What is the management and treatment of falcine meningiomas?

Falcine Meningiomas: Epidemiology, Pathophysiology, Presentation, and Management

Epidemiology

Falcine meningiomas, together with parasagittal meningiomas, represent the second most common location of intracranial meningiomas, accounting for approximately 9% of all intracranial meningiomas. 1, 2

• The middle third of the falx is the most frequently involved site (55-78% of cases), followed by the anterior third (26-31%) and posterior third (17-89%). 2
• Most falcine meningiomas are benign (WHO grade 1), with transitional and meningothelial subtypes occurring in approximately 69% of patients. 2
• High-grade (atypical or malignant) meningiomas are uncommon, occurring in only about 2% of cases in surgical series. 2

Pathophysiology

Falcine meningiomas are defined as meningiomas arising from the falx cerebri, covered by overlying brain parenchyma, and not involving the superior sagittal sinus. 1

• These tumors originate from arachnoid cap cells within the falx and grow by displacing rather than invading adjacent brain tissue. 1
• The growth pattern significantly influences surgical planning, with tumors classified by their relationship to the falx and degree of hemispheric involvement. 3
• Calcifications are common, occurring in up to 50% of meningiomas, and may be more frequent in certain subtypes. 4

Clinical Presentation

Approximately one-third of patients with falcine meningiomas are asymptomatic at diagnosis, with tumors discovered incidentally on imaging. 2

Symptomatic Presentations:

• Headaches are the most common symptom, occurring in approximately 27-28% of patients. 2
• Seizures occur in approximately 14-15% of cases, related to cortical irritation from mass effect. 2
• Lower extremity weakness presents in approximately 9-10% of patients, due to compression of the motor cortex along the interhemispheric fissure. 2
• Progressive cognitive changes including abulia and behavioral changes may develop with large anterior falcine tumors. 5
• Urinary incontinence can occur with bilateral frontal lobe involvement. 5
• Symptoms typically develop gradually over months to years as the tumor slowly enlarges. 5

Diagnostic Evaluation

MRI with contrast is the gold standard for evaluating falcine meningiomas, revealing homogeneous dural-based enhancement with characteristic dural tail sign. 4, 6

Key Imaging Features:

• Typical MRI findings include isointense or hypointense masses on T1-weighted images, hyperintense on T2-weighted images, with strong uniform contrast enhancement. 6
• Coronal MRI sequences are essential for surgical planning, demonstrating tumor growth patterns and relationship to the falx. 3
• CT scan provides complementary information, particularly for visualizing calcifications and hyperostosis. 6
• Somatostatin receptor (SSTR) PET imaging should be considered when tumor extension is unclear or for differentiation between recurrence and post-treatment changes. 4, 6

Surgical Classification and Planning

A classification scheme based on tumor growth patterns on coronal MRI facilitates surgical planning and approach selection. 3

Classification System:

• Type I (Hemispheroid): Tumors invaginating deeply into one hemisphere without shifting the falx—approach ipsilaterally via interhemispheric corridor. 3
• Type II (Olive-shaped): Tumors shifting the falx substantially to the contralateral side—approach contralaterally via transfalcine route. 3
• Type IIIA (Asymmetric dumbbell): Tumors extending into both hemispheres to different extents—approach from the side with smaller tumor burden. 3
• Type IIIB (Symmetric dumbbell): Tumors extending equally into both hemispheres—approach from the non-dominant hemisphere. 3

Surgical Management

Complete surgical resection including removal of the dural attachment is the optimal treatment when feasible, with Simpson grade I resection achievable in 83-100% of cases in experienced centers. 7, 4, 3, 2

Surgical Approaches:

Interhemispheric Approach (Traditional):

• Ipsilateral interhemispheric approach in supine or prone position is the standard technique for most falcine meningiomas. 2
• This approach provides direct access to the falx and tumor attachment site. 2
• Critical considerations include preservation of bridging veins, anterior cerebral artery branches, and cortical venous drainage. 1

