Aberrant internal carotid artery

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

Gross anatomy

There is consequent enlargement of the usually small collaterals which course through the middle ear, appearing as an artery that passes lateral to the cochlear promontory.

The two vessels that enlarge to form the aberrant internal carotid artery are:

• inferior tympanic artery: a branch of the external carotid artery (usually ascending pharyngeal artery) which enters from below via the inferior tympanic canaliculus
• caroticotympanic artery: a branch of the petrous portion of the internal carotid artery known as the hyoid artery when enlarged

The vessels rejoin the horizontal segment of the petrous portion of the internal carotid artery.

The anomaly may be associated with a persistent stapedial artery ⁷.

Clinical presentation

Patients may present with pulsatile tinnitus, particularly if there is stenosis in the vessel. On otoscopic examination, it appears as a retrotympanic vascular mass. If mistaken for a paraganglioma and biopsied, the results can be disastrous.

Radiographic features

CT

Findings of aberrant internal carotid artery on CT include:

• enlarged inferior tympanic canaliculus within the caroticojugular spine with small vessel traversing it
• retrotympanic mass, as vessel enters the posterior mesotympanum and courses across the inferior cochlear promontory to the anterior mesotympanum
• absent carotid plate, as vessel connects to the normal horizontal portion of the petrous internal carotid artery
• absent or hypoplastic vertical segment of the carotid canal

Angiography

Characteristic findings of aberrant internal carotid artery on angiography include:

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

Differential diagnosis

• lateralized internal carotid artery: protrudes into the anterior mesotympanum but does not course across the cochlear promontory from the posterior mesotympanum nor enlarge the inferior tympanic canaliculus  ⁷
• aneurysm of the petrous segment of the internal carotid artery
• glomus tympanicum
• glomus jugulare
• dehiscent jugular bulb