Atypical Meningioma in the Medulla Oblongata Parenchyma

Background: Glioma is the most common tumor occurring in the brainstem. A primary intraparenchymal meningioma located in the brainstem without dura attachment is rare. Meanwhile, atypical meningiomas that occur in the medulla oblongata parenchyma, and without dura coverage, are extremely rare. In this study, we report the rst case of atypical meningioma in the medulla oblongata parenchyma and review the existing literature. Case presentation: A 38-year-old female was admitted at our hospital with a 2-week history of progressive neck and occipital pain. Magnetic resonance imaging revealed a presence of a 1.5x0.9cm mass lesion, located in the left side of the medulla oblongata, which was hypointense on T1-weighted and hyperintense on T2-weighted images, and with inhomogeneous enhancement following gadolinium-diethylenet-riamine pentaacetic acid (Gd-DTPA) administration. The initial preoperative diagnosis was glioma or angioblastoma. The patient underwent a total surgical resection of the left medulla oblongata tumor and the histopathological examination indicated that the lesion was an atypical meningioma. The patient returned to normal life after surgery. Conclusions: Although glioma is the most common tumor occurring in the brainstem parenchyma, the possibility of meningioma cannot be ruled out in this area. this the case of in the oblongata parenchyma and review the existing cell atypia, the high Ki-67 index, and pathological mitosis, the nal diagnosis indicated an atypical meningioma in the medulla oblongata parenchyma. Progesterone brillary


Introduction
Glioma is the most common tumor occurring in the brainstem [1]. However, primary meningiomas that occur subcortically in the brainstem, and without dura coverage, are rare. Meanwhile, atypical meningiomas that occur in the medulla oblongata parenchyma, and without dura coverage, are extremely rare. Our review of the literature revealed fteen well-described cases of complete intraparenchymal meningioma. These mostly affected the cerebral hemispheres of patients aged between 14-month and 66-year-old [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Only one case occurred in the medulla oblongata parenchyma, and was identi ed as meningothelial meningioma in 1985. In this study, we report the rst case of atypical meningioma in the medulla oblongata parenchyma and review the existing literature.

Case Presentation
Clinical history A 38-year-old female presented with a 2-week history of progressive neck and occipital pain. In the pre-admission week, the patient experienced increased pain, vomiting, dizziness and discomfort, coughing after swallowing and drinking water, and voice hoarseness. In addition to the later symptoms, the physical examination revealed that the patient was conscious and able to reasonably answer questions. The pupil was 3.0 mm on both sides, re ecting light sensitivity.
There were no central face paralysis, tongue paralysis and facial numbness. The neck stiffness suggested weak positivity, and the left limb muscle strength was grade 4 with normal muscle tension. The left side instead of right side of the Babinski sign was positive. Magnetic resonance (MR) imaging revealed the existence of a 1.5 × 0.9 cm mass lesion, located in the left side of the medulla oblongata, that was hypointense on T1-weighted and hyperintense on T2weighted images (Fig. 1A-B). The mass also showed an inhomogeneous enhancement following gadolinium-diethylenet-riamine pentaacetic acid (Gd-DTPA) administration ( Fig. 1C-E). The initial preoperative diagnosis indicated glioma and angioblastoma.
Under general anesthesia, the patient underwent a total surgical resection of the left medulla oblongata tumor using the far-left lateral approach. The tumor had a rotting sh meat appearance and was completely buried in the brain parenchyma with no dura mater around the tumor. The tumor was completely removed, and the operative course was uneventful.
The most common tumor ,without dura in the brainstem parenchyma, was glioma, but immunohistochemical ndings showed that the tumor cells GFAP and Oligo-2 were negative in this case. On the other hand, neurogenic tumors should also be considered from the perspective of imaging, and angioblastoma should not be excluded. So we tested S-100, NSE, NeuN, CD34, CD31. The results were also negative. In addition, we considered the possibility of neuroendocrine tumor and metastatic carcinoma (transparence renal cell carcinoma, grade ), while CD56, CK and PAX-8 were all negative. The immunohistochemistry pro le showed positivity for Vimentin, EMA and PR. Eventually we favored the diagnosis of meningioma based on the morphological and immunohistochemical ndings.
There was no evidence of tumor recurrence on postoperative MR imaging at the patient's 3-month follow-up visit ( Fig. 3A-E). The patient's physical condition signi cantly improved after ten months follow-up period. She can independently eat, swallow, and normally communicate with others, without hoarseness.

