Central Neurocytoma

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Article initiated by:

Pamela Davila-Siliezar, MD

All contributors:

Aaron Chen, Abigail Louis, MBE, Andrew Go Lee, MD, Mohammad Pakravan, Nagham Al-Zubidi, MD, Pamela Davila-Siliezar, MD, Nagham Al-Zubidi, MD, Pamela Davila-Siliezar, MD

Assigned editor:

Osama Al Deyabat, MBBS

Review:

Assigned status Update Pending

 by Osama Al Deyabat, MBBS on September 15, 2022.

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Disease Entity

Central Neurocytoma (CN) is a benign primary neuronal tumor of the central nervous system (CNS) most often found in the lateral ventricles. CN comprises less than 1% of brain tumors and predominantly affects young adults. According to World Health Organization (WHO) classification, CN is a grade II brain tumor. The origin of central neurocytoma is unknown, but it is speculated to arise from neuronal cells of the septum pellucidum and the subependymal cells of the lateral ventricles.

Epidemiology

CN was first reported in 1982 and remains a rare diagnosis. Much of the information about CN comes from small series and isolated case reports. There have been more reported cases of CN in Asian populations than in Caucasian populations, with greater numbers reported in Korea, India, and Japan. CN predominantly affects adults in their second or third decade of life and appears to equally affect both males and females.

General Pathology

Macroscopically, CNs appear similar in color to grey matter with areas of hemorrhage and may often be calcified. On histology, central neurocytomas typically demonstrate moderately dense areas of small, uniform, round cells. Additional features include fibrillary areas closely resembling neutrophils. CN is difficult to distinguish on light microscopy as the histopathology may appear in a honeycomb pattern with scant cytoplasm and stippled chromatin like oligodendroglioma and can also demonstrate perivascular rosettes or straight lines similar to those present in ependymoma. Immunohistochemical markers are therefore helpful to diagnose CN.

Clinical Features

Patients with CNs most often present with signs of increased intracranial pressure. CN may obstruct the intraventricular foramen leading to symptoms including headache, nausea, vomiting, seizures, and memory or visual disturbance. One case series involving 32 patients reported that 37% of patients with CN presented with a visual complaint. Papilledema is a common finding with obstructive hydrocephalus and is seen in up to 43% of patients. Some patients present with intraventricular hemorrhage.

Ophthalmic Complications

The most common ophthalmic presentation of CN is progressive vision impairment accompanied by headache. Patients may present with blurred vision and visual changes that typically lasts for less than 6 months. Some visual changes include decreased visual acuity and diplopia. These presentations are typically attributed to increased intracranial pressure and obstructive hydrocephalus. In patients presenting with papilledema, increased intraocular pressure or optic nerve head pressure leads to transient optic nerve ischemia which may cause sudden vision loss. Increased intracranial pressure results in blocked axoplasmic flow, which further exacerbates axonal swelling. As a result, an increase in intraneural tissue pressure impinges on the blood vessels in the pre-laminar region. Patients may also present with a visual field defect, a result of mass effect.

Diagnostic Imaging

On imaging, CN appears as a solitary mass most often attached to the septum pellucidum, expanding into the lateral ventricles, and less commonly expanding into the third ventricle. Computed tomography (CT) demonstrates an isodense or hyperdense mass with uniform contrast enhancement. CN appears with calcified changes on imaging in up to half of the reported cases. Magnetic resonance imaging (MRI) typically reveals flow voids on both T1 and T2 weighted images, indicating vascularity of the mass.

Clinical Diagnosis

The diagnosis of CN is made histologically on either stereotactic biopsy or surgical specimens. Due to histological similarities with other brain lesions, tumor immunoreactivity for various neuronal proteins aid in the diagnosis. The most reliable diagnostic marker is synaptophysin, a transmembrane glycoprotein found in presynaptic neuronal vesicles. Synaptophysin reactivity is assessed with western blotting or immunohistochemistry, but it is important to note that the lack of synaptophysin does not exclude the diagnosis of CN. Studies suggest that an immunohistochemical panel consisting of Epithelial Membrane Antigen (EMA), vimentin, and neuronal nuclear protein (NeuN) allows distinction between CN and other CNS neoplasms. Negativity for EMA and vimentin with positivity for NeuN favors the diagnosis of CN over ependymoma or oligodendroglioma.

Differential Diagnosis

The differential diagnosis includes oligodendrogliomas, ependymomas, dysembryoplastic neuroepithelial tumor (DNT), cerebellar medullocytomas, and cerebellar liponeurocytoma. CN is histologically similar to oligodendroglioma and ependymoma; it is distinguished based on immunoreactivity for synaptophysin and immunonegativity for GFAP.

General Treatment

Management of CN is guided by institutional case series. Gross total resection (GTR) surgery is the standard of care for the treatment of CNs with studies indicating that GTR has been achieved in 30-50% of cases and corresponds to a 99% 5-year survival rate. Patients receiving subtotal resection (STR) have an increased risk for recurrence and are treated with adjuvant radiotherapy or radiosurgery. Studies have been inconclusive as to whether adjuvant fractionated radiotherapy or adjuvant stereotactic radiosurgery is better for local tumor control, but both have proved superior when GTR cannot be achieved.

Medical Therapy

Chemotherapy has not been widely used or studied for CN and is typically reserved for inoperable cases or those not responsive to radiotherapy. There have been no studies directly comparing the efficacy of chemotherapy against radiotherapy, but various chemotherapeutic agents have been tried. Combination regimes of procarbazine, lomustine, and vincristine as well as topotecan, carboplatin, and iposphamide are currently being studied.

Follow Up

The National Comprehensive Cancer Network (NCCN) recommends serial neuroimaging of WHO Grade II tumors.

Prognosis

CNs are typically benign tumors amenable to surgical resection with low rates of local recurrence. The five-year survival for CN after GTR has been as high as 99% in some studies with the five-year survival for CN only achieving STR being 86%. The most accurate tool available to predict tumor relapse and grade are the MIB-1 Labeling Index (MIB-1 LI). MIB-1 LI can be used for estimating survival and recurrence of CN with a MIB-1 LI > 2% having a significantly greater rate of recurrence and a decreased 10-year survival rate.