Ventricular system-unrelated cerebellar ependymoma: A case report

Abstract

BACKGROUND

An ependymoma is a glial tumor that usually occurs in or near the ventricle, close to the ependyma. It rarely occurs exclusively in the brain parenchyma without being associated with the ventricle.

CASE SUMMARY

Here, we report a rare case of a cerebellar ependymoma completely located in the brain parenchyma. A previously healthy 32-year-old female with a 1-month history of dizziness was admitted to our hospital. During hospitalization, magnetic resonance imaging of the brain revealed a space-occupying lesion measuring 57 mm × 41 mm × 51 mm in the right cerebellar hemisphere and inferior cerebellar vermis. The patient underwent surgical resection for the right cerebellar mass. Postoperative pathological examination revealed an ependymoma. At 1 year follow-up, the patient was doing well and showed no recurrence.

CONCLUSION

We conducted a literature review and summarized three theories regarding ependymomas located exclusively in the brain parenchyma, which are key to the diagnosis of intraparenchymal cerebellar ependymomas. Surgery and postoperative radiotherapy are the primary treatment options for ependymomas.

Key Words: Cerebellar ependymoma; Brain parenchyma; Mechanisms; Surgery; Case report

Core Tip: Ependymomas seldom occur exclusively in the brain parenchyma without being associated with the ventricles. Here, we report a rare case of cerebellar ependymoma completely located in the brain parenchyma. Moreover, we conducted a literature review to summarize three theories of brain parenchymal ependymoma and treatment options for this type of tumor to strengthen clinicians’ capacity to identify and treat cerebellar ependymoma located in the brain parenchyma.

INTRODUCTION

Ependymomas are a series of glial tumors that account for only 2%–6% of intracranial tumors[1,2]. Its pathological basis involves ependymal cells originating from the ventricles and ependymal cell nests in the extraventricular white matter. It usually occurs in the infratentorial area in the pediatric population and in the supratentorial area in adults[3-5]. Approximately 70% of ependymomas are infratentorial and usually originate from the fourth ventricle[4,6]. Ependymomas rarely occur in the brain parenchyma alone, and more commonly, ventricular lesions can locally extend into the adjacent parenchyma through the intima of the ependyma[4,7]. To date, only a few cases of infratentorial ependymoma located entirely within the cerebellar brain parenchyma have been reported. In the present case, dizziness was the first symptom, with no obvious evidence to support the ependymoma diagnosis. However, intraoperative frozen sections indicated an ependymoma. Owing to the rare location of cerebellar ependymomas, their characteristic imaging findings are limited, and their diagnosis is relatively difficult. However, early diagnosis, combined with surgery and radiotherapy, remains the main treatment for this tumor.

CASE PRESENTATION

Chief complaints

A 32-year-old Chinese female presented to our neurosurgery clinic with complaints of dizziness that had persisted for more than 1 month.

History of present illness

The patient’s physical examination more than 1 year prior revealed an intracranial space-occupying lesion with no discomfort; therefore, no treatment was administered. Moreover, more than 1 month prior, the patient had no obvious dizziness symptoms.

History of past illness

The patient had been previously healthy with no history of hypertension, heart disease, diabetes, infectious disease, surgery, trauma, blood transfusion, food allergies, or drug allergies.

Personal and family history

She denied any history of exposure to chemicals or radiation, alcohol consumption, or smoking and has no hereditary or similar diseases in her family.

Physical examination

On physical examination, the vital signs were as follows: Body temperature, 36.7 °C; blood pressure, 115/76 mmHg; heart rate, 65 beats per minute; respiratory rate, 16 breaths per minute. Neurological examination demonstrated no obvious positive signs.

Laboratory examinations

There were no obvious abnormalities in blood routine, electrolyte, biochemistry, urine routine and coagulation function.

Imaging examinations

Magnetic resonance imaging (MRI) of the brain revealed a space-occupying lesion measuring 57 mm × 41 mm × 51 mm in the right cerebellar hemisphere and inferior cerebellar vermis. T1-weighted images showed a low signal intensity, whereas T2-weighted images showed slightly heterogeneous hyperintensities (Figure 1). No obvious signs of cerebral edema were noted around the lesions. No abnormalities in the size or shape of the cerebral ventricles were observed. The differential radiological diagnoses were hemangioblastoma or glioma.

Figure 1 Preoperative and postoperative magnetic resonance imaging of patients. A-C: Preoperative magnetic resonance imaging (MRI) indicated a space-occupying lesion in the right cerebellum; D-F: Postoperative follow-up MRI showed that the lesion had been resected.

FINAL DIAGNOSIS

Ependymal fissures were detected by hematoxylin and eosin staining of tumor sections postoperatively. The cells surrounding the blood vessels were blurred, and the cytoplasm gathered around the blood vessels (Figure 2). Immunohistochemical study revealed tumor cells: Glial fibrillary acidic protein (+), S100(+), EMA (punctate positivity), and oligodendrocyte transcription factor 2 (-); according to histomorphology and immunohistochemistry staining, a diagnosis of ependymoma (World Health Organization grade Ⅱ) was made (Figure 3).

Figure 2 Hematoxylin eosin staining of postoperative tumor tissue sections. A-B: Ependymal fissure visible; C-D: The arrangement of cells around the blood vessels is blurred, and the cytoplasm gathers around the blood vessels.

Figure 3 Postoperative immunohistochemical analysis of tumor tissue. GFAP: Glial fibrillary acidic protein; Olig2: Oligodendrocyte transcription factor 2.

TREATMENT

The patient underwent surgical resection of the right cerebellar mass, and she recovered well and was discharged 2 weeks postoperatively. One month postoperatively, the patient underwent radiotherapy in the oncology department.

OUTCOME AND FOLLOW-UP

At 1 year follow-up, the patient was doing well and showed no recurrence (Figure 1).

DISCUSSION

Ependymomas typically occur in or near the ventricle, ependyma, occasionally, in the brain parenchyma. However, as in this case, posterior fossa ventricular system-unrelated ependymomas located exclusively in the cerebellar parenchyma are extremely rare[8,9].

To further explore the characteristics of cerebellar ependymomas, we reviewed recently published English literature. To the best of our knowledge, only 10 cases of cerebellar ependymomas have been reported. The mean age of the seven patients with cerebellar ependymoma with reported age and sex was 48.88 years (28–78 years). Among them, five (62.5%) were female. Maximal surgical resection is the primary treatment option for cerebellar ependymoma. Total resection was achieved in all six patients with reported treatment modalities, three of whom (including this patient) received adjuvant radiotherapy postoperatively. The patients were followed for an average of 11.1 months (8–24 months), and none of the patients died during the follow-up period (Table 1)[4,8,10-15].

Table 1 Review the literature on ependymomas of cerebellar parenchyma in the past ten years.

No.	Ref.	year	Age/sex	Location of the tumor	Diagnose	Therapy	Follow-up (months)
1	Losa et al[20]	2019	44/F	Cerebellomedulllary cistern and surrounding brain tissue	CCE (WHO II)	GTTR	NS
2	Zhang et al[21]	2017	62/F	Right cerebellum	TE + CCE (WHO II)	GTTR	9
3	Ebrahimi et al[8]	2020	36/F	Left cerebellopontine angle	PE (WHO II)	GTTR + AR	12
4	Lan et al[22]	2019	28/M	Left cerebellopontine angle	NS (WHO II)	GTTR + AR	24
5	Schild et al[23]	2017	78/F	Fourth ventricle and surrounding brain tissue	NS	GTTR	9
6	Gill et al[24]	2015	48/M	Right cerebellopontine angle	NS (WHO II)	GTTR	NS
7	O'Donnell et al[4]	2016	63/M	Right cerebellum	NS (WHO II)	NS	NS
8-10	Leng et al[25]	2016	NS	Cerebellar hemisphere	AE (NS)	NS	NS (mean, 8)

AE: Anaplastic ependymoma; AR: Adjuvant radiotherapy; CCE: Clear cell ependymoma; GTTR: Gross total tumor resection; TE: Tanycytic ependymoma; M: Male; F: Female; PE: Papillary ependy; NS: Not stated or not known; WHO: World Health Organization.

