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LETTER TO EDITOR
Year : 2016  |  Volume : 64  |  Issue : 6  |  Page : 1355--1358

Densly calcified cystic extraventricular neurocytoma: Radiological–pathological correlation

Oktay Gurcan1, Atilla Kazanci1, Ahmet G Gurcay1, Serdar Balci2, Halil C Kucukyildiz1, Omer F Turkoglu1, Murad Bavbek1,  
1 Department of Neurosurgery, Ankara Ataturk Training and Research Hospital, Turkey
2 Department of Pathology, Ankara Ataturk Training and Research Hospital, Turkey

Correspondence Address:
Oktay Gurcan
Department of Neurosurgery, Ankara Ataturk Training and Research Hospital
Turkey




How to cite this article:
Gurcan O, Kazanci A, Gurcay AG, Balci S, Kucukyildiz HC, Turkoglu OF, Bavbek M. Densly calcified cystic extraventricular neurocytoma: Radiological–pathological correlation.Neurol India 2016;64:1355-1358


How to cite this URL:
Gurcan O, Kazanci A, Gurcay AG, Balci S, Kucukyildiz HC, Turkoglu OF, Bavbek M. Densly calcified cystic extraventricular neurocytoma: Radiological–pathological correlation. Neurol India [serial online] 2016 [cited 2019 Sep 20 ];64:1355-1358
Available from: http://www.neurologyindia.com/text.asp?2016/64/6/1355/193824


Full Text

Sir,

Central nervous system neoplasms that show a neuronal differentiation are extremely rare. Central neurocytomas (CNs), which are a form of neuronal tumors, arise predominantly within the ventricular system, especially in the lateral ventricles and in the third ventricle, near the foramen of Monro. CNs, which were initially reported by Hassoun et al., are rare tumors accounting for 0.1–0.4% of all central nervous system tumors.[1] CNs are more commonly observed in Asians. Uniformly small, round cells with neuronal differentiation are the characteristic histopathological finding of CNs.[2],[3],[4],[5],[6],[7] In 1989, Ferreol et al., first described histologically similar tumors, which occur outside the cerebral ventricular system and are called extraventricular neurocytomas (EVNs).[8] EVNs have been listed as a separate entity in the 2007 World Health Organization (WHO) Classification [International Classification of Diseases-O code (9506/1)]. EVNs are tremendously rare entities of the central nervous system. The current literature provides inadequate information regarding the EVNs. EVNs have been misdiagnosed as dysembryoplastic neuroepithelial tumors, ependymomas, and oligodendrogliomas. The clinical findings of EVNs depend upon the location of the tumor and include headache, cranial nerve palsies, and seizure. In the studies evaluating their computed tomography (CT) and magnetic resonance imaging (MRI) findings, EVNs have been shown to have multiple manifestations. EVNs are usually well-circumscribed, sometimes calcified masses with varying degrees of contrast-enhancement. Surgery is the gold standard treatment modality along with adjuvant radiation therapy.[1],5,[7],[8],[9]

We report an extremely rare case of excessively calcified EVN in a middle-aged female patient treated by subtotal surgical excision and adjuvant radiotherapy.

A 46-year-old female patient was admitted to our clinic with the complaint of headache for a month. There was no seizure or neurological and/or behavioral deterioration. The neurological examination revealed no pathological findings. An excessively calcified, extraventricular, right frontal mass was detected on the CT and MRI imaging [Figure 1]a,[Figure 1]b,[Figure 1]c,[Figure 1]d. The lesion was heterogeneous, having variably a solid consistency along with a cyst formation. With a probable radiological diagnosis of a meningioma, an oligodendroglioma, or an EVN, we performed subtotal resection of the mass via a right frontal transcortical approach [Figure 2]. In our case, the neoplasm was composed of small, uniform, neurocyte-like cells and larger ganglion-like cells with a clear cytoplasm. There were microcalcifications within the tumor. There was no mitotic activity, atypical mitosis, microvascular proliferation, pseudopalisading, or geographic necrosis. Neoplastic cells showed a negative glial fibrillary acidic protein (GFAP) staining and were negarive for p53, isocitrate dehydrogenase 1 (IDH-1) and epithelial membrane antigen (EMA). Synaptophysin highlighted the neuropil background. Nuclear NeuN positivity was seen in the neoplastic cells. The Ki-67 proliferation index was 1% [Figure 3]a,[Figure 3]b,[Figure 3]c,[Figure 3]d.{Figure 1}{Figure 2}{Figure 3}

Immunohistopathological studies combined with radiological findings revealed the diagnosis of an extraventricular neurocytoma. The patient was discharged uneventfully and underwent adjuvant radiotherapy. At a follow up of 15 months, the MRI findings revealed the residual right frontal mass that did not show any significant progression.

