An intrathoracic giant tumour and vanishing lung cyst after tumour resection

A 65‐year‐old woman was brought to the emergency unit with an approximately 6‐month history of persistent fever and cough. Chest computed tomography (CT) demonstrated a 16‐cm heterogeneous mass with adjacent large cyst (approximately 4.0 cm). The patient underwent CT‐guided biopsy, and benign solitary fibrous tumour (SFT) was immunohistochemically diagnosed. As the symptoms were thought to be due to enlargement of the tumour, surgery was deemed necessary, and the tumour was successfully resected. Based on morphological and immunohistochemical examination of the resected specimen, the final diagnosis was dedifferentiated SFT (DSFT). Follow‐up CT verified disappearance of the pulmonary cyst. The cyst was speculated to be caused by a check valve mechanism, which may also suggest a rapid growth of the tumour. At the time of writing, 2 years post‐operatively, no tumour recurrence has been identified. This represents the first report of intrathoracic giant DSFT with a cystic lesion returning to normal lung parenchyma.