Discussion
After literature review [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], we found fteen well-described cases of complete intraparenchymal meningioma [ Table 1]. The male-to-female ratio was 11:4 and their age ranged from 14-month to 66-year-old, and the median age was 15-year-old. It is more frequently encountered in children and adolescent, with most of lesions affecting the cerebral hemispheres. We found only three primary meningioma in the parenchyma of the posterior fossa and without dural attachment. There was only one case occurred in the medulla oblongata in all of the English-language literatures, which was a meningothelial meningioma in 1985 and our case is the rst atypical meningioma in the medulla oblongata parenchyma. The patient is a 38-year-old female, who is elder than most of the patients, but younger than common sites meningioma patients.
Meningiomas that are usually attached to the dura, are thought to originate from the (meningothelial) arachnoid cells or arachnoid cap cells [2,11].
Nevertheless, the pathogenesis of primary intraparenchymal meningiomas is unclear. It was proposed that some arachnoid cap cells were located in the arachnoid or cerebral pia mater and far from the dura mater [2]. However, the cause of meningiomas in the intraparenchymal posterior fossa is unknown. This may be due to arachnoid cells of the piamater, which enter the brain along with perforating blood vessels, or due to an ectopy of the arachnoid cells that are localized in the white matter, or due to arachnoid cells that rest during the brain development migratory progress [5,9]. As one gets older, arachnoid cells proliferate and form tumors.
In general, gliomas are most common tumor in the brainstem [1]. But there are no typical radiological features of gliomas in this case. During the surgery, the tumor was observed in the medulla oblongata parenchyma, without dura mater around the tumor. Thus, it was di cult to distinguish meningioma from glioma at the preoperative and intraoperative stage.
The postoperative immunohistochemical staining showed negativity for GFAP, Oligo-2, S-100, NSE, CD34, CD31 and PAX8. Gliomas, neurogenic tumors, angiogenic tumors, and high-grade clear cell carcinoma of kidney origin were excluded. Positivity for Vimentin, EMA and PR proteins con rmed the meningioma of the lesions. According to the obvious cell atypia, the high Ki-67 index, and pathological mitosis, the nal diagnosis indicated an atypical meningioma in the medulla oblongata parenchyma.
Most meningiomas can be completely excised by surgery [22]. Some patients received postoperative radiotherapy due to the atypical characteristic of the meningioma and residual tumor growth [2,5]. Whether atypical meningiomas patients need postoperative radiation therapy, remains controversial. Some studies showed that there was no signi cant bene t for progression-free survival or overall survival after adjuvant radiotherapy for atypical meningiomas [23][24][25]. Compared with benign meningioma, atypical meningioma is a tumor with a relatively poor prognosis and with a recurrence rate of approximatively 29%-52% [22].The main recurrence factors that affect are related to the extent of the surgical resection, the tumor site and invasion extent, the vital adjacent structure of the tumor and the surgeon skills [22,25]. In this case, the tumor localized in the medulla oblongata parenchyma of the brainstem. The tumor was completely removed. Postoperatively, the patient refused radiotherapy.

Conclusions
Glioma is the most common tumor occurring in the brainstem [1]. In this case, a 38-year-old female patient was diagnosed with atypical meningiomas that localized in the medulla oblongata parenchyma of the brainstem. The lesion preoperative diagnosis was di cult due to the atypical imaging features. This study is the rst to report atypical meningiomas in the medulla oblongata parenchyma, which will help clinicians and imaging doctors to better understand this disease and pay more attention to the differential diagnosis of tumors in the brainstem parenchyma. The possibility of meningioma cannot be ruled out in this area. A complete resection is important for favorable prognosis, but long-term follow-up is necessary.

Funding
There is no any nancial support for this work.

Availability of data and materials
All data generated or analyzed during this study are included in this published article.
Ethics approval and consent to participate Not applicable. Table 1 Literature summary of well-described cases of complete intraparenchymal meningioma.