The Rarest of Rare Thymic Lesions: A 10-Year Surgical Pathology Experience

Simple Summary The thymus is the last organ in the human body to have its mechanisms fully understood. Its intrinsic complex morpho-functional structure reflects the complexity and variety of the pathological lesions of the gland. These include some variants of neoplastic and nonneoplastic processes, which are considered the rarest of the rare ones. The aim of this work is to describe the rarest lesions of the thymus in a large case series in order to update the epidemiology, to improve diagnostic awareness, and finally to promote a collaborative network between referral centers. The thymus is a specialized primary lymphoid organ located in the midline pre-vascular mediastinum. The organ is the site of various pathological processes, neoplastic and not, whose rarity has not allowed in-depth studies on clinical or histological features of rarest and unusual variants. Herein, we report a 10-year Padova experience in the surgical pathology of the thymus, focusing on the pathological description of nonneoplastic lesions and rare epithelial and mesenchymal tumors recorded in our database, which comprises over 600 thymectomies. The extrapolated rare cases have been categorized into four groups that included 15 cysts, 18 carcinomas, 5 neuroendocrine tumors, and 2 soft tissue tumors. The cases are described from a clinical and pathological point of view and discussed in dedicated sections with a review of the most important literature. In this case, review series, we aim to update the epidemiology of these rare entities, improve diagnostic awareness, and finally, promote a collaborative network between referral centers.