Meningioma 42

• -Most common primary intracranial tumors
• -usually slow growing, circumscribed (non-infiltrating), benign lesions
• -Actually arise from arachnoid cap cells (not dura)
• -Histologically malignant (incidence: ≈ 1.7% of meningiomas)
• -May be multiple in up to 8% of cases, this finding is more common in neurofibromatosis
• -Found anywhere that arachnoid cells are found (between brain and skull, within ventricles, and along spinal cord)
• -Incidence peaks at 45 years age.
• -Female:male ratio is 1.8:1.
• -1.5% occur in childhood and adolescence, usually between 10–20 years age and occur in patients with neurofibromatosis type I (von Recklinghausen’s)

• parasagittal 20.8
• convexity 15.2
• tuberculum sellae 12.8
• sphenoidal ridge 11.9
• olfactory groove 9.8
• falx 8
• lateral ventricle 4.2
• tentorial 3.6
• middle fossa 3
• orbital 1.2
• spinal 1.2
• intrasylvian 0.3
• extracalvarial 0.3
• multiple 0.9

• Three basic categories:
• -lateral sphenoid wing (or pterional): behavior and treatment are usually similar to convexity meningioma
• -middle third (or alar)
• -medial (clinoidal): tend to encase the ICA and the MCA as well as cranial nerves in the region of the superior orbital fissure and the optic nerve. May compress brainstem. Total removal is often not possible

• -Up to 50% invade the superior sagittal sinus (SSS)
• -Based on location along AP direction of SSS as:
• 1 anterior (ethmoidal plate to coronal suture): 33%. Most often present with H/A and mental status changes
• 2 middle (between coronal and lambdoidal sutures): 50%. Most often present as Jacksonian seizure and progressive monoplegia
• 3 posterior (lambdoidal suture to torcular Herophili): 20%. Most often present with H/A, visual symptoms, focal seizures, or mental status changes
• #Parasagittal meningiomas may originate at the level of the motor strip, and a common initial manifestation of these is a contralateral foot drop

• Classification systems by Sindou et al 
• Type I= attachment to lateral wall of sinus
• Type II= invasion of lateral recess
• Type III= invasion of lateral wall
• Type IV= invasion of lateral wall and roof
• Type V= total sinus occlusion, contralateral wall
• spared
• Type VI= total sinus occlusion, invasion of all walls
• 

• Presentation (usually asymptomatic until they are large) may include:
• -Foster Kennedy syndrome:anosmia (patient is usually unaware of this), ipsilateral optic atrophy, contralateral papilledema
• -mental status changes: often with frontal lobe findings (apathy, abulia…)
• -urinary incontinence
• -posteriorly located lesions may compress the optic apparatus causing visual impairment
• -large lesions may compress the fornix and cause short-term memory loss
• -seizure

• Pre-op MRA, CTA or angiogram may be helpful to assess location of anterior cerebral arteries relative to the tumor
• 70–80% of these get the majority of their blood supply from the anterior ethmoidal artery, which is usually not embolized due to risk to ophthalmic artery (and blindness)

• Arise from the flat part of the sphenoid bone anterior to the chiasmatic sulcus in the posterior part of the anterior cranial fossa
• 

• -The tuberculum sellae is th e bony elevation between the chiasmatic sulcus and the sella turcica
• -site of origin of these tumors is only about 2 cm posterior to that of olfactory groove meningiomas
• -These tumors originate in the middle fossa (unlike planum sphenoidale meningiomas which are in the anterior fossa).

(By definition, the anterior margin of the chiasmatic sulcus (the limbus sphenoidale) is the demarcation between the anterior and middle cranial fossa)

• -TSMs are notorious for producing visual loss (chiasmal syndrome = primary optic atrophy + bitemporal hemianopsia)
• -When a TSM grows posteriorly into the sella turcica it may be mistaken for a pituitary macroadenoma

• -The neurologic symptoms and signs can be very confusing
• -In the French Cooperative Study, there were 106 FM meningiomas, 31% arose from the anterior lip, 56% were lateral, and 13% arose from the posterior lip of the FM
• -Most are intradural, but they can be extradural or a combination

• Four critical histopathological variables:
• 1. grade 
• 2. histological subtype 
• 3. proliferation indices 
• 4. brain invasion

WHO Grade Meningiomas(2000 classification)

• WHO I
• meningothelial or syncytial (m/c. Sheets of polygonal cells)
• fibrous (fibroblastic):cells separated by connective tissue stroma. Consistency is more rubbery than meningotheliomatous or transitional
• transitional (mixed):intermediate between meningotheliomatous and fibrous. Cells tend to be spindle shaped
• psammomatous:calcified meningothelial whorls
• angiomatous: AKA“humid” or vacuolated meningioma.Dilated extracellular spaces are usually emptycontain fat and PAS positive
• microcystic
• secretory
• lymphoplasmacyte-rich
• metaplastic

• WHO II
• chordoid
• clear cell (intracranial)
• atypical(increased mitotic activity (1–2 mitotic figure/hpf),increased cellularity, focal areas of necrosis, giant cells)

