A brief report on malignant triton tumour of the brachial plexus

Abstract

A 37-year-old shoe repairer presented with a small mass in the right supraclavicular fossa, together with a six-month history of pain in the right arm and cramp in the hand — worse over the previous two months. His general health was otherwise good. A provisional diagnosis of metastatic lymphadenopathy was made, and an incision biopsy performed. Histology reported a low-grade, malignant schwannoma. The patient was referred for an orthopaedic opinion. The mass had increased in size in the two months following surgery, and now occupied most of the supraclavicular fossa and was producing symptoms of respiratory obstruction and dysphagia. Neurological examination revealed weakness of the intrinsic muscles of the hand and reduced sensation in C8 and T1 dermatomes. A CT scan showed that the tumour was arising from the C7/T1 intervertebral foramen and extending from the aortic arch into the neck, with displacement of the trachea and great vessels. Intra-arterial digital subtraction angiography (DSA) suggested no encasement of the vessels. At operation, the tumour was approached by elevation of the manubrium, the sternoclavicular joint, and the medial half of the clavicle on a pedicle of the sternomastoid.1 It was found to arise from the T1 root, with extensive infiltration into the muscles of the thoracic inlet and the carotid sheath, and only a subtotal excision was possible. Definite histology revealed that it was a malignant triton tumour. The patient received a course of radiotherapy and made a good recovery, with neurological deficit limited to C8 and T1. Within five months, however, the tumour recurred and required further debulking and radiotherapy. The patient died as a result of further extensive local recurrence within a year of presentation. Schwannomas of the brachial plexus are rare tumours; Gyhra et al found just 24 cases of brachial plexus schwannoma in a review of 480 cases of all types of schwannoma recorded in the literature.2 Malignant schwannomas are rarer still; Lusk reported just four in a total of 40 neural sheath tumours of the brachial plexus. Both authors emphasise that while benign schwannomas usually present with a palpable mass as their only symptom, the malignant variant almost always presents with pain or neurological deficit.3 Intrathoracic extension of the tumour is rare but has been reported2 — in one case, the tumour presented as a thoracic outlet syndrome.4 Diagnosis is often delayed since, as in this case, the mass is frequently mistaken for metastatic lymphadenopathy. A tumour of neural origin should be considered when sensory signs or symptoms are present, however, and the production of sensory changes distally when local pressure is applied is a diagnostic clue.5 Motor loss usually indicates a malignant lesion and a poor prognosis. Computerised tomography or magnetic resonance imaging is essential in diagnosis and preoperative planning, because it enables the anatomical relationships to surrounding tissues to be demonstrated.7 The malignant triton tumour is a rare variant of malignant schwannoma, with fewer than 70 cases reported in the world literature.8 Three criteria have been proposed for its diagnosis: origin in peripheral nerve or occurrence in patients with von Recklinghausen's disease; predominance of Schwann cell-type growth characteristics; presence of neoplastic rhabdomyoblasts.9 Although the histogenesis of this unusual tumour has not been proven, it seems most likely to originate in primitive neural crest cells.8 The malignant triton tumour carries a grave prognosis and, although radical excision followed by radiotherapy is the recommended treatment, a two-year survival rate of 33% and a five-year survival of 12% are reported.