What critical brain structures are near or most affected by an interhemispheric Falx meningioma that is 1.4cm?

Critical Brain Structures Near a 1.4cm Interhemispheric Falx Meningioma

A 1.4cm interhemispheric falx meningioma primarily threatens the superior sagittal sinus, parasagittal cortical bridging veins, medial frontal/parietal cortex (including the motor homunculus for lower extremities), and the anterior cerebral arteries.

Primary Vascular Structures at Risk

The most critical structures are the venous drainage pathways, as their compromise leads to venous infarction and devastating neurological outcomes:

• Superior sagittal sinus - Falcine meningiomas arise directly from the falx and frequently involve or compress this major venous drainage structure 1, 2
• Parasagittal cortical bridging veins - These drain into the superior sagittal sinus and are at high risk during surgical manipulation, with injury causing venous infarction 3, 2
• Inferior sagittal sinus and straight sinus - Located at the inferior free edge of the falx, these are particularly vulnerable in posterior falcine lesions 4
• Anterior cerebral arteries - These vessels run in close proximity to anterior falcine meningiomas and can be compressed or encased by tumor 3

Eloquent Cortical Regions

The medial hemispheric cortex adjacent to the falx contains critical functional areas:

• Paracentral lobule - Contains the motor and sensory representation for the lower extremities, explaining why lower extremity weakness occurs in 9% of falcine meningioma patients 2
• Supplementary motor area - Located on the medial frontal surface, injury causes abulia and motor planning deficits 3
• Precuneus - In the medial parietal lobe, involved in visuospatial processing and self-referential thought 4
• Superior frontal gyrus - The transcortical approach through this structure is considered relatively safe, though carries seizure risk 3

Location-Specific Anatomical Considerations

The specific structures at risk depend on the tumor's position along the falx:

Anterior Third Falcine Meningiomas (26-31% of cases)

• Anterior cerebral arteries and their pericallosal branches 3
• Supplementary motor area bilaterally 3
• Frontal bridging veins 2

Middle Third Falcine Meningiomas (55-78% of cases - most common)

• Paracentral lobule with lower extremity motor/sensory cortex 2
• Multiple parasagittal bridging veins at their most numerous 2
• Superior sagittal sinus at its widest caliber 2

Posterior Third Falcine Meningiomas (17-89% of cases)

• Falcotentorial junction and confluence of venous sinuses 4
• Vein of Galen and internal cerebral veins 4
• Precuneus and visual association cortex 4
• Tentorial edges bilaterally 4

Clinical Manifestations Related to Structural Involvement

The neurological symptoms directly reflect which structures are compressed:

• Seizures (30% of cases) - Result from cortical irritation and edema affecting the medial motor/sensory cortex 5, 1
• Lower extremity weakness - Indicates paracentral lobule compression 3, 2
• Headaches (27% of cases) - From increased intracranial pressure, dural stretch, or venous congestion 2
• Abulia and frontal symptoms - Suggest bilateral supplementary motor area involvement 3
• Urinary incontinence - Associated with bilateral medial frontal lobe dysfunction 3

Surgical Risk Considerations

The greatest surgical morbidity (5-18%) stems from venous complications, not direct tumor removal 6:

• Sacrifice or injury to major bridging veins causes venous infarction with permanent deficits 2
• Superior sagittal sinus involvement significantly increases surgical complexity and risk 1, 2
• Bilateral tumor extension across the falx increases risk of bilateral cortical injury 3, 4
• Peritumoral edema (occurring in 40-80% of cases) increases mass effect on eloquent cortex 5, 6

Size-Specific Implications for 1.4cm Tumor

At 1.4cm, this tumor is relatively small and potentially amenable to complete resection with lower morbidity:

• Asymptomatic meningiomas <30mm can be observed, though surgery is preferred if accessible and neurological consequences are minimal 6
• Smaller size reduces likelihood of extensive venous sinus involvement 2
• Less peritumoral edema expected compared to larger tumors 5
• Complete Simpson grade I or II resection more achievable, reducing recurrence risk 1, 2