Aberrant internal carotid artery as a cause of pulsatile tinnitus and an intratympanic mass. (Imaging Clinic).

An aberrant internal carotid artery is a potentially serious anomaly that can manifest clinically as pulsatile tinnitus and a vascular retrotympanic mass. However, the first clinical impression might be that of another intratympanic vascular mass, such as a paraganglioma or a glomus tympanicum tumor. The appearance of an aberrant internal carotid artery on high-resolution computed tomography (CT) is characteristic (figure). On high-resolution CT, the artery can be seen entering the tympanic cavity through an enlarged tympanic canaliculus or a dehiscent carotid plate anteriorly and across the cochlear promontory. (1-3)

Aberrant internal carotid arteries are caused by an embryogenic malformation of the first and second branchial arches. The malformation results in the persistence of embryonic vessels and anomalous anastomoses in the middle ear. (2, 3)

Other vascular variants in the middle ear and mastoid of the temporal bone can also cause pulsatile tinnitus and a retrotympanic mass. One of these variants is a jugular-bulb anomaly, such as a high-riding bulb that is caused by a dehiscence of the bone of the roof of the jugular fossa. A jugular-bulb anomaly is sometimes associated with a persistent stapedial artery and a diverticulum of the jugular bulb that protrudes into the hypotympanum. It is crucial to differentiate a jugular-bulb anomaly from an intratympanic paraganglioma. (4)

Another common vascular variant is asymmetry of the jugular bulb. As a rule, when asymmetry is present, the right jugular bulb is larger than the left, and it can mimic a vascular mass. High-resolution CT can identify asymmetry in the size of the jugular fossa with preservation of the roof and jugular spine. If the jugular fossa is dehiscent, the jugular bulb in the hypotympanum can appear as a mass. (4, 5)

A persistent stapedial artery is a rare vascular anomaly, and it can occur with or without an associated aberrant internal carotid artery. Again, high-resolution CT findings are characteristic. They include the absence of the foramen spinosum on the affected side and the enlargement of the proximal tympanic segment of the facial nerve canal adjacent to the cochleariform process. (6)

Conventional and/or magnetic resonance angiography can improve the imaging view of the characteristic features of an aberrant internal carotid artery and other vascular anomalies.

References

(1.) Botma M, Kell RA, Bhattacharya J, Crowther JA. Aberrant internal carotid artery in the middle-ear space. J Laryngol Otol 2000;114:784-7.

(2.) Sismanis A. Pulsatile tinnitus. A 15-year experience. Am J Otol 1998;19:472-7.

(3.) Ridder GJ, Fradis M, Schipper J. Aberrant internal carotid artery in the middle ear. Ann Otol Rhinol Laryngol 2001;110:892-4.

(4.) Jain R, Marotta TR, Redekop G, Anderson DW. Management of aberrant internal carotid artery injury: A real emergency. Otolaryngol Head Neck Surg 2002;127:470-3.

(5.) Jacobsson M, Davidsson A, Hugosson S, et al. Aberrant intratympanic internal carotid artery: A potentially hazardous anomaly. J Laryngol Otol 1989;103:1202-5.

(6.) Henriksen SD, Kindt MW, Pedersen CB, Nepper-Rasmussen HJ. Pseudoaneurysm of a lateral internal carotid artery in the middle ear. Int J Pediatr Otorhinolaryngol 2000;52:163-7.