Neurosurgery notes/Tumours/Gliomas, Glioneuronal Tumors, and Neuronal Tumors/Glioneuronal and neuronal tumours/Extraventricular neurocytoma

Extraventricular neurocytoma

View Details
Status
Done
logo
Parent item
Glioneuronal and neuronal tumours

Definition

  • Essential:
    • Extraventricular neurocytic neoplasm without IDH alteration AND
    • Synaptophysin expression AND (for unresolved lesions)
      • Methylation profile of extraventricular neurocytoma
  • Desirable:
    • FGFR1 alteration (mostly FGFR1::TACC1 fusion)
  • Caveat:
    • Diagnosis should be heavily weighted towards molecular findings because morphological analyses frequently result in mistyping

Grading

  • WHO Grade 2
  • More aggressive → Atypical: elevated Ki67 index (>3%) but have not established grading criteria yet

Number

  • Any age: 1 to 79 yrs
  • Male:female 1:1

Clinical features

  • Depends mass effect and its location
    • Hemispheric:
      • Seizures
      • Headaches
      • Visual disturbances
      • Hemiparesis
      • Cognitive disturbances;
    • Thalamic and hypothalamic lesions with increased intracranial tension
    • Spinal lesions with motor, sensory, and sphincter dysfunction

Localisation

  • Cerebral hemispheres (71%)
    • Frontal lobes (30%)
  • Spinal cords 14%
  • Rare: thalamic, hypothalamic, extra craniospinal compartment

Genetic profile

  • FGFR1::TACC1 fusion
  • Lack of
    • IDH1/2 mutation
    • MGMT methylation

Origin

  • Mislocated neural progenitor cells

Radiology

  • General
    • Lesions tend to be generally circumscribed, complex and sometimes large, complex, and variably enhancing masses.
    • They are often partly or mainly cystic and calcification is not uncommon(>10%).
    • They may or may not be associated with peritumoral oedema.
  • MRI
      • Well-defined, often mixed cystic heterogeneously solid lesions that involve the deep white matter or the cortical grey matter of the cerebral hemispheres.
      • T1: iso/hypointense
      • T1 C+: solid portions may show varying degrees of enhancement
      • T2/Flair: hyperintense
      Fig. 6.44 Extraventricular neurocytoma. A Hyperintense frontal mass on T2-weighted MRI. B Hypointense mass with no contrast enhancement is seen on Tl -weighted MRI after gadolinium administration.
      Extraventricular neurocytoma. A, Hyperintense frontal mass on T2-weighted MRI. B, Hypointense mass with no contrast enhancement is seen on T1-weighted MRI after gadolinium administration.

Histopathology

Microscopic

  • They look histologically so similar to other CNS tumours they haven't had proper screening of IDH mutation to exclude them from oligodendrogliomas, pilocystic astrocytomas etc
  • Are less cellular and have an oligodendroglioma-like appearance due to small, uniform round cells with artefactually cleared cytoplasm embedded in a fibrillar matrix.
Machine generated alternative text: Fig. 6.45 Extraventricular neurocytoma. A Spinal extraventricular neurocytoma composed of monomorphic cells that have round nuclei with fine nuclear chromatin. B Focal ganglionic differentiation. C The cells, often with perinuclear haloes, have round nuclei with finely stippled chromatin and small nucleoli. D Occasional neoplastic cells express GFAP. E Nuclear expression of NeuN. F Diffuse cytoplasmic Immunoreactivity for synaptophysin is characteristic of extraventricular neurocytoma. The sparse neuropil between tumour cells is also stained.
Extraventricular neurocytoma. A, Spinal extraventricular neurocytoma composed of monomorphic cells that have round nuclei with fine nuclear chromatin. B, Focal ganglionic differentiation. C, The cells, often with perinuclear haloes, have round nuclei with finely stippled chromatin and small nucleoli. D, Occasional neoplastic cells express GFAP. E, Nuclear expression of NeuN. F, Diffuse cytoplasmic immunoreactivity for synaptophysin is characteristic of extraventricular neurocytoma. The sparse neuropil between tumour cells is also stained.

Immunophenotype

  • Synaptophysin: positive and essential to the diagnosis
  • GFAP: may be positive if an astrocytic component is present
  • IDH R132H: negative

Management

  • Complete resections are helpful in controlling EVNs, but may be difficult to achieve because of tumour size or location.
  • STR: Radiotherapy

Prognosis

  • Benign and has a low rate of recurrence
  • Kane et al., 2012:
      • Extraventricular neurocytoma
      5 yrs. recurrence rates
      5 year mortality rate
      Typical
      36%
      4%
      Atypical
      68%
      44%
    • Good prognosis
      • Young <50
      • Gross total resection
  • Craniospinal dissemination can occur as
    • Remote metastasis
    • Along the surgical route

Differential diagnosis

  • Ganglioglioma and gangliocytoma
  • Pleomorphic xanthoastrocytoma
  • Pilocytic astrocytoma
  • Oligodendroglioma
    • Absence of (in Extraventricular neurocytoma)
      • IDH mutation
      • 1p/19q codeletion
  • Diffuse astrocytoma, particularly gemistocytic astrocytoma and oligodendrogliomas
  • Papillary glioneuronal tumour
    • BRAF V600E mutation and for SLC44A1-PRKCA fusion, a recurrent genetic alteration reported in PGNT
  • Rosette-forming glioneuronal tumours (usually midline and often posterior fossa)
  • Diffuse leptomeningeal glioneuronal tumour (when leptomeningeal spread is prominent)
    • Similarities with DLGT
      • Histological and immunohistochemical features, including proliferation of a uniform population of oligodendrocyte-like cells expressing synaptophysin
    • Difference
      • Extraventricular neurocytoma: Do not express R132H-mutant IDH1
  • Unlike in central neurocytoma, ganglion cell differentiation is common in extraventricular neurocytoma.