INTRODUCTION
Intracranial aneurysms (IAs) are among the most frequently treated cerebrovascular diseases in neurosurgery, identified in approximately 1-3% of the general population [6,9]. Meanwhile, meningiomas (MNGs) are the most common primary brain tumors, accounting for about 30% of all intracranial neoplasms [5,8]. Although both conditions are relatively common, their coexistence in the same patient is a rare occurrence [2].
Most existing literature addresses cases where MNGs were clearly identified on preoperative imaging [1,3]. During routine cerebrovascular evaluations, which primarily rely on non-enhanced magnetic resonance angiography (MRA) or computed tomography angiography (CTA), small meningiomas might be radiologically missed. This study reports cases of such “clinically occult” or radiologically missed MNGs that were incidentally discovered through biopsy of suspicious dura mater during IA clipping surgery. Through these case reports, we highlight the importance of meticulous intraoperative observation of subtle changes in the surgical field and the necessity of proactive tissue sampling for suspicious findings.
CASE DESCRIPTION
Case 1
A 57-year-old female presented with a history of a ruptured right posterior communicating artery (PcomA) aneurysm treated with stent-assisted coiling, followed by clipping for recanalization after coil embolization. After returning to daily life following the treatment of the right PcomA aneurysm, she experienced a sudden, severe headache and underwent coil embolization for a ruptured de novo left PcomA aneurysm, which was not present at the time of the initial treatment. However, during follow-up, recanalization of the left aneurysm (max. 5.1 mm) was revealed. Considering the repeated recurrences and incomplete occlusion despite prior endovascular treatments, surgical clipping was selected as the definitive management strategy.
The surgery was performed via a left pterional approach. Upon opening the dura, hemosiderin deposition and generalized yellowish discoloration were observed, sequelae of the previous subarachnoid hemorrhage (SAH). Additionally, a thickened hypervascularized dura mater was identified around the anterior clinoid process (Fig. 1). To secure the proximal internal carotid artery (ICA), intradural anterior clinoid process (ACP) drilling was performed. During this procedure, tissue suspicious for a calcified meningioma was identified and harvested for biopsy (Fig. 2). After ACP removal, the recanalized aneurysm was successfully clipped using a fenestrated clip.
Histopathological examination confirmed a WHO grade I meningioma, psammomatous type, with a Ki-67 index of 1%. Both c-Met and EGFR were negative (Fig. 3). The patient was discharged without neurological sequelae.
Case 2
A 50-year-old female presented to the emergency department complaining of tinnitus and diplopia. Subsequent diagnostic imaging revealed a right carotid-cavernous fistula (CCF) and multiple IAs. The right CCF spontaneously occluded during an attempted endovascular treatment, but multiple IAs remained. She underwent a left craniotomy for the surgical management of aneurysms at the left PcomA, paraclinoid, and middle cerebral artery (MCA).
Intraoperatively, a hypervascularized dura mater at the ACP was noted (Fig. 4). To secure space for proximal control, intra-dural ACP drilling was performed, during which the abnormally thickened dural tissue was harvested for biopsy (Fig. 5). Subsequently, all three IAs were successfully clipped, and the surgery was concluded.
The biopsy result confirmed a meningioma, meningothelial type. The Ki-67 index was 2%, and immunohistochemistry revealed overexpression of both c-Met (2+/3) and EGFR (2+/3) (Fig. 6). The patient recovered without complications and was discharged.
DISCUSSION
The coexistence of MNGs and IAs is a rare phenomenon, with previous studies reporting a concurrent incidence of 0.13-1.17% [4]. However, recent literature suggests that the actual prevalence may be significantly higher [1,2]. Notably, Kim et al. reported a significantly higher prevalence of 7.7%, suggesting that the true incidence is likely underestimated due to the lack of routine tumor-protocol imaging [7]. Consistent with this potential for underdiagnosis, this study demonstrates the discovery of MNG, which were not visible or suspected on preoperative imaging, through biopsy of suspicious dural changes found during aneurysm surgery.
While the hemodynamic stress hypothesis is well-established, it offers a limited explanation for our cases [7]. It is highly possible that the concurrent finding of IA and MNG in our cases is merely a coincidental co-existence. While one might cautiously speculate about potential underlying associations such as local inflammation, direct evidence is lacking, and over-interpretation should be avoided.
Another speculative factor is the potential for radiation-induced tumorigenesis following endovascular treatment. Radiation is a well-established risk factor for meningioma development [10,11]. While complex scenarios involving repeated endovascular procedures can result in cumulative radiation exposure, attributing the MNG solely to radiation in our cases requires caution due to the lack of precise dosimetric data and definitive latency periods.
Regardless of the exact pathogenesis, the primary clinical takeaway from these cases is the importance of intraoperative vigilance. In patients undergoing craniotomy for IA clipping, especially those evaluated primarily with non-enhanced MRA or CTA, where small tumors could be radiologically missed, neurosurgeons should not overlook abnormal dural changes. Thickened or hypervascularized dura mater, particularly around the anterior clinoid process, where proximal control is often obtained, should prompt active tissue biopsy.
CONCLUSIONS
The possibility of concomitant or radiologically missed MNGs should be considered. Therefore, during IA clipping surgery, if hypervascularization, abnormal discoloration, or dural thickening is observed, active biopsy should be strongly considered. This has significant clinical implications for the early detection of meningeal-origin lesions.
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