Malignant transformation of intrathoracic ancient neurilemmoma in a patient without von Recklinghausen's disease

Malignant transformation of a neurilemmoma is an exceedingly rare event. We describe a case of intrathoracic ancient neurilemmoma undergoing a malignant change in a 39-yr-old man. The patient presented with right flank and chest pain for several months. Plain radiography and CT scan of the chest showed a soft tissue mass lesion at the extrapleural space with erosion of surrounding ribs at the right basal lung area. The excised mass was encapsulated and measured 4.5x3.5x2.3 cm. The cut surface showed grayish-white and glistening with a focal cystic change and hemorrhage. Necrosis was not seen. Histologically, the tumor showed the features of classic neurilemmoma composed of the Antoni type A and B areas with perivascular hyalinization. In addition, obviously histologically malignant foci manifested by presence of markedly increased cellularity with fascicular arrangement, active mitotic activity, hyperchromasia, and gradual loss of original neurilemmomatous feature were noted.