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A 60-year-old man complained of dyspnoea and recurrent pulmonary infections. He was an ex-smoker. Medical history was unremarkable. He denied cough, haemoptysis, and chest pain. Physical examination did not show any abnormalities. Basic laboratory studies and an electrocardiogram were normal. A chest X-ray showed a subtle mediastinal abnormality (figure 1), so a computed tomography (CT) scan of the chest was done. It showed a large mass in the mediastinum (figure2).
- What is the differential diagnosis?
- What biopsy techniques are appropriate?
- What is the treatment?
The CT shows a homogenous mass with a tissue density consistent with fat. The differential diagnosis of mediastinal fatty tumours includes lipoma, liposarcoma, thymolipoma, and herniated peritoneal fat (hiatus or diaphragmatic hernia). Thymolipomas arise in the thymus gland (anterior mediastinum). Small fatty ‘masses’ in the inferior-posterior mediastinum often represent hiatus hernias, but it is unusual for large mediastinal fatty masses to be hernias. Large hernias usually consist of stomach or bowel, in addition to herniated peritoneal fat. The main differential diagnoses in this case are lipoma and liposarcoma.
Needle biopsies, either fine needle or core, are often inadequate for accurate diagnosis of lipomatous tumours. Low-grade liposarcomas are difficult to distinguish from benign lipomas on needle biopsy. Larger tissue specimens, from incisional or excisional biopsies, are usually required.
Complete excision (resection), when feasible, is the preferred treatment for lipomatous mediastinal tumours. This provides the pathologist with adequate tissue for diagnostic purposes, and the procedure is therapeutic as well.
Mediastinal lipomas and liposarcomas are rare.1-3They comprise less than 1% of all mediastinal tumours. A small tumour may be asymptomatic, but as the tumour increases in size compression of intrathoracic structures causes symptoms. Our patient's dyspnoea, for example, was relieved by tumour removal. Liposarcomas invade adjacent organs, so they are more likely to be symptomatic than benign lipomas, which simply compress adjacent structures.
Given the difficulty of accurate diagnosis with needle biopsies of lipomatous masses, complete excision is the diagnostic and therapeutic procedure of choice whenever possible. However, if the CT scan suggests that complete resection cannot be accomplished, there is little point in proceeding with a surgical procedure that leaves tumour in situ.2 In this situation an attempt at needle biopsy, or thoracoscopic incisional biopsy, are appropriate diagnostic procedures. Our patient's tumour was completely excised through a limited muscle-sparing thoracotomy. Final pathology showed a benign lipoma. The resection provided a diagnosis, relieved symptoms (dyspnoea) and prevented potential future problems from tumour growth.
Recurrence of a completely resected benign mediastinal lipoma is unlikely. However, if a liposarcoma had been found, the prognosis would have been quite poor.1 Mediastinal liposarcomas often invade adjacent vital organs, and microscopically complete tumour resection is difficult. Unfortunately, adjuvant treatment with radiation therapy or chemotherapy has not been very effective in intrathoracic mediastinal liposarcomas.1 4
Benign mediastinal lipoma.