Radiology of Meningioma

Overview

WHO Classification

Location

• 90% are supratentorial, arising in decreasing frequency from:
  • Parasagittal region
  • Cerebral convexities
  • Sphenoid ridge
  • Olfactory groove
• Infratentorial meningiomas are most frequent on the posterior surface of the petrous bones and clivus; can mimic vestibular schwannomas
• Multiple meningiomas occur in neurofibromatosis type 2 (NF2)

General Signs of Extra-Axial Location

• "Buckling" and medial displacement of the grey-white matter interface
• A CSF cleft separating the base of the mass from adjacent brain
• A broad base along a dural or calvarial surface

CT Appearances

• 60% are spontaneously hyperdense on unenhanced CT
• Up to 20% contain calcification
• Enhancement is usually intense and uniform
• Hyperostosis of adjacent bone is associated with benign (WHO grade I) meningiomas
• Bone destruction raises suspicion of atypical meningiomas
• CT is particularly well-suited to demonstrate these bone changes

MRI Appearances

• Frequently isointense to cerebral cortex on both T1 and T2 sequences - may be difficult to detect without IV contrast
• Vivid and homogeneous enhancement on post-gadolinium sequences
• Exception: cystic or very densely calcified tumours produce foci of low signal within the mass
• 'Capping cysts' of CSF-equivalent signal intensity may be seen
• Vasogenic oedema is not infrequently associated; even small lesions can cause extensive oedema
  • The presence of intra-axial oedema corresponds to an increased likelihood of recurrence

The "Dural Tail" Sign

• A linear, contrast-enhancing band extending from the tumour along the dura mater
• Once thought to be pathognomonic for meningioma
• Now known to also be seen with schwannoma and metastasis - not pathognomonic

Venous Sinus Involvement

Advanced / Physiological MRI

MR Spectroscopy (MRS)

• May show an alanine peak - characteristic for meningioma
• Seen in less than 50% of cases
• No MRS data have been clinically correlated to patient outcomes

Diffusion-Weighted Imaging (DWI)

• Used to differentiate typical from atypical meningiomas, but results are conflicting
• Earlier reports suggested lower ADC values in non-typical meningiomas; more recent studies do not show a significant correlation

Perfusion-Weighted Imaging (PWI)

• Meningiomas usually have a markedly elevated rCBV - can differentiate from dural metastases, which tend to have lower rCBV
• CBV of peritumoural oedema is higher when surrounding malignant meningiomas

PET Imaging

• Meningiomas show high uptake of ⁶⁸Ga-DOTATOC (somatostatin receptor PET)
• Useful for:
  • Differentiating meningioma from other dural-based tumours
  • Distinguishing residual/recurrent tumour from postoperative enhancement
  • Radiotherapy planning for skull base meningiomas

Angiography

• Now mostly performed for preoperative embolisation to minimise intraoperative blood loss
• Cardinal findings:
  • Blood supply from meningeal vessels
  • A dense, homogeneous, persistent tumour blush
• Parasitisation of cortical vessels (convexity tumours) or ophthalmic artery branches (subfrontal masses) is not rare
• Post-embolisation MRI: typical decrease in enhancement and reduced perfusion of the devascularised segment

Intraventricular Meningioma

• The commonest cause of a mass in the trigone of the lateral ventricle after the first decade of life
• CT and MRI appearances are similar to extraventricular meningiomas:
  • Well-defined, globular lesion
  • Usually hyperdense on CT
  • May give similar signal to cerebral cortex on T1 and T2
  • Marked contrast enhancement on both CT and MRI

Spinal Meningioma

• Slightly hyperintense to spinal cord on T2
• Avid contrast enhancement on gadolinium-enhanced T1
• Broad dural attachment with a dural tail
• Can cause severe spinal canal narrowing and cord compression

Optic Nerve Sheath Meningioma

• Arises from the arachnoid sheath of the optic nerve (primary) or spreads from intracranial tumour (secondary)
• Most frequent in middle-aged women; bilateral = feature of NF2
• Imaging features:
  • Generalised circumferential or fusiform enlargement of the optic nerve-sheath complex
  • Calcification in 20-50% of cases on CT - relatively specific (not seen in optic nerve glioma)
  • "Tram-track sign": peripheral enhancement of the tumour around the nerve on post-gadolinium fat-suppressed MRI (or hypoattenuation of the nerve on CT) - not specific; also seen in pseudotumour, optic neuritis, sarcoid, lymphoma, and metastatic disease

Differential Diagnosis

• Infratentorial location: bone sclerosis favours meningioma; enlargement of the internal auditory meatus favours schwannoma
• Dural tail: also seen in schwannoma and metastasis