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Oligodendroglioma

Summary

  • Oligodendroglioma is a slow-growing, diffusely infiltrating glial tumour of the central nervous system
  • Typically affects adults in their 4th-5th decades of life
  • Characterised by classic "fried egg" appearance histologically and 1p/19q co-deletion genetically

Cases

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  • A 40-year-old patient presented after a tonic-clonic seizure.
  • MRI showed a relatively well-demarcated tumour in the left frontal lobe that involved cortex.
  • Phase data from SWI showed diamagnetic susceptibility artefact consistent with dystrophic calcification.
  • There was punctate enhancement and elevated CBV (ratio of 2.5 relative contralatera normal appearing brain tissue).
  • MRS showed elevated choline and reduced NAA (indicating the replacement of normal neurons with mitotically active cells).

Pathophysiology

  • Typically occurs in the cerebral hemispheres, particularly the frontal lobes
  • Molecular markers include 1p and 19q co-deletion and IDH1/2 mutuation
  • Typical findings of histopathological include "fried egg" oligodendrocytes, chicken-wire neovascularisation and microcalcification

Demographics

  • Accounts for approximately 5-20% of all gliomas and 5-10% of all intracranial tumours
  • Peak incidence in 4th-5th decades of life
  • Slight male predominance (M:F ratio 1.1-2:1)

Diagnosis

  • Clinical presentation:
  • Seizures (50-80% of cases)
  • Headaches
  • Focal neurological deficits
  • Cognitive changes

Imaging

  • CT:
  • Hypoattenuating cortical/subcortical mass
  • Calcifications in 50-90% of cases
  • May cause remodelling of the overlying skull (representing slow growth)
  • MRI:
  • ++T2/FLAIR++ hyperintense
  • T1 hypointense to isointense
  • T1+C Minimal to moderate enhancement with contrast
  • SWI Hypointensity/blooming due to calcification (or, more rarely, haemorrhage)
  • Advanced imaging:
  • MR spectroscopy: elevated Cho/NAA ratio, presence of lactate/lipid peak
  • Perfusion imaging: CBV may be elevated even in grade 2 lesions

Treatment

  • Maximal safe surgical resection is the initial treatment of choice
  • Adjuvant therapy based on grade and molecular profile:
  • Grade II: observation or radiotherapy ± chemotherapy
  • Grade III (anaplastic): radiotherapy + chemotherapy (typically PCV or temozolomide)
  • Chemotherapy:
  • PCV (procarbazine, lomustine, vincristine) regimen
  • Temozolomide as an alternative
  • Radiotherapy:
  • Typically 54-60 Gy in 1.8-2 Gy fractions
  • Prognosis:
  • Generally better than astrocytomas
  • 1p/19q co-deletion and IDH mutation associated with improved survival
  • 5-year survival rates: 50-80% for grade II, 30-60% for grade III
Differential Diagnosis Differentiating Feature
Astrocytoma Lack of calcifications on imaging; less well demarcated/more infiltrative; absence of 1p/19q codeletion
Dysembryoplastic neuroepithelial tumor (DNET) Cortical location; multinodular architecture
Ganglioglioma Presence of neuronal component; lack of 1p/19q codeletion
Glioblastoma Central necrosis and peripheral enhancement; lower ADC values reflecting hypercellularity