Thursday 22 March 2012

Internal carotid artery Anatomy

Among various classification available for describing the portions of ICA the most simple and widely used is based on the description by Gibo and colleagues.
ICA on either side divided in to four segments or portions.
1. Cervical
2. Petrous
3. Cavernous
4. Supraclinoid
1. Cervical portion 
This portion begins at the carotid bifurcation (usually at the level of C3) and ends at the skull base and usually has no branches. The ICA receives approximately 80% of flow from the CCA.
Further divided into two divisions.
a. Carotid bulb, a focal dilation of the ICA at the origin, ~ 7.4 mm in diameter, compared to 7.0 mm diameter for the CCA.
b. Ascending cervical segment ~4.7mm diameter which remains relatively constant throughout its course.

2. Petrous portion 
The petrous portion extends from the opening of the carotid canal in the skull base to the posterior edge of the foramen lacerum. The proximal portion is vertical followed by horizontal portion with a genu portion which is a bend in the vessel of ninety degree.

3. Cavernous portion
The cavernous segment is S-shaped, extends through the cavernous sinus, is surrounded by areolar tissue, fat, postganglionic sympathetic fibers and the interconnecting venous chambers of the cavernous sinus. The ICA rests directly against the lateral surface of the body of the sphenoid bone in a groove called the carotid suclus. Further divided into five sub segments.
a. Posterior vertical,
b. Posterior bend,
c. Horizontal,
d. Anterior bend,
e. Anterior vertical.

4. Supraclinoid portion 
The supra clinoid portion further divided into three sub segments.
a. Clinoidal segment,
b. Ophthalmic segment and
c. Communicating segment.
The clinoidal segment comprises a tiny wedge-shaped part of the ICA between the proximal and distal dural rings. The anterior clinoid process lies superior and lateral to the clinoidal ICA, over the part of widest separation between the dural rings.
The Ophthalmic segment is the most proximal intradural part of the ICA and extends from the distal dural ring to the origin of the posterior communicating artery gives the ophthalmic artery, which arises from the anterior aspect of the ICA medial to the anterior clinoid process.
The communicating segment begins just proximal to the origin of the posterior
communicating artery and ends with the bifurcation of the ICA into the ACA and the MCA. Gives off posterior communicating artery.

Handbook of Cerebrovascular Disease and Neurointerventional Technique.  Mark R. Harrigan, John P. Deveikis and Agnieszka Anna Ardelt

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