Can a parasagittal meningioma with possible compression of the sagittal sinus cause abducens palsy leading to diplopia in an adult patient?

Can Parasagittal Meningioma Cause Abducens Palsy and Diplopia?

Yes, a parasagittal meningioma can cause abducens palsy leading to diplopia, though this is an uncommon presentation that occurs through indirect mechanisms rather than direct nerve compression.

Mechanism of Abducens Palsy from Parasagittal Meningioma

The abducens nerve (CN VI) is uniquely vulnerable to stretching and compression along its long intracranial course, making it susceptible to increased intracranial pressure and mass effect from distant lesions 1. The most likely mechanism in parasagittal meningioma is "pseudoentrapment" of the abducens nerve at Dorello's canal, where linear forces in the midsagittal plane from the tumor's mass effect temporarily increase local cerebrospinal fluid pressure and compress the nerve just before it enters under the petrolingual ligament 2.

Key Anatomical Considerations

• The sixth nerve ascends through the subarachnoid space and passes underneath the petroclinoid ligament before entering the cavernous sinus 1
• Tethering of the nerve along this pathway makes it susceptible to stretching from increased intracranial pressure, cerebrospinal fluid inflammation, infection, infiltration, or compression from distant mass lesions 1
• Parasagittal meningiomas can create mass effect and alter CSF dynamics without directly contacting the abducens nerve 2

Clinical Presentation Pattern

Isolated unilateral abducens nerve palsy can develop rapidly (within days to weeks) from parasagittal meningioma, even in the absence of overt signs of elevated intracranial pressure such as papilledema 2. This distinguishes it from the typical bilateral sixth nerve palsy seen with generalized increased intracranial pressure 1.

Expected Symptoms

• Acute to subacute onset of horizontal diplopia, worse at distance than near 1
• Diplopia worse on lateral gaze toward the affected side 1
• Possible compensatory head turn to minimize diplopia 1
• Incomitant esotropia on examination 1

Critical Diagnostic Evaluation

Neuroimaging with MRI of the brain with and without gadolinium contrast is mandatory for any patient with sixth nerve palsy who lacks compelling vasculopathic risk factors (diabetes, hypertension in elderly patients), has other neurologic findings, or is young 1.

Specific Red Flags Requiring Immediate Imaging

• Age under 50 years 1
• Bilateral sixth nerve involvement 1
• Other cranial neuropathies 1
• Signs of elevated intracranial pressure (papilledema, optic atrophy) 1
• Any additional neurologic deficits 3
• Absence of vasculopathic risk factors 1

Imaging Protocol

• MRI brain with and without gadolinium contrast is the study of choice 1
• If meningioma is identified near the sagittal sinus, additional MR venography (MRV) or CT venography (CTV) should be obtained to assess sagittal sinus patency and potential compression 1
• CT head is insufficient for detecting parasagittal pathology and should not be relied upon 3

Management Approach

The primary treatment is directed at the underlying meningioma, with symptomatic management of diplopia during the observation or treatment period 1.

Tumor-Directed Treatment

• For smaller tumors (<3 cm) with patent sagittal sinus, stereotactic radiosurgery alone may be appropriate as first-line therapy 4
• Larger tumors or those causing progressive neurologic deficits require surgical resection, potentially followed by planned radiosurgery for residual disease 4
• Abducens palsy from skull base meningiomas treated with Gamma Knife radiosurgery shows 83% resolution rate, with median time to improvement of 4.5 months when treated early (within 1.5 months of symptom onset) 5

Symptomatic Diplopia Management

While awaiting tumor treatment or nerve recovery:

• Monocular occlusion using eye patch, Bangerter filter, or satin tape on glasses eliminates diplopia immediately 1
• Fresnel prisms can be applied temporarily if fusion is achievable 1
• Botulinum toxin injection to the medial rectus may reduce secondary contracture and compensatory head position 1

Expected Recovery Timeline

Following gross total resection of parasagittal meningioma causing abducens palsy, gradual improvement typically occurs within 3 weeks 2. This contrasts with vasculopathic sixth nerve palsy, where most cases resolve within 6 months 1.

Common Pitfalls to Avoid

• Assuming all sixth nerve palsies in diabetic or hypertensive patients are vasculopathic without considering tumor as a differential, especially if the patient is younger or lacks typical risk factors 1
• Failing to obtain neuroimaging when the clinical picture doesn't fit a typical vasculopathic pattern 1
• Not recognizing that isolated abducens palsy can occur from parasagittal lesions without papilledema or other signs of generalized increased intracranial pressure 2
• Delaying radiosurgery consultation for skull base meningiomas causing diplopia, as earlier treatment (within 1.5 months) correlates with better outcomes 5
• Overlooking sagittal sinus patency assessment when parasagittal meningioma is identified, as sinus compression affects surgical planning 1

Prognosis

The prognosis for abducens palsy resolution is excellent when the underlying parasagittal meningioma is appropriately treated, with most patients experiencing complete recovery within weeks to months 2, 5. However, if no improvement occurs by 6 months in any sixth nerve palsy case, approximately 40% demonstrate serious underlying pathology requiring further investigation 1.