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Arachnoid Granulations of the Posterior Temporal Bone Wall: Imaging Appearance and Differential Diagnosis

V. VandeVyvera,c, M. Lemmerlinga, B. De Foerb, J. Casselmanb and K. Verstraetec

a Department of Radiology, AZ Sint-Lucas, Gent, Belgium
b Department of Radiology, AZ Sint-Augustinus, Antwerp, Belgium
c Department of Radiology, University Hospital, Gent, Belgium


Figure 1
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  		Fig 1. A, The axial HRCT image of the right temporal bone in case 1 shows an erosion in the posterior temporal bone wall (arrow). The erosion does not contain calcifications or bone spicules and was identified as an arachnoid granulation.

B, On the axial HRCT image obtained 3 mm below A, the normal endolymphatic duct (black arrowhead) is identified anterior to the arachnoid granulation (black arrow). Tympanosclerosis is present (white arrowhead).

C, The axial 0.7-mm-thick T2-weighted image of the posterior fossa confirms the right (arrowhead) and left (arrow) arachnoid granulation. On the right side, the internal fibrous structure is seen as hypointense lines within the granulation.


Figure 2
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  		Fig 2. A, On the axial HRCT image of the left temporal bone in case 2, a defect is seen at the posterior surface of the left temporal bone (black arrow), with a normal endolymphatic duct (arrowhead). Note the presence of a hypoattenuated otospongiotic focus in the fissula antefenestram region (white arrow).

B, The axial 0.4-mm-thick T2-weighted image again demonstrates the arachnoid granulation (arrow). It has the same signal intensity as CSF.

C, The axial 0.8-mm-thick T1-weighted image after intravenous administration of gadolinium shows a hypointense nonenhancing arachnoid granulation (arrows).


Figure 3
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  		Fig 3. A, The axial HRCT image of the opacified temporal bone in case 3 shows the presence of an arachnoid granulation (arrows), easily differentiated from an endolymphatic sac tumor by identifying the normal and unenlarged endolymphatic duct (arrowhead).

B, The axial 0.4-mm-thick T2-weighted image confirms the arachnoid granulation (arrow), with CSF signal intensity.





Copyright © 2008 by the American Society of Neuroradiology. Print ISSN: 0195-6108 Online ISSN: 1936-959X