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High Parietal & Occipital Bilateral Parafalcine Meningioma (Redo): A Neurosurgery Resident's Complete Reference

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1. Anatomy and Surgical Relevance

The Falx Cerebri and Parafalcine Space

• Parasagittal = attached to, invades, or occludes the SSS
• Parafalcine = attached to the falx below the SSS, growing into the interhemispheric fissure, often pushing into the medial hemispheres bilaterally

High Parietal Region: Critical Structures

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2. Epidemiology

• Meningiomas = 20-25% of all intracranial tumors; parasagittal/parafalcine = ~25% of all convexity/parasagittal locations (the most common single location group, ~50% combined with convexities) - Bradley and Daroff's Neurology, p. 1531
• F:M ratio = 2:1; peak incidence >50 years
• NF2 association: bilateral or multiple meningiomas suggest NF2 (chromosome 22 mutation)
• WHO grade: ~80% grade I, 15-20% grade II (atypical), ~1-2% grade III (anaplastic) - Bradley and Daroff's Neurology
• Recurrence data (Khanna et al., Acta Neurochir 2023, n=110): 33.6% recurrence at median 42 months; parafalcine meningiomas had better PFS than parasagittal ones (p=0.045) [PMID: 37987849]

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3. Clinical Presentation

By Location (High Parietal / Occipital Parafalcine)

• Leg/foot weakness - often the presenting symptom, as medial M1 controls lower extremity; may be bilateral for large bilateral tumors
• Gait disturbance - from bilateral proximal leg weakness
• Urinary incontinence - from medial frontal/parietal dysfunction
• SMA syndrome (if anterior paracentral lobule compressed) - transcortical motor aphasia if dominant side, akinetic mutism
• Jacksonian march seizures beginning in the foot/leg - very characteristic

• Contralateral homonymous hemianopia or quadrantanopia (V1 involvement)
• Visual aura seizures
• May be asymptomatic for long periods (silent area)

• Bilateral leg weakness / spastic paraparesis - mimics spinal cord disease
• Sphincter dysfunction
• Cognitive change (bilateral medial frontal involvement)

• Slowly progressive (months to years)
• Headache (raised ICP, large tumors)
• Papilledema in large tumors
• Seizures (any cortical irritation)

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4. Imaging

MRI - the key modality

Key imaging findings specific to parafalcine:

• Coronal gadolinium-enhanced T1 is the most informative view: shows interhemispheric location, falx attachment, bilateral extension, displacement of pericallosal arteries, and relationship to SSS
• Look for "hypointense flow void" of pericallosal arteries trapped between tumor and medial brain - ACA displacement or encasement is a major surgical hazard
• Assess whether the tumor is unilateral or bilateral through the falx
• Grade sinus involvement (Sindou classification)

MR Venography / CT Venography:

• Essential preoperative study - determines SSS patency
• Classify SSS involvement:
  • Grade 0: tumor touches outer wall
  • Grade 1: outer wall invaded
  • Grade 2: lateral recess invaded
  • Grade 3: one lateral wall invaded
  • Grade 4: both lateral walls invaded
  • Grade 5: completely occluded sinus

CT:

• Hyperdense on non-contrast CT
• Calcification (psammoma bodies) - gritty texture on surgery
• Hyperostosis of calvarium
• Perilesional edema
• Bone windows for craniotomy planning

Angiography (DSA):

• "Mother-in-law sign" - contrast stasis in tumor during venous phase (hypervascular blush)
• Assess feeding arteries (branches from middle meningeal artery, posterior branches for occipital lesions)
• Preoperative embolization if hypervascular: reduces intraoperative blood loss
• Assess collateral venous drainage if SSS is compromised

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5. Pathology

WHO Classification (2021)

• Meningothelial (most common) - whorls, psammoma bodies, EMA+
• Fibroblastic - spindled cells, collagen
• Transitional (mixed)
• Psammomatous, angiomatous, microcystic, secretory, lymphoplasmacyte-rich, metaplastic

• ≥4 mitoses per 10 HPF
• OR ≥3 of 5 minor criteria: sheeting architecture, hypercellularity, macronucleoli, small cell formation, necrosis
• Clear cell variant or chordoid variant (by definition grade II regardless)
• Ki-67 (MIB-1) elevated; progesterone receptor reduced

• 20 mitoses per 10 HPF

• OR frank anaplasia (sarcoma-like or carcinoma-like)
• Papillary variant or rhabdoid variant (by definition grade III)
• Median survival <2 years
• Bradley and Daroff's Neurology, p. 1532

Key immunohistochemistry:

• EMA positive (best marker of meningothelial differentiation)
• Progesterone receptor positive in >50% of grade I (decreases with higher grade)
• S-100 variable
• Ki-67 index: important prognostic marker

Molecular biology:

• Majority: loss of chromosome 22 / NF2 mutations (explains NF2 association)
• Non-NF2 group: TRAF7, SMO, AKT1, or KLF4 mutations
• Higher grades: CDKN2A/B deletion, TERT promoter mutations = worst prognosis
• SMO and AKT1 mutations = potentially druggable targets
• Bradley and Daroff's Neurology, p. 1532

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6. Surgical Management

6a. Patient Positioning

• Supine with head flexed and rotated or lateral decubitus (park-bench) for unilateral approach
• For midline bilateral tumors - prone position (Concorde/prone) is preferred for occipital parafalcine lesions - gives gravity-assisted retraction away from the sinus
• Head fixed in Mayfield/Sugita 3-pin clamp
• Ipsilateral shoulder elevated 15-30° to reduce neck strain

6b. Craniotomy Design

1. High parietal parafalcine: Parasagittal craniotomy straddling the midline (bicoronal or "lazy S" incision), crossing the SSS to allow bilateral access to the interhemispheric fissure
2. Occipital parafalcine: Occipital craniotomy, may need to extend contralaterally
3. Burr holes placed lateral to the SSS first, then a burr hole medially (close to but not over the SSS) - joining with a craniotome
4. The bone flap should allow full visualization of the falx from the SSS superiorly to the inferior sagittal sinus

6c. The Interhemispheric Approach: Key Steps

1. Open dura in a "C" or "U" flap based away from SSS
2. Retract the hemisphere GENTLY using gravity and self-retaining retractors (avoid prolonged pressure >20 mmHg); irrigation with saline helps open the fissure
3. Identify the falx - the tumor arises from its lateral surface or may have eroded through it
4. Identify and protect the pericallosal arteries - these run in the interhemispheric fissure and can be draped over, displaced by, or incorporated within the tumor
5. Debulk the tumor internally first (ultrasonic aspirator - CUSA) before dissecting the capsule
6. Bipolar coagulation of the dural base (falx) to devascularize
7. Work systematically to dissect the tumor from medial brain surface
8. For bilateral tumors - work from the larger side first, then the contralateral side through the same corridor or via a contralateral opening

6d. Critical Intraoperative Hazards

• NEVER sacrifice the SSS in its posterior two-thirds - this causes bilateral venous infarction, cerebral edema, and death
• The anterior third can be ligated if already occluded and collaterals are established
• If the sinus wall is invaded but not occluded: leave the sinus wall intact (Simpson grade II resection)
• If completely occluded with established collaterals: en bloc resection with reconstruction may be possible (only by experienced teams with sinus reconstruction capability)

• Multiple bridging cortical veins drain from medial parietal/occipital cortex into the SSS
• Sacrifice must be minimized - loss of dominant bridging veins causes venous infarction
• For redo surgery, these veins are often adherent to scar/tumor and distinguishing viable from non-functional veins is harder

• Displacement is common; encasement is dangerous
• Never sacrifice - bilateral ACA territory infarction = bilateral leg paralysis
• Doppler probe or ICG angiography intraoperatively confirms vessel patency

