Abstract: Background Extraventricular neurocytoma (EVN) is an unusual tumor and has been recently accepted as a new brain tumor entity by World Health Organization (WHO) classification. It has been reported in several locations outside the typical supratentorial ventricular system, including the cerebral hemispheres, cerebellum, pons, spinal cord, cauda equine and retina. Only a few cases have been described in the spinal cord in the literature. It is a diagnostic challenge for clinicians and histopathologists to differentiate EVN from other spinal tumors because of its similarities in histological and immunohistochemical findings, as well as its non-specific radiological manifestation. Herein we describe a case of unusual intramedullary EVN in spinal cord. The clinicopathology of this tumor and its differential diagnosis are discussed.  Methods The clinical manifestation of a patient with primary EVN occurring C6-T3 level of spinal cord was presented retrospectively. Gross totally resected mass was routinely paraffin-embedded and stained with hematoxylin and eosin. Dako EnVision immunohistochemical staining system was used to detect the tumor antigen expressions, including vimentin (Vim), cytokeratin (CK), epithelial membrane antigen (EMA), glial fibrillary acidic protein (GFAP), S-100 protein (S-100), synaptophysin (Syn), chromogranin (CgA), neuron-specific enolase (NSE), Neuronal nuclei (NeuN), oligodendrocytes transcription factor-2 (Oligo-2) and Ki-67.  Results A 47-year-old male patient presented with 1 year history of weakness in both upper limbs associated with an increasing neck back pain. There was no paraesthesia in limbs. MRI of the whole spine revealed a heterogeneous intramedullary mass resembling an ependymoma extending from the C6 to T3 level with heterogeneous enhancement after contrast administration. Laminectomy and midline opening of the dura were performed. The spinal lesion appeared to have no capsule and locate intramedullary. The lesion did not attach the dura mater and invade the surrounding tissues. The tumor was removed totally. Microscopic examination showed that a moderate cellular tumor was composed of uniform cells and arranged in sheets. The tumor cells had round nuclei, finely speckled chromatin and clear cytoplasm. Some cells had perinuclear haloes resembling oligodendroglioma. In some areas, the tumor cells with elongated cytoplasmic processes arranged radially around the blood vessels with myxoid degeneration, forming a structure of "perivascular pseudorosette", resembling the ependymoma. Mitotic activity and necrotic area were not observed. The tumor cells were strongly immunopositive for Syn, focally positive for NSE, S-100 and Oligo-2, but negative for Vim, CK, EMA, NeuN and GFAP. Ki-67 index was less than 1% in our case. Based on clinical presentation and histological findings, a final histological diagnosis of primary EVN in spinal cord was made according to the criteria of WHO classification. The patient has not received radiotherapy and attended follow-up for 6 months, without any neurological deficit or signs of recurrence.  Conclusion Spinal EVN is extremely rare and there are no more than 20 bona fide cases reported previously all over the world. It might originate from neuronal precursor cells surrounding the region of central canal in fetal life. The definite diagnosis of this tumor should be made under the microscopical examination because the preoperatively radiological appearance of the tumor does not differ from other tumors occurring in spinal cord. Although good prognosis obtained from gross total resection in most of reported patients with this tumor, adjuvant radiotherapy is recommend for those tumors with atypical histological features to avoid the tumor recurrence. Due to the rarity of its site, the tumor can easily be confused with other tumors of spinal cord with clear cells features and ependymoma-like structure. The strictly differential diagnosis should be made when the tumor is encountered in spinal cord.

Key words: Neurocytoma, Cerebral ventricles, Spinal cord, Immunohistochemistry, Pathology

摘要： 研究背景 脑室外神经细胞瘤是新近分类的肿瘤实体，可发生于中枢神经系统除脑室外的任何部位，但发生于脊髓者极为少见。由于缺乏特征性影像学表现，术前难以明确诊断；又因其组织形态学和免疫组织化学表型的相似性，易误诊为好发于脊髓的其他肿瘤。鉴于此，本文着重探讨原发于脊髓的脑室外神经细胞瘤的临床病理学特征，并通过对以往文献的复习，分析其诊断要点，以期提高临床对脑室外神经细胞瘤的鉴别诊断能力。方法与结果 男性患者，47 岁。因近1 年进行性双上肢无力和颈部疼痛入院。颈部MRI 显示脊髓C6 ~ T3 节段髓内占位性病变，T₁WI 呈等或低信号、T₂WI 呈高信号，增强后病灶呈不均匀强化。术中可见肿瘤位于脊髓内，无包膜，与周围组织分界清楚，血运丰富，与硬脊膜无粘连。肿瘤组织由弥漫片状或团簇状分布的肿瘤细胞构成，部分区域肿瘤细胞呈圆形，大小形态较一致，有核周空晕，呈少突胶质细胞瘤样特点；部分区域肿瘤细胞排列较致密，呈短梭形，无核周空晕，呈放射状排列或围绕在血管周围形成不典型“菊形团”结构，类似室管膜瘤样结构。肿瘤组织中未见无核神经纤维岛和神经节样细胞，以及核分裂象和出血坏死。免疫组织化学染色显示两种形态肿瘤细胞弥漫性强阳性表达突触素，灶性表达神经元特异性烯醇化酶、S-100 蛋白和少突胶质细胞转录因子-2，但不表达波形蛋白、细胞角蛋白、上皮膜原、神经元核抗原和胶质纤维酸性蛋白，Ki-67 抗原标记指数< 1%。病理诊断为脊髓脑室外神经细胞瘤。结论 脊髓脑室外神经细胞瘤临床罕见，可能起源于胚胎时期脊髓中央管周围的神经元前体细胞，须经组织学观察明确诊断。尽管大多数脑室外神经细胞瘤患者肿瘤全切除后预后良好，但出现不典型组织学表现者建议术后辅助放射治疗以减少复发。应注意与具有透明细胞特征、室管膜瘤样特征及其他具有相似组织学结构的脊髓肿瘤相鉴别。

关键词: 神经细胞瘤, 脑室, 脊髓, 免疫组织化学, 病理学