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 |