What is Falx syndrome?

Falx Syndrome

Falx syndrome is a neurological presentation characterized by contralateral hemiparesis with crural (lower extremity) dominance, typically caused by an interhemispheric subdural hematoma (iSDH) compressing the medial motor cortex along the falx cerebri. 1, 2

Clinical Presentation

The syndrome manifests with distinctive motor deficits:

• Contralateral leg weakness is the predominant feature, with the lower extremity affected more severely than the upper extremity due to compression of the parafalcine motor cortex where leg motor fibers are located 2, 3
• Facial weakness is typically absent or minimal in most cases 2
• Immediate loss of consciousness following trauma is usually absent, with focal neurological symptoms developing within 8-48 hours after injury 2
• Vertex headaches may be present 3

Etiology and Risk Factors

The underlying pathophysiology involves specific mechanisms:

• Interhemispheric subdural hematomas are the primary cause, typically occurring after head trauma with linear brain acceleration that tears parafalcic bridging veins 2
• Elderly patients are predominantly affected (mean age 56-73 years) 1, 2
• Anticoagulant or antiplatelet therapy is present in the vast majority of cases (92% in one series) 1, 2
• Skull fractures are rare 2

Diagnostic Approach

Imaging characteristics are critical for diagnosis:

• CT scan demonstrates a spontaneously hyperdense parafalcic area in a flat-convex lenticular shape along the interhemispheric fissure 2
• MRI with multiplanar reconstructions can precisely localize where the hematoma emerges from the interhemispheric fissure to the brain convexity, allowing targeted surgical planning 2
• Angiography is unreliable for diagnosing interhemispheric collections and negative results cannot exclude the diagnosis 4

Management Strategy

Prompt surgical evacuation via craniotomy before neurological deterioration occurs is the treatment of choice for patients with falx syndrome. 1

Surgical Indications

• Large iSDH with neurological deficits warrants craniotomy for evacuation 1
• Timing is critical: patients who deteriorate neurologically before surgery have significantly worse outcomes (83% vs 15% mortality, p=0.0095) 1
• Patients who are comatose prior to surgery have 100% 30-day mortality compared to 23% in non-comatose patients (p=0.0031) 1

Surgical Outcomes

When performed promptly, craniotomy yields favorable results:

• 89.5% of surgical patients experience improvement or resolution of motor deficits postoperatively 1
• No instances of venous infarction, reaccumulation, or infection after evacuation in contemporary series 1
• Median modified Rankin Scale score of 1 at mean 22-month follow-up among surgical survivors 1
• Overall surgical mortality of 27-32% in historical series, with good recovery in 58% and improvement in 15% 1, 2

Conservative Management

• Selected patients may be managed nonoperatively, though this carries 50% 30-day mortality 1
• Conservative management resulted in 14% mortality in historical series 2

Critical Pitfalls to Avoid

• Delaying surgery until neurological deterioration occurs dramatically worsens outcomes 1
• Relying on negative angiography to exclude interhemispheric collections 4
• Failing to recognize partial falx agenesis on preoperative imaging, which precludes interhemispheric approaches 5
• Assuming facial weakness must be present—its absence does not exclude the diagnosis 2