgical specimen of resected encapsulated thymic cyst, and magnification of histologic examination

A: Median sternotomy for complete surgical excision of the cystic lesion; B: Surgical specimen of resected encapsulated thymic cyst; C, D: A small and large magnification of the histologic examination reveals the presence of focal calcification as well as focal dense inflammatory infiltrates. The cyst is lined with either single or multiple layers of squamous epithelium where the presence of epithelioid cells and some multinucleated foreign type giant cells are also noted, in accordance with the cholesterol granulomas observed macroscopically. These findings are more consistent with an acquired rather than a congenital thymic cyst.