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. 

Gross anatomy

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.

Relations

• superior margin contains the superior sagittal sinus

• free edge between its attachments inferiorly closely related to the superior surface of the corpus callosum and contains the inferior sagittal sinus ^2,3

• straight sinus is included in the line of attachment between the falx cerebri and the tentorium cerebelli ³

Variant anatomy

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.  

Radiographic features

CT

• anterior midline linear density near the vertex

• triangular density inferiorly and posteriorly on axial sections ⁴

• partially calcified in 7% of individuals

MRI

• thin membrane on T1W and T2W images 

• calcifications visible on T1W imaging as hyperintensities and hypointensities on T2W imaging ⁵

History and etymology

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

Related pathology

• normal intracranial calcifications

• falx ossification

• meningioma

• subdural hemorrhage