Table 4.

Anatomic variations of the foramen rotundum

Variation/Entity	Defining anatomy (Key feature)	Communication/Extracranial opening	Likely transmitted structure(s)/Unctional interpretation	Distinctive notes (incl. “true vs false” duplication context)	Citations
True duplication of the FRC	Two canals both communicating with the pterygopalatine fossa	Both canals reach pterygopalatine fossa	Contains duplicated segment of V2	Should be distinguished from the false duplications	[18, 22]
Persistent foramen lacerum anterius due to absent maxillary strut	The maxillary strut normally separates FR from SOF; failure to form leads to a persistent foramen lacerum anterius	Persistence of a developmental communication at the skull base (between regions normally separated by the strut)	Not specified	Seen in some lower mammals; quite rare in humans	[11]
Inferior rotundal canal	Small (1–3 mm) opening in the floor of FR	Leads to infratemporal fossa or space between pterygoid plates	Emissary veins	Considered a more common FR variant	[8, 11, 20]
Inferior rotundal canal	A 1.77/7.63 mm canal opened on the posterior side of the pterygoid base	Leads in the pterygoid fossa, above the medial pterygoid muscle and laterally to the tensor veli palatini	Emissary vein	Unilateral evidence	Present study (Case #2)
Lateral rotundal canal	Canal opening lateral to FR with inferolateral trajectory	To the infratemporal fossa, extracranial opening not precisely located by Ginsberg et al.	Emissary vein	Defined by Ginsberg et al. as a named variant	[11]
Lateral rotundal canal	Lateral rotundal canal (as above)	Extracranial opening identified in the infratemporal roof	Emissary vein	Reported distinctively from the contralateral alar cribriform zone	Present study (Case #1)
Unusual foramen adjacent to FR (UF)	Accessory foramen adjacent to FR; most often anterolateral (frequently bilateral), rarely posterolateral	In some specimens a short canal directed inferomedially toward the pterygopalatine fossa; in others the canal is blind/shallow	Interpreted as an emissary venous or incomplete venous/diploic channel (not described as transmitting duplicated V2)	Reported in 5/512 skulls (0.98%); important CT/CBCT differential (may mimic pathology); best regarded as a para-rotundum accessory foramen/canal, not a “true duplication” of the FRC	[17]
Alar cribriform zone	Cribriform area of the alar region	Corresponds to the infratemporal roof	Emissary vein	Reported as a contralateral counterpart to a lateral rotundal canal	Present study (Case #1)
Sphenopterygoid canal (SPC) traversing to a pterygoid foramen (PF)	SPC opens superiorly on the lateral side of FR; opens inferiorly at a PF located at the superior end of the posterior margin of the lateral pterygoid plate	Middle fossa region → PF → pterygoid region	Sphenoidal emissary vein draining to the pterygoid plexus	Presented as another alternative emissary venous pathway	[19]

FR = foramen rotundum; FRC = foramen rotundum canal; SOF = superior orbital fissure; V2 = maxillary nerve; UF = unusual foramen adjacent to FR; SPC = sphenopterygoid canal; PF = pterygoid foramen