Primary epidermal inclusion cyst of the anterior mediastinum mimicking a thymic cyst: a rare diagnostic pitfall

Abstract Background Epidermal inclusion cysts (EICs) are common benign cutaneous lesions; however, their occurrence in the mediastinum is exceedingly rare. Case presentation We report a 29-year-old woman with a well-circumscribed mediastinal mass detected on imaging. The lesion was excised via video-assisted thoracoscopic surgery. Gross examination revealed a 6 × 5 × 3 cm cystic mass filled with whitish keratinous material. Histopathologic analysis demonstrated a cyst lined by stratified squamous epithelium with a well-developed granular layer and abundant laminated keratin debris. No adnexal structures or cytologic atypia were identified. Conclusion Primary mediastinal EIC is a rare benign entity that may radiologically simulate other mediastinal cysts. Accurate diagnosis relies on histopathologic evaluation, and complete excision is curative. Awareness of this entity is important to prevent overdiagnosis and ensure appropriate surgical management. This case emphasizes the importance of considering epidermal inclusion cyst in the differential diagnosis of anterior mediastinal cystic lesions to avoid misdiagnosis and unnecessary aggressive management.