Ancient schwannoma of the thigh mimicking a malignant tumour: a report of two cases, with emphasis on MRI findings.

Ancient schwannomas are rare, encapsulated tumours of long duration and are benign in nature. The tumour is solitary and may grow to a large size before detection of notable degenerative changes. The term "ancient schwannoma" is used to describe a tumour that has undergone such changes, typified by relative loss of Antoni type A tissue, perivascular hyalinisation, calcification, cystic necrosis, haemorrhage and the presence of degenerative nuclei that may be misinterpreted as sarcomatous pleomorphism. We report two cases of ancient schwannoma in the thigh mimicking malignancies. Identifying the fibrous capsule of the mass and a split fat sign using MRI is important for differentiating ancient schwannoma from other malignant tumours.