Table 1:

Different origin of the MMA with modifications associated and embryologic explanation

Variations in the Origin of the MMA		Embryologic Implications
Type	Associated Changes	Embryologic Explanation	Embryo Size (mm)
IMA origin	Normal anatomy	Normal embryology
Basilar artery origin	Absence foramen spinosum	Anastomosis between SA and trigeminal artery; anastomosis between SA and lateral pontine artery	12
Cavernous ICA origin	Absence foramen spinosum	Anastomosis between inferolateral trunk and SA	16
Partial persistent SA	Absence foramen spinosum; enlargement of the facial canal	Regression of the proximal part of the maxillomandibular branch; persistence of the intratympanic segment of the SA	24
Complete persistent SA	Enlargement of the facial canal	Lack of annexation of the maxillomandibular branch by the ventral pharyngeal artery; persistence of the intratympanic segment of the SA	24
Pseudopetrous ICA origin	Absence foramen spinosum; enlargement of the facial canal; absence of the exocranial opening of the carotid canal	Agenesis of the first and second segments of the ICA; intratympanic anastomosis between inferior tympanic and caroticotympanic arteries; persistence of the intratympanic segment of the SA	4–5; 24
Cervical ICA origin	Absence foramen spinosum; enlargement of the facial canal	Intratympanic anastomosis between inferior and superior tympanic arteries; regression of the proximal part of the maxillomandibular branch; persistence of the intratympanic segment of the SA	16; 24
Occipital artery origin	Absence foramen spinosum; enlargement of the facial canal	No clear explanation
Distal petrous ICA origin	Absence foramen spinosum	Lack of annexation of the mandibular artery (first aortic arch) by the SA (second aortic arch)	9