Positional change in the carotid arteries on serial imaging and the potential to mimic retropharyngeal pathology on MRI cervical spine

A 46-year-old lady was referred by her neurologist for a cervical spine MRI. She presented with a 10-month history of worsening neck stiffness, weakness, and shooting pain radiating down both arms and hands with pins and needles sensation. She was dropping things unintentionally and had stiff legs with balance difficulty.

The presenting MRI cervical spine (Figure 1) demonstrates T2W hyperintensity in the prevertebral soft tissues, not seen on the MRI cervical spine performed four years earlier (Figure 2). The reporting neuroradiologist sought a second opinion from a head and neck neuroradiologist, querying potential retropharyngeal pathology such as calcific tendinitis.

The head and neck neuroradiologist noticed that both internal carotid arteries had moved from a parapharyngeal location four years earlier into the retropharyngeal space (arrows on Figure 1 and Figure 2). The retropharyngeal T2W hyperintensity was not related to an underlying pathology but mobility of the internal carotid artery and displacement of retropharyngeal fat.

The patient also had a CT cervical spine study (Figure 3). Interestingly, the scan shows a retropharyngeal right internal carotid artery (ICA), while the left internal carotid artery is in a parapharyngeal location.

Retropharyngeal ICA is an anatomical variant characterised by ICA medialisation to the retropharyngeal space, recognised since 1925 [1]. This variant poses a higher risk of intraoperative vascular injuries, such as during tonsillