Neurosurgery notes/Tumours/Meningioma/Convexity Meningiomas

Convexity Meningiomas

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Meningioma

General

  • Difficulties often lie in deciding when to operate and how to manage recurrent or residual disease

Definition

  • Convexity refers to those meningiomas that do not extend into the dura mater of the skull base and do not involve the dural venous sinuses

Epidemiology

  • 15% of all meningiomas
    • Most common tumors of the cranial vault
    • Second-highest incidence after parasagittal meningiomas

Classification

  • Cushing and Eisenhardt: Recognizes the eloquent (or non-eloquent) nature of the underlying cortex
    • Precoronal
    • Coronal
    • Postcoronal
    • Paracentral
    • Parietal
    • Occipital
    • Temporal
  • Radiographic appearance:
    • Globose:
      • Classic spherical, lobulated mass
    • En plaque.
      • Lesions that have a flatter, carpet like appearance infiltrating the dura.

Presentation

  • Protracted clinical course and larger-than-expected tumors at the time of diagnosis
    • Due to slow growing nature of meningiomas
  • Incidental diagnosis (14 to 20%)
  • “Symptomatic”
    • Most patients present with signs and symptoms attributable to mass effect and the tumor site.
    • Headache
      • Most common symptom (39 to 48%)
    • Seizures
      • (20 to 34%) remains common in modern-day studies and is most often seen with temporal meningiomas.
    • Site-specific symptoms can include
      • Frontal: confusion, memory loss, depression/personality alteration
      • Perirolandic lesions: motor or sensory deficit
      • Occipital: visual field deficits, including field cuts, disturbances in color perception and tracking objects;
      • Parietal: neglect, alexia, and difficulty with calculation
      • Dominant-sided pterional or posterior temporal lesions: aphasias

Pathology

  • Dural tail
    • Due to (theories)
      • Neoplastic infiltration of surrounding dura (65%)
      • Reactive inflammatory response (35%)
        • Nonneoplastic meningothelial proliferation, hypervascularity, and vascular dilatation
  • Blood supply
    • Meningeal arteries
    • Additional cortical blood supply

Natural history of convexity meningioma

  • Yano and Kuratsu-37% of meningiomas showed growth on imaging during observation for 3.9 years
  • The growth rate of meningiomas might be linear and not logarithmic (as seen with malignant astrocytomas)
    • The growth of observed lesions can often be erratic (or intermittent) where lesions that have been stable on serial imaging can demonstrate relatively rapid growth within a short time period.

Radiology

  • CT
    • Hyperostotic changes
  • MRI
    • T1:
      • 60% of meningiomas are isointense,
      • 30% are hypointense compared with gray matter
    • T1+C: Strong enhancement
    • T2
        • CSF cleft around the lesion
        • Peritumoral edema
          • Vascular supply from pial-cortical arteries
          • Cortical invasion
          • Meningothelial, anaplastic, microcystic, and angiomatous subtypes display higher edema indices than other types
          • Venous flow obstruction
        • Local vasculature: vascular flow-voids
        • Hard vs soft tumour
          • T2 Hyperintensity: higher water content indicating a softer tumor
          • T2 Hypointensity: fibrous or calcified tumor
        notion image
         
  • MRA/CTA
    • Not normally used
    • For assessing
      • The extent and pattern of vascularity,
      • The extent of tumor encroachment on vascular structures,
      • The feasibility of embolization

Management

Conservative

  • Indication
    • Asymptomatic patients AND
    • >70 age OR have poor medical status AND
    • Do not have any associated peritumoral edema
  • Danger of observation
    • Higher-grade meningiomas can be missed, with subsequent delay in surgery resulting in potentially higher operative risk and possibly affecting the long-term outcome.

