Extra-axial posterior fossa lesions simulating intra-axial lesions on computed tomography.

Differentiation of extra- from intra-axial posterior fossa lesions is sometimes not possible on computed tomography. Six cases are presented wherein the lesion appeared to be intra-axial on computed tomograms yet angiographically and surgically proved to be extra-axial. False localization on computed tomography occurs with slowly growing masses which burrow into brain parenchyma.