Meningiomas of the Skull Base

Introduction - Brain's Unwanted Tenant

• Most common primary intracranial tumors; generally benign & slow-growing.
• Origin: Arachnoid (meningothelial) cap cells.
• Peak incidence: 40-60 years; F:M ratio ~2:1 (intracranial), ~10:1 (spinal).
• Common skull base locations:
  • Sphenoid wing
  • Olfactory groove
  • Tuberculum sellae
  • Petroclival region
  • Foramen magnum
• WHO Classification: Grade I (benign, ~90%), Grade II (atypical), Grade III (malignant).

⭐ Multiple meningiomas or association with schwannomas/gliomas suggests Neurofibromatosis type 2 (NF2).

Pathology & Grading - Growth's True Colors

• Origin: Arachnoid cap cells.
• WHO Grading (2021):
  • Grade I (Benign, ~80%): Meningothelial, Fibroblastic, Transitional, Psammomatous. Slow growth.
  • Grade II (Atypical, ~15-20%): Mitotic index ≥4/10 HPF, brain invasion, or 3+ atypical features (e.g. ↑cellularity). Includes Chordoid, Clear Cell.
  • Grade III (Malignant, ~1-3%): Mitotic index ≥20/10 HPF, anaplasia. Includes Papillary, Rhabdoid.
• IHC: EMA+, Vimentin+, SSTR2A+. Ki-67 index correlates with grade.
• Risk: NF2 mutation, radiation.

⭐ Brain invasion automatically upgrades a meningioma to WHO Grade II, irrespective of other histological features.

Clinical Features - Cranial Nerve Chaos

Symptoms reflect tumor location & compressed cranial nerves (CNs).

• Olfactory Groove: Anosmia (CN I), personality changes.
• Tuberculum Sellae/Suprasellar: Visual loss (CN II), bitemporal hemianopia, optic atrophy.
• Sphenoid Wing: Proptosis; CN II, III, IV, V, VI deficits (vision loss, diplopia, facial numbness).
• Cavernous Sinus: Multiple ophthalmoplegias (CN III, IV, VI), trigeminal sensory loss (V1/V2).
• Petroclival: CN V-VIII dysfunction (facial pain, diplopia, hearing loss, facial weakness), ataxia.
• Foramen Magnum: Lower CN palsies (IX-XII), motor deficits, hydrocephalus.

⭐ Foster Kennedy Syndrome: Ipsilateral anosmia & optic atrophy + contralateral papilledema (olfactory groove meningioma).

Diagnostic Imaging - Spotting the Shadow

• MRI (Gold Standard):
  • T1: Iso/hypointense.
  • T2: Iso/hyperintense; peritumoral edema.
  • T1 C+ (Gad): Intense, homogenous enhancement.
  • Dural Tail Sign: Enhancing adjacent dural thickening (📌).
• CT Scan:
  • Often hyperdense.
  • Calcification, bony hyperostosis/erosion.
• Angiography (DSA):
  • Feeding vessels (ECA branches).
  • Pre-op embolization.
  • Sunburst/Mother-in-law sign.

⭐ The "dural tail sign" on contrast-enhanced MRI, seen in ~60-70% of cases, is highly suggestive but not pathognomonic for meningioma.

Management Strategies - Taming the Tumor

• Goal: Symptom relief, tumor control, preserve/improve neurological function.
• Options: Observation, Surgery, Radiotherapy.

• Surgery:
  • Aim: Maximal safe resection to achieve GTR.
  • Approaches: Transcranial, Endoscopic Endonasal.
  • Complications: Cranial nerve deficits, CSF leak.
• Radiotherapy:
  • Stereotactic Radiosurgery (SRS) or Fractionated (FSRT).
  • Indications: Adjuvant post-STR, recurrent, primary for inoperable/high-risk tumors.
  • Consider for WHO Grade II/III.

⭐ Simpson Grade I resection (complete tumor removal including dural attachment and abnormal bone) offers the lowest recurrence rate for benign meningiomas.

High‑Yield Points - ⚡ Biggest Takeaways

• Most common benign intracranial tumor, frequently at the skull base.
• WHO Grade I is most common; Grades II & III have higher recurrence.
• Characteristic histology: Psammoma bodies.
• Simpson grading of surgical resection predicts recurrence rates.
• Symptoms often include cranial nerve deficits depending on tumor location.
• Maximal safe surgical resection is the goal; radiotherapy for adjuvant/salvage.
• Higher incidence in females; associated with Neurofibromatosis Type 2 (NF2).