General
- Meningiomas arising in the vicinity of the anterior clinoid process.
- Hyperostosis involving the anterior clinoid process strongly suggestive of a clinoidal meningioma
- Arising from the anterior clinoid process
- Most appear like this
- May grow into the region of the mesial sphenoid wing
- Can be confused with medial sphenoid wing meningiomas
- When very large grow into
- Parasellar region
- Cavernous sinus
- Posterior clinoid
- Petroclival region
Numbers
- Clinoidal meningiomas are more common in females.
- However, the ratio of females to males is larger in clinoidal meningiomas compared with other meningiomas.
Anatomical Considerations
- Anterior clinoid process
- A complex anatomical entity
- CN3 courses along the superolateral aspect of the anterior clinoid process.
- ICA crosses the inferior aspect of the anterior clinoid process
- CN2 passes along its superomedial aspect
Al-Mefty classification
- Based on surgical findings and observations regarding the site of origin and the adhesiveness of the tumor to the internal carotid artery and its branches, suggested that clinoidal meningiomas be classified into 3 different types:
Type I clinoidal meningiomas
- Originate
- Subclinoidal dura at the most proximal point of intradural entry of the internal carotid artery, just before the carotid enters into the arachnoidal cisternal space.
- These tumors are extraarachnoidal and because of this tend to become more adherent to the internal carotid artery and much more difficult to remove surgically.
- Higher rate of subtotal resection → higher recurrence.
- Al-Mefty also makes the observation that the growth of type I and II clinoidal meningiomas starts at a distance from the optic nerve; as a result, the arachnoid membranes of the chiasmatic cistern invest the optic nerve and help protect it from immediate invasion by the tumor.
Type II clinoidal meningiomas
- Originate
- From the superolateral aspect of the anterior clinoid process.
- When these tumors grow, they are invested by the arachnoid layers around the carotid cistern. As a result, the tumor is separated from the internal carotid wall by arachnoidal layers that prevent the significant adherence of the tumor to the adventitia of the internal carotid artery wall.
- This makes the tumors easier to dissect off the wall of the internal carotid artery; as a result, a more complete resection is achievable.
- Al-Mefty also makes the observation that the growth of type I and II clinoidal meningiomas starts at a distance from the optic nerve; as a result, the arachnoid membranes of the chiasmatic cistern invest the optic nerve and help protect it from immediate invasion by the tumor.
Type III clinoidal meningiomas
- Originate
- From the region of the optic foramen and extend into the optic canal.
- Because of the pattern of their growth within the region of the optic canal, these tumors become symptomatic at an early stage and are diagnosed earlier before they achieve a large size, unlike types I and II.
Clinical Presentation
- Visual disturbances
- Common
- Headaches
- Common
- Other clinical symptoms usually correlate with the size of the tumor and its extension.
- Parasellar structures
- Lateral extension result in symptoms
- Cranial neuropathies
- Extension of the tumor into the cavernous sinus region
- Seizures
- Tumors extend to the middle temporal fossa → compress the temporal lobe
- Hemiparesis
- Compress brain stem
- Proptosis and orbital pain
- Hyperostosis of the sphenoid wing
Radiological Evaluation
CT scan
- Hyperostosis involving the anterior clinoid process strongly suggestive of a clinoidal meningioma
MRI
- Thin-cut MRI with fat suppression through the optic canal can help identify the presence of tumor extension into the orbit.
Angiography
- DSA/MRA/CTA
- Relationship of the tumour to the supraclinoid internal carotid artery and its branches.
- However, in recurrent cases or in patients who have had previous radiation, four-vessel cerebral angiography with balloon test occlusion may be necessary to have a plan in place in case of injury to the carotid artery.
Management
Surgery
General
- Surgery remains the most effective treatment modality for clinoidal meningiomas.
- This is true even for small lesions that may be considered for radiosurgery in other locations, because of their proximity to the optic apparatus and the higher possibility of radiation injury.
- Decision to leave some tumor behind to preserve function is a more appropriate decision than attempting gross radical resection and increasing the risk of arterial injury and ischemia.
Resection goals and safety
- While gross total resection is the primary goal, surgeons exercise judgement in Type I tumours where the arachnoid layer is absent.
- In these cases, the tumour may be dangerously adherent to the ICA wall, necessitating subtotal resection to avoid morbidity.
- Following resection, underlying bone is further drilled using a diamond drill with copious irrigation to ensure complete resection and hemostasis.
Surgical Steps
Craniotomy and initial exposure
- A wide frontoorbital craniotomy, (Aka: extended pterional or pretemporal approach) is utilised to establish access.
- Surgeons often include the orbital roof in the craniotomy flap (cranioorbitozygomatic approach) to allow access to suprasellar extensions while minimising frontal lobe retraction.
Extradural work and devascularisation
- The initial phase involves dissecting the pretemporal and subfrontal dura away from the sphenoid wing and the posterior roof of the orbit.
