A huge cerebral parenchymal meningioma in sylvian fissure: case report and literature review

Abstract

Background & Introduction

Meningiomas are tumors that originate from non-neuroepithelial progenitor cells, meningothelial cells and the arachnoid cap cells, thus they usually appear with attachment to the dura mater. But sylvian fissure meningiomas are a rare type of meningioma that has no dural attachment.

Case presentation

A rare case of sylvian fissure meningioma is presented. The patient is a 34-year-old male with headache, and preoperative images showed a massive lesion in his right frontotemporal lobe that had no contact with the dura mater. Postoperative histopathological examination confirmed the diagnosis of a clear cell meningioma, which is a WHO grade 2 atypical meningioma and a rare subtype of meningioma that only accounts for less than 1% of all meningiomas.

Conclusion

Preoperative diagnosis of sylvian meningiomas can be challenging, leading to inappropriate operation plan and postoperative treatment. Thus, we present this case and a brief review of past cases reported, hoping to improve our understanding of the origin of meningiomas and accuracy in diagnosis of similar lesions.

Key message

A rare case of massive sylvian fissure meningioma is presented, which is a clear cell meningioma and WHO grade 2 atypical type. Based on previous reports, which confirm our case as the largest lesion so far, we analyzed the origin of intraparenchymal meningiomas and difficulty in its differential diagnosis.

Background

Meningiomas are tumors that originate from non-neuroepithelial progenitor cells, meningothelial cells and the arachnoid cap cells [1, 2]. Meningiomas are usually characterized by dural attachment, and the “dural tail sign” has a sensitivity of 58% and a specificity of 94% in the diagnosis of meningiomas [3]. However, intraparenchymal meningiomas without dural attachment also exist and are often discovered in the pineal region, the intraventricular region and within the sylvian fissure [2]. Among these locations, meningiomas within the sylvian fissure are rarer and more atypical, and clear cell type sylvian meningioma is more rarely reported. Here we present a rare case of huge clear cell meningioma which was underneath the sylvian fissure without dural attachment in a 34-year-old male who received surgical resection and followed-up.

Case presentation

Clinical history and physical examination

A 34-year-old male was admitted to our hospital in July 2024, and his main symptoms included intermittent headache with nausea and discomfort for 4 months. Physical examination showed no dysfunction of movement and sensation. The patient’s cognition, emotion, memory, and intelligence were all normal. The patient had no symptoms of aphasia and his dominant hand was right hand. Furthermore, the patient had no previous medical history of illness.

Imaging findings

The patient underwent multi-dimensional contrast-enhanced MRI head scan (Fig. 1). The result showed a mainly solid lesion with some cysts within the right frontotemporal lobe, which was about 9.7 × 5.3 × 6.4 cm in size and not well demarcated from the surrounding brain parenchyma. The lesion showed mixed intensity on both T1- and T2-weighted images. Contrast-enhanced imaging revealed significant enhancement of the solid components. Computed tomography (CT) of brain revealed a high-density area which was close to calcification, but without apparent calcification. It was believed that the mass was located under the sylvian fissure within the brain cortex and impressing the midline structure to the left. However, no clear sight of the “dural tail sign” was observed and the lesion is separated with the dura mater, indicating the absence of dural attachment.

Fig. 1

T1 transverse MRI scan (A) and T2 transverse MRI scan (B) demonstrated a massive lesion (97 × 53 × 64 mm) in the sylvian fissure. Transverse (C), sagittal (D), and coronal (E) weight-enhanced T1 MRI scans showed mixed intensity on both T1- and T2-weighted images. Preoperative computed tomography brain scan (F) revealed a massive lesion with high density area only closed to calcification without specific calcification

Surgical procedure

The patient was positioned supine, and a right frontotemporal craniotomy was performed via a right pterional approach. We applied the trans-Sylvian approach in the surgery. The dura mater was found to be intact, with no evidence of tumor invasion or adherence to the underlying brain parenchyma. Upon opening the dura mater, the tumor was not immediately visible on the cortical surface. However, through the lateral sylvian fissure, the lesion was visible beneath the cerebral cortex. Intraoperatively, the tumor was found to be situated between the sylvian vein and the middle cerebral artery, with its deep surface likely extending into the arachnoid layer surrounding the MCA. The tumor exhibited a grayish-white, fish-flesh-like appearance, was firm in consistency, and demonstrated calcification. It had poorly defined margins and lacked a obvious vascular supply. The interface between the tumor and the adjacent cortex was indistinct, and the blood supply to the tumor was not abundant. Gross total resection of the tumor was performed, and somatosensory evoked potentials (SEP) and motor evoked potentials (MEP) electrical monitoring were used during the surgery. To minimize bleeding, the tumor was removed piecemeal by using the Cavitron Ultrasonic Surgical Aspirator (CUSA) after the separation of the boundaries. The patient experienced no postoperative neurological deficits, and follow-up MRI confirmed complete resection of the tumor (Fig. 2).

