General
- Commonly
- Meningothelial and fibrous types
Numbers
- Account for 9 to 18% of all meningiomas
CNS WHO grading
- Grade I meningiomas
Location
- Region of the frontosphenoid suture
- May involve any part of the area from the crista galli to the planum sphenoidale
- Sub classification (Not useful)
- Anterior
- Middle
- Posterior
Anatomy
- Adjacent bone involvement
- Commonly cause hyperostosis of the floor of the anterior cranial fossa.
- They may also erode the bone and grow into the ethmoid sinus in 15 to 20% of cases
- Olfactory nerves
- Rarely found to be completely encased by tumor
- Can usually be identified displaced laterally by the tumor over the orbital roofs
- Anterior cerebral artery
- ACAs are thus found posterosuperior and lateral to OGMs
- The medial orbitofrontal and frontopolar branches may become incorporated into the tumor capsule.
- Tumour blood supply
- Anterior and posterior ethmoidal arteries
- Sphenoidal branches of the middle meningeal artery
- Pial supply from the anterior cerebral and anterior communicating arteries
- Occasionally
- Will be present when the tumors are quite large
Clinical features
- Present insidiously
- Due to their
- Slow growth
- Subfrontal location
- Can grow very large
- Change in personality, judgment, or motivation
- More common
- Noted by family members or close contacts, but not usually by the patient.
- Headaches and visual disturbances
- When lesions may grow to a very large size
- Late in the course of the disease.
- Olfactory dysfunction
- Patients rarely complain of altered smell or taste, despite the olfactory tracts becoming distorted early.
- Foster-Kennedy syndrome
- Features
- Anosmia
- Unilateral optic atrophy
- Contralateral papilledema
- Initially described in a midline frontal meningioma and in 24% of Cushing’s cases
- Rarely seen in modern series.
- Visual field defect
- Less common
- Inferior field defect
- Because of the growth pattern (posteriorly and inferiorly) → compress the optic nerves
Imaging features
CT
- Look for
- Extent of hyperostosis
- Frontal air sinus
MRI
- Modality of choice for definition of the pathological anatomy
- Look for
- Paranasal sinus involvement by tumor
- Location of the optic chiasm
- Location of cerebral vessels
- Any tumor extending posteriorly to involve the sella
- T2
- Degree of frontal lobe edema,
- Correlate with the extent of pial blood supply.
- Infarction of the frontal lobe
- Brain invasion
- Identifying
- Vascular flow voids of blood vessels in proximity to the tumour
DSA
- Rarely required because the major feeding vessels can be surgically divided early in the operative procedure
- Embolization is rarely required or technically possible.
Management
Conservative
- Incidentally identified + asymptomatic tumours >2.5 cm can almost always be managed, at least initially, by serial clinical, neuropsychological, ophthalmological, and magnetic resonance (MR) observation.
- Should evidence of tumour growth or clinical, neuropsychological, or ophthalmological deterioration become evident, then surgical excision is the management of choice for those medically fit.
Surgery
- Aim
- Completely resect the tumour, including involved bone and any tumour extending into the ethmoid sinus, with preservation of neurological function.
- Approaches
- For larger tumours (>3 cm), a bicoronal flap is turned.
- For smaller tumours (<3 cm), a unicoronal flap is turned.
- Advantages
- Early devascularization along the skull base with division of feeding vessels
- Allows for access into orbits to coagulate the ethmoidal arteries that supply the majority of the tumor
- Orbital osteotomies minimize frontal lobe retraction.
- Allows for harvesting of vascularized pericranium for skull base reconstruction
- Disadvantages
- Opens frontal sinus, the increasing risk of CSF leak and infection
- Sacrifice of anterosuperior sagittal sinus
- General
- For large tumour
- Advantage
- Good anatomical view
- Good access to the anterior skull base for those tumours causing hyperostosis and particularly those invading the ethmoid sinuses
- Devascularize the tumour early in the procedure
- Ability to create a robust vascularized reconstruction.