Transcortical Approach (Alternative):

• Transcortical resection through the superior frontal gyrus can be used as a safe alternative for large, bilobed falcine meningiomas. 5
• This approach avoids risks of venous infarction and cortical injury associated with extensive interhemispheric dissection. 5
• Particularly useful for giant tumors with significant bilateral involvement. 5

Endoscopic Contralateral Transfalcine Approach (Minimally Invasive):

• Endoscopic contralateral keyhole approach with approximately 3 cm craniotomy offers less-invasive option for large falcine meningiomas. 8
• Mean operation time of 265 minutes with Simpson grade I removal achievable in all cases. 8
• Advantages include smaller craniotomy, shorter operation time, and reduced risk of venous complications. 8

Surgical Outcomes:

• Gross total resection is achieved in 83-100% of cases in modern series. 3, 2
• Mortality is essentially zero in contemporary surgical series. 3, 2
• New or worsened neurological deficits occur in approximately 3% of patients postoperatively. 2
• Perioperative complications including significant blood loss, venous injury, and infection occur in approximately 6% of cases. 2

Radiation Therapy

External beam radiation therapy is indicated for WHO grade 3 (malignant) meningiomas after surgery and for subtotally resected WHO grade 2 (atypical) meningiomas. 4

• Adjuvant radiotherapy for incompletely resected benign meningiomas improves progression-free survival from approximately 50% to over 80% in adult series. 7
• Stereotactic radiosurgery is effective for residual or recurrent meningiomas, particularly those <3 cm in diameter. 9
• For larger meningiomas or those with pre-existing edema, fractionated stereotactic radiotherapy may be preferred. 9
• The indication for adjuvant radiotherapy in adults with incompletely resected benign, grade I meningioma remains controversial. 7

Observation Strategy

Asymptomatic, incidentally discovered small falcine meningiomas (<30 mm) can be managed with observation and serial MRI surveillance. 4

• Observation is particularly appropriate for elderly patients or those with significant comorbidities. 4
• In adult series, cumulative relative survival for non-surgical management was 49% at 3 months and 25% at 15 years, compared to 93% at 3 months and 79% at 15 years for surgical patients. 7
• Up to 20% of completely resected benign meningiomas recur within 25 years, indicating the need for lifelong follow-up. 7

Post-Treatment Surveillance

MRI without and with contrast every 6-12 months is recommended for follow-up of falcine meningiomas. 4, 9

• After achieving stable disease status (typically after 5-10 years), follow-up intervals can be extended. 9
• SSTR PET imaging may be useful in distinguishing tumor recurrence from post-treatment changes. 4
• Clinical follow-up should include routine neurological examinations and assessment for signs of increased intracranial pressure. 9

Critical Surgical Considerations

Several anatomical factors must be carefully evaluated during surgical planning to minimize morbidity:

• Bridging veins: Preservation is essential to prevent venous infarction. 1
• Anterior cerebral artery branches: Must be identified and protected throughout resection. 1
• Arterial feeders: Early identification and coagulation reduces intraoperative blood loss. 1
• Superior sagittal sinus involvement: Must be assessed preoperatively as it changes surgical classification from falcine to parasagittal meningioma. 1
• Modern surgical techniques including image-guided surgery (frameless stereotaxy) improve precision and may reduce surgical side effects. 4

Common Pitfalls to Avoid

• Failing to recognize that not all enhancing dural-based lesions are meningiomas; brain metastases, gliomas, and primary CNS lymphoma can mimic meningiomas. 6
• Underestimating blood loss risk, particularly with large or intraventricular tumors requiring high-dose steroids, head elevation, and close monitoring. 9, 6
• Inadequate preoperative venous mapping can lead to inadvertent sacrifice of critical bridging veins causing venous infarction. 1
• Incomplete dural resection increases recurrence risk; the dural attachment must be completely excised when feasible. 4