Fig. 2

Transverse (A), coronal (B) and sagittal (C) postoperative MRI revealed a complete resection of the tumor. The repeat MRI 6 months (B) after surgery revealed no recurrence of the tumor

Pathological results

Histopathological specimens revealed that the tumor consisted of polygon-shaped cells with a transparent cytoplasm rich in glycogen (Fig. 3). Immunohistochemistry (IHC) analysis showed that the cells of the tumor were positive for SSTR2, D2-40, epithelial membrane antigen (EMA) and progesterone receptor (PR) expression. Furthermore, the tumor cells were negative for STAT6, GFAP, Oligo-2, SOX10, SOX2, S-100, Desmin, P53 and without the deletion of ATRX. Besides, the nuclear-associated antigen (Ki-67) showed a positive result, with a labeling index of 15%. For the special stains the periodic acid-Schiff staining (PAS) was positive but negative for AB and PAS digestion. Furthermore, Trichrome staining revealed interstitial collagen fibers. No mutations at 228 and 250 sites of TERT gene promoter were detected. These findings suggested that the lesion was a clear cell meningioma (CCM) [4, 5]. In conclusion, the pathologic diagnosis is an atypical meningioma, classified as a World Health Organization (WHO) grade II tumor.

Fig. 3

Hematoxylin and eosin staining (A and B) of the tumor consisted of polygon-shaped cells with a transparent cytoplasm rich in glycogen, with Ki-67 labeling index of 15% (C). The result of periodic acid-Schiff staining (PAS) was positive (D), and Trichrome staining revealed rich interstitial collagen fibers stained blue (E). Cells of the tumor were also positive for SSTR2 (F), which is a characteristic indicator for meningiomas. These findings suggested a clear cell meningioma

Postoperative treatment and Follow-up

The patient underwent Intensity-Modulated Radiation Therapy (IMRT) one month after surgery, considering the malignant features of grade 2 and the huge volume of the tumor, without going through chemotherapy. The repeat MRI 6 months after surgery revealed no recurrence of the tumor (Fig. 2). Serial MRI scanning will be performed every year to monitor tumor recurrence.

Discussion

The dural tail sign can be a supportive factor in the diagnosis of meningiomas as it can be discovered in convexity meningiomas and in meningiomas that grows at the falx, tentorium, sphenoid wing, skull base, and posterior fossa which includes nearly all extra-axial locations [6]. As meningiomas originate from arachnoid cells, in most situations it has adhesion to the dura mater [7].

However, intraparenchymal meningiomas without dural attachment have also been reported, although rare. This kind of meningiomas are more likely to be discovered in the pediatric population and more often in the infratentorial region [8]. Intraparenchymal meningiomas can be found in pineal region, the intraventricular region and within the sylvian fissure. Pineal region meningiomas are believed to be originated from the tentorium or the falx with inapparent dural tail sign, while the intraventricular meningiomas arise from choroid plexus. But meningiomas that located in sylvian fissure have neither visible connection to the dura mater nor adhesion to the ventricular system, and thus increasing the difficulty of diagnosis. However, in some cases the tumors are originated from dura mater on sphenoid bone, which can also appear in deep sylvan region and be misjudged as sylvian meningiomas. So far there are 11 reported cases of adult sylvian fissure meningiomas in PubMed with clear images, previous reports that do not present images or the tumors are considered not sylvian meningiomas are not included (Table 1).

Table 1 Summary of the Sylvian fissure meningiomas in adult patients reported in the literature which possess clear images evidence