- Cutting the dural fold at the meningioorbital band disconnects the temporal dura from the frontal dura, making the anterior clinoid process more superficial.
- This extradural work leads to significant tumour devascularisation by interrupting supply from the middle meningeal, meningioorbital, and posterior ethmoidal arteries.
- Exposing the clinoidal internal carotid artery (ICA) provides a critical roadmap for the vascular tree as the tumour is resected.
- Optic canal and nerve management
- The optic canal is decompressed by removing the optic strut and the optic roof.
- The dural layer over the canal is opened to access tumour segments extending into the optic canal or the orbit.
- Extreme caution is required to preserve the small blood vessels from the superior hypophyseal branches and the ophthalmic artery that supplies the optic nerve
- Pealing off the temporal dura away from the lateral wall of the cavernous sinus may be extended to a more posterior point to remove tumor extending into the region of the cavernous sinus.
Intradural resection
- The Sylvian fissure is routinely opened from the level of the limen insulae toward its proximal point
- To visualise the entire course of the middle cerebral artery.
- Together with the MCA branches and the Clinoidal ICA, one can map out the medial aspect of the tumour
- Start debulking the tumour with intermittent dissection of the mass away from adjacent brain tissue and blood vessels.
- Once adequate debulking is achieved and the course of the different arterial branches is visualized, final tumor removal is performed.
- The dura at the base of the skull and over the clinoid region is totally removed. The underlying bone, which has partially been removed during the extradural removal of the anterior clinoid process, is further drilled and resected with a high-speed diamond drill and copious irrigation aiming at as complete a resection as possible and at the same time achieving bone hemostasis.
- The dural ring around the ICA is dissected to widen the space between the ICA and the optic nerve, providing access to subchiasmatic and retrochiasmatic regions.
- For tumour extensions along the tentorial edge, the third nerve can be identified extradurally at the level of the superior orbital fissure and followed from its extradural to its intradural segments under full visualization to mobilize and avoid its injury during tumor resection.
Reconstruction and closure
- The dural defect is reconstructed using fascia lata or pericranium.
- The clinoidal space is obliterated with subcutaneous fat (often harvested from the abdomen) and reinforced with fibrin glue.
- Lumbar drains are generally avoided as these robust closure techniques effectively prevent spinal fluid leakage.
Postoperative Care
- Observation and monitoring
- Patients spend a minimum of one night in the intensive care unit for close observation following the procedure.
- Once the patient is in a stable condition, they are transferred to a standard hospital bed floor.
- Physical activities are increased gradually as the patient recovers.
- Fluid and dietary management
- Patients are typically started on half normal saline running at approximately 80 mL per hour.
- An oral diet is usually initiated the day after surgery and increased gradually based on patient tolerance.
- Pharmacological interventions
- Dilantin is administered to provide prophylaxis against seizures.
- Patients receive 100 mg of hydrocortisone every 8 hours, which is then tapered by the time of discharge.
- Postoperative imaging
- A postoperative MRI scan is routinely performed within the first 24 hours after the operation.
- Thrombosis prevention
- Prophylaxis for deep vein thrombosis is essential because meningioma patients have a predisposition to this condition and the subsequent risk of pulmonary embolism.
- Preventive measures include the use of sequential compression devices, ted hose, and subcutaneous anticoagulants.
- Discharge
- Most patients are discharged from the hospital within 2 to 3 days of their surgery.
Outcomes
- Resection rates and factors affecting outcomes
- The rates of total resection for clinoidal meningiomas vary significantly across different series, ranging from 43% to 91%.
- These variations are primarily attributed to differences in patient mix, as well as the size and type of the tumour.
- Higher rates of mortality and morbidity are often observed in series with a higher percentage of cavernous sinus involvement, or in cases involving recurrent or previously radiated tumours.
- Postoperative morbidity
- Visual deterioration is the most common morbidity following the surgery of these tumours.
- The primary cause of visual decline is ischemic injury resulting from compromised blood supply to the optic apparatus.
- While major ischemic complications should generally be avoidable and occur at a very low rate, they are a risk if anatomical knowledge is insufficient.
- In cases of Type I tumours, surgeons may choose a subtotal resection to preserve function and avoid the high risk of arterial injury and ischemia associated with dense adhesions.
- Postoperative CSF leakage
- Rare
- Persistent leaks may be managed with lumbar drainage for 3 to 4 days if the initial reconstructive repair was satisfactory.
- If leaks continue, surgical re-exploration or an endonasal–transsphenoidal approach may be required depending on whether the leak manifests as wound drainage or rhinorrhea.
- Recurrence and long-term prognosis
- The risk of tumour recurrence or progression is closely linked to the extent of the initial resection.
- Because recurrence is also dependent on the length of time since the procedure, patients must be followed for no less than 10 years.
- Some clinical evidence suggests that follow-up should ideally continue for 20 to 25 years before a patient is permanently discharged.
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