Primary intrathoracic neural tumours.

TERMINOLOGY Each axon cylinder is encased in a sheath of Schwann cells, and the tumour arising from this, the specific nerve sheath, is the Schwannoma or neurilemmoma. Groups of axon cylinders comprising a peripheral nerve are enmeshed in a non-specific sheath of fibrous tissue, and tumours arising from this non-specific nerve sheath are neurofibromata. In some nerve sheath tumours clear histological distinction between a neurilemmoma and a. neurofibroma may not be possible, and mixed forms of these tumours are common. Malignant change in either of these tumours will give rise to a sarcoma, a neurosarcoma if the neural origin of the malignant tumour can be verified. The tumour which arises from a peripheral nerve cell is called a ganglioneuroma, and it is recognizable by its content of ganglion cells. When this tumour undergoes malignant change and ganglion cells are still recognizable it is called a ganglioneuroblastoma. The less differentiated malignant nerve cell tumour is called simply a neuroblastoma. Tumours arising from " potential " nerve tissue are called chromaffin tumours and may be either hormonally active, the phaeochromocytoma, or hormonally inactive, the paraganglioma or chemodectoma (Schlumberger, 1951).