Intrathoracic Desmoid Tumor Mimicking Pleural Mass: A Case Report

Desmoid tumor (fibromatosis) is a histologically benign fibrous neoplasm showing locally infiltrating growth. This type of tumor commonly occurs in the abdomen, but intrathoracic desmoid tumor is uncommon. To date, 12 cases of intrathoracic desmoid tumor protruding into the pleural cavity, radiologically mimicking pleural masses, have been reported. Here, we report on a case of intrathoracic desmoid tumor protruding into the pleural cavity, and partially covered by parietal pleura. The main preoperative differential diagnoses included pleural solitary fibrous tumor, inflammatory pseudotumor or malignant mesothelioma. A near-total mass excision was performed. Pathologically, the tumor was composed of a paucicellular arrangement of spindle-shaped cells with fibromyxoid stroma. The resection margin was partially involved with spindle cells present. On histochemical staining, the spindle cells were strongly positive for vimentin and negative for CD34, consistent with a desmoid tumor. The patient was stable without further adjuvant treatment during 6-years of follow-up.