Aberrant internal carotid artery

Aberrant internal carotid artery is a variant of the internal carotid artery (ICA) and represents a collateral pathway resulting from involution of the normal cervical portion (first embryonic segment) of the ICA ⁵.

There is consequent enlargement of the usually small collaterals which course through the middle ear. The result of this enlargement is an artery that passes lateral to the cochlear promontory and appears during otoscopic examination as a retrotympanic vascular mass. If mistaken for a paraganglioma and biopsied, the results can be disastrous.

The two vessels that enlarge to form the aberrant ICA are:

• inferior tympanic artery: a branch of the external carotid artery (usually maxillary artery or superficial temporal artery) which enters from below via the inferior tympanic canaliculus
• caroticotympanic artery: a branch of the petrous portion of the ICA known as the hyoid artery when enlarged

The two vessels enlarge, sometimes with a stenosis producing objective tinnitus, and rejoin the horizontal segment of the petrous portion of the ICA.

Radiographic features

CT

Findings of aberrant ICA on CT include:

• absent or hypoplastic vertical segment of the carotid canal at the carotid plate
• enlarged inferior tympanic canal within the caroticojugular spine with reduced caliber aberrant ICA traversing through it

Angiography

Characteristic findings of aberrant ICA  on angiography include:

• enlarged tympanic branch of ascending pharyngeal artery
• more lateral and posterior route of petrous part of ICA than usual
• lateral extension of the ICA well (pinched contour of the vessel) beyond the vestibular line of Lapayowker

Differential diagnosis

• aneurysm of the petrous segment of the ICA
• glomus tympanicum
• glomus jugulare
• dehiscent jugular bulb