• For tumors abutting the paracentral lobule: intraoperative neurophysiologic monitoring (IONM) is mandatory
• Motor Evoked Potentials (MEPs) for lower extremity motor cortex
• Somatosensory Evoked Potentials (SSEPs)
• Direct cortical stimulation if awake craniotomy is performed

6e. Neurophysiologic Monitoring (IONM)

• MEPs (transcranial or direct cortical) - lower extremity leads are critical
• SSEPs - bilateral lower extremity monitoring
• EEG - for seizure detection under anesthesia
• Changes in MEPs (>50% amplitude drop, >10% latency increase) = stop retraction, reassess vascularity
• In redo cases: baseline values may be abnormal; interpret trends rather than absolute values

6f. Simpson Grading - Extent of Resection

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7. The Redo (Recurrent/Reoperation) Surgery

7a. Why Redo Is Harder

7b. Preoperative Planning for Redo

1. Complete MRI protocol: 3T with gadolinium, MR spectroscopy (to distinguish recurrence vs. radiation necrosis), perfusion MRI
2. MRV/CTV: Reassess SSS status - may have changed since first surgery
3. Functional MRI (fMRI) and DTI tractography: Map motor/sensory cortex and corticospinal tract - especially critical because prior surgery may have shifted eloquent cortex
4. PET scan: DOTATATE PET is highly sensitive for meningioma recurrence; distinguishes active tumor from scar
5. DSA with embolization planning: Embolize feeder vessels 24-72 hours preoperatively
6. Surgical simulation/neuronavigation: Import MRI/MRV data; plan craniotomy to avoid prior scar burden zones
7. Multidisciplinary team decision (neurosurgery, radiation oncology, neuro-oncology): Is repeat surgery the best option, or is SRS appropriate?

7c. Indications for Redo Surgery vs. SRS

• Redo surgery preferred: Mass effect with neurological decline, tumor >3-3.5 cm (too large for SRS alone), suspected high-grade transformation, need for tissue diagnosis, failed prior SRS
• SRS (adjuvant or upfront for recurrence): WHO grade I residual/recurrence without significant mass effect, tumors ≤3 cm, patients unfit for surgery
• Meta-analysis (De Nigris Vasconcellos et al., Neurosurg Rev 2024): SRS achieved tumor control in >80% overall, 97% in upfront SRS group; adverse radiation effects 7.3%; edema 25% (usually medically manageable) [PMID: 38514580]

7d. Redo Surgical Strategy

1. Extend the old craniotomy or make a fresh adjacent craniotomy - avoid pulling scarred skin flap
2. Extradural dissection first: Carefully separate dura from bone before opening - the dura may be stuck to the bone flap
3. Open dura away from scar - find a virgin dural plane before approaching the tumor
4. Identify normal brain first at the margins, then dissect toward tumor
5. CSF drainage early: Lumbar drain or external ventricular drain to relax the brain before retraction
6. Internal debulking priority: CUSA from inside out; never pull the tumor away from the brain
7. Leave adherent tumor on eloquent cortex: Better to leave a small amount on M1/S1 than cause permanent deficit - radiosurgery for residual
8. Sinus reconstruction: If the SSS needs to be opened (completely occluded), synthetic or autologous graft reconstruction is performed; saphenous vein or PTFE graft can be used
9. Dural repair: Pericranium, fascia lata, or synthetic dural substitute - ensure watertight closure to prevent CSF leak

7e. Independent Predictors of Recurrence After Surgery

• WHO grade II/III (HR 3.62, p=0.002)
• Complete sinus invasion (HR 3.00, p=0.024)
• Subtotal resection (HR 3.10, p=0.006)

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8. Adjuvant and Non-Surgical Management

Stereotactic Radiosurgery (SRS)