CNs generally originate from lateral ventricular walls, fornix, and septum pellucidum. Neurocytomas can be observed either in the periventricular areas or may even occur in locations distant from the ventricles. In the latter situations, they are known as EVNs. EVNs demonstrate a wide spectrum of morphology when compared with CNs. CNs are generally diagnosed in young adults. EVNs may also be diagnosed at an older age but there are some reports of childhood EVNs.[10],[11] The male:female ratio in CNs is similar; EVNs also do not have a gender predilection. CNs are categorized as WHO grade II tumors, and their prognosis is generally good; on the other hand, some of the EVNs have a more aggressive behavior.[7] EVNs have a 36% recurrence rate and a 4% mortality rate.[12] The mean age at presentation for EVNs is in the mid-twenties (range 2–75).[7]

In the literature, EVNs have been observed in different parts of the central nervous system, such as the occipital lobe, frontal lobe, temporal lobe, parietal lobe, the parasellar region, pons, cerebellum, spinal cord, and cauda equina.[2],[6],[7],[13] In this case, we report a right frontal lobe lesion, that was excessively calcified and was within the vicinity of the lateral ventricle. The mass was observed as a well-circumscribed lesion with an associated cystic component.

The clinical symptoms of EVNs are related to the location and size of the tumor. Raised intracranial pressure causes most of the complaints. Seizures (usually partial) and headache are the other common symptoms of EVNs.[2] In the literature, EVNs have been reported to present with uncommon features such as behavioral disorders in children, and gait disturbance.[2],[7] In the present report, the patient was admitted to our clinic with the complaint of headache without any history of seizure.

In the radiological examinations of these patients, EVNs can easily be misdiagnosed. Appearance of EVNs has a noteworthy overlap in most imaging series with other primary brain neoplasms; therefore, it is not always possible to make a precise diagnosis solely on the basis of the patient's radiology, and a pathological examination of the excised tumor tissue becomes mandatory. In the CT and MRI scans, most EVNs are observed as slightly enhancing, well-circumscribed lesions that may be solid or cystic. In the literature, EVNs revealed calcifications in approximately 10–13% of cases; however, excessive calcification is rare.[12] In the CT scans, EVNs can be observed as isodense or hyperdense lesions. In the T1-weighted images of MRI, EVNs are seen as isointense or hypointense mass lesions; in the T2-weighted images, these lesions exhibit a high intensity.[9] Our patient's imaging, however, revealed a right frontal, excessively calcified, mass lesion. The lesion was heterogeneous in character exhibiting both solid areas as well as cyst formation. It arose from the deep white matter of the frontal lobe. The lesion was slightly and irregularly enhancing. The radiological appearance of EVNs may lead to the misdiagnosis of an oligodendroglioma (with larger calcified areas and an infiltrative appearance), a high grade astrocytoma (with unusual forms of calcification), or even a meningioma, an ependymoma, or a ganglioglioma. In the MRI spectroscopy of EVNs, N-acetylaspartate is decreased and choline is elevated, with a detectable creatinine resonance; however, the spectroscopic picture is not specific for an EVN.[7],[14] In addition to the immunohistochemical examination, genetic investigations are needed for a precise diagnosis. Perry et al., reported 2 cases of EVNs with 1p19q deletion, which made their distinction from an oligodendroglioma difficult, especially due to the fact that they are extraventricular in location.[15]

In most of the tumors, the extent of surgical resection and the administration of adjuvant therapies predict the patient's outcome and the recurrence rate of tumors. Surgical excision is the initial preferred treatment modality for EVNs. The aim of the surgery is total excision; however, sometimes total excision cannot be achieved because of tumor extension into the eloquent areas. Adjuvant radiotherapy can be added to the treatment modality. In this case, we performed subtotal resection of the mass, and 2 months after discharge, the patient was administered adjuvant radiotherapy. Kane et al., stated that total resection of the mass and aggressive adjuvant radiotherapy may improve the prognosis and lower the recurrence rates.[12]

Histopathological examinations of CNs and EVNs revealed that both these types of tumors are composed of small, uniform, round cells. These tumors also have neuropil-like islands (which can be considered as a feature that permits neuronal differentiation), with a honeycomb appearance and perivascular fibriller zones. Immunohistopathology revealed that the tumor cells of EVNs have synoptophysin (neuronal marker) positivity, and to some degree, NeuN (a neuronal marker) positivity, but they were GFAP (a glial marker) and Olig2 (a glial marker) negative; they also show EMA (an ependymal marker) negativity. These findings reveal that in these lesions, the inactive mitototic cells are arrested in the neurocyte stage. They neither progress to the stage of neuronal differentiation nor regress to the neuroblastic stage.[3],[6] In this case, the histopathological examination revealed the presence of psamommatous calcification with a clear cytoplasm and round cells [Figure 3]. Rarely, these lesions may be classified as atypical EVNs that are associated with unusual features such as the presence of an increased proliferative index (Ki-67 index above 3%), vascular proliferation, necrosis, and frequent mitoses. These patients may often be older (age >50 years). In our case, we did not observe necrosis, microvascular proliferation, or an atypical mitosis. The Ki-67 proliferation index was 1–2%. We conclude that this entity was not an atypical EVN. Atypical EVNs have a definitely poorer outcome (36% recurrence and 4% mortality rate) compared to the typical EVNs.[4],[12] An extremely young age, the presence of recurrent or residual lesions and the presence of an atypical EVN are associated with a poorer outcome even after adjuvant radiotherapy has been administered to them.[7] Despite their rarity, EVNs should be considered in the differential diagnosis of intracranial mass lesions that are associated with calcification and cyst formation.

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Conflicts of interest

There are no conflicts of interest.

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