General
- Can occur in any type of diffuse glioma but most common in anaplastic astrocytoma
Definition
- At least three lobes AND
- Has frequent bilateral growth
- May extend to infratentorial structures
- Lack of a single discrete mass AND
- Pathological confirmation of diffuse glioma
Numbers
- Peak incidence is 20-40 years of age
- M:F of 1.5:1 in one sequential series of 54 patient
Classification
- Type 1:
- No discrete mass
- Usually IDH wild-type
- Type 2:
- Discrete mass with further diffuse CNS involvement
- IDH mutation is more common in this subtype
Radiographic features
CT
- CT can be normal
- Lesions are often isodense to normal brain parenchyma.
- A relative lack of mass effect and distortion compared to the extensiveness of involvement.
- There may be an ill-defined asymmetry or subtle hypoattenuation of the involved brain parenchyma.
MRI
- Mass effect and enhancement are often minimal despite large portions of the brain being involved.
- There is a loss of grey-white matter differentiation and diffuse gyral thickening.
- Diffuse T1 and T2 prolongation throughout both white and grey matter:
- T1: iso to hypointense to grey matter
- T2: hyperintense to grey matter
- T1 C+ (Gd): typically no or minimal enhancement
- DWI: usually no restriction
- MR spectroscopy
- Elevated Cho:Cr and Cho:NAA ratios 2
- Marked elevation of myo-inositol (mI)
- Perfusion MR
- Low/normal rCBV: correlates with no vascular hyperplasia
PET
- FDG-PET shows marked hypometabolism
Treatment
- Surgery
- Is not a viable option due to the diffuse nature of this tumour
- Biopsy
- Treatment of complications such as hydrocephalus or mass effect.
- Radiation therapy
- Increase survival
- However, the large field usually required in these lesions increases the risk of severe toxicity
- Chemotherapy
- There is a lack of evidence in its use (both positive and negative)
Poor prognosis
- Average survival
- 50% at 1 year
- 25% at 3 years
- Transformation into glioblastoma may occur a few years later.
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