Intracranial schwannoma

Intracranial schwannomas (also referred to as neurinomas) are common benign tumours, accounting for 6 - 8% of all intracranial tumours¹. 

Epidemiology

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

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:

• trigeminal schwannoma
• facial nerve schwannoma
• acoustic schwannoma (most common)
• jugular foramen schwannoma

Multiple schwannomas, are a characteristic of neurofibromatosis type 2 (NF2). 

Pathology

Two histological types of schwannomas are described:

1. 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 
2. Antoni type B
   • reticular structure
   • cells have lymphocyte like nuclei
   • intracranial schwannomas typically have both Antony type A and B structure

Radiographic features

Although the appearance of individual schwannomas will be influenced by the nerve of origin and surrounding anatomy, they naturally share similar imaging characteristics. 

CT

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.

Bone algorithm is excellent at assessing bony margins, especially useful when the tumour extends into or thorough a foramen. As these lesions are slow growing they remodel the bone, with smooth borders. 

MRI

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. 

• T1
  • typically isointense to brain
  • cystic areas, if present, are hypointense
• T2
  • typically somewhat hyperintense to brain
  • cystic areas are hyperintense
• T1 C+ (Gd)
  • prominent enhancement
  • heterogenous in 70% of cases ¹
• DWI / ADC
  • often higher signal on both DWI and ADC (T2 shine through - not restricted diffusion)