Table 3:

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