Angiomatoid Spindle Cell Thymomas (WHO Type A): An Unusual Histological Subtype That Can Mimic a True Vascular Neoplasm

Ten spindle cell thymomas with prominent angiomatoid features are presented. The patients, consisting of 8 men and 2 women, are between the ages of 47 and 62, with an average age of 54.5. Clinically, 8 patients experienced chest pain, cough, and dyspnea, while 2 patients were asymptomatic. Diagnostic imaging revealed an anterior mediastinal mass in all patients, leading to surgical resection. The resected neoplasms varied in size from 3 to 5 cm in diameter and were described as well-circumscribed, hemorrhagic, with solid areas. Histologically, they exhibited extensive areas of hemorrhage with scant cellularity. In the more solid areas, the spindle cell proliferation was mixed with dilated vascular structures. Seven neoplasms were encapsulated, while three were minimally invasive, with tumoral cells invading the perithymic adipose tissue. Immunohistochemical stains showed the spindle cells were positive for keratin AE1/AE3, keratin 5/6, p63, and weakly positive for p40, but negative for vascular markers CD31 and CD34. Clinically, eight patients are alive without recurrence, while two were lost to follow-up. The histopathological features of these spindle cell thymomas represent an unusual subtype that can mimic primary vascular neoplasms, which may require different treatment and have varied outcomes.