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Q1: Describe the abnormalities shown in figs 2 and 3 (see p 629)
The chest radiograph suggests that the lesion arises in the posterior mediastinum as it is visualised above the clavicle. Figure 2 is a computed tomogram of the thorax that demonstrates a well marginated lesion extending from the neural canal at right T2/T3 level, with significant widening of the neural foramen at this level. There is no evidence of mediastinal lymphadenopathy or lung parenchymal involvement. Figure 3 is a MRI scan that demonstrates a dumbbell shaped neoplasm measuring 40 × 30 mm arising from the right T2/T3 nerve root. It is of high signal intensity on T2-weighted images with a heterogenous area of lower attenuation centrally. The lesion measures 15 mm within the canal and 21 × 30 mm within the thorax and is expanding the neural canal at this level, consistent with a neoplasm of neural origin. The medial aspect of the tumour extends to the lateral border of the spinal cord, which is minimally displaced.
Q2: What is the differential diagnosis?
Mediastinal neoplasms encompass a long list of histologically diverse lesions that can arise from a wide variety of mediastinal structures. In adults, most primary mediastinal neoplasms can be classified in one of four categories: thymus-derived neoplasms, neurogenic tumours, lymphomas, or germ cell neoplasms.1 The differential diagnosis of masses in the posterior mediastinum includes neurogenic neoplasms (often neurofibromas and schwannomas), aneurysms of the descending aorta, oesophageal tumours, infectious processes including abscesses, and disorders of the thoracic spine, such as sarcomas. In adults, most posterior mediastinal tumours are of nerve sheath origin and are often benign and asymptomatic.
Q3: What was the definitive procedure?
Given the likelihood of this lesion being a benign neurogenic neoplasm, the patient proceeded to a right posterolateral thoracotomy with excision of the lesion.
Q4: Based on the radiological appearances, what potential complication might arise if the lesion was left untreated?
The MRI scan (see p 629) demonstrates that the tumour extends medially to the lateral border of the spinal cord and is causing minimal displacement of the cord. If the tumour were to extend further medially, neurological symptoms resulting from cord compression might arise. Similarly, if the lesion was to further deform the structure of the vertebral body, vertebral collapse might arise.
In view of the proximity of the lesion to the spinal cord, thoracotomy rather than thoracoscopic resection was considered the preferred surgical approach. The patient proceeded to a right posterolateral thoracotomy in the fourth intercostal space, and a soft yellow dumbbell shaped mass measuring 30 × 30 mm was discovered in the right third intercostal space, extending into the transverse foramen. The lesion was excised and histological examination showed a partially encapsulated tumour composed of spindle cells in a loose fibrillary background. Antoni type A and B components were present with focal Verocay body formation. The histopathologist concluded that the lesion was a benign intercostal schwannoma. The patient had an uneventful postoperative recovery. Four months after her operation, she remains well, her symptoms have resolved, and there is no radiological evidence of recurrence of the lesion.
Neurogenic mediastinal tumours account for approximately 20% of all mediastinal tumours in adults and 40% in children. These tumours may be of nerve sheath, autonomic ganglia, or paraganglionic origin and are generally located in the posterior mediastinum. Neurogenic tumours of the mediastinum with an intraspinal component connected by a narrowed segment in the intervertebral canal are generally described as dumbbell or hourglass tumours. Tumours of nerve sheath origin classically present as paraspinal masses. These tumours may be neurofibromas, schwannomas, granular cell tumours, melanotic schwannomas, or malignant schwannomas. Schwannomas are most often benign tumours originating from the sheath of peripheral nerves and usually present as solitary and well encapsulated tumours. Most are asymptomatic and are detected incidentally on a routine chest radiograph. Schwannomas arising from the intercostal nerve are well described and may be multiple. Intrathoracic schwannomas may also arise from other nerves, such as the phrenic and glossopharyngeal nerves.2 Schwannomas are usually benign but may occasionally be malignant. Malignant schwannomas have been described in patients with neurofibromatosis.3
Of special concern in the management of neurogenic tumours arising in the thorax is spinal cord compression resulting from either intraspinal lesions or vertebral body destruction and collapse.4 Predictably, this complication makes for a more difficult surgical excision. Intercostal schwannomas have been successfully resected thoracoscopically. This technique may reduce hospital stay and minimise postoperative complications, but is best reserved for lesions in which there is no evidence of intraspinal extension.5
The diagnosis of mediastinal tumours has been aided by recent advances in computed tomography, MRI, ultrasonography, radionucleotide scanning, and fine needle aspiration. MRI is the preferred modality for imaging neurogenic tumours, because of its multiplanar capability and high contrast resolution. MRI can best demonstrate the number and nature of the lesions (differentiating cysts from neoplasms) and the intraspinal and craniocaudad extent of the lesion, and thus determine the optimal surgical approach for patients. This technique is also especially useful for evaluation of the mediastinum of patients for whom the administration of iodinated contrast material is contraindicated. In cases where intraspinal extension is demonstrated, open thoracotomy is the more suitable approach, as the likelihood of conversion to open thoracotomy during thoracoscopic resection is high. However, the definitive diagnosis of schwannoma requires histological examination.
Benign schwannoma, fourth intercostal space.