Meningiomas are believed to originate from non-neuroepithelial progenitor cells, meningothelial cells and the arachnoid cap cells. These cells are normally located in the arachnoid layer that present generally in granulations and throughout the surface coverings, sometimes also in the dura mater, pia layer and other locations [8]. It is possible that these cells can exist in places that are not adjacent to the dura mater and develop into meningiomas, which is a presumable explanation of the appearance of intraparenchymal meningiomas. In previous reported cases, the possible origins of deep sylvian meningiomas are described as the follows: (1) a cluster of arachnoid cap cells located in the pial layer(or a pia-arachnoid crypt [9]) of the deep sylvian fissure [8]; (2) meningothelial or arachnoid cap cells in a Virchow-Robin space along a small branch of the MCA [8, 10]; (3) a pia arachnoid crypt adjacent to the junction of the M1 and M2 segments of the MCA [11]. In our case, the tumor is speculated to originate from arachnoid cells located in the pial layer of the deep sylvian fissure, or pia arachnoid plexus along the MCA. In conclusion, cell of origin of the tumor can locate in multiple locations other than the arachnoid layer present in the granulations and throughout the surface coverings. Thus, deep sylvian meningiomas are likely to originate from these cells that located in the sylvian fissure or around certain MCA segment, which are not adjacent to the dura mater or the ventricular system.

In the aspect of intraoperative observation, most of these studies reported that the tumors were not exposed until the sylvian fissure was dissected, and the tumors free of attachment with lateral ventricular wall or choroid plexus. This is consistent with what we have seen during the operation and can be an important intraoperative feature in the diagnosis of sylvian fissure meningioma.

The radiological features shown in these cases are similar to common meningiomas. In presented cases MRI usually shows isointensity or hypointensity with homogeneous or heterogeneous enhancement on both T1W or T2W images. Besides, slight to severe peritumoral edema is often described in these cases (8 cases, 66.7%). Although the presence of intralesional calcification can be a distinguishing factor in the diagnosis of meningiomas, it is not specific enough, as only 3 presented cases reported clearly showed calcification on CT, and occasionally oligodendrogliomas can also present with calcification. In our case the preoperative CT images only presented a high density area closed to calcification, the presence of calcification was confirmed during surgery.

The present case is likely the largest tumor (9.7 × 5.3 × 6.4 cm) among the reported cases of adult sylvian fissure meningiomas to date. And in this case the pathological findings suggest a clear cell meningioma, which is an atypical type classified as WHO grade 2 and rarely reported (CCM accounts for less than 1% of all meningiomas [12]). Most cases reported so far are WHO grade 1 (8 cases, 66.7%), with 4 cases are WHO grade 2 tumor and most of them are atypical (3 cases). Compared to other parts, WHO grade 2 tumors appear to have a higher proportion. The proportion of WHO grade 2 tumors may change because of the updates to the recommended WHO criteria for the classification of brain tumors. In this case, the diagnosis of clear cell meningioma, which is associated with more aggressive behavior, supported the final judgement of atypical type meningioma with WHO 2 grade.

Due to their rarity, misdiagnoses such as high-grade gliomas, tuberculous granulomas, lymphomas, or metastatic brain tumors can be given to this kind of meningiomas [11]. In this case, the location and some features of the lesion showed on CT and MRI images had made it difficult for us to make differential diagnosis of glioma and meningioma. The high density area close to calcification on the CT image and characteristic of enhancement led to the diagnosis of meningioma while absence of dural attachment supported the judgement of glioma. The final surgical resection and pathological findings determine the diagnosis of atypical meningioma.

Surgical removal of the tumor appears to be the ideal treatment protocol. Most patients in previous cases that underwent gross total removal were free from neurological deficits with uneventful post-operative course. As sylvian meningiomas are close to MCA, it is possible that the tumor can strongly adhere to MCA and its branches, making it difficult to preform complete resections. Subtotal removal can be adopted in these situations along with adjuvant radiotherapy to effectively avoid relapse or progression [13]. National Comprehensive Cancer Network (NCCN) guidelines clearly suggest that patients with incomplete resection of WHO grade 2 meningiomas should consider postoperative radiation therapy [14]. It is controversial whether patients with completely resected WHO grade 2 tumors should receive radiation therapy, as previous studies have shown that radiation therapy may not prolong progression free survival (PFS) in patients with atypical meningiomas after gross total resection [15]. However, NCCN guidelines [14] and other literature [16,17,18] still recommend considering postoperative radiation therapy for complete resected WHO grade 2 meningiomas. Given the tumor’s grade 2 malignancy and large volume, we performed radiotherapy in this case. In most presented cases, the patients have a good prognosis without neurological deficiencies.

Conclusion

In conclusion, we present a rare case of a massive intraparenchymal meningioma in the sylvian fissure that has no dural attachment in a 34-year-old male, which is an even rarer clear cell type sylvian meningioma. This case may help us understand the origin of meningiomas, and better distinguish the characteristics of deep sylvian meningiomas. As a result, an accurate preoperative diagnosis can be made so that proper treatment strategy and operative techniques can be determined.