A falcine meningioma arises from the dura of the falx cerebri and is entirely concealed beneath the medial cerebral cortex. Unlike parasagittal meningiomas, it does not originate from the superior sagittal sinus (SSS) or the main dural roof, though it frequently abuts the SSS superiorly or the inferior sagittal sinus (ISS) along its free margin. 

 

The real surgical difficulty comes from its deep location between the hemispheres: it displaces the anterior or posterior cerebral arteries, pushes the cingulate gyrus, and buries critical cortical draining veins (like the veins of Trolard or Labbé, and the internal cerebral veins) along its capsule.

 

Q. How does location along the anterior-to-posterior axis of the falx alter tumor behavior and surgical risk?

 

Location dictates everything in falcine meningiomas:

 

Anterior Third (Pre-coronal): Tends to grow silently to massive sizes before detection. The primary risk is traction on the A2/A3 segments of the anterior cerebral arteries (ACA) and pericallosal branches.

 

Middle Third (Coronal to Rolandic): Presents early with focal seizures or contralateral leg weakness. The surgical risk here is highest because of the motor cortex and crucial rolandic bridging veins running directly over the tumor capsule.

 

Posterior Third (Parieto-occipital to Torcular): Causes visual field deficits (homonymous hemianopia) or cognitive changes. Deep posterior tumors compress the vein of Galen, straight sinus, and distal PCA branches, making deep dissection treacherous.

 

Q. How do you differentiate a true falcine meningioma from a parasagittal meningioma?

 

It comes down to the origin of the dural base:

Parasagittal Meningioma: Arises from the dural convexity immediately adjacent to or within the wall of the SSS. It involves the superior sinus wall directly and often invades or occludes the SSS lumen early.

 

Falcine Meningioma: Arises purely from the falx curtain itself, strictly below the superior sagittal sinus. While a large falcine tumor can expand superiorly to push against the SSS, normal dural tissue or a clear arachnoid plane usually separates its origin from the sinus wall.

 

Q. What is the vascular supply of falcine meningiomas?

 

Primary blood supply comes from the anterior and posterior ethmoidal arteries (for anterior falcine lesions) and the anterior and posterior meningeal arteries branching from the external carotid system. Middle-third lesions receive heavy supply from the middle meningeal artery via falcine branches. As these tumors enlarge, they parasitize secondary blood supply from distal pial branches of the anterior cerebral artery (callosomarginal and pericallosal) and posterior cerebral artery.

 

Q. How do patients with falcine meningiomas typically present?

 

Presentation depends on location and size:

Middle Third: Most common presentation is progressive contralateral lower extremity weakness (due to compression of the homunculus along the medial motor strip) or focal Jacksonian motor seizures starting in the foot or leg.

 

Anterior Third: Patients present with cognitive slowing, personality changes, apathy, urinary incontinence (similar to normal pressure hydrocephalus or bifrontal injury), or raised ICP headaches.

 

Posterior Third: Presents with homonymous hemianopia, visual spatial agnosia, or pressure-related headaches.

 

Bilateral Extension: Falcine meningiomas frequently grow through the falx into both hemispheres ("dumbbell" or "saddle" shape), leading to bilateral lower limb monoparesis or paraparesis.

 

Q. What are the key MRI and angiographic findings to evaluate before surgery?

 

MRI (T1+C / T2 / FLAIR): Identifies the extra-axial mass attached to the falx, defines dural tailing, assesses peritumoral cortical edema, and demonstrates whether the tumor is unilateral or dumbbell-shaped across the midline.

 

MR Venography (MRV) / Digital Subtraction Angiography (DSA): Essential to verify the patency of the Superior Sagittal Sinus, assess displacement of the Inferior Sagittal Sinus, and map critical bridging veins crossing the interhemispheric fissure.

 

MR Angiography (MRA): Visualizes displacement, encasement, or stretching of the A2/A3 pericallosal and callosomarginal arteries.

