A patient presents with mediastinal mass with sheets of epithelial cells giving arborizing pattern of reactivity alongwith interspersed lympoid cells. The apt diagnosis would be -

A thymoma is a tumor originating from the epithelial cells of the thymus that may be benign or malignant. Thymomas are frequently associated with the neuromuscular disorder myasthenia gravis;thymoma is found in 20% of patients with myasthenia gravis. Once diagnosed, thymomas may be removed surgically