Neurosurgery notes/Tumours/Gliomas, Glioneuronal Tumors, and Neuronal Tumors/Glioneuronal and neuronal tumours/Rosette forming glioneuronal tumour (RGNT)

Rosette forming glioneuronal tumour (RGNT)

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Glioneuronal and neuronal tumours

Definition

  • Essential:
    • Biphasic histomorphology with a AND
      • Neurocytic component (rosettes and/ or perivascular pseudorosettes)
      • Glial component (resembling pilocytic astrocytoma)
    • Uniform neurocytes forming rosettes and/or perivascular pseudorosettes associated with synaptophysm expression AND (for unresolved lesions)
      • Small biopsies showing only one tumour component (neurocytic or glial) and a methylation profile of rosette-forming glioneuronal tumour
  • Desirable:
    • FGFR1 mutation with co-occurring PIK3CA and/or NF1 mutation

Grading

  • WHO Grade 1

Number

  • Rare not much data on it

Clinical features

  • Obstructive hydrocephalus
    • H/A
  • Cerebellar signs
    • Ataxia

Localisation

  • Midline
  • 4th ventricle and/or aqueduct
    • Can extend to involve adjacent brain stem, cerebellar vermis, pineal gland, or thalamus
  • Other sites rare (20%)
    • Pineal region
    • Optic chiasm
    • Spinal cord
    • Septum pellucidum

Origin

  • Brain tissue surrounding the ventricular system

Radiology

General

  • Variable solid-cystic components:
    • Entirely solid: 40%
    • Mixed solid and cystic: 35%
    • Entirely cystic: 25%

CT

  • On CT these tumours are of variable appearance reflecting the solid and cystic components. Calcification is seen in approximately a quarter of cases.

MRI

  • As expected, the cystic components demonstrate high T2 signal, whereas the solid components demonstrate variable gadolinium enhancement.
Images
A close-up of a brain scan AI-generated content may be incorrect.
T1
A mri of a brain AI-generated content may be incorrect.
FLAIR
A close-up of a brain mri AI-generated content may be incorrect.
T1+C
A close-up of a brain scan AI-generated content may be incorrect.
Gradient Echo
A close-up of a brain scan AI-generated content may be incorrect.
T2
 

Histopathology

Macroscopic

  • Cystic and solid component

Microscopic

  • Biphasic neurocytic and glial architecture
    • Uniform neurocytes forming rosettes and/ or perivascular pseudorosettes
    • Astrocytic in nature and resembling pilocytic astrocytoma.
  • Proliferation index (Ki-67) is usually low, <3%
6.30 Rosette-forming glioneuronal conlists
Rosette-forming glioneuronal tumour consists of two components: neurocytic (left) and astrocytic (right).
Fig. 6.31 Rosette-forming glioneuronal tumour. A Neurocytic rosette: a ring-like array of neurocytic tumour cell nuclei around an eosinophilic neuropil core. B Perivascular pseudorosette with delicate cell processes radiating towards a capillary. C Synaptophysin immunoreactivity in the pericapillary area of a perivascular pseudorosette.
Rosette-forming glioneuronal tumour. A, Neurocytic rosette: a ring-like array of neurocytic tumour cell nuclei around an eosinophilic neuropil core. B, Perivascular pseudorosette with delicate cell processes radiating towards a capillary. C, Synaptophysin immunoreactivity in the pericapillary area of a perivascular pseudorosette.

Immunophenotype

  • The glial component demonstrates:
    • GFAP: positive
    • S100: positive
  • The neurocytic component demonstrates:
    • MAP2: positive
    • Neurone-specific enolase: positive
    • Synaptophysin: positive in the centre of the neurocytic rosettes

Genetic profile

  • Some association with NF1 but not part of diagnostic criteria
  • Missense mutation in exon 20 of PIK3CA
  • FGFR1 mutation

Management

  • Surgery
    • Difficult because of
      • Tumour location
      • Adherence and/ or infiltration of adjacent structures
    • Resulting in relatively high rate of new postoperative deficits.
    • Zhang et al., 2013
      • Failed to show the superiority of a gross total over a subtotal resection

Prognosis

  • Good prognosis but most patient suffer complication of surgery
  • Metastatic dissemination has been seen in as many as 7%

Differential diagnosis

  • Pilocytic astrocytoma (most commonly mistaken with)
    • Pilocystic astrocytoma has BUT Rosette-forming glioneuronal tumour do not
      • KIAA1549-BRAF fusions
      • BRAF V600E
    • Histologically the glial component very similar
  • Gangliogliomas and gangliocytomas
  • Pleomorphic xanthoastrocytoma (almost always hemispheric)
  • Papillary glioneuronal tumour (usually hemispheric)