Intracranial schwannomas (also referred to as neurinomas) are common benign tumours, accounting for 6-8% of all intracranial tumours 1.
Schwannomas can occur essentially anywhere in the body. See also the general schwannoma article.
Schwannomas are most frequently encountered in middle aged and elderly adults with a predilection for females (F:M = 1.5-2:1), although they are found in all age groups.
Clinical presentation depends on the both the size of the tumour, the nerve of origin and the exact location. In general they will present with symptoms pertaining to the parent cranial nerve. Larger tumours will also exert mass effect on adjacent structures. Specific features are discussed separately:
- acoustic schwannoma (most common)
- trigeminal schwannoma (second most common)
- facial nerve schwannoma (third most common)
- jugular foramen schwannoma
Multiple schwannomas, are a characteristic of neurofibromatosis type 2 (NF2). In this setting, any cranial nerve can be involved, including those that are very rarely seen in sporadic cases (e.g. oculomotor nerve) 2.
Two histological types of schwannomas are described 1,2:
- Antoni type A
- cells are elongated and bipolar with unclear borders
- arranged parallel to each other (palisade-like structures)
- pure Antony type A tumours are typical of spinal schwannomas
- Antoni type B
- reticular structure
- cells have lymphocyte like nuclei
Intracranial schwannomas typically have both Antoni type A and B structure 1,2.
Although the appearance of individual schwannomas will be influenced by the nerve of origin, composition (Antoni type B typically demonstrate higher T2 signal) and surrounding anatomy, they naturally share similar imaging characteristics.
Schwannomas are typically isodense to brain, and can be difficult to identify, depending on location. Cystic areas (usually found in larger tumours) are hypodense, similar to CSF. Following administration of contrast they moderately enhance, often heterogeneously due to cystic areas 1,2.
Bone algorithm is excellent at assessing bony margins, especially useful when the tumour extends into or through a foramen. As these lesions are slow growing they remodel the bone, with smooth borders, rather than destroy the bone 1,2.
MRI is the investigation of choice for assessment of intracranial schwannomas, not only due to greater contrast resolution, but also exquisite anatomical details, which allows for precise localisation of the tumour. This is particularly the case with high resolution T2 sequences (e.g. FIESTA, CISS, SPACE).
Typical signal characteristics are 1,2:
- isointense to hypointense to brain
- low signal cystic areas, if present
T1 C+ (Gd)
- prominent enhancement
- heterogeneous in 70% of cases 1
- typically somewhat hyperintense to brain
- cystic areas are hyperintense
T2* (GE / SWI)
- haemosiderin staining may be encountered, particularly in larger tumours 2
- often higher signal on both DWI and ADC (T2 shine through - not restricted diffusion)
Treatment and prognosis
Although the details of therapeutic options will depend on the location of the tumour, size and patient circumstances, generally surgical resection is curative if complete resection is achieved.
Radiotherapy is an alternative to surgery.
The differential diagnosis will depend mostly on the specific location of the tumour and which nerve it arises from. As such, this is discussed separately in individual articles (see above).
- 1. Kornienko VN, Pronin IN. Diagnostic Neuroradiology. Springer Verlag. (2008) ISBN:3540756523. Read it at Google Books - Find it at Amazon
- 2. Skolnik AD, Loevner LA, Sampathu DM et-al. Cranial Nerve Schwannomas: Diagnostic Imaging Approach. Radiographics. 2016;36 (5): 150199. doi:10.1148/rg.2016150199 - Pubmed citation