Central neurocytoma is a rare intraventricular WHO grade II tumour, typically affecting young adults, characterised by cells mimicking neurons, and demonstrating a heterogeneously enhancing lesion on MRI, commonly centred on the foramen of Monro.
Description
Central neurocytoma is a slow-growing, benign (WHO grade II) intraventricular brain tumour, more specifically found in the lateral ventricles and commonly centred on the foramen of Monro. This tumour arises from neuronal precursor cells and is characterised by a mixture of neuronal and glial elements, hence the name “neurocytoma”. It is not associated with any specific predisposing conditions and has no recognised hereditary patterns.
Pathogenesis
The exact pathogenesis is unknown. However, these tumours are believed to arise from multipotent precursors in the subependymal plate, which differentiates into a neuronal phenotype.
Subtypes
There are no recognised subtypes of central neurocytoma.
Epidemiology, Risk Factors & Associations
- Most commonly diagnosed in young adults, with a peak incidence in the third decade (70% of patients are aged 20-40 years).
- No recognised gender predilection.
- No known risk factors or associations.
Clinical Features
- Headaches and symptoms of increased intracranial pressure due to obstruction of the foramen of Monro are common.
- Visual disturbances may also be present, such as diplopia or blurred vision.
- Cognitive changes and symptoms relating to raised intracranial pressure may also occur.
Complications
- Although typically benign, there is a small risk of malignant transformation (<3%), usually into a high-grade neuroepithelial tumour.
- Potential for hydrocephalus due to obstruction of the ventricular system.
Pathological Features
Histopathology
- Macroscopic: These tumours are usually well-circumscribed, firm and lobulated.
- Microscopic: They are characterised by uniform round cells with clear cytoplasm, mimicking neurons (referred to as neurocytes). A dense fibrillary matrix is often present. Calcifications and perivascular pseudorosettes may be seen. Immunoreactivity stains show neuronal markers (synaptophysin). Electron microscopy shows neurosecretory granules. Similar histologically to oligodendroglioma
Serology
No specific serological markers.
Biochemistry
No specific biochemical markers.
Radiological Features
General Features
- Intraventricular lobulated mass attached to the septum pellucidum with cystic components (85% of cases) and calcifications (50% of cases).
- May be associated with obstructive hydrocephalus due to obstruction of foramen of Monro.
- It can be sometimes seen in the third ventricle.
- Extraventricular neurocytomas are exceedingly rare, reported in the hemispheres and suprasellar region. Extremely rare craniospinal dissemination
- Pitfalls: Lack of or mild enhancement does not preclude diagnosis
CT
- Non-contrast: Hyperattenuating compared to the surrounding brain parenchyma. Calcifications are seen in half of the cases.
- C+ Arterial: Shows heterogeneous enhancement.
MRI
- T1: Hypointense to isointense to gray matter.
- T2/FLAIR: Hyperintense cystic areas (bubbly or swiss cheese appearance). Prominent flow voids may be seen.
- DWI/ADC: Restricted diffusion may be seen in the solid components.
- GRE/SWI: Susceptibility artefact due to calcifications
- T1 Gad+: Shows heterogeneous enhancement.
- MRS: Increase Cho, decreased NAA
Grading and Staging
Central neurocytomas are classified as WHO grade II tumours. No specific staging system is used due to their benign nature and intraventricular location.
Diagnosis
Diagnosis is typically made by neuroimaging, particularly MRI, and confirmed by histopathological analysis of surgical specimens.
Differential Diagnosis
- Ependymoma – Usually arises from ventricular wall, often with a broad-based attachment. More frequent in childhood, typically the 4th ventricle. Heterogenously enhances, rarely intraventricular when supratendorial.
- Choroid plexus papilloma – Usually arises within the choroid plexus and shows avid enhancement. Mainly in children. In adults, usually located in the 4th ventricle.
- Subependymoma – Does not appear as a bubbly mass due to lack of intratumoral cysts. Less enhancement than neurocytoma, typically found in the 4th ventricle of older individuals rather than lateral ventricle.
- Subendeymal Giant Cell Astrocytoma – Seen in patients with tuberous sclerosis, demonstrates vivid enhancement. Associated cortical and subcortical hamartomas (tubers) may be seen.
- Meningioma – Usually a more solid mass seen in the trigone. Usually seen in older adults.
- Intraventricular metastasis – A history of primary malignancy is key.
Prognosis
Prognosis is generally favourable due to the benign nature of the tumour. Five-year survival rates are above 90%.
Management
Management typically involves complete surgical resection, which can be curative. Radiotherapy may be considered for residual or recurrent tumours.