 

Q. What anatomical factors dictate the choice of surgical approach?

 

The primary driver is the tumor's center of mass along the anteroposterior plane, its vertical depth relative to the SSS, and whether it is strictly unilateral or bilateral. The absolute rule in falcine surgery is to plan the craniotomy so that you arrive directly over the tumor base, avoiding unnecessary brain retraction or division of critical bridging veins.

 

Q. What are the indications, advantages, and limitations of the standard surgical routes?

 

Interhemispheric Approach (Standard Workhorse)

 

Key Indications: 

Standard choice for the vast majority of falcine meningiomas across anterior, middle, and posterior thirds.

Primary Advantages: Uses a natural anatomic plane (the interhemispheric fissure) straight down to the falx. Allows early identification of the main tumor attachment along the falx and provides direct access to debulk the mass internally without invading the cerebral cortex.

 

Main Limitations: Working in a deep, narrow fissure with tight boundaries. Over-retraction of the medial hemisphere risks venous infarction if rolandic bridging veins are stretched or sacrificed.

 

Transcortical / Transsulcal Approach

 

Key Indications: Massive, deeply seated lesions with significant lateral cortical mantle thinning, or cystic components extending far into the subcortical white matter.

 

Primary Advantages: Provides a wide, short working distance directly into the center of the tumor, bypassing a crowded interhemispheric fissure filled with critical bridging veins.

 

Main Limitations: Requires breaching non-disrupted cerebral cortex or dissecting through a sulcus, carrying an inherent risk of post-operative seizure foci, permanent focal neurological deficit, or local encephalomalacia.

 

Bilateral / Interhemispheric Transfalcine Approach

 

Key Indications: Large "dumbbell" falcine meningiomas that cross the midline and occupy both cerebral hemispheres.

 

Primary Advantages: A single craniotomy crossing the midline allows the surgeon to resect the primary tumor on the dominant side, resect the attached falx, and then work straight through the defect in the falx to remove the contralateral extension without a separate brain approach.

 

Main Limitations: Requires crossing the SSS during bone flap removal (risk of sinus tear or air embolism) and handling dual sets of pericallosal vessels.

Surgical Technique, Execution, & Intraoperative Pearls

 

Q. Step-by-step, how do you perform an interhemispheric approach for a middle-third falcine meningioma?

 

Positioning & Craniotomy: Supine with head elevated 15 to 20 degrees and kept strictly in neutral (or side-lying with the tumor side down to let gravity pull the hemisphere away from the falx). A rectangular craniotomy is fashioned crossing the midline to expose the edge of the SSS.

 

Dural Opening: Open the dura in a C-shaped flap based toward the SSS. Take extreme care near the sinus border to preserve entering bridging veins.

 

Interhemispheric Dissection: Under the microscope, gently release CSF from the callosal cisterns. Dissect the arachnoid along the interhemispheric fissure, carefully preserving every bridging vein (especially near the rolandic cortex).

 

Devascularization & Internal Debulking: Coagulate the dural attachment on the falx around the margin of the tumor to cut off its primary blood supply. Gut the center of the tumor aggressively using an ultrasonic aspirator.

 

Capsule Mobilization & Resection: Once the shell is thin and mobile, peel the capsule away from the surrounding cortex, identifying and preserving the A2/A3 pericallosal branches in their arachnoid planes. Cut the attachment off the falx (or resect the falx completely) and remove the specimen.

 

Closure: Verify hemostasis along the falcine rim, perform a watertight dural closure (using a patch if needed), and secure the bone flap.

 

Q. How does internal debulking protect the medial motor cortex and pericallosal vessels?

 

Internal debulking is the single most important maneuver for preventing stroke and motor deficits. By hollowing out the center of the tumor, the rigid capsule collapses into itself. This creates space within the interhemispheric fissure, allowing you to peel the thin outer shell away from the brain without pushing against the surrounding motor cortex. Crucially, it allows you to dissect the pericallosal and callosomarginal arteries off the capsule under zero tension.

 

Q. What is the management of bridging veins during an interhemispheric dissection?

 

Bridging veins, particularly those draining the motor strip (vein of Trolard) into the SSS, must be treated as irreplaceable. Sacrifice of a major rolandic bridging vein causes venous infarction, massive brain swelling, permanent hemiplegia, or status epilepticus. Mobilize the tumor around the veins rather than sacrificing them. If a vein is tethered to the capsule, dissect the tumor off the vein or leave a small cuff of tumor capsule attached to the vessel.

