Extra-axial ependymoma of the cerebral convexity: A very rare intracranial adult tumor

Abstract

Background

Ependymomas are rare adult tumors that originate from the ventricular system or the ependymal surface of the central canal. Extra-axial supratentorial ependymomas are extremely rare, and only five cases have been reported to date in the English literature.

Case presentation

A 46-year-old previously healthy male presented with a gradual painless loss of vision in the right eye. Cerebral MRI showed a right parietal-occipital lesion resembling an atypical meningioma. Surgical resection was performed, and immunohistochemical staining results concluded that it was a very uncommon location of a grade 3 ependymoma. Favorable outcome was observed one year after completion of postoperative radiotherapy.

Conclusion

Clinical and imaging aspects are misleading in rare brain tumors, and immunohistochemistry is essential to re-address diagnosis.

Background

Less frequent than in the pediatric population, ependymoma accounts for only 1.8% of all adult brain tumors.¹ It has a relatively slow growth but a trend toward local invasion. It characteristically originates from the ependymal surface of the ventricular system or the spinal central canal.^2,3 Less than one-third are found in the supratentorial region, where they are almost always intra-axial, but extra-axial intracranial location of ependymoma is extremely rare.^4,5

Today there is still no consensus on the mechanism of this extra-axial neoplasm development.⁶ Several hypotheses have been proposed regarding its origin, such as heterotopic ependymal cell residue during fetal development that subsequently increases in size.^7–9 Other authors suggest that the extra-axial tumor growth could arise from subcortical ependymal residue, which undergoes necrosis and calcification leaving an extra-axial ependymoma.¹⁰

We present in this article a case of extra-axial supratentorial ependymoma that was radiographically diagnosed as an atypical meningioma.

Case presentation

A 46-year-old previously healthy white-skinned male presented with a gradual painless loss of vision in the right eye lasting for one month. The initial workup found a right papilledema, without any other sign of intracranial hypertension or neurological deficit. Cerebral magnetic resonance imaging (MRI) showed a 65 mm right parietal-occipital extra-axial process of atypical appearance. The lesion had heterogeneous isosignal to hypersignal on T2-weighted images, with vascular contrast enhancement, associated with peritumoral brain edema and midline shift (Figure 1). Atypical meningioma or hemangiopericytoma was suspected.

Figure 1.

Preoperative T2-weighted axial (a) and T1-weighted parasagittal (b) magnetic resonance images showing the parietal occipital tumor with perilesional edema and mass effect on the ventricular system.

Subtotal neurosurgical resection was performed through a right parietal-occipital parasagittal craniotomy. Pathology (on hematoxylin and eosin staining) found a malignant process with classical aspect of pseudo-rosettes. Immunohistochemical study was performed in two cytopathology labs (Ibn Sina University Hospital lab in Rabat, and Ibn Rochd University Hospital lab in Casablanca). They both showed strong positive immunoreactivity of tumor cells for the glial fibrillary acid protein (GFAP) and the S 100 protein, focal positive staining for epithelial membrane antigen (EMA), AE1/AE3, and negative staining for Neurofilament (NF), CD34, CD31, Vimentine, human melanoma black (HMB) 45, Melan A, Reticulin protein (RP), actin and desmin (Figure 2). These morphological and immunohistochemical features confirmed the diagnosis of a World Health Organization (WHO) grade III extra-axial ependymoma of the cerebral convexity.

Figure 2.

(a) Numerous perivascular “pseudo-rosettes” and severe nuclear atypia on hematoxylin and eosin staining (×20). (b) Immunohistochemistry study showing positive epithelial membrane antigen (EMA) labeling (×10), and (c) strong PS100 immunoreactivity (×20).

Postoperative MRI, performed six weeks later, found a residual lesion of 20 mm in diameter, with perilesional edema, and without mass effect (Figure 3(a) and (b)). Eye examination at the same date found bilateral papilledema and right peripapillary hemorrhage.

Figure 3.

Postoperative T2-weighted axial (a) and T1-weighted parasagittal (b) magnetic resonance images showing a 20 mm residual lesion with perilesional edema, without mass effect. T2 fluid-attenuated inversion recovery (FLAIR)-weighted axial (c) and T1-weighted parasagittal (D) magnetic resonance imaging showing the residual tumor and reactive gliosis six months after completion of radiotherapy.

The patient received adjuvant three-dimensional (3D) conformal radiotherapy. Fifty-four Grays (Gy) were delivered in 30 fractions (1.8 Gy/fraction) to the tumor bed and edema zone, followed by three-fractions boost to the residual macroscopic lesion, thus total radiation dose was 59.4 Gy in 33 fractions. Six-megavolt X-rays were used in a tri-field technique including a 90-degree couch rotation to comply with the surrounding healthy organ dose limitations.

