Page 165 - Edited - Webster HEAD AND NECK - part 1

HN 135

THE INTERNAL CAROTID ARTERY 2

SUMMARY OF INTRACRANIAL COURSE- SCHEMATIC LATERAL VIEW

ANTERIOR
CLINOID POSTERIOR CHINOID PROCESS
PROCESS (SPHENOID)

MI MIDDLE RIDGE.
“CAROTID CRA CRANIAL
SIPHON” FOSSA POSTERIOR

CRANIAL FOSSA.
PETROUS
CAVERNOUS TEMPORAL
VENOUS
SINUS

KEW

BÓDY OF FORAMEN INTERNAL
SPHENOID LACERUM OPENING OF CAROTID ARTERY
CAROTID CANAL

NOTICE that, as both are alongside the body of the sphenoid bone and the cavernous venous sinus occupies
the entire lateral surface of that bone, the internal carotid artery is accommodated by being enclosed
within the venous sinus (although separated from the venous blood by the endothelium of the sinus).
Within the sinus, the internal carotid artery again runs anteriorly, then exits by turning sharply upwards,
only to execute yet another turn, which is such that the artery partially retraces its path, but
ABOVE the body of the sphenoid bone. This horizontal U-shaped part of the carotid trajectory is referred
to by radiologists as the “carotid siphon”. It has, of course, no hydrodynamic “siphonic” function,
but is a useful landmark for interpreting carotid angiograms (HN 137 ), since it just below the
optic chiasma (Neuro notes Vol I pp. 146 et seq. & Vol II Figs. 6, 16, 157 etc. See also HN ).
KEW