The tumor in this case exhibited components that showed perinuclear halos, which were suggestive of central neurocytoma. However, the tumor differed from central neurocytoma because it exhibited a small number of ganglion cells or ganglioid cells that were immunohistochemically positive for multiple neuronal markers. Additionally, the glial components observed in this tumor are uncommon in central neurocytomas. Although there is a possibility that these glial components might be trapped cell in the tumor, we regarded them as neoplastic cells because these components in the present case were too much as trapped cells. On the contrary, neuronal differentiation was not sufficient for central neurocytoma. Furthermore, the spongy pattern and abundant hyalinized vessels observed in this tumor were not consistent with the histological features of central neurocytoma. Hyalinized vessels are more frequently observed in papillary glioneuronal tumors (PGNT). However, the tumor of this case had less papillary structures and less ganglion cells than PGNTs, in which tumor cells are typically arranged around vessels, forming pseudopapillary structures [2
Spongy patterns, Rosenthal fibers, hyalinized vessels, and honeycomb-like components have often been associated with PA [3
]. However, PA is usually found in younger people. Additionally, the lateral ventricle is not a typical site for PA, which usually derives from the optic chiasm, hypothalamus, thalamus, basal ganglia, cerebral hemispheres, or cerebellar hemispheres [4
Along with PGNTs, rosette-forming glioneuronal tumors of the fourth ventricle (RGNT) were recently listed in the fourth edition of the World Health Organization Classification of Tumours of the Central Nervous System [4
]. It is notewothy that RGNTs have been reported to partly include similar features to PA, such as Rosenthal fibers, oligodendroglial components, and hyalinized vessels [6
]. The tumor of the present case may have been more similar to a RGNT rather than a PGNT because it exhibited PA-like features, a small amount of ganglion cells, and perivascular pseudorosettes that are unlikely in PGNTs [2
]. The average age of onset in RGNT is reported to be higher than that in PGNT [4
]. The present patient had another lesion in the fourth ventricle. However, we suggest that the lesion was a dissemination from the tumor of the lateral ventricle because of the tumor size and because of the patient's initial clinical symptoms. Thus, the fourth ventricle was not the primary site of the tumor in this case, which differs from RGNT cases.
The moderately high Ki-67 labeling index (LI) was another clue for the diagnosis of this tumor. The Ki-67 LI of ordinary glioneuronal tumors or central neurocytoma is less than 3%. The differential diagnoses were atypical central neurocytoma and PA with atypical features. Considering these histological variabilities of neuronal and glial component and the atypical histological findings, we finally diagnosed this case as an intraventricular tumor with atypical glioneuronal differentiation. According to Ishizawa et al. [7
], there was a case of PGNT with proliferation of minigemistocytic component, which showed a high Ki-67 LI. This findings were considered to coincide with our case. However, it was reported that high Ki-67 LI in a case of PGNT was not nessesary associated with poor prognosis [8
To the best of our knowledge, 11 cases of intracranial glioneuronal tumors (1 cases of PGNTs [9
], 9 of malignant glioneuronal tumors [10
] and 1 of RGNT [11
]) presenting dissemination in the clinical course have been reported. There are also 3 cases of spinal cord glioneuronal tumors with neuropil-like islands presenting meningeal dissemination [12
]. Javahery et al. [9
] reported on a case of a 13-year-old girl with PGNT. She had a primary cystic lesion in the left frontal lobe, which was totally removed. However, 43 months after the initial surgery, the tumor relapsed adjacent to the primary site with dissemination to the pulvinar nucleus and the medial left thalamus, which disappeared with radiation therapy and concomitant temozolomide therapy. Varlet et al. [10
] reported a summary of 9 cases with malignant glioneuronal tumors that exhibited dissemination with a median time to the event of 19 months after the initial treatment. Wang et al. [11
] reported a case of 16-year-old girl with RGNT initially presenting intraventricular dissemination. She underwent a neuroendoscopic biopsy and postoperative radiotherapy. Accordingly, there were only 2 cases of intracranial glioneuronal tumors presenting with intraventricular dissemination at such an early time including our case. Attention may need to be paid to the dissemination in the case with glioneuronal tumor including the case of spinal cord origin.
Varlet et al. [10
] reported that gross total resection of a malignant glioneuronal tumor was an independent and statistically significant prognostic factor. Additionally, they also stated that focal or craniospinal radiation therapy seemed neither to control local tumor growth nor to prevent dissemination of these tumors. Although our case underwent a partial resection of the tumor, the subsequent IMRT and adjuvant chemotherapy with temozolomide greatly reduced the residual tumors in the fourth ventricle and the anterior horn of the lateral ventricle. MRI with Gd demonstrated no recurrence of the residual small tumor 30 months after the surgery.
Following surgery, radiation therapy with concomitant administration of TMZ has recently become the standard therapy for malignant gliomas. As shown by the cases of Javahery et al. [9
] and the present case, this therapy may also be effective for glioneuronal tumors.