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Extraventricular neurocytomas, previously known as cerebral neurocytomas, are rare WHO grade 2 primary CNS neoplasms usually arising in the cerebral hemispheres. They are, as the name implies, extraventricular versions of central neurocytomas.
These tumors are reported at essentially all ages without a sex predilection 5.
No specific clinical features are present, with presentation depending on the size and location of the tumor. Seizures, headaches and focal neurological defects are typical manifestations.
Extraventricular neurocytomas can occur anywhere in the CNS, including the spinal cord 5.
The tumors are of neuronal origin and are similar to the comparatively more common central neurocytomas which are intraventricular. They too demonstrate a variety of histological patterns but are generally less densely cellular 5.
synaptophysin: positive and essential to the diagnosis 5
GFAP: may be positive if an astrocytic component is present
IDH R132H: negative
Additionally FGFR (FGFR1-TACC1 fusion) is commonly identified and is an important diagnostic feature 6.
When a distinct ganglion cell population is present the term ganglioneurocytoma can be used 5.
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 edema.
In most instances, they are well-defined, often mixed cystic heterogeneously solid lesions that involve the deep white matter or the cortical grey matter of the cerebral hemispheres.
T1 C+: solid portions may show varying degrees of enhancement
Treatment and prognosis
As these are relatively indolent and well-demarcated tumors, complete surgical resection can effect a cure 5. CSF dissemination is reported but is rare 5.
rosette-forming glioneuronal tumors (usually midline and often posterior fossa)
diffuse leptomeningeal glioneuronal tumor (when leptomeningeal spread is prominent)