- Disadvantages
- Anomia
- Positioning
- Advantages
- Early exposure of optic apparatus and carotid artery prior to tumour manipulation
- Early access to basal cisterns for CSF drainage for brain relaxation 4
- Shorter distance to tumour 4
- Avoids entry into frontal sinus 1
- Spares venous structures
- Less frontal lobe retraction unless orbital osteotomies are performed with subfrontal approach
- Disadvantages
- Narrow working angle
- May be blinded in upper portion of tumour, which may require extensive frontal lobe retraction
- Difficult to access ethmoid arteries
- Difficult to repair basal skull defects
- PB
- Positioning
- Supine, 3 pins, Shoulder roll, head turn 10-15 degrees.
- Skin incision
- Curve incision starting from just anterior to tragus crossing midline
- Does not need to go too low down to the EAM
- Craniotomy
- Do not need to go below the sphenoid wing.
- Do first burr hole at the keyhole and go above the sphenoid wing
- Care not to get into frontal air sinus
- Keep away from midline
- Durotomy U shaped towards midline.
- Get fixed retractor to retraction frontal lobe from the midline towards lateral and posteriorly.
- Advantages:
- Preserves superior sagittal sinus
- Frontal sinus not opened
- Careful dissection can minimize frontal lobe elevation/retraction
- Disadvantages:
- Higher risk of contusion to frontal lobes
- Operative route is long and narrow
- Risk to bridging veins
- Difficult to access vascular supply
- Advantages:
- Direct exposure of tumor with minimal brain retraction
- Early devascularization of tumor
- Easy access to tumor that has invaded paranasal sinuses
- Disadvantages:
- Learning curve associated with endoscopic technique
- Unable to access large intracranial extensions of tumor
- May have increased rates of CSF leak and recurrence rates compared to open surgical techniques
- Lateral-orbital
Subfrontal (with orbital osteotomy) approaches
Bifrontal
Pterional
Approach | Advantage | Disadvantage |
Pterional | - Optic apparatus and ACA seen early - Early cistern opening drains cerebrospinal fluid - Avoids frontal sinus entry - Shorter operative time - Shorter distance to ipsilateral tumor | - Narrow working space - Upper portion of tumor may be hidden - Greater distance to contralateral tumor - Orbital roof height obscures base |
Subfrontal | - Wide frontal exposure - Direct access to cranial base - Early division of main blood supply - Easier to repair cranial base | - Frontal sinus opened - SSS divided - ACA and optic apparatus seen late |
Interhemispheric
Endoscopic endonasal transcribriform
- Key steps
- Devascularize
- Bipolar the base of the meningioma to cut the anterior and posterior ethmoids off
- Debulk
- The tumour with suction or sonopet
- Disconnect
- From lateral and superior surface of the tumour
- Look out for ACA vessels
- Visualization of origin along cranial base
- Dissection, not resection, of frontal lobes
- Tumour debulking and continued devascularization
- Identification and preservation of optic apparatus, olfactory nerve, cerebral vessels
- Resection of involved bone and dura in the cranial base
- Repair of surgical defects
Radiotherapy
- Primary radiation should be reserved for patient refusal of surgery or for medically unfit patients
Prognosis
- These tumors may have a high predilection for late recurrence at the cranial base and sinuses, with rates as high as 23 to 41% at 10 years.
- Due to the increased difficulty and risks associated with reoperations, aggressive primary resection including drilling of hyperostotic bone, removal of dura as well as resection of sinus extension to reduce the chance of recurrence should be a goal of this surgery.
- In these circumstances, reconstruction of the skull base is a necessity to prevent postoperative CSF leaks and meningitis.
Summary
Features | Olfactory groove meningiomas (OGM) | Planum sphenoidale (PSM) | Tuberculum sellae meningiomas (TSM) |
% of all intracranial meningioma | 10% | 5% | 10% |
Site of origin | Frontosphenoid suture | Anterior to the limbus sphenoidale | Posterior to the limbus sphenoidale: Tuberculum sella, limbus sphenoidale, chiasmatic sulcus, diaphragma |
Main blood supply | - Anterior and post ethmoidal - Sphenoidal branch of MMA - Pial supply from anterior cerebral and anterior communicating arteries | - Post-ethmoidal - Capsular arteries (from cavernous ICA) | |
Olfactory nerves | Lateral | Inferior | |
Optic apparatus | Inferolateral | Superolateral | |
Displacement of chiasm | Depression | Depression | Elevation |
Visual field deficit | Inferior | Inferior | Bitemporal |
Anterior cerebral arteries | Posterosuperior | Posterosuperior | Posterosuperior |
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