mercoledì 14 maggio 2008
Persistent hypoglossal artery
Axial images demonstrate abnormal bifurcation of the right internal carotid artery, giving rise to a persistent hypoglossal artery, which is seen entering the hypoglossal canal.
Figure 1: Abnormal bifurcation of the right internal carotid artery.
Figure 2: Abnormal bifurcation of the right internal carotid artery.
Figure 3: Persistent right hypoglossal artery entering through the hypoglossal canal.
Figure 4: Persistent right hypoglossal artery entering through the hypoglossal canal and forming the right vertebral artery.
Sagittal images demonstrate abnormal bifurcation of the right internal carotid artery, giving rise to a persistent hypoglossal artery, which is seen entering the hypoglossal canal.
Figure 5: Abnormal bifurcation of the right internal carotid artery.)
Figure 6: Persistent right hypoglossal artery entering through the hypoglossal canal.
Figure 7: Bifurcation of ICA and persistent hypoglossal artery.
Figure 8: Persistent hypoglossal artery entering hypoglossal canal at the occipital condyle.
Figure 9: Angiogram from a different patient. Arrow points to the origin of the presistent hypoglossal artery. Please note the absence of vertebral arteries originating from the subclavian arteries.
Figure 10: Injection of left ICA opacifies a large persistent hypoglossal artery, shown to pass through the hypoglossal canal. It perfuses the entire posterior circulation.
Diagnosis: Persistent hypoglossal artery
Persistent carotid-basilar artery anastomosis occurs when there is failure of regression of the otic, hypoglossal, trigeminal and proatlantal intersegmental segments formed early during embryogenesis at day 24-28. These connections form to provide blood to the hindbrain while the posterior circulation and vertebral arteries develop.
The otic artery regresses first at the 4th week of gestation. The hypoglossal, trigeminal and proatlantal intersegmental arteries all regress by the 7th to 8th week of gestation.
Persistent trigeminal artery is the most common persistent carotid-basilar anastomosis with an incidence of 0.1-0.2% Persistent hypoglossal artery is the second most common with an incidence of 0.03-0.26%. Approximately 40 cases of persistent proatlantal intersegmental artery have been reported. Most rare is the persistent otic artery, of which there are only two well documented cases.
Persistent hypoglossal artery typically originates from the cervical portion of the ICA at the C1–C2 level and continues medially and posteriorly to enter the skull through the hypoglossal canal in conjunction with the XII nerve. With persistent carotid-basilar anastomoses the vertebral arteries are usually absent or severely hypoplastic, and there are no posterior communicating arteries. Persistent hypoglossal artery is associated with aneurysms due to the abnormal flow dynamics that often accompany this anatomical variant. They are also associated with arteriovenous malformations. It is also important to identify this anatomical variant before any endarterectomy or skull base surgery is performed as the posterior circulation is dependent on the anterior circulation.
At the 4–5mm embryonic stage bilateral longitudinal neural arteries (arrows)—one set of longitudinal neural arteries, dorsal aorta, and cervical intersegmental arteries is shown—are supplied by trigeminal artery (TA), otic artery (OA), hypoglossal artery (HA), proatlantal intersegmental artery (PA), and cervical intersegmental arteries. Internal carotid artery (ICA), external carotid artery (ECA), aortic arch (AA), dorsal aorta (DAo) and ventral aorta (VAo) are also labeled.