Benign mesenchymoma of the mediastinum: a report and review of the literature.

Benign mesenchymoma is a rare type of germ cell tumour. An extensive literature search revealed only one described case of mediastinal mesenchymoma in Europe and three cases in Asia. We describe our recent experience of a mediastinal mesenchymoma and present the fascinating imaging and operative findings. The preoperative diagnosis of these lesions remains difficult and therefore surgical resection is recommended.

Case report

A 57 year old man was found to have a large radio-opacity on chest x-ray (Figure 1 (Fig. 1)) whilst undergoing investigation for renal calculi. He was experiencing some mild excertional dyspnoea but was otherwise asymptomatic. The patient underwent bronchoscopic examination which revealed subtle extrinsic compression of the left main bronchus. Contrast CT scan (Figure 2 (Fig. 2)) demonstrated a large calcified mediastinal mass compressing the left main bronchus and left upper lobe pulmonary arteries. He underwent thoracotomy and left upper lobectomy to excise the mass. Histopathological diagnosis was of benign mesenchymoma (hamartoma). The lesion measured 12 x 12cm, was roughly spherical and consisted of firm, grey, glassy tissue. Microscopically it contained mature cartilage, cellular fibrous tissue, collections of fat cells and muscle. There were also areas of focal ossification with haemopoesis. The patient recovered well from surgery, was discharged from hospital 6 days later and was well (without dyspnoea) at last follow up.

Figure 1

Plain PA chest radiograph

Figure 2

Contrast CT scan

Literature review

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], [2], [3], [4].

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], [2], [6]. A literature search revealed only one case of mediastinal mesenchymoma described in Europe and 3 cases described in Asia [2], [5], [6], [7]. 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].

Conclusion

This lesion had unusual appearances both on plain x-ray and CT scan and the operative findings and histological diagnosis were both unusual and informative. Preoperative diagnosis of benign mesenchymoma may be difficult and surgical resection will be curative. Although rare, this case illustrates the need to consider the more uncommon benign and malignant neoplasms in the differential diagnosis of unusual appearances on chest x-ray.