Schwannoma

Schwannoma, also known as neurilemoma or neuroma, is a usually benign nerve sheath tumour composed of Schwann cells, which are responsible for producing the insulating myelin sheath covering peripheral nerves. These tumours are homogeneous, consisting solely of Schwann cells, and are generally slow-growing. Schwannomas are mostly benign, with malignant transformation occurring in less than 1% of cases, resulting in a neurofibrosarcoma. Given their encapsulated nature, surgical removal of schwannomas is often successful.

Signs & Symptoms

Schwannomas can manifest in various parts of the body, most frequently affecting the head, neck, and limbs. Vestibular schwannomas, which occur on the vestibulocochlear nerve, are common and can lead to tinnitus and hearing loss on the affected side. Outside cranial nerves, these tumours may present on the flexor surfaces of limbs. Although rare, schwannomas can also occur in unusual locations such as the penis.

Diagnosis

Schwannomas are universally S-100 positive, indicating their origin from neural crest cells. Histologically, they display distinct Antoni A and Antoni B areas. Antoni A areas are densely cellular regions, while Antoni B areas are looser and less cellular. Verocay bodies, which are characteristic of schwannomas, can also be identified.

Variants

Pleural Schwannoma

Pleural schwannomas are extremely rare and typically develop in superficial locations. They may or may not be encapsulated and can be challenging to differentiate from malignant peripheral nerve sheath tumours (MPNST) when occurring in deeper anatomical sites. MRI imaging often shows hyper or iso-intensity on T1-weighted images and heterogeneous hyperintensities on T2-weighted images due to fatty degeneration, haemorrhage, and cystic formation. Complete surgical removal is the preferred treatment.

Cellular Schwannoma

Cellular schwannomas are characterised by a fascicular proliferation of well-differentiated Schwann cells, lacking Verocay bodies and showing minimal Antoni B growth. These tumours have a variable local recurrence rate, ranging from 5-40%, which is potentially higher than in typical schwannomas.

Melanotic Schwannoma

Melanotic schwannomas are rare and potentially malignant, featuring epithelioid cells with substantial melanin deposition. These tumours can be identified by their distinctive histological appearance and may require more aggressive management due to their malignant potential.

Treatment

The primary treatment for schwannomas is surgical excision, given their generally benign nature and encapsulation. Complete removal often results in a favourable prognosis. However, close monitoring is essential due to the small risk of malignant transformation and the potential for local recurrence, particularly in cellular and melanotic variants.

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Self-assessment MCQs (single best answer)

Schwannomas are composed of which type of cells?

What percentage of schwannomas undergo malignant transformation?

Vestibular schwannomas commonly lead to which symptoms?

What histological feature is characteristic of schwannomas?

Which immunohistochemical marker is universally positive in schwannomas?

Which variant of schwannoma is characterised by a high recurrence rate and lacks Verocay bodies?

What is the preferred treatment for schwannomas?

Which variant of schwannoma features significant melanin deposition and potential malignancy?

MRI imaging of pleural schwannomas typically shows what kind of intensity on T2-weighted images?

In schwannomas, what are Verocay bodies?