The mechanism of posterior fossa ependymoma remains unclear, and evidence for its molecular “driving” alterations and cellular origin is still lacking. In ependymomas occurring only in the posterior fossa without invading the spinal cord, a basically balanced chromosomal profile is shown. Only chromosome 1q gain, 6q loss, and 9q gain were observed. Notably, among the many prognostic correlates, the gain of chromosome 1q has been shown to be an independent prognostic factor that is positively associated with poor prognosis[16,17]. A study by Mack et al[18] showed that central pattern generator methylation was relatively increased in isolated posterior fossa ependymomas and that these CpG hypermethylated regions were concentrated at the target of the polycomb repressor complex 2 (PRC2). However, PRC2 inhibits stem cell differentiation and maintains pluripotency through trimethylation of H3K27, suggesting that this may be a driver of posterior fossa ependymoma[19,20]. In addition, three theories have been postulated regarding ependymomas located exclusively in the brain parenchyma: (1) The tumor originates from ectopic ependymal cells caused by migration disorders of the germinal matrix, which develop from ependymal cysts (subarachnoid space)[21,22]; (2) A microscopic cell bundle may exist between the ventricular system and the tumor area in the brain parenchyma, which facilitates tumor extension into the subarachnoid space, eventually extending from the subarachnoid space to the brain parenchyma[21,23]; and (3) The tumor originates around the ventricular wall and gradually grows, invading and penetrating the arachnoid membrane, and it extends out of the ventricle, but the tumor cells in the ventricle necrose or calcify[21-23].

Most patients experience dizziness and headaches. Owing to the nature of brain parenchymal tumors, the typical symptoms of elevated intracranial pressure occur relatively late. Cerebellar parenchyma ependymomas may develop into a large, asymptomatic mass until intracranial hypertension occurs. Depending on the tumor location, various symptoms of nerve compression may occur, suggesting that this type of tumor may not have the typical symptoms[23].

Ependymomas can spread into the cerebrospinal fluid (CSF) through the subarachnoid space. The key factor in the staging, prognosis, and treatment of tumors is the spread of tumor cells into the CSF[24]. MRI or CSF cytology can be used to determine the spread of a lesion into the CSF. In the absence of CSF invasion, maximum surgical resection with safe and localized radiation to the surgical area has been defined as the standard treatment for these tumors[17]. The most important factor affecting overall survival and progression-free survival is total tumor resection, and postoperative radiotherapy is associated with longer progression-free survival for tumors that are not completely resected. To date, no chemotherapeutic regimen has demonstrated a clear overall survival benefit in clinical trials of ependymoma[2,7,17,25]. In addition, ependymomas occurring outside the midline may have a worse prognosis than midline lesions, possibly due to the involvement of key structures such as cranial nerves[6]. In the present case, no abnormalities occurred in the size and morphology of the ventricle and cistern, the midline structure was not compressed, and the occupying effect was not obvious, potentially an important factor in the good prognosis of the patient.

CONCLUSION

Intraparenchymal cerebellar ependymomas are rare. The location of the lesion highlights the necessity and difficulty of the differential diagnosis of such tumors. Histopathology is key to diagnosing intraparenchymal cerebellar ependymomas. Surgery and postoperative radiotherapy are the primary treatment options for patients with ependymomas. Total tumor resection should be performed to the extent possible to reduce tumor recurrence.