Pseudoaneurysm of the internal carotid artery: a late complication of otomastoiditis

Clinical History

Our patient is a 70-year-old female hospitalized in Intensive Care Unit (ICU) with a sepsis following otomastoiditis. After right open mastoidectomy surgery, there is a complication with a deep parapharyngeal space abscess and inflammatory changes surrounding the right Internal Carotid Artery (ICA). The findings persist in following controls.

Imaging Findings

CT of the temporal bone shows occupation of the right middle ear and mastoid cells, erosive lysis and ill-defined irregular edges of the petrous apex, suggesting right petrous apicitis (Fig 1).
Inflammatory changes in deep parapharyngeal space and surrounding right ICA persist over time in successive controls with spasm and decrease in diameter of the artery (Fig 2).
MRI control after four months (Fig 3) shows a parapharyngeal abscess and a vascular dilatation image adjacent to the right ICA proximal to the entrance in the skull base as a late complication of otomastoiditis. It is confirmed with CT angiography (Fig 4). After conventional arteriography (Fig 5a) the lesion was successfully treated by coil embolization (Fig 5b).

Discussion

Pseudoaneurysms of the extracranial Internal Carotid Artery (ICA) are a rare but potentially lethal complication.
False aneurysms or pseudoaneurysms means that there is a leak through the wall of the artery and therefore the blood is contained by the adventitia or surrounding perivascular soft tissue. They lack a true wall and develop when a thrombus and fibrous tissue capsule forms in response to injury to all layers of the arterial wall. The injury may result from several mechanisms including trauma, infections, inflammation or radiation. Chronic otomastoiditis, pharyngeal infections and cholesteatomas have been implicated in the development of these aneurysms [1], [2]. In our case it was the consequence of a late complication after four months of a process of otomastoiditis with inflammatory changes in deep parapharyngeal space.
ICA pseudoaneurysms of infectious aetiology probably originate secondary to adventitial infection of the artery because of closeness to the middle ear rather than hematogenous seeding. The natural evolution is progressive enlargement of the lesion with high risk of rupture.
Infected aneurysm is a serious clinical condition that is associated with significant morbidity and mortality. The risk of rupture is higher than the rupture risk of a true aneurysm [3]. The lack of structural integrity of the wall of a pseudoaneurysm may result in rapid expansion because of the turbulent flow and poor support of the wall. Treatment consists of antibiotic therapy combined with surgical therapy [4]. Direct surgical repair with preservation of the ICA may be technically difficult and is associated with relatively high morbidity and mortality. Endovascular coil embolization or stent placement with preservation of the artery is the alternative treatment.
In our case, coil embolization of the pseudoaneurysm was successfully performed with complete obliteration of the cavity and without suffering permanent neurological sequelae. The endovascular method provides an effective, relatively low-risk treatment for these lesions.

Differential Diagnosis List

Final Diagnosis

Pseudoaneurysm of the internal carotid artery as a late complication of otomastoiditis.

URL:	https://eurorad.org/case/12569
DOI:	10.1594/EURORAD/CASE.12569
ISSN:	1563-4086