A 67‐year‐old man with a spinal extramedullary mass

Access at https://isn-slidearchive.org/?col=ISN&fol=Archive&file=BPA-2895627.svs. A 67-year-old man presented with low back pain, for which he underwent a magnetic resonance imaging (MRI) scan (Figure 1A). This revealed a spinal T12-L1 intradural extramedullary lesion measuring 20 × 15 × 13 mm, with contrast enhancement, in contact with the spinal nerve roots of the cauda equina, which were displaced to the left. The first radiological diagnostic hypothesis was schwannoma. In light of the clinico-radiological features and the absence of neurological symptoms at the time of examination, a 6 months follow-up was recommended. Subsequent MRI revealed an increase in the size of the lesion (25 × 20 × 16 mm), with significant compression of the cauda equina nerves (Figure 1B). At surgery, the mass appeared as an expansive, yellowish, friable intradural lesion originating from the nerve root and it was partially resected. Histological examination revealed a tumor primarily composed of spindle cells with round to oval nuclei and fibrillary processes arranged to form perivascular pseudorosettes (Figure 2A, Box 1). Hyalinized vessels were also noted. Additionally, focal tumor areas exhibited marked anaplasia and a mitotic index of up to 8 mitoses per 1.6 mm2 (Figure 2B). Necrosis and microvascular proliferation were present at all (Figure 2C). Tumor cells, diffusely positive for GFAP (Figure 2D), were negative for SOX10 (inset) and showed dot-like positivity for EMA (Figure 2E). H3 K27me3 expression was retained. Ki-67 labeling index in the most cellular areas was 25%. MYCN diffuse and strong nuclear staining was present in higher-grade areas (Figure 2F), suggesting amplification. MYCN amplification was confirmed by Real-time PCR using TaqMan Copy Number Assays (copy number: 53.6) (Figure 2G). Spinal ependymoma, MYCN-amplified. MYCN-amplified ependymoma is a rare and highly aggressive type of spinal ependymoma, first introduced in the 2021 World Health Organization (WHO) Classification.1 These tumors involve primarily thoracic and cervical segments. They can be intramedullary with an exophytic component or mostly extramedullary and frequently show leptomeningeal dissemination. Morphologically, they may show classic perivascular pseudorosettes or at times a papillary architecture. They are frequently high-grade with high cellularity and cytologic anaplasia, high mitotic rate, microvascular proliferation, and necrosis. They are genetically defined by the presence of MYCN amplification, and they form a distinct and unique methylation class subgroup, out of previously described ependymoma subgroups.2 In our case, tumour was entirely extramedullary, attached to a nerve root suggesting, radiologically and intra-operatively, a diagnosis of schwannoma. Although histologically the tumor had a spindle cell morphology, Verocay bodies, typical of schwannoma, were absent. The presence of perivascular pseudorosettes suggested at first sight the diagnosis of ependymoma, supported by the immunoreactivity for GFAP and EMA (dot-like staining pattern), along with SOX-10 absence. Myxoid changes typical of myxopapillary ependymoma, the most common ependymoma at the level of the cauda equina, were not observed in this case. Owing to MYCN amplification, our tumor was finally diagnosed as ependymoma MYCN-amplified with an infrequent lumbar location at initial presentation. Extramedullary ependymoma may occasionally arise in the spinal nerve roots from ependymal rests after neural tube closure. Spinal nerve root attachment is commonly identified during intraoperative surgical procedures, and when the connection to the nerve root is too hard to disrupt, nerve root resection is unavoidable.3 Due to these intraoperative findings, schwannoma and neurofibroma are the most common pathologies considered in the differential diagnosis, as was our case. In conclusion, albeit rare, ependymoma attached to nerve roots should be kept in mind when facing an extramedullary spinal tumour with spindle cell morphology and perivascular pseudorosettes. Also, the presence of high-grade features should prompt the analysis of MYCN amplification. MC drafted the manuscript; FC collected clinical data; RP performed and interpreted molecular analyses; VB reviewed and edited the draft. All the authors approved the final version of the manuscript. This study was supported by Ministero della Salute as Fondi Ricerca Corrente 2025 to Fondazione IRCCS Istituto Neurologico Carlo Besta, Milan, Italy. The authors declare no conflict of interest. All data related to this case were identified. The data that support the findings of this study are available from the corresponding author upon reasonable request.