Tanycytic ependymoma is a histologically distinct rare subtype of ependymoma and is recognized as a grade II tumor in the latest World Health Organization classification in 2016 [1]. This tumor is usually found in the cervical and thoracic spine as an intramedullary mass but can also rarely present as an extramedullary mass in the lower spine [2]. Diagnosis in this location is difficult because the pathologic features resemble the findings of schwannoma and pilocytic astrocytoma. We present a case of tanycytic ependymoma in the lumbar spine and a brief literature review.

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A 44-year-old woman with complaints of a 4-year history of progressively worsening low back pain and sensory loss in her lower extremities visited our neurosurgery clinic. Four years prior, she had visited another hospital during which magnetic resonance imaging (MRI) revealed a 6-mm-sized intradural extramedullary mass in her lumbar spinal cord at level 2-3 (L2-3). The well-demarcated solid mass showed high signal intensity on T1-weighted imaging and low-to-intermediate signal intensity on T2-weighted imaging (Fig. 1). Surgery was recommended, but the patient refused. She had been intermittently treated with conservative therapy. However, recently, the pain in her low back, right buttock, and posterior aspect of her calf had aggravated. No muscle weakness or movement impairment was observed. Follow-up MRI showed that the mass had increased to 10 mm at L2-3. Her past medical history was unremarkable. The results of laboratory tests, including complete blood counts and liver and renal function tests, were within normal ranges. Under the preoperative diagnosis of schwannoma, the patient underwent L2 hemilaminectomy. The opening of the dura revealed a well-demarcated tumor mass at the L2-3 spinal cord, which was not attached to the nerve root (Fig. 2). The gross total excision of the mass was performed.

Histopathologic analysis of the tumor mass revealed a non-encapsulated cellular neoplasm comprising short, vaguely intertwining fascicles of spindle cells. The tumor cells had oval or elongated nuclei with rich fibrillary processes resembling pilocytic astrocytoma. The nuclei displayed speckled chromatin and mitotic activity was inconspicuous. Hyalinized blood vessels and occasional perivascular pseudorosettes of elongated tumor cells were also observed (Fig. 3). However, true ependymal rosettes were absent. These histopathologic features resulted in a differential diagnosis including schwannoma, pilocytic astrocytoma, or other spindle cell neoplasm of the spinal cord. Immunohistochemical analyses, including those for glial fibrillary acidic protein (GFAP), vimentin, epithelial membrane antigen (EMA), S100 protein, CD34, and calretinin, showed tumor cells diffusely positive for GFAP and vimentin. S100 protein was focally positive, and EMA showed positive perinuclear dot-like or ring-like patterns consistent with ependymal differentiation (Fig. 4). The tumor cells were negative for CD34 and calretinin. Thus, a definitive diagnosis of tanycytic ependymoma was established. The postoperative results were uneventful, and the patient’s symptoms improved.

Ependymomas of the spinal cord usually arise within the cervicothoracic segment and are the most common intramedullary neoplasms of adulthood. The typical histopathologic features include a dense meshwork of fibrillary cytoplasmic processes forming perivascular pseudorosettes. Tanycytic ependymoma exhibits distinctive histologic features and was initially described by Friede and Pollak [3] in 1978. The term “tanycytic” refers to the spindle elongated cell morphology and the origin of the tumor cells from tanycytes, which are special and unique ependymal cells. Tanycytes are most commonly located in the wall of the third ventricle, in the circumventricular organs, and in the spinal cord [4]. In the spinal cord, they surround the spinal canal and radiate toward the grey matter. They are considered to participate in the communication between the cerebrospinal fluid, brain parenchyma, and vasculature [5].

Tanycytic ependymomas are commonly found in the cervical and thoracic spinal cord [2,6]. Tumors arising in the lumbar or thoracolumbar regions are very rare [2,4,7-9]. Extramedullary tanycytic ependymomas in the filum terminale are rarely reported [7-9]. According to the 40 cases of spinal cord tanycytic ependymoma reported by Tao et al. [2], only one and four cases were lumbar lesion and in extramedullary locations, respectively. Extramedullary tumors were found in the lower thoracic or lumbar spine. Tanycytic ependymoma accounted for approximately 1% of spinal cord tumors (40 of an estimated 4,000) and one patient had tumor recurrence after surgery. Thus, patients are usually expected to show long-term survival with a low rate of recurrence. Rare cases of tanycytic ependymoma associated with multiple endocrine neoplasia type 1 or neurofibromatosis type 2 have been also reported [7,10,11]. We found only one published case of tanycytic ependymoma in Korea in a Medline search of the English literature [10]. In that case, the patient had neurofibromatosis type 2 and was diagnosed with tanycytic ependymoma of the cervical spine.

The differential diagnosis on radiologic imaging features included schwannoma, neurofibroma, or myxopapillary ependymoma. In this case, the preoperative diagnosis was schwannoma. However, schwannoma may demonstrate more heterogeneous T2 signal hyperintensity. Most of the MRI features in previously reported cases of tanycytic ependymoma were T1-isointense and T2-hyperintense; however, the findings can be variable and non-specific. Therefore, the radiologic diagnosis of tanycytic ependymoma remains challenging. While tanycytic ependymoma is typically solid, cystic components were reported in half of the cases [12].

The histologic features show fascicles of spindle fibrillary tumor cells with low to moderate cellularity that can be misinterpreted as schwannoma, pilocytic astrocytoma, meningioma, or neurofibroma [2,6,12,13]. Myxopapillary ependymoma can be differentiated from tanycytic ependymoma because there are no pathological findings of a papillary arrangement of the tumor cells or deposition of basophilic mucinous materials. Immunohistochemical staining shows strong positivity for GFAP and focal reactivity for S100 protein in tanycytic ependymoma. The perinuclear dot-like or ring-like positive patterns of EMA are a peculiar feature in ependymoma. In contrast, schwannoma is negative for GFAP and EMA and uniformly positive for S100 protein. Moreover, schwannoma tends to be more cellular and has typical Antoni A and B patterns. Pilocytic astrocytoma can resemble tanycytic ependymoma. A pilocytic astrocytoma is strongly positive for GFAP but negative for vimentin. The findings of Rosenthal fibers and eosinophilic granular bodies are helpful in the diagnosis of pilocytic astrocytoma.

A case series of ependymoma reported that the Ki-67 labeling index appeared to be an important prognostic factor [14]. While Ki-67 labeling index values of less than 4.0 have been associated with long survival times, a predictive threshold has not been established [15]. In our case, the Ki-67 labeling index was estimated to be less than 2%. Radiotherapy can be considered for cases with incomplete resection and aggressive treatment such as chemotherapy is usually not indicated. There has been no evidence of tumor recurrence during the 1-year follow-up period after gross total resection (Fig. 1C).

The present case is a rare intradural extramedullary tanycytic ependymoma that developed in the L2-3 spine with slow tumor growth over 4 years. The histopathologic features were unique but accurate diagnosis was challenging and difficult due to unusual location and rarity. The precise diagnosis of tanycytic ependymoma is important because local recurrence is possible.