 

Q. When should you resect the falx versus leaving it intact?

 

Resect the Falx (Simpson Grade 1): Indicated when the tumor is unilateral or dumbbell-shaped and the falx is hypervascular, thick, or tumor-infiltrated. Cutting a wide margin of falx around the origin drastically reduces the risk of long-term recurrence.

 

Leave the Falx Intact (Simpson Grade 2/3): Indicated when the tumor is easily peeled off the dural surface, when the falx is intimately attached to the deep ISS or straight sinus, or when aggressive dural resection risks injuring contralateral pericallosal vessels or bridging veins.

 

Q. When is planned subtotal resection indicated over radical excision?

 

Planned subtotal resection is the correct choice when the tumor capsule is densely adherent to the pericallosal/callosomarginal arteries, when it encases deep draining veins (like the ISS or internal cerebral veins), or when it is firmly bound to the eloquent motor cortex. Stripping a vessel or tearing a deep vein to achieve a "gross total resection" leads to catastrophic stroke or severe disability. The thin remnant left behind can be safely followed or treated with stereotactic radiosurgery.

 

Q. What are the primary causes of immediate versus delayed postoperative neurological deterioration?

 

Immediate Deterioration: Caused by surgical trauma to the primary motor cortex, intraoperative arterial occlusion/spasm of the pericallosal or callosomarginal arteries, acute venous infarction from sacrifice or thrombosis of a major rolandic bridging vein, or acute interhemispheric hematoma.

 

Delayed Deterioration: Caused by progressive venous infarction edema (peaks at 48–72 hours), delayed ACA territory ischemic stroke, post-resection seizures/status epilepticus, or hydrocephalus.

 

Q. What clinical and surgical factors predict postoperative neurological recovery?

 

Favorable Prognosis: Younger age, short symptom duration, soft tumor consistency allowing easy debulking, preservation of all major bridging veins and pericallosal branches, and absence of deep cortical invasion or severe preoperative peritumoral edema.

 

Unfavorable Prognosis: Long-standing preoperative motor deficits, dense tumor encasement of the pericallosal arteries, requirement for bridging vein sacrifice, firm or calcified tumor texture, and extensive preoperative edema on FLAIR sequences.

 

Q. What other postoperative complications can occur, and how are they managed?

 

Seizures: Very common due to intraoperative manipulation of the medial motor strip. Patients are routinely placed on prophylactic anti-seizure medications (e.g., levetiracetam) in the perioperative period.

 

Venous Thrombosis & Edema: Managed with head elevation, strict avoidance of dehydration, and aggressive steroid tapering.

 

CSF Leak & Hydrocephalus: Can occur if the frontal sinus was breached or if deep subarachnoid blood disturbs CSF resorption. Managed with lumbar drainage or permanent shunting if persistent.

 

Q. What is the role of adjuvant radiotherapy, what are recurrence rates, and what is the follow-up protocol?

 

Adjuvant Radiotherapy / SRS: 

Indicated for subtotal resections, recurrences, WHO Grade 2 (atypical) or Grade 3 (anaplastic) tumors, or tumors with high-risk molecular features (TERT promoter mutations, CDKN2A/B deletions). Stereotactic Radiosurgery (SRS) is excellent for small, residual falcine remnants.

 

Recurrence Rates: Low (around 10% at 10 years) for Simpson Grade 1 resections of WHO Grade 1 tumors. Recurrence jumps to 20–30% for Simpson Grade 2/3 resections and is significantly higher for Grade 2/3 histology.

 

Follow-up Protocol: Baseline contrast-enhanced MRI within 48 hours post-op. For WHO Grade 1 GTR, perform serial MRIs at 6 months, 12 months, and then annually for 5 to 10 years. For subtotal resections or higher-grade tumors, repeat imaging every 3 to 6 months with early multidisciplinary discussion for radiosurgery.