Neurogenic Tumours of the Mediastinum

Overview

Neurogenic tumours are the most common mediastinal tumours overall (20%), arising predominantly in the posterior mediastinum (paravertebral compartment). They arise from peripheral nerves, nerve sheaths, or the sympathetic chain. In adults, the majority are benign; in children, malignant neurogenic tumours (neuroblastoma, ganglioneuroblastoma) are more common and carry a worse prognosis.

Nerve sheath tumours

Schwannoma (neurilemmoma)

The most common benign neurogenic tumour. Well-encapsulated, soft, yellowish tumours attached to peripheral nerves — stain with S-100 protein. Two histological patterns: Antoni A (organised palisading pattern — Verocay bodies) and Antoni B (loose reticular pattern). Complete excision within the capsule is curative. Association with neurofibromatosis type 2 (NF2). May be associated with von Recklinghausen disease (NF1).

Neurofibroma

Benign nerve sheath tumour arising from non-myelinating Schwann cells, fibroblasts, and axons. Commonly associated with neurofibromatosis type 1 (NF1 / von Recklinghausen disease). Pseudo-encapsulated and appear to be part of the nerve of origin rather than attached to it — unlike schwannoma, cannot be separated from the nerve. Plexiform neurofibromas in NF1 carry a 10–15% lifetime risk of malignant transformation to MPNST.

Malignant peripheral nerve sheath tumour (MPNST)

Malignant schwannomas occur predominantly in von Recklinghausen disease. Locally aggressive with high local recurrence. Radical surgical excision with clear margins is the cornerstone of treatment — chemotherapy and radiotherapy have limited efficacy. Prognosis is poor for unresectable or metastatic disease.

Autonomic ganglia tumours

Ganglioneuroma

Well-differentiated, benign tumour arising from neural crest cells of the sympathetic ganglia. Typically found in children and young adults. Paravertebral location — may extend into multiple intercostal foramina. Complete resection is curative. Can produce VIP (vasoactive intestinal peptide) causing watery diarrhoea syndrome.

Neuroblastoma and ganglioneuroblastoma

Malignant tumours arising from primitive sympathetic neuroblasts. Most common in children under 5 years. May secrete catecholamines and VIP. Staging by International Neuroblastoma Staging System (INSS). Treatment: multimodal — surgery, chemotherapy, radiation, bone marrow transplantation in advanced disease.

Pheochromocytoma / paraganglioma

2% of extra-adrenal pheochromocytomas occur in the chest. Associated with multiple endocrine neoplasia (MEN 2A, 2B), von Hippel-Lindau syndrome, and Carney triad (pulmonary chondromas + gastric GIST + extra-adrenal paraganglioma). Mediastinal pheochromocytomas have a higher propensity for malignancy than adrenal counterparts. Functional tumours produce catecholamines causing paroxysmal hypertension, headache, sweating, and palpitations.

Dumbbell tumours

Some posterior mediastinal neurogenic tumours extend through the intervertebral foramen into the spinal canal — giving a "dumbbell" or "hourglass" shape on MRI. This is critical to identify pre-operatively because inadequate decompression of the intraspinal component risks spinal cord injury from haematoma or swelling.

Investigations

• MRI: investigation of choice — better than CT for delineating intraspinal extension, neural foraminal involvement, and cord compression
• CT chest: characterises the mass, rib erosion, calcification
• 24-hour urinary catecholamines and metanephrines: mandatory for posterior mediastinal tumours to exclude functional pheochromocytoma
• MIBG scan: for paraganglioma and neuroblastoma — identifies multifocal disease and metastases

Treatment

Surgical excision in toto without breaching the capsule is curative for benign neurogenic tumours. Approach by thoracotomy, VATS, or robotic surgery. Recurrence is rare for benign tumours. For malignant tumours, local recurrence is common and overall prognosis is poor despite multimodal therapy.