The distal dural ring is an anatomical landmark that separates the extradural from the intradural intracranial internal carotid artery (ICA). It is located at the junction of the cavernous, clinoid and ophthalmic segments of the ICA.

Gross anatomy

Anatomy of this region is complex and varied and includes several important structures within a small area (1 cm³) ¹.

The distal dural ring is ²:

• tightly and circumferentially attached to the ICA
• continuous with the roof of the cavernous sinus along its lateral aspect
• continuous with the tuberculum sellae along its posteromedial aspect
• at or below the level of the tuberculum sellae
• 2 mm above the base of the optic strut ⁶

Related pathology

This anatomical landmark is used to determine the intradural or extradural location of a transitional aneurysm located at the level of the carotid cave (medial aspect of the ICA). Aneurysms above and below the distal dural ring are respectively considered intradural and extradural ².

Hence, aneurysms can be either extradural (within the cavernous sinus) or intradural (paraclinoid). Knowing the dural location of the aneurysm substantially alters management, since the latter is at risk of subarachnoid haemorrhage and will usually require endovascular or surgical repair whereas the former will usually not require an intervention ^2-4.

Radiographic features

MRI

The superior border of the cavernous sinus is often used as an indirect landmark for the distal dural ring. It is best seen on thin slices with high-resolution sequences such as 3D-CISS (T1 C+ or T2) ^2,3, 3D T2 SPACE ³, 3D T2 FSE ⁴ and fusion of MRA with 3D cisternography ⁵.

See also

• transitional aneurysm
• carotid cave