Persistent embryonic circulation

Question 1

Persistent proatlantal intersegmental artery

Answer 1

Originates from cervical ICA (rarely from ECA) and courses posterosuperiorly to rest on transverse process of atlas, then pursues characteristic horizontal suboccipital course to enter foramen magnum and anastomose with the ipsilateral vertebral artery

Question 2

Persistent hypoglossal artery

Answer 2

Another type of residual embryonic anastomosis connects the cervical ICA to the basilar artery
-Passes through the anterior condyloid foramen and joins the cervical ICA to the basilar artery

Question 3

Persistent stapedial artery

Answer 3

Rare variant that represents continuation of the primitive hyoid branch of the ICA and presents as branch of the petrous ICA
Runs superiorly where it courses through the obturator foramen of the stapes, passes anteriorly for short distance within the facial canal and enters the middle cranial fossa through a bony foramen along the anterior aspect of the petrous bone and terminates as the middle meningeal artery

Question 4

Aberrant petrous ICA

Answer 4

Rare but clinically important anomaly
ICA traverses middle ear cavity and presents as retro-tympanic pulsatile mass
As ancillary finding, all the external carotid branches arise from a single vessel that passes superiorly from the aortic arch to the petrous canal, no carotid bifurcation present
The ICA then enters the temporal bone posterior to the external auditory meatus, ascending between the facial canal and the jugular bulb entering the middle ear fossa, the ICA is sharply angulated anteriorly
Tomography shows absent vertical portion of the carotid canal
Soft tissue outside the aberrant ICA may be identified within the middle ear cavity
Clinically, an aberrant ICA can simulate a glomus tympanicum tumor (paraganglioma), and such cases have resulted in sudden and fatal hemorrhage if surgery is performed without pre-op angiography

Question 5

Persistent trigeminal artery

Answer 5

• Most common carotid-basilar anastamosis anomaly (0.1-0.2% of all cases)
• One of fetal carotid-basilar anastomotic channels; in utero, the trigeminal artery supplies the basilar artery before development of the posterior communicating and vertebral arteries
• Arises from ICA below the abducens nerve as ICA enters cavernous sinus, then passes posteriorly and slightly inferiorly to join upper basilar artery
• Arises from ICA proximal to origin of meningohypophyseal trunk, runs posterolaterally along the trigeminal nerve
• Characteristic tau sign on sagittal MRI
• Usually associated with small posterior communicating and vertebral arteries and hypoplastic basilar artery caudal to the anastomosis

Question 6

Ophthalmic artery anomaly

Answer 6

• Usually OA arises just as ICA pierces dura, but in 8%, it arises much more proximally within the cavernous sinus
• Another anomaly is the origin of the middle meningeal artery from the ophthalmic (0.5%)

Question 7

Longitudinal neural arteries

Answer 7

Paired precursors of the basilar and vertebral arteries
-Several primitive embryonic anastomoses between the ICA and longitudinal neural arteries including the trigeminal, otic, hypoglossal, and proatlantal intersegmental arteries

Question 8

Persistent otic artery

Answer 8

• Rare

- Anastomosis between anterior inferior cerebellar artery and intrapetrous portion of ICA