Ependymoma is a glial tumor that arises from the ependyma, a tissue of the central nervous system. Ependymomas generally present as centrally situated intramedullary tumors within the thoracic/cervico-thoracic cord7). Ependymal cells spring from primitive progenitor, the ependymoglia cell, also called “tanycyte”. On tracing ependymal and progenital development, transitional types of ependymomas exist. On the World Health Organization (WHO) classification, ependymomas are divided in three major groups: subependymoma (WHO grade I), myxopapillary ependymoma (WHO grade I), ependymoma (WHO grade II), and anaplastic ependymoma (WHO grade III). Conventional (WHO grade II) ependymomas, includes the tanycytic variant.

Tanycytic ependymoma (TE) is a WHO grade II tumor with histological characteristics distinct from the typical features of commonly encountered ependymomas4). TE is one of the transitional types of ependymoma2). The most common symptoms of TE is the gradual deterioration of motor functions and/or sensory disturbances, such as heaviness, numbness, and weakness of the low back and lower extremities including the waist (paraparesis) accompanied with gait disturbance and urinary incontinence. TE has specific molecular structure. The classic ependymal rosettes and perivascular pseudorosettes of ependymoma are replaced by more fibrillar, spindle cells of tanycyte. The cellular appearance and arrangement may mimic other tumors such as schwannoma and astrocytoma, which makes the diagnosis challenging and hence warrants further evaluation. Since the first case of Friede and Pollak2) was reported in 1978, only 34 cases have been reported by 2016. Herein, we present four cases (Table 1) of rare ependymoma, TE, which were initially thought to be schwannoma or astrocytoma.

TE is of low-to-moderate cellularity characterized by a flow of elongated cells with nuclear pleomorphism. Mitotic figures are usually absent. It has inconspicuous features that are not typical of ependymoma. The distinctive perivascular pseudorosette pattern of ependymoma cells is infrequently encountered3). Their nuclei are oval to spindle shaped with evident pleomorphism. The cell processes are not fluffy as with the cellular type of ependymoma8). Radiologically, ependymoma is almost always intramedullary. In our cases the tumor was an extramedullary lesion that also avidly enhanced on T1-WI with gadolinium contrast enhancement. Pilocytic astrocytomas are rarely enhanced11). TE cells may mimic other tumor cells with similar features under light microscopy often lending to a challenging diagnosis3,5,6,9). The spindle appearance of the cells, for instance, is similar to that of schwannoma cells. TE stains positive for GFAP and vimentin but rarely stains for S-100. This helps to differentiate it from schwannoma, which is S-100 positive and GFAP negative. Although pilocytic astrocytoma is GFAP positive, it almost never stains for vimentin, which helps to discriminate it from TE (Table 2)5), Pilocytic astrocytoma also presents Rosenthal fibers and eosinophilic granular bodies1,7). Recently, Tao et al.13) reported 40 cases of TE in 2017. Approximately 4000 spinal cord tumors were resected surgically, of which 40 were identified with TE. In terms of prognosis, at a median follow-up of 43 (range, 1-101) months, 1- and 5-year progression-free survival rates were 100.0% and 97.5%, respectively13). The current management is radical excision of spinal TE. It is unlikely to recur if the tumor is completely removed12). Repeat resection or radiation treatment will be recommended in the event of recurrence10). Adjuvant chemotherapy is not recommended14). Through this paper, we reported four cases of TE diagnosed in Korea. Until now, only one case was reported in Korea6). Our histologically confirmed four cases will contribute greatly to research on TE in Korea. We also hope these Korean cases will be used as valuable material for interracial and intercontinental study of TE.

Rare cases of spinal TE were presented. TEs are an uncommon fibrillary variant of ependymomas with typical pathological characteristics. A careful and detailed histological inspection with utilization of immunohistochemical stains and ultrastructural microscopy may be necessary to distinguish TE from other neoplasms such as schwannoma and pilocytic ependymoma. We believe that this paper could help in the accurate diagnosis and giving appropriate treatment to such population.