• Indications: residual tumor after surgery, recurrence not amenable to repeat surgery, high-grade features
• Gamma Knife / CyberKnife / LINAC radiosurgery
• Fractionated SRS preferred for larger volumes (>3 cm) near eloquent cortex
• Control rates: 80-97% at 5 years for grade I
• Main complication: radiation-induced edema (25%) - often managed with dexamethasone; rarely requires surgery
• De Nigris Vasconcellos et al., Neurosurg Rev 2024 [PMID: 38514580]

Conventional Radiotherapy (EBRT)

• For grade II/III post-resection
• Total dose: 54-60 Gy for grade II-III
• Reduces recurrence risk in high-grade meningiomas

Systemic Therapy

• No established chemotherapy for meningioma
• Investigational: anti-angiogenic agents (bevacizumab for recurrent grade II/III), SMO inhibitors (vismodegib), AKT1 inhibitors - based on molecular targets
• Hydroxyurea historically used but minimal benefit
• Somatostatin receptor-based therapy (DOTATATE) under investigation

Observation ("Watch and Wait")

• Small, incidentally discovered, asymptomatic, elderly patient
• Serial MRI every 6-12 months initially
• Growth rate <3 mm/year = favorable
• For the redo scenario, observation after incomplete resection is only appropriate if IONM-guided decision leaves residual on eloquent cortex with confirmed grade I histology

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9. Postoperative Care

Immediate (ICU/HDU - 24-72h)

• Neurological checks every hour - watch for new leg weakness, worsening prior deficits, speech changes
• MEP/SSEP monitoring if available in neuro-ICU
• Blood pressure control: MAP 70-90 mmHg; avoid hypotension (vasogenic edema risk) and hypertension (hemorrhage risk)
• Steroids (dexamethasone): Continue perioperatively; taper over 5-7 days to reduce cerebral edema
• Anticonvulsants: Levetiracetam perioperatively; continue if prior seizures or if cortex was manipulated
• DVT prophylaxis: Pneumatic compression devices; LMWH after 24-48 hours (balance with bleeding risk)
• Fluid management: Euvolemia; avoid hyperosmolar states; mannitol for acute ICP spikes

Complications to Watch For

Late Follow-up

• MRI with gadolinium at 3 months (postoperative baseline after blood resorption)
• Then at 6 months, then annually for grade I
• More frequent (every 6 months) for grade II/III
• Clinical neurological examination and functional assessment at each visit
• Rehabilitation (physiotherapy, occupational therapy) for leg weakness/spasticity

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10. Functional Outcomes

• Motor deficits (leg weakness) are the most common morbidity - both new and worsening pre-existing
• SMA syndrome: transient in most cases (resolves over 2-6 weeks); caused by SMA manipulation during interhemispheric dissection
• Visual field deficits: for occipital lesions; permanent if calcarine cortex injured
• Cognitive/higher cortical deficits: from medial parietal (precuneus) disruption
• Overall functional outcome is highly dependent on the degree of cortical involvement and quality of neurophysiological monitoring
• Published redo series (Hanakita & Oya, J Clin Med 2024) confirm that reoperation for recurrent meningioma carries higher morbidity than primary surgery, but is still feasible with acceptable outcomes in experienced centers [PMID: 38929885]

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11. Summary Table: Key Points for the Redo Parafalcine Case

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• Bradley and Daroff's Neurology in Clinical Practice, pp. 1531-1532 (meningioma classification, molecular features)
• Adams and Victor's Principles of Neurology, 12th Edition (parafalcine MRI, surgical principles)
• K.J. Lee's Essential Otolaryngology, pp. 165-166 (Simpson grading, imaging features)
• Khanna O et al. Predictors of recurrence after parafalcine/parasagittal meningioma resection. Acta Neurochir 2023 [PMID: 37987849]
• De Nigris Vasconcellos F et al. Upfront vs. adjuvant SRS for parasagittal/parafalcine meningiomas: systematic review and meta-analysis. Neurosurg Rev 2024 [PMID: 38514580]
• Hanakita S & Oya S. Surgical outcomes following reoperation for recurrent intracranial meningiomas. J Clin Med 2024 [PMID: 38929885]