Schwannoma are slow growing benign nerve sheath tumours.
These are usually solitary lesions. Multiple lesions are rare and may occur in the following clinical settings: -
i) multiple localized tumours.
ii) In association with neurofibroma in von Recklinghausen's disease.
iii) In schwannomatosis, a non hereditary disease characterized by multiple subcutaneous and intradermal schwannomas together with
tumours of internal organs.
Age: Common in patients between the ages of 20 and 50.
Site: These are usually located on the head and neck and flexor surface of upper and lower extremities.
The spinal roots, cervical, sympathetic, vagus and ulnar nerves are commonly involved.
The deeply located lesions are situated in the retroperitoneum and the posterior mediastinum.
Gross: The tumour is surrounded by true capsule consisting of the epineurium.
Tumour arising in a small nerve resemble a neurofibroma and often obliterate the nerve of origin.
Tumours arising in larger nerves present as eccentric masses.
Cut surface reveals smooth, glistening , grey-white appearance.
There may be cystic areas with areas of hemorrhage and calcification.
Microscopic features: Schwannomas are usually solitary, well circumscribed, encapsulated lesions, mostly confined to the subcutis.
Multinodular lesions may be present in the dermis, this is known as 'plexiform neurilemmoma'.
The characteristic features include presence of alternating Antoni A and Antoni B areas
Antoni A area is composed of spindle shaped Schwann cells arranged in interlacing fascicles.
There may be nuclear palisading. In between two compact rows of well aligned nuclei , the cell processes form eosinophilic Verocay bodies.
Mitotic figures may be present (usually less than 5 per 10 high power field).
Antoni B area consists of loose meshwork of gelatinous and microcystic tissue.
Large, irregularly spaced, thick walled blood vessels are noted in Antoni B area. These may contain thrombus material in the lumina.
Immunohistochemistry: S100 is strongly expressed by most cells of schwannoma.The cells also express Vimentin and myelin basic protein.
Differential diagnosis: Neurofibroma ; Palisaded encapsulated neuroma (more number of axons and Schwann cells in interlacing fascicles together with cleft like spaces.; Cutaneous leiomyoma (smooth muscle actin and desmin positive) ; Palisaded myofibroblastoma ( involve lymph nodes, contain fibroblastic and myofibroblastic cells and are S100 protein negative).
This is a variant of Schwannoma displaying prominent degenerative changes.
The degenerative changes include cyst formation, calcification, hemorrhage and hyalinization.
Macroscopically these are large tumours which are usually deeply located (eg. retroperitoneum).
There is prominent cellular atypia characterized by hyperchromatic nuclei and coarse clumping of chromatin.
These changes are purely degenerative.
No mitotic figures are identified. These tumours behave as ordinary schwannomas.
Cellular Schwannoma: Image
This variant is usually found in the deeper tissues (retroperitoneum or mediastinum).
Histologically ,there are compact spindle shaped cells arranged in a fascicular or whorled growth pattern.
Verocay bodies and Antoni B areas are not conspicuous. Mitotic figures are present (more that 10 per10 high power fields).
The thick fibrous capsule around the tumour shows a dense lymphocytic infiltrate.
Differential diagnosis include low grade malignant peripheral nerve seath tumour and leiomyosarcoma.
Immunohistochemistry reveals strong and diffuse positivity with S100 protein. Desmin is negative.
This rare variant usually occurs in middle aged adults and commonly arises from the posterior spinal nerve roots.
Melanotic schwannomas are well circumscribed, partly encapsulated lesions characterized by polygonal and vesicular cells with grooved nuclei.
These cells contain abundant melanin pigment.
In psammomatous melanotic schwannoma , varying numbers of psammoma bodies are present.
Some of these cases are associated with Carney's complex (myxoma, spotty pigmentation and endocrinopathy).
Malignant melanotic schwannoma usually arises from the sympathetic chain and is characterized by brisk mitosis and prominent nucleoli.
Immunohistochemistry reveals that tumour cells stain positively for S100, HMB45, MART-1, synaptophysin and vimentin.
Neuroblastoma - Like Schwannoma :
Benign schwannomas may contain rosette-like
structures mimicking neuroblastoma/PNET.
Tumour cells are positive for S100 protein and negative for neuronal
markers synaptophysins and neurofilament protein.
MIC2 is negative (rules out PNET type
differentiation). Individual cells were surrounded by type IV collagen.
This is a feature characteristically seen in schwannian but not in
Benign schwannomas may contain rosette-like structures mimicking neuroblastoma/PNET.
Tumour cells are positive for S100 protein and negative for neuronal markers synaptophysins and neurofilament protein.
MIC2 is negative (rules out PNET type differentiation). Individual cells were surrounded by type IV collagen.
This is a feature characteristically seen in schwannian but not in neuronal tumours.