• WHO III
• papillary
• rhabdoid (usually have malignant features and behave aggressively)
• anaplastic
• -Malignant meningiomas: AKA anaplastic, papillary or sarcomatous: Characterized by frequent mitotic figures, cortical invasion, rapid recurrence even after apparent total removal.Frequent mitotic figures (≥ 4 mitoses per high-power field) or the presence of papillary features are strong predictors of malignancy. May be more common in younger patients

• The presence of brain invasion increases the likelihood of recurrence to levels similar to atypical meningiomas but is not an indicator of malignant grade.
• Adding the phrase “with brain invasion” is suggested to denote higher risk of recurrence

• -Very rarely a meningioma may metastasize outside the CNS
• -Most of th ese are angioblastic or malignant
• -Lung, liver, lymph nodes and heart are the most common sites

• 1 Multiple meningiomas: suggests neurofibromatosis 2 (NF2)
• 2 Pleomorphic xanthoastrocytoma (PXA): peripherally located and may have a dural tail
• 3 Rosai-Dorfman disease:  A connective tissue disorder with sinus histiocytosis and massive painless lymphadenopathy (most have cervical lymphadenopathy). Usually in young adults. MRI: duralbased enhancing mass with signal characteristics similar to meningioma, may have dural tail.Most common intracranial locations: cerebral convexities, parasagittal, suprasellar, cavernous sinus. stains for CD68 & S-100. Foamy histiocytes are characteristic. Surgery and immunosuppressive therapy not effective. Low-dose XRT may be the best option

• Symptoms depend on the location of the tumor
• -Seizures may occur with supratentorial meningiomas (irritation of the cerebral cortex)
• Asymptomatic meningiomas: most remain asymptomatic throughout the patient’s life. Routine use of CT & MRI for numerous indications discover incidental (asymptomatic) meningiomas

• Treatment is indicated for lesions that produce symptoms that cannot be satisfactorily controlled medically, or for those that demonstrate significant continued growth on serial imaging studies
• When surgery was performed, the perioperative morbidity rate is > 70 years old (23%) than in those <70 (3.5%)

MRI--Isointense with brain on T1WI and T2WI, but most enhance with gadolinium. Calcifications appear as signal voids on MRI.Gives information regarding patency of dural venous sinuses. “Dural tail” is a common finding.

• CT: --homogeneous, densely enhancing mass with broad base of attachment along dural border. Psammomatous calcifications. 
• Prostate cancer may mimic meningioma (prostate mets to brain are rare, but prostate frequently goes to bone, and may go to skull and can cause hyperostosis)

Angiography:--Classic pattern: “comes early, stays late” (appears early in arterial phase, blush persists beyond venous phase). Meningiomas characteristically have external carotid artery feeders

• Low frontal median (e.g. olfactory groove) meningiomas which feed from the ICA (ethmoidal branches of the ophthalmic artery).
• Suprasellar meningiomas may also be fed by large branches of the ophthalmic arteries.
• Parasellar meningiomas tend to feed from the ICA.
• Secondary vascular supply may be derived from pial branches of the anterior, middle, and posterior cerebral arteries.
• Artery of Bernasconi & Cassinari AKA artery of tentorium (a branch of the meningohypophyseal trunk) AKA “Italian” artery: enlarged in lesions involving tentorium (e.g. tentorial meningiomas)
• Angiography also gives in formation about occlusion of dural venous sinuses, especially for parasagittal/ falx meningiomas, confirm diagnosis by the distinctive prolonged homogeneous tumor blush, opportunity for pre-op embolization.
• Pre-op embolization : Reduces the vascularity of tumors, facilitating surgical removal. Timing of subsequent surgery is controversial. Some advocate waiting 7–10 days to permit tumor necrosis which simplifies resection. Complications: hemorrhage (intratumoral and SAH), cranial nerve deficits (usually transient), stroke from embolization through ICA or VA anastomoses, scalp necrosis, retinal embolus, and potentially dangerous tumor swelling.

Plain xrays:-- calcifications within the tumor (in ≈10%), hyperostosis or blistering of the skull, enlargement of vascular grooves (especially middle meningeal artery)

• Surgery is the treatment of choice for symptomatic meningiomas
• Serial imaging: Incidental meningiomas with no brain edema or those presenting only with seizures that are easily controlled medically
• Radiation therapy:  patients who are not surgical candidates, deep inaccessible tumors, recurrent meningiomas or atypical or malignant meningiomas either after initial subtotal resection or after first recurrence

• 1. early interruption of the blood supply to the tumor
• 2. internal decompression (using ultrasonic aspirator, cautery loops…)
• 3. dissection of the tumor capsule from the brain by cutting and coagulating vascular and arachnoid attachments while infolding the tumor into the area of decompression with minimal retraction on adjacent brain
• 4. removal of attached bone and dura when possible

