Falx cerebri

Last revised by Daniel J Bell on 17 Oct 2019

The falx cerebri (plural: falxes/falces cerebrorum) is the largest of the four main folds (or septa) of the intracranial dura mater, separating the cerebral hemispheres 1

The falx cerebri is a double-fold of dura mater that descends through the interhemispheric fissure in the midline of the brain to separate the two cerebral hemispheres.

The falx cerebri is relatively thin anteriorly where it attaches to the crista galli of the ethmoid bone, but is broader posteriorly where it attaches to the superior surface of the tentorium cerebelli inferiorly 1,2. It attaches superiorly to the midline of the cranium and extends posteriorly to attach to the internal occipital protuberance 3.

For blood supply and innervation, see dura.

The falx is rarely abnormal as an isolated variant; rather it is usually deficient as part of a broader congenital abnormality such as holoprosencephaly 6. The most common variants are seen anteriorly where the falx may be deficient or fenestrated 6. Abnormalities of the falx are frequently associated with abnormalities of the superior sagittal sinus 6.  

  • anterior midline linear density near the vertex
  • triangular density inferiorly and posteriorly on axial sections 4
  • partially calcified in 7% of individuals
  • thin membrane on T1W and T2W images 
  • calcifications visible on T1W imaging as hyperintensities and hypointensities on T2W imaging 5

The word originates from the Latin falx meaning sickle, due to its sickle-like shape.

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Cases and figures

  • Figure 1: falx cerebri
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  • Case 1
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  • Figure 2: falx cerebri as a dural fold
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