Anatomic variations implicating the SA
| Anatomic Variations | Embryologic Implications | |||
|---|---|---|---|---|
| Type | Incidence | Direct and Indirect Signs | Embryologic Explanation | Embryo Size (mm) |
| Complete persistence of the SA | 2 cases | Petrous ICA origin of the MMA; petrous ICA origin of the internal maxillary artery; enlarged foramen spinosum; eroded cochlear promontory | Lack of annexation of the maxillomandibular branch by the ventral pharyngeal artery; persistence of the tympanic segment of the SA | 24 |
| Partial persistence of the SA | 0.4% | Petrous ICA origin of the MMA; absent foramen spinosum; enlarged facial canal | Regression of the proximal segment of the maxillomandibular branch; persistence of the tympanic segment of the SA | 24 |
| Tympano-carotico-tympanic variant; aberrant flow of the ICA plus persistent SA | 5 cases | Intratympanic course of the ICA; petrous ICA origin of the MMA; enlarged inferior tympanic canal; absent exocranial carotid canal | Regression of the proximal segment of the maxillomandibular branch; persistence of the tympanic segment of the SA; agenesis of the first 2 segments of the ICA; anastomosis between inferior tympanic artery and caroticotympanic artery | 24; 4–5 |
| Pharyngo-tympano-stapedial variant | 2 cases | Cervical ICA origin of the MMA; absent foramen spinosum | Regression of the proximal segment of the maxillomandibular branch; persistence of the tympanic segment of the SA; anastomosis between the inferior tympanic artery and the caroticotympanic artery | 24 |
| MMA origin of the OA | n = 2% | MMA origin of the OA; no OA from the ICA or only the central retinal artery | Lack of annexation of the supraorbital branch by the OA; persistence of the sphenoidal part of the supraorbital branch | 24 |