Meningioma

Figure 1: Axial unenhanced CT image of the brain shows an isodense mass in the left posterior fossa with minimal, if any, mass effect.
Figure 2: Axial contrast-enhanced T1W MR image shows a large homogeneously enhancing extra-axial mass (star) near the left petrous bone overlying the sigmoid venous sinus (arrow).

Facts: Meningioma

• Tumors of meningeal cells (typically arising from meninges but can also be found in the choroid plexus, tela choroidea and arachnoid villi); therefore meningiomas can be seen in the meninges, spinal canal, intraventricular, and pineal regions
• Common, greater than 20% of all primary intracranial neoplasms
• Female:male = 3:2 to 2:1; mostly in late middle age
• Pathology: benign, atypical and malignant

Imaging Features

• Homogeneous, lobulated, well-circumscribed mass with uniform dense enhancement following contrast administration
• Common locations: parasagittal > convexity > sphenoid ridge
• High attenuation on unenhanced CT, iso- to mildly hypointense on T1W MR images
• May calcify in up to 1/4 of all cases, best seen on CT. Calcifications can be microscopic, punctate, large, peripheral or central. Malignant meningiomas rarely calcify.
• Hyperostosis can be seen in up to 1/2 of cases that meningiomas are immediately adjacent to the bone. Common in 'en plaque' meningioma
• Uncommon to have bone destruction (if pure destruction think of metastasis, sarcoma or myeloma)

Our case: benign meningioma overlying the sigmoid sinus without invasion. It is important to note if the meningioma is adjacent vascular structures for optimal surgical planning.

References:

1. Drevelegas A. Imaging of brain tumors with histological correlation, 2002.

2. DeAngelis LM, Gutin PH, Leibel SA. Intracranial tumors: diagnosis and treatment, 2002.