Spontaneous parotid pseudoaneurysm of the external carotid artery

92 year old lady who presented with a history of non-painful lump on the right side of her face for 4 weeks and was gradually increasing in size. There were no complaints of fever, weight loss, night sweats, difficulty in swallowing or pain on swallowing. She had surgical history of excision of squamous cell carcinoma from her groin 2 years prior to presentation.

MRI Neck with contrast showed well-circumscribed intensely enhancing lesion in the superficial lobe of the right parotid gland measuring 2.7 x 2.6 cm in maximum axial dimensions and 3.3

cm in craniocaudal extent. It shows some flow void like appearance and pulsation artefacts along the phase-encoding direction. There was a prominent supply vessel seen arising from the external carotid artery. Features are highly suspicious of a pseudoaneurysm. No pathological cervical lymphadenopathy was seen. There was a well-circumscribed small T2 hyperintense slightly septated lesion in the left parotid tail measuring 1.4 x 1.1 cm in maximum axial dimensions and 1.1 cm in craniocaudal extent. The patient was referred for an ultrasound of the neck and fine-needle aspiration.

Ultrasound showed a right parotid cystic lesion measuring 3.3 x 2.6 cm. Colour Doppler of the lesion shows turbulence of blood flow with a classical ‘yin yang’ appearance. No fine needle aspiration performed from the right parotid lesion. FIne needle aspiration was done in the left parotid lesion and confirmed to be adenoma.

Pseudoaneurysm is caused when there is an injury to the blood vessel wall (tunica intima and media) leading to extravasation of blood in the surrounding tissue. This usually occurs secondary to trauma, iatrogenic such as surgery or infection. In regards to carotid artery involvement, patients who have had radiotherapy in the head and neck region can also present with pseudoaneurysm due to external carotid artery blow-out. Repeated Valsalva manoeuvre has also been noted as a cause of pseudoaneurysm of the carotid artery. Patients usually present with findings of pain, pulsatile swelling and associated palpable bruit or audible bruit [1].

Background: Pseudoaneurysms commonly involve the internal carotid arteries, and rarely does it affect the external carotid arteries [1]. There have been only 15 cases found in literature where a triggering factor has been discovered, which was either traumatic or iatrogenic [2]. This is the third clinical case to describe a case of a pseudoaneurysm of the external carotid artery after Fernandez et al. [3] and Iziki et al. [4]. An interesting aspect of this case is that previous literature usually describes a younger or middle-aged patient, whereas here the patient is quite elderly.

Clinical Perspective: With the patient's background of excision of squamous cell carcinoma along with her age and risk factors, it was suspected that the nature of the parotid mass may be neoplastic in nature. She did not present with the typical findings consistent with parotid pseudoaneurysms like pain or pulsatility. Usually, a duplex ultrasound (doppler) would be the first investigation of choice, however, due to her background of cancer, it was decided to do an MRI neck instead.

Imaging Perspective: MRI Neck with contrast showed pulsatile artefacts as well as contrast pick-up which pointed towards a vascular lesion being the source. It was then decided to do a duplex ultrasound (Doppler) for confirmation. The scan showed the classical ‘yin yang’ sign of turbulent blood flow seen in pseudoaneurysms. Literature research has shown that MRI angiography is the best form of imaging to confirm carotid dissection with sensitivity of 95% and specificity of 99% as opposed to MRI with contrast on its own (sensitivity of 84% and specificity of 99% ) [5]. In this case, both investigations combined confirmed the diagnosis of pseudoaneurysm of the external carotid artery.

Outcome: Pseudoaneurysms can be managed either by wait & watch, pressure dressings, surgical excision or embolization [6, 7]. The choice of patient depends on various factors such as compression of adjacent structures, size of the lesion, associated symptoms (due to facial nerve involvement) and patients choice. In this case the patient opted for waitful watching.

Written informed patient consent for publication has been obtained.