What is a Parafalcine Meningioma?
A parafalcine meningioma is a benign brain tumor that arises from the arachnoid cells of the falx cerebri (the dural fold separating the two cerebral hemispheres), covered by overlying brain tissue and not involving the superior sagittal sinus. 1
Origin and Cellular Basis
Parafalcine meningiomas arise from arachnoid cells present in the meninges along the falx cerebri. 2 These tumors can develop anywhere meninges exist, though the parafalcine location represents one of the most common intracranial sites. 2
Anatomical Location and Classification
The key distinguishing feature is that parafalcine meningiomas arise from the falx itself and are covered by overlying brain parenchyma, without involving the superior sagittal sinus. 1 This distinguishes them from parasagittal meningiomas, which do involve the superior sagittal sinus. 1, 3 Together, these two locations represent the second most common site for intracranial meningiomas. 1
Parafalcine meningiomas can be further classified based on growth patterns on coronal MRI: 4
- Type I: Hemispheroid-shaped tumors invaginating deeply into one hemisphere without shifting the falx
- Type II: Olive-shaped tumors shifting the falx substantially to the contralateral side
- Type IIIA: Globular or dumbbell-shaped tumors extending into both hemispheres to different extents
- Type IIIB: Globular or dumbbell-shaped tumors extending into both hemispheres to approximately equal extent
Clinical Presentation
Presenting symptoms depend on tumor dimensions and location. 1 Common manifestations include: 2
- Symptoms of raised intracranial pressure: headaches, drowsiness, and vomiting
- Focal neurological deficits affecting the limbs
- Cranial nerve palsies
- Epilepsy (presenting symptom in up to 30% of cases)
- Visual field deficits (as demonstrated in the case of a 78-year-old with subtle left-sided peripheral visual field loss) 5
Imaging Characteristics
MRI is the radiological imaging modality of choice. 2 Typical features include: 2, 6
- Homogeneous dural-based enhancement
- Isointense or hypointense on T1-weighted images
- Hyperintense on T2-weighted images
- Strong and uniform contrast enhancement
- Dural tail sign (characteristic but not pathognomonic)
- CSF cleft between tumor and brain
- Vasogenic edema in subjacent parenchyma (40-80% of cases, particularly large tumors)
- Calcifications (up to 50% of cases)
Pathology and Grading
Approximately 94% of meningiomas are benign (WHO grade I), 5% are atypical (WHO grade II), and 1% are malignant/anaplastic (WHO grade III). 2 However, even WHO grade I tumors can exhibit unexpectedly aggressive behavior with recurrence. 7
Important prognostic factors include: 7
- Ki-67 proliferative index (higher values associated with decreased progression-free survival)
- NF-2 genetic alterations (associated with poorer outcomes)
- Supratentorial location
- 1p and 14q deletions (associated with higher risk of tumor recurrence) 2
Management Implications
Complete surgical resection remains the treatment of choice when feasible. 2 However, parafalcine meningiomas present unique surgical challenges due to proximity to critical venous structures and eloquent cortex. 1, 8
Stereotactic radiosurgery (SRS) provides superior tumor control compared to active surveillance for asymptomatic parafalcine meningiomas, with tumor control achieved in >97% of upfront SRS cases versus 61.2% with observation alone. 3, 9 SRS-related neurological deficits occur in only 3.1% of patients and are typically transient. 9
For recurrent grade I tumors despite their benign histological classification, salvage stereotactic radiation therapy represents a viable option after multiple surgical resections. 7