• As usual, the head should be elevated ≈ 30° above the right atrium
• 1 tumors involving the anterior third of the SSS: supine semi-sitting position
• 2 tumors of the middle third of the SSS: lateral position with the side of the tumor down, the neck tilted 45° toward the upward shoulder
• 3 tumors of the posterior third of the SSS: prone position
• -Sinus involvement--leave residual tumor and consider treating it with radiation therapy than to cause a venous infarction

Superior sagittal sinus (SSS). If the tumor occludes the SSS, it has been suggested that the sinus can be resected carefully preserving veins draining into the patent portions of the sinus

• Before ligating the sinus, the lumen should be inspected for a tail of tumor within partial occlusion of superior sagittal sinus
• 1. anterior to the coronal suture, the sinus may usually be divided safely
• 2. posterior to the coronal suture (more accurately – posterior to the vein of Trolard), it must not be divided or else severe venous infarction will occur
•     a) with superficial involvement: tumor may be dissected off the sinus with care to preserve patency
•      b) with extensive involvement: sinus reconstruction is hazardous. Thrombosis rate using venous graft 50% & 100% with artificial grafts. Best is to leave residual tumor, and follow with CT or MRI. If the residual tumor grows or if the Ki-67 score is high, SRS may be used

• -Once tumor is exposed a partial internal debulking is performed.
• -Then the point of attachment (to the falx or sphenoid bone) is peeled away using bipolar cautery to divide feeding vessels.
• -Then the main portion of the tumor may be separated from brain

• Parasagittal and falx meningiomas:-
• -Middle or posterior third tumors are exposed using a horseshoe incision based in the direction of the major scalp feeding vessels with patient in a lateral or sitting position
• -Anterior third tumors are approached using a bicoronal skin incision with the patient supine position
• (The inferior portion of the tumor may adhere to branches of the anterior cerebral artery)

• Sphenoid wing meningiomas:
• -A pterional craniotomy done and  neck is extended to allow gravity to retract the brain off of the floor of the skull.
• Lateral sphenoid wing meningiomas: approach to these tumors is often similar to convexity meningiomas.
• Medial sphenoid wing meningiomas: A lumbar drain is used. The head is turned 30° o the vertical.An FTOZ approach may provide additional exposure.The sylvian fissure is split widely. The ICA and MCA are often encased by tumor. The optic nerve is best identified at the optic canal. The deep portion of the tumor often has numerous small parasitic vessels from the ICA (which makes this part very bloody), and may also invade the lateral wall of the cavernous sinus (which creates risk of cranial nerve deficits with attempted removal). Therefore, the recommendation is to leave some tumor behind and use radiosurgery to deal with it.

• Olfactory groove meningiomas:
• -Approached via a bifrontal craniotomy (preserving the periosteum to cover the fron tal air sinus and floor of frontal fossa at the end of the case)
• -For large tumors, a lumbar CSF drain will help with brain relaxation
• -The head is rotated 20° to one side to facilitate dissection of the anterior cerebral arteries and optic nerve while preserving visualization of both sides of the tumor involvement
• -The neck is slightly extended
• -The dura is opened low, and the superior sagittal sinus is ligated and divided at this location
• -Amputation of the frontal pole should be done if necessary to avoid excessive retraction
• -Initially, the anterior tumor capsule is opened and the tumor debulked from within heading towards the floor of the frontal fossa
• -The posterior capsule of the tumor is dissected carefully as this portion of the tumor may encase branches of the ACA and/or optic nerves and chiasm
• -Post-op risks include CSF leak through the ethmoid sinuses

• Tuberculum sellae meningiomas:
• -Tumors typically displace both optic nerves posteriorly and laterally
• -Occasionally, the nerves are completely engulfed by tumor

• Cerebellopontine angle meningiomas:
• -Usually arise from the meninges covering the petrous bone.
• -May be divided into those that occur anterior to, and those that occur posterior to the IAC

• Foramen magnum meningiomas:
• -Posterior or posterolateral lip of the foramen magn um (FM) are removed relatively easily by Posterior suboccipital approach
• -Anterior and lateral FM tumors may be operated by the posterolateral approach (transcondylar approach may alternatively for anterior)

• -ineffective as primary modality of treatment
• -not to use XRT for “benign” lesions
• -Efficacy of XRT in preventing recurrence is controversial
• -For recurrent atypical or anaplastic meningioma with residual disease post-op, XRT with 55– 60 Gy is recommended

• 5 year survival for patients with meningioma: 91.3%
• The extent of surgical tumor removal is the most important factor in the prevention of recurrence.
• The Simpson grading system for the extent of meningioma removal
• Recurrence after gross total tumor removal (11–15%) & incomplete removal(29%)
•  
• Simpson grading system for removal of meningiomas
• Grade I: macroscopically complete removal with excision of dural attachment and abnormal bone (including sinus resection when involved)
• II:  macroscopically complete with endothermy coagulation (Bovie, or laser) of dural attachment
• III: macroscopically complete without resection or coagulation of dural attachment or of its extradural extensions (e.g. hyperostotic bone)
• IV: partial removal leaving tumor in situ
• V: simple decompression (± biopsy)