Thymic Epidermoid Cyst: Clinical and Imaging Manifestations of This Rare Anterior Mediastinal Mass

Abstract

Thymic epidermoid cysts are an extremely rare entity. These arise from epidermal cells that migrate to the thymus. The radiologic diagnosis of this rare lesion is challenging. We describe a case of an otherwise healthy 35-year-old woman who presented with an acute onset of chest pain and shortness of breath. She was found to have an anterior mediastinal mass. The imaging findings were, however, not characteristic for any single diagnostic entity. Since the imaging was inconclusive, surgical resection was performed for definitive diagnosis. The mass was found to be a thymic epidermoid cyst. This case underlines the significance for radiologists to be aware that epidermoid cysts can occur in the thymus and should be considered in the differential diagnosis for a heterogeneous anterior mediastinal mass.

Figure 1

Axial CTA through the level of the aortic arch shows a homogenous anterior mediastinal mass (red arrow).

Figure 2

Sagittal reconstruction shows the same mass in the vertical plane (red arrow).

Figure 3

(MR T2) axial T2 fat saturated image showing a hyperintense heterogenous mass suggestive of cystic components (yellow arrow).

Figure 4

(MR T1 postcontrast) heterogeneous anterior mediastinal mass (yellow arrow) without obvious enhancement.

Figure 5

(PET) no significant metabolic activity in the anterior mediastinal mass (yellow arrow).

Figure 6

Gross specimen with keratinaceous debris within the cyst (black arrow).

Figure 7

H&E 10x image showing abundant keratin debris (∗) within the cyst.

Figure 8

H&E 2.5x image showing the epidermoid cyst wall (yellow arrow) and the normal thymus tissue (∗).