One year after the end of radiotherapy, the patient’s health condition was good, without any neurological deficit, and he gradually recovered vision. MRI showed no further significant regression of the residual tumor, with a surrounding reactive gliosis (Figure 3(c) and (d)).

Discussion

Ependymomas are common neoplasms of the primary central nervous system in pediatric patients, but are rare in adults.⁵ Forty percent of intracranial ependymomas are supratentorial.¹¹ They are intra-axial and usually originate from ependymal cells in the cerebral ventricular surface.¹²

Intracranial extra-axial ependymomas (IEAEs) are extremely rare. To date, only 14 adult cases and one pediatric case of IEAEs have been reported in the English literature: Five of them were adult patients with supratentorial location in the cerebral convexity.^4,9,13–15 Our case is the sixth one. Clinical characteristics and outcomes of these six cases are summarized in Table 1. Other reported IEAEs were infratentorial, localized in the cerebellar pontine angle (n = 6), the petroclival region (n = 2), and the ambient cistern (n = 1).¹⁶

Table 1.

Summary of adult supratentorial extra-axial ependymoma case reports.

First author, yearreference	Sex/age (years)	Clinical manifestation	Tumor location	MRI (T1-WI/T2-WI/ enhancement)	Adjuvant therapy	Follow-up
Hanchey, 197613	M/29	Headache	Interhemispheric	NA	Radiotherapy, chemotherapy	NA
Winer, 198914	M/81	Visual fields failure, diplopia	Pituitary fossa	NA	NA	NA
Donich, 19999	F/22	Headache, facial paralysis	Interhemispheric	NA/high/heterogeneous	Radiotherapy	18 months/tumor free
Youkilis, 20014	M/20	Seizure	Frontal convexity	Iso/iso/heterogeneous	No	One year/tumor free
Kasliwal, 200715	F/50	Headache, vomiting	Frontotemporal convexity	Iso/iso/NA	Radiotherapy	NA
Present case	M/46	Gradual vision loss	Parietooccipital region	Iso/hyper/heterogeneous	Radiotherapy	One year/stable residual tumor

M: male; F: female; MRI: magnetic resonance imaging; WI: weighted imaging.

Preoperative MRI diagnoses in previous reports were meningioma (n = 10) and schwannoma (n = 3).⁵

Ependymoma appears on MRI as an iso- to hypointense lesion on T1-weighted images, and hyperintense on T2-weighted images with vascular contrast enhancement. Supratentorial ependymomas usually have cystic components, calcification, necrosis and hemorrhage.⁶ In our patient, MRI led us to suspect a supratentorial atypical meningioma, appearing isointense and hyperintense respectively on T1- and T2-weighted images, with intense heterogeneous contrast enhancement, and without cystic spaces. The differential diagnosis before pathology included astrocytoma, oligodendroglioma, supratentorial primitive neuroectodermal tumor and ganglioglioma.

Extra-axial ependymomas are so uncommon and they often exhibit unusual structural features that they may be neglected during pathology study, hence the importance of the immunohistochemical evaluation. GFAP is an important marker that eliminates major differential diagnosis when positive (including meningioma). It highlights glial processes in perivascular rosettes, unlike occasional schwannomas that express GFAP but not perivascular rosettes. Oligodendroglioma have round nuclei in scant and clear cytoplasm resembling ependymoma, but they lack EMA and perivascular rosettes. Central neurocytomas have aspects like ependymomas but express neuronal markers and lack GFAP.⁴ The immunohistochemical panel used in our case confirmed that the parietal-occipital lesion was an ependymal tumor.

Maximal surgical resection is the initial treatment of ependymomas. Surgery alone may be sufficient in selected cases; however, the standard of care for most patients is postoperative irradiation to improve the five-year survival rate.^17–19 It seems that tumor response is related to radiation dose, and tumor control increased with doses >50 Gy. Thus doses of 54 to 59.4 Gy at 1.8 to 2 Gy per fraction are typically prescribed.²⁰ We followed this radiation schedule to provide our patient the best chance for prolonged disease-free survival, though we must note that the partial resection and the supratentorial location seem to represent significant predictors of recurrence.^21,22

This report was a pure IEAE with no radiographically or intraoperatively observed attachments to the tentorium or the midbrain, and likely originated from the heterotopic ependymal cell residue existing in the subarachnoid space throughout embryonic life.

Conclusion

Clinical and imaging aspects are usually misleading in rare brain tumors. A complete immunohistochemical study is essential to re-address diagnosis in order to offer the patient the most appropriate postoperative treatment.

Conflict of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.