Aberrant internal carotid artery

• Retrotympanic vascular mass crossing the inferior cochlear promontory on CT or MRI
• Enlarged inferior tympanic canaliculus within the caroticojugular spine
• Absent or hypoplastic vertical segment of the carotid canal with lateral displacement of the petrous ICA
• Laterally positioned petrous internal carotid artery well beyond the vestibular line of Lapayowker on angiography

• CT shows an enlarged inferior tympanic canaliculus containing a small vessel that traverses it, representing the enlarged inferior tympanic artery (branch of ascending pharyngeal artery) coursing through the middle ear.
• A retrotympanic mass is visible on CT as the enlarged caroticotympanic artery and inferior tympanic artery enter the posterior mesotympanum and course across the inferior cochlear promontory to reach the anterior mesotympanum.
• The carotid plate is absent on CT imaging, as the collateral vessels connect directly to the horizontal segment of the petrous internal carotid artery without the normal bony separation.
• The vertical segment of the carotid canal is absent or hypoplastic on CT, with the petrous internal carotid artery taking a more lateral course than normal.
• On digital subtraction angiography, there is an enlarged tympanic branch of the ascending pharyngeal artery clearly filling from the external carotid system.
• The petrous portion of the internal carotid artery follows a more lateral and posterior route than typical anatomy on angiography.
• On DSA, the internal carotid artery extends well beyond the vestibular line of Lapayowker with a pinched contour, indicating lateral displacement.
• The anomaly may be associated with a persistent stapedial artery, which should be carefully evaluated on imaging studies.

• Lateralized internal carotid artery: protrudes into the anterior mesotympanum but does not course across the cochlear promontory from the posterior mesotympanum and does not enlarge the inferior tympanic canaliculus.
• Tympanic paraganglioma: may present as a retrotympanic mass, but lacks the characteristic enlarged vascular canaliculus and would enhance homogeneously without the branching vascular pattern.
• Jugular paraganglioma: typically arises at the jugular foramen and displaces rather than comprises the jugular vein.
• Aneurysm of the petrous internal carotid artery: would show a dilated, rounded vascular structure rather than a linear vessel coursing through the middle ear.
• Dehiscent jugular bulb: projects into the middle ear but does not traverse the cochlear promontory and is typically located more posteriorly.

Describe the finding as: "Aberrant internal carotid artery with an enlarged inferior tympanic canaliculus and collateral vascular course through the middle ear crossing the cochlear promontory, connecting the external carotid system below to the petrous internal carotid above—no biopsy is recommended given the vascular nature of this normal variant."

• Mistaking the retrotympanic vascular mass for a paraganglioma and performing an ill-advised biopsy, which can result in severe hemorrhage and arterial injury.
• Failing to recognize the enlarged inferior tympanic canaliculus as a key diagnostic clue, instead attributing the middle ear mass to other pathology.
• Not distinguishing from a lateralized internal carotid artery, which does not course across the cochlear promontory from the posterior mesotympanum.
• Overlooking the absence of the carotid plate and the hypoplastic vertical carotid canal segment, which are essential CT findings for diagnosis.