Benign mesenchymoma is a rare type of germ cell tumour which histologically contains two or more differentiated mesenchymal elements not usually found within the same tumour [1
]. It can be referred to as a type of hamartoma (a benign tumor-like malformation resulting from faulty development in an organ and composed of an abnormal mixture of tissue elements that develop and grow at the same rate as normal elements).
Descriptions in the medical literature are uncommon and rarely occur in the mediastinum. These tumours most frequently occur in the renal and peri-renal regions although cases have been described affecting the oral cavity, the chest wall and breast and the gastrointestinal tract [1
Mediastinal mesenchymomal tumours are extremely rare and presentation to the thoracic surgeon may be incidental but symptoms can result from compression of local structures [5
]. A literature search revealed only one case of mediastinal mesenchymoma described in Europe and 3 cases described in Asia [2
]. The size of the lesion we report is the largest described in the literature. Benign mesenchymoma may cause local complications through compression of surrounding structures with growth. Despite the benign nature of these tumours, malignant transformation can occur and has been described [8
]. Little is known about the stage at which this transformation occurs or the stimulus for malignant change. The principle for treatment is to undertake diagnostic tests as applicable to the tumour site and arrange both local and systemic staging if malignant transformation is suspected. If biopsy cannot be safely undertaken (as in this report), surgical excision is required. Chemotherapy and radiotherapy have been shown to have a limited role and prognosis is poor with high rates of local and systemic reccurrence [9