Aberrant internal carotid artery in the middle ear

Abstract

An aberrant internal carotid artery (ICA) in the middle ear space can present in 1% of the population. the clinical diagnosis can be difficult as most patients with this anomaly are either asymptomatic or have nonspecific clinical symptoms and signs. Moreover the diagnosis can easily be missed and only discovered when injurey occur to the ICA during middle ear surgey with resulting life-threatning complications. A knowledge of this anomaly and its differential diagnosis is of high importance to any practitioner dealing with otologic diseases and performing otologic surgeries. We report a 7-year-old girl with a right aberrant ICA presenting with hearing loss and review published studies concerning this disease entity presentation, diagnosis, and management.

The presence of a vascular mass in the middle ear is rare. The diagnosis can range from an aberrant internal carotid artery (ICA), to a glomus tumor, to a hemangioma, to serous otitis media.¹ Hence, if the diagnosis is not made before middle ear surgery is performed, a large loss of blood may occur as a result of injury to the vessel. To prevent this, it is important to the physician to be knowledgeable about this disease entity.

A dehiscent ICA canal is present in approximately 1% of the population² and could result in the presence of an aberrant ICA through the middle ear space. We report a patient in whom this condition was suspected on the basis of clinical examination of the ear. The radiological examination in the form of a CT scan and magnetic resonance angiography (MRA) confirmed the diagnosis of an aberrant ICA in the middle ear.

CASE

A 7-year-old girl presented with decreased hearing in the right ear. The examination of the ear revealed a red pulsatile retrotympanic mass (Figure 1). Pure tone audiometry showed a right mild conductive hearing loss of 15 dB. The left ear seemed normal. The tympanometry and stapedial reflex measurement was normal. The subsequent CT scan and MRA of the petrous bones demonstrated a right aberrant ICA (Figure 2). The condition was thoroughly explained to parents and the patient. Regular follow-up was planned.

Figure 1.

Tympanic membrane findings (right ear). A red shadow is observed extending in the anteroinferior direction from the central portion of the pars tensa.

Figure 2.

Coronal CT of the temporal bone showing protrusion of the right internal carotid artery into the middle ear space through a dehiscence of the lateral carotid plate (arrow).

DISCUSSION

Vascular anomalies of the middle ear space are uncommon. Their symptoms and signs are nonspecific, causing a diagnostic problem. Patients with these anomalies may be asymptomatic or may complain of hearing loss, pulsatile tinnitus, ear pain, or aural fullness. On otoscopic examination, a vascular red-to-dark red or bluish swelling extending from the tympanic membrane to the middle or lower tympanic cavity was observed. Such an observation should first raise the clinician’s suspicion to one of the following possibilities: an aberrant ICA, a dehiscent jugular bulb, a glomus tumor, other vascular temporal bone lesions, cholesterol granuloma, or petrous carotid aneurysm with dehiscent bone.² Hence, it is important to obtain a CT scan and/or an MRA before performing any surgical intervention. Unfortunately, many of the published reports reveal that there was suspicion of acute otitis media, otitis media with effusion, or a tumor, that tympanotomy or biopsy was performed, and that the diagnosis was achieved only after a large loss of blood.³

Clinical diagnosis can be confirmed by performing the appropriate imaging examination such as a high-resolution CT scan of the temporal bone, MRA CT angiography, or conventional angiography. CT findings reveal such a characteristic feature as an intratympanic mass contiguous with the ICA through a dehiscence of the lateral carotid plate and dilatation of the inferior tympanic artery canal.^4,5 Although it has been suggested that the CT scan alone is sufficient to confirm the diagnosis of vascular anomalies, it does not always differentiate between a vascular anomaly and a highly vascularized glomus tumor.⁶ MRA is a noninvasive technique compared with the conventional vascular angiography, and is useful for establishing the diagnosis in the assessment of vascular supply, in the exclusion of an aneurysm, when intervention is planned, and in follow-up of patients.⁷ Today, MRA has almost superseded the need for conventional intraarterial contrast-enhanced angiography.⁸ However, despite the advantage of a noninvasive technique, the resolution of details is less precise in MRA than in angiograms, and imaging artifacts due to turbulent flow or patient movement may present limitations to MRA.^9,10 For some authors, conventional carotid angiography remains the standard of reference for defining the anomalies of the ICA.⁷ The classic finding in an aberrant ICA is that the medial bend of the ICA is lateral to a line drawn vertically through the vestibule, as described by LaPayowker et al, in 1971.^7,11 Also, common is displacement of the ICA posterior to the overlying image of the external auditory canal.¹² The CT angiogram is fast becoming the radiological test of choice to look at disease of blood vessels.¹³ The first report of an aberrant ICA was published in 1899.¹³ A total of 87 patients, including our case, matched this diagnosis.¹³ It has been shown that the number of reports iof this rare entity has increased recently most likely due to rising knowledge and improved techniques in radiology.¹³ Wiindfuhr¹³ found that 68.6% of patients were females, and in 73% of cases, the right side was affected. He also found in his review that most patients were found to be under 10 years of age. The published data indicates a 15% incidence of bilaterality.¹⁴

The treatment of an aberrant ICA in the middle ear space is controversial. In general, it is preferable to avoid any manipulation in the middle ear after the diagnosis has been established.^5,15–17 Paralysis of the facial nerve and deafness,¹⁶ Horner syndrome, conductive hearing loss,¹⁸ hemiparesis,⁵ aphasia, and intractable vertigo¹⁹ had been reported because of middle ear manipulation. However, several management strategies had been described. Sinnreich et al described the placement of a thick silicone sheet between the ossicular chain and the aberrant ICA to reduce the pulsatile tinnitus.²⁰ To prevent perforation of the vessel by the malleus handle, the malleus was removed²¹ or the incudostapedial joint disarticulated.¹⁸ Ruggles and Reed recommended separating the ICA by covering it with facia, compressing it into the promontory, and placing a bone and facia grafts in the defect.²²

An emergency treatment in situations of severe bleeding requires packing of the ear canal and nasopharynx in case of nasal bleeding.^2,13,23 Even if the packing must be replaced and left in place for several weeks because of recurrent bleeding,²⁴ overpacking may damage the ICA and cause serious neurologic deficits.¹⁹ Recurrent mild bleeding does not indicate intervention: ICA ligation in the neck, balloon occlusion, or embolization should be reserved for emergency situations to avoid possible severe complications or death.^23,25,26

In conclusion, awareness of the existence of vascular anomalies in the middle ear is essential. Failure to suspect or diagnose such anomalies could lead to disastrous consequences. Once an anomaly is suspected, radiological investigations in the form of high-resolution CT scan or, preferably, MRA should be performed before any middle ear surgery. Once diagnosed, patients should be followed up and manipulation should be avoided. The treatment of this condition is controversial and should be determined by the patient’s symptoms and radiological results.