Definition
- Essential:
- Histopathology of schwannoma, such as Antoni A or Antoni В areas AND
- Extensive S100 or SOX10 expression
- Desirable:
- Verocay bodies
- Subcapsular lymphocytes
- Hyalinized blood vessels
- Lack of a lattice-like pattern of CD34 staining
- Loss of SMARCB1 (INI1) expression (epithelioid schwannoma), or a mosaic pattern of SMARCB1 (INI1) expression (syndrome-associated schwannoma)
CNS WHO grading
- Grade I
Origin
- Perineural Schwann cells
Epidemiology
- 8% of all intracranial tumours,
- 85% of cerebellopontine angle tumours, and
- 29% of spinal nerve root tumours
- 90% of cases are solitary and sporadic
- 4% arise in the setting of NF2.
- 5% of schwannomas that are multiple but not associated with NF2
- Some may be associated with schwannomatosis
- No sex predilection
- Female predominance among intracranial tumours
- Parenchymal tumours
- Cerebral intraparenchymal schwannomas
- Younger patient age
- Male predominance
- Schwannomas of spinal cord parenchyma are too rare for their epidemiology to be assessed
Localisation
- Outside of CNS schwannomas
- Vast majority
- Peripheral nerves in the skin and subcutaneous tissue are most often affected
- Intracranial schwannomas
- CN8 most common
- In NF2
- In CP angle
- At the transition zone between central and peripheral myelination
- Affect the vestibular division.
- Cochlear division is almost never the site of origin.
- This characteristic location, which is not shared by neurofibromas or malignant peripheral nerve sheath tumours, results in diagnostically helpful enlargement of the internal auditory meatus on neuroimaging.
- Intralabyrinthine schwannomas are uncommon
- Facial (2nd most common)
- Trigeminal 2nd division most common division
- Any CN can have schwannoma except CN2
- Jugular
- Grows intracranially > extra-cranially
Feature | Jugular schwannoma | Paraganglioma |
Jugular foramen margin | Smooth | Irregular |
Sclerosis | Bone is sclerotic | Non sclerotic |
Jugular vein | Compression | Invade |
Growth towards the post. fossa | Yes | No |
Presentation | Hearing loss and vertigo | CN9 deficits: loss of Afferent arm of gag reflex, loss of post 1/3 taste, loss of afferent arm carotid sinus reflex. |
- Intraspinal schwannomas
- Strong predilection for sensory nerve roots
- Motor and autonomic nerves are affected far less often
- Peripheral nerve schwannomas, (unlike neurofibromas)
- Tend to be attached to nerve trunks
- Most often involving the head and neck region or flexor surfaces of the extremities
Genetic
- Loss of TSH @ Chr22
Clinical features
- Paraspinal tumours: incidental (asymptomatic)
- Spinal nerve tumours with radicular pain and signs of nerve root / spinal cord compression,
- CN8 tumours with related symptoms
- Pain is the most common presentation for schwannomas in patients with schwannomatosis
- Jugular foramen
- Collet-Sicard syndrome
- Vernet syndrome, consisting of motor paralysis of
- Glossopharyngeal nerve (CN IX)
- Vagus nerve (CN X)
- Accessory nerve (CN XI)
- Motor paralysis of hypoglossal nerve (CN XII)
Imaging
- General imaging features of schwannomas include:
- Well circumscribed masses which displace adjacent structures without direct invasion
- Cystic and fatty degeneration are common
- The larger a schwannoma, the more likely it is to show heterogeneity because of cystic degeneration or haemorrhage
- Haemorrhage occurs in 5% of cases
- Calcification is rare
- CT
- Useful in assessing bony changes adjacent to the tumour
- Low to intermediate attenuation
- Intense contrast enhancement
- Small tumours typically demonstrate homogeneous enhancement
- Larger tumours may show heterogeneous enhancement
- Adjacent bone remodelling with smooth corticated edges
- MRI
- T1: isointense or hypointense
- T1 C+ (Gd): intense enhancement
- T2: heterogeneously hyperintense
- Antoni A: densely packed fibrous and neural tissue → lower intensity
- Antoni B: looser tissue density with myxomatous tissue → higher intensity
- Cystic degenerative areas may be present, especially in larger tumours
- T2*: larger tumours often have areas of haemosiderin
- A number of signs can also be useful:
- Split-fat sign: thin peripheral rim of fat best seen on planes along long axis of the lesion in non-fat-suppressed sequences
- Target sign
- Peripheral high T2 signal
- Central low signal
- Rarely seen intracranially
- Fascicular sign: multiple small ring-like structures
- Enlargement of the porous acoustics
- Enlargement of the ipsilateral cistern
Histopathology
- Macroscopy
- Most schwannomas are globoid masses measuring < 10 cm.
- The cut surface of the tumour typically shows light-tan glistening tissue interrupted by bright yellow patches, with or without cysts and haemorrhage
- Microscopy
- Conventional schwannoma is composed entirely of neoplastic Schwann cells
- Two basic architectural patterns, in varying proportions, are typically present:
- Antoni A pattern:
- Densely packed spindled tumour cells arranged in fascicles running in different directions
- The tumour nuclei may show a tendency to align in alternating parallel rows, forming nuclear palisades
- When marked, nuclear palisades are referred to as Verocay bodies.
- Antoni B pattern:
- Less cellular
- Loosely textured cells
- Tumour cells are loosely arranged
- Indistinct processes
- Variable lipidization
- In NF2, VS show a predominance of Antoni A tissue, whorl formation, and a lobular grape-like growth pattern on low-power examination
- Molecular data suggest that these are polyclonal and likely constitute the confluence of multiple small schwannomas
- Malignant transformation rarely occurs in conventional schwannomas.
Immunophenotypes
- Positive
- Diffuse
- S100 protein
- Focal
- GFAP
- Often express SOX10, LEU7, and calretinin
- All schwannoma cells have surface basal lamina, so membrane staining for collagen IV and laminin is extensive and most commonly pericellular
- Low level p53 protein immunoreactivity may be seen, particularly in cellular schwannomas
Genetic profile
- NF2 gene as a tumour suppressor integral to the formation of sporadic schwannomas
- Inactivating mutations of NF2 in 60% of schwannomas
- NF2-inactivating mutations have been detected in approximately 50-75% of sporadic cases
- Other genetic changes are rare in schwannomas, although small numbers of cases with loss of chromosome 1p, gain of 9q34, and gain of 17q have been reported
- Bilateral vestibular schwannomas are pathognomonic of NF2, whereas multiple, mostly non-vestibular schwannomas in the absence of other NF2 features are characteristic of schwannomatosis
- Schwannomatosis present with multiple, often painful schwannomas, which in some cases are segmental in distribution
- Germline SMARCB1 mutations at 22q11.23 have been found in half of all familial and < 10% of all sporadic schwannomatosis cases
- Somatic NF2 inactivation has been shown in tumours, but germline NF2 mutations are absent
- Germline loss-of-function mutations in LZTR1 predispose individuals to an autosomal dominant inherited disorder of multiple schwannomas, and are identified in approximately 80% of 22q-related schwannomatosis cases that lack mutations in SMARCB1
Prognosis
- Benign, slow-growing tumours that infrequently recur and only very rarely undergo malignant change
- Recurrences are more common (occurring in 30-40% of cases) for cellular schwannomas of the intracranial, spinal, and sacral regions and for plexiform schwannoma
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