Aberrant arachnoid granulations

Aberrant arachnoid granulations are arachnoid granulations that penetrated the dura but failed to migrate normally in the venous sinus. They are most often located in the greater wing of the sphenoid bone. Occasionally, they are seen in the posterior temporal bone wall.

Although mostly an incidental finding, cerebrospinal fluid rhinorrhoea is the characteristic clinical presentation when symptomatic.

Aberrant arachnoid granulations can be seen at the floor of the anterior and middle cranial fossa and, less frequently, at the posterior temporal bone wall. They contain cerebrospinal fluid but do not communicate with the dural venous sinuses. Instead, the pressure of the cerebrospinal fluid will cause bone erosion.

As they grow, these arachnoid granulations can cause defects in the posterior temporal bone wall or the tegmen tympani. Thus, cerebrospinal fluid otorrhoea can occur. Arachnoid granulations in this specific location may also potentially spread bacterial infection to the meninges. In this context, it is important to report their presence, especially since they are known to enlarge with age.

Sometimes an incidental finding, they are characterised by multiple CSF isodense focal bone erosions in the sphenoid bone bilaterally. A direct communication with the paranasal sinuses may be seen.

HRCT temporal bone reveals erosions along the posterior wall, without bone spicules and often with a lobulated surface.

Focal dural rim enhancement may be seen on CECT.

If large, the arachnoid granulations may be outpouching in the sphenoid sinus.

  • T1: hypointense on T1 (isointense to CSF)
  • T2: hyperintense on T2 (isointense to CSF)
  • T1 C+ (Gd): faint dural rim enhancement may be seen

Imaging differentials of temporal bone aberrant arachnoid granulations include:

Anatomy: Brain
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Article information

rID: 24988
Section: Anatomy
Synonyms or Alternate Spellings:
  • Aberrant arachnoid granulation
  • Aberrant arachnoid granulations (AbAG)
  • Ectopic arachnoid granulation
  • Ectopic arachnoid pit
  • Ectopic arachnoid pits
  • Aberrant arachnoid pit
  • Aberrant arachnoid pits

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