Persistent stapedial artery (PSA)

• Small canaliculus originating from the petrous segment of the internal carotid artery on high-resolution CT temporal bone
• Linear soft tissue density crossing the cochlear promontory in the middle ear on axial imaging
• Three-eyed snail sign on coronal CT reconstructions (persistent stapedial artery canal intersecting the facial nerve canal) or N-shaped appearance on axial reconstructions
• Aplastic or hypoplastic foramen spinosum suggesting possible stapedial origin of the middle meningeal artery

• Small canaliculus originates from the petrous portion of the internal carotid artery and courses medially toward the stapes footplate.
• Linear soft tissue density representing the persistent vessel crosses over the cochlear promontory in the middle ear space on axial imaging.
• The vessel passes through the obturator foramen of the stapes and may be visualized as a thin enhancing structure on contrast-enhanced CT or MRI.
• Characteristic three-eyed snail sign appears on coronal CT reconstructions when a separate bony canal of the PSA intersects the facial nerve canal, creating three round lucencies.
• N-shaped appearance on axial CT reconstructions results from the PSA canal running parallel or intersecting with the facial nerve canal.
• Enlarged or duplicated facial nerve canal may be present, or a separate canal parallel to the facial nerve can occur as the PSA follows its embryologic path.
• Foramen spinosum is typically aplastic or hypoplastic, indicating that the middle meningeal artery arises from the persistent stapedial artery rather than from the external carotid.
• Association with other middle ear anomalies and possible concurrent aberrant internal carotid artery (with enlarged inferior tympanic canaliculus) should be assessed.

• Aberrant internal carotid artery: distinguished by the vessel arising directly from the ICA and bulging prominently into the middle ear without passing through the stapes; associated with enlarged inferior tympanic canaliculus.
• Enlarged inferior tympanic artery: occurs as normal variant or in vascular supply anomalies; lacks the characteristic pathway through the stapes obturator foramen.
• Accessory facial nerve canal: can mimic the PSA on coronal imaging; lacks the vascular origin from the petrous ICA and does not contain flowing blood on angiography.
• Normal variant middle meningeal artery supply: when the MMA arises from the ophthalmic artery, foramen spinosum is hypoplastic but no additional canal through stapes is present.
• Cholesteatoma or granulation tissue: may appear as soft tissue in middle ear but lacks bony canal formation and vascular enhancement on imaging.

Describe the finding as: "A small bony canaliculus arises from the petrous ICA and courses medially to the stapes obturator foramen, consistent with a persistent stapedial artery. The foramen spinosum is [aplastic/hypoplastic], indicating the middle meningeal artery likely derives from the persistent stapedial artery. Clinical correlation for pulsatile tinnitus or preoperative counseling regarding intraoperative hemorrhage risk is recommended."

• Mistaking the PSA canaliculus for a cholesteatoma defect or ossicular erosion; careful attention to the bony canal arising from the petrous ICA and coronal imaging helps distinguish.
• Overlooking a hypoplastic foramen spinosum as a clue to stapedial origin of the middle meningeal artery; always evaluate foramen spinosum caliber when small canaliculi are noted near the stapes.
• Failing to identify PSA preoperatively and creating surgical hazard; explicit mention in reports of patients undergoing stapes surgery reduces hemorrhage risk.
• Confusing the three-eyed snail sign with normal facial nerve canal variants; knowledge of the exact midline position of the N-shaped PSA canal on axial imaging helps clarify.