Surgical treatment

Indication

  • Based on: patient’s age/medical status, tumor size, symptom complex, and associated edema.
  • If younger patient AND Asymptomatic AND tumour smaller than 3cm AND no oedema
    • Let patient decide between conservative vs surgery

Goal

  • Grade zero resection (tumor resection plus excision of a surrounding 2 cm dural margin

Preop

  • Dexamethasone is started at least 2 weeks preoperatively
    • For patient with peritumoural oedema
  • Antiepileptics
    • Patient presenting with seizure: started preoperatively
    • Patient without seizure: loading dose of an anticonvulsant is given intraoperatively at the start of surgery

Operative Technique

Patient Positioning
  • Patient is positioned in such a way as to allow the surgeon to operate in a plane parallel to the floor.
    • Allows the surgeon to work in an ergonomically comfortable position
    • Ensuring that any blood pooling occurs at the bottom of the resection cavity—ensuring good visualization.
  • Frontal pole tumors
    • Supine + slight head turn
    • Bicoronal incision placed behind the hairline
      • A unilateral craniotomy
  • Lateral sphenoid wing or frontotemporal tumors
    • Supine +head turned 45 degrees
    • Standard pterional incision is performed
      • Scalp and temporalis dissected separately
  • Posterior temporal and lateral parietal region tumours
    • Supine + head turned +Shoulder roll
    • Large linear skin incision
  • Medial parietal or occipital lobe tumors
      • Straight prone OR Park-bench with the head turned.
      • A linear incision or a mitre flap
        • Depending on the size of the lesion
      (C) Inion Hockey-stick incision Mitre flap U-shaped horseshoe incision Retromastoid curvilinear incision
Incision
  • Planned, using neuronavigation to ensure a large enough craniotomy can be created to encompass the entire tumor and surrounding dural margin.
  • Scalp flap should be planned to avoid cosmetic deformity and to avoid division of vascular pedicles supplying the scalp.
  • A two-layer dissection during the exposure, harvesting a large pericranial graft that can be used for dural closure
Craniotomy
  • A craniotomy large enough to completely expose tumour and surrounding dura is performed.
  • After creation of the flap, the underlying dura is carefully dissected free with a Penfield dissector.
  • The bone flap is lifted gently to gain more space for dural dissection in an effort not to manipulate the underlying meningioma, which could inadvertently tear the dura and pia–capsule connections between the tumour capsule and surrounding cortex.
  • Bleeding should be controlled with bipolar coagulation, hemostatic agents, or rapid dural incision/ early devascularization.
  • Tumors with calvarial involvement
    • Attempting to dissect the tumor–calvarial interface with a Penfield dissection as with standard craniotomies can be difficult and even harmful to underlying brain parenchyma.
    • Technique
      • Use neuronavigation (with CT and MRI) to delineate the margins of the tumor–calvarial interface.
      • A series of burr holes ~2 mm apart surrounding the invaded bone are created, with the intervening bone removed by rongeur or drilling.
      • Bleeding from the bone edges is controlled with bone wax.
      • Subsequently, if necessary, a larger craniotomy flap can then be created to expose the remaining intradural component of the tumor.
    • Sometime with these tumours the overlying pericranium may also be infiltrated with tumor;
      • This segment of the harvested pericranial graft must be excised and cannot be used in reconstruction.
Dural Incision and Early Devascularization
  • A dural incision is made circumferentially around the tumour with approximately a 2 cm margin from the contrast-enhancing component of the lesion based on MR neuronavigation.
  • Meningiomas can be quite vascular
    • Coming from hypertrophied and tortuous branches of the meningeal arteries.
  • Due to the possibility for significant blood loss, early devascularization is critical and facilitates a meticulous and bloodless extracapsular dissection as opposed to a hurried and bloody dissection.
    • With convexity meningiomas, this step is easily performed at the time of dural incision where the tumor’s vascular pedicles are encountered and sacrificed
Internal Debulking
  • Ultrasonic Aspirator
    • To debulk medium and large tumour to reduce brain retraction
    • Not effective with fibrous or calcified tumors
    • Use can be tedious with vascular tumors
      • Use yttrium-aluminum-garnet laser because it slices tumor tissue with direct contact while providing hemostasis.
  • The process of debulking is performed until a thin rim of capsule remains.
Capsular Dissection
  • Surgical microscope is critical
  • Goal is to dissect the capsule free from any attached pia while preserving all adjacent neurovascular structures
  • First identify and preserve the layer of arachnoid at the brain–tumor interface.
  • As the dissection proceeds circumferentially around and toward the apex of the tumor, the capsule (as opposed to brain) is manipulated to any cortical attachments or adherent vascular structures.
  • Any small pial–tumor adhesions are bipolared and sharply divided.
  • Arteries: No artery is sacrificed unless the vessel is confirmed to be a tumor feeder.
    • A majority of arterial structures encountered are often en passant vessels or loops of vessels that have become encased by tumor or adherent to the capsule.
    • Lateral sphenoid wing meningiomas can often dive into the sylvian fissure, engulfing middle cerebral artery (MCA) branches;
    • Convexity meningiomas rarely have feeders directly coming from large cerebral arteries;
      • Hence these branches must be preserved.
  • Veins
    • Sizeable cortical veins may be encountered and also must be carefully dissected to prevent local and distant venous infarction.
  • Tumor–arachnoid plane must be maintained such that the arachnoid is dissected free from the tumor and not from the brain.
    • Cottonoid patties are sequentially and circumferentially placed to preserve already dissected brain-arachnoid and any major vascular structures
  • Difficulty can be encountered with aggressive meningiomas with brain invasion.
    • The decision to chase tumor into underlying parenchyma is based on whether the invaded cortex is eloquent or noneloquent.
      • In this decision making, diffusion tensor imaging and cortical stimulation can serve as useful adjuncts to anatomically and functionally identify critical white fiber tracts.
  • After complete dissection, the tumor is completely removed, exposing the tumor bed and patties
Dural Reconstruction and Closure
  • After tumour resection, the surrounding dura is carefully inspected for any residual tumor.
  • A watertight dural closure is obtained utilising a harvested pericranial graft (preferable) or an artificial dural substitute.
  • The dural suture line is then reinforced with glue (i.e., fibrin glue).
  • For convexity meningiomas with calvarial invasion and resection, a recessed titanium cranioplasty is performed

Postoperative Management

  • The onset of a new postoperative neurological deficit or seizure must be investigated with vigilance, including
    • Blood tests
    • Imaging to rule out a haemorrhage or infarction
      • Secondary to intraoperative sacrifice of a critical arterial or venous structure.
  • MRI + C is obtained postoperatively to document the extent of resection.
  • Seizure prophylaxis is typically continued for at least 3 months postoperatively, at which point an electroencephalogram is obtained to rule out any epileptic focus.
  • In symptomatic patients or those with peritumoral edema, steroids are slowly weaned postoperatively over the course of days.
  • DVT prophylaxis should be used
    • Patients with meningiomas have among the highest rates of thromboembolic complications in the neurosurgical population.

Radiosurgery

  • Reluctant to recommend radiosurgery as the initial treatment for any tumor where histological grade is not known
    • For fear of improperly treating WHO grade II and III meningiomas,
      • Where a combined surgical and radiation therapy approach is preferable
  • Focused radiation in convexity meningiomas tumor control rates 71% at 5-year follow-up-Kondziolka et al 2009
    • This is mixture of different grades of meningioma and some resected and non resected meningiomas

Outcome

  • Good outcome in general
    • Due to their anatomical location and ease of access
    • WHO grade I convexity meningiomas are considered a surgically curable entity.
  • Recurrence rate
    • Overall recurrence rate of 3 to 4%.
    • 0% recurrence with grade zero resection and World Health Organization (WHO) grade I meningiomas
    • Recurrence is primarily seen with atypical and anaplastic tumors or subtotally resected lesions.
    • The mean time to recurrence has been reported to be anywhere from 11 to 14 months—highlighting the importance of close imaging follow-up.
  • Survival
    • 5-year survival of 90%.
    • 30-day mortality rate: 0%
    • Surgical morbidity is 1.7 to 3%.
      • New-onset neurological deficit/seizure
      • Surgical site hematoma
      • CSF leaks
      • Wound infection.

Management of Residual and Recurrent Disease

  • Primarily an issue with grade II and III tumors with or without brain invasion;
  • For subtotally resected grade I meningiomas, perform regular follow-up imaging to assess for growth.
  • Focused stereotactic radiation for recurrent meningiomas.
  • Controversy around postoperative radiation therapy.
    • Modha and Gutin have suggested that grade II and III tumors that are either subtotally excised, invade the brain, or have a mindbomb homog-1 (MIB-1) index greater than 4.2% should be treated with radiation.
  • Repeat microsurgical resection
    • Indication for
      • Young patients
        • Where the long-term effects of radiation are best avoided
      • Symptomatic patients with associated edema
      • WHO grade II and III meningiomas that have demonstrated growth despite postoperative radiation.