At present, there are almost 201 cases of EVN reported, mostly from Asian populations (6). Among these cases, 28% were in the frontal lobe, 18% were in the temporal lobe, and only 13 cases of EVNs were located in the cerebellum (7). At symptom onset, the lesion was located in the area postrema, which mimicked neuromyelitis optica spectrum disorder (8). However, the AQP-4 antibody was negative in both the cerebral spinal fluid and serum, and the lesion was not responsive to steroid therapy. Two months after the steroid treatment, the lesion was enlarged with marked oedema. The diagnosis of EVN was established based on the pathological results. Additionally, glioma, lymphoma and oligodendroglioma were excluded by the immunohistochemistry results.
Although neurocytomas are tumours of WHO grade II, indicating that they have better outcomes, some EVNs may have more infiltrative and aggressive progression, leading to a poor prognosis and a high rate of recurrence. These EVNs were given the attribute name “atypical” and are characterized by a Ki-67 index > 2% or MIB-1 > 3% and/or with atypical histological features (9, 10). Neurocytomas with high FDG uptake also showed an increased proliferative index associated with atypical histological features (11). In the current case, the tumour showed benign features with Ki67 < 1% (12). However, the tumour grew rapidly after needle biopsy. Some reports have also indicated that although neurocytomas are considered indolent, they may have aggressive biologic behaviour, including postoperative rapid regrowth (13, 14). Increased glucose metabolism may also indicate high proliferative activity of the brain tumour (15).
Gross total resection (GTR) is the preferred strategy for EVNs, with the best outcome and a low recurrence rate (5, 9). However, because some EVNs are located close to eloquent areas, surgery often results in subtotal resection (STR). Radiotherapy is recommended for atypical EVNs, among which only 13% have the chance to undergo GTR (16). The effectiveness of GTR and STR combined with adjuvant radiotherapy was reported to be comparable (5, 9, 16). Among the cases with treatment details available, 48.4% underwent gross total resection (GTR), 15.6% underwent subtotal resection (STR), and 28.7% received adjuvant radiation. Only 4 patients received biopsy and radiation as the only therapy. The current case is the only report of a cerebellar EVN that showed a good response to only radiotherapy without STR. However, little is known about the prognosis of EVN under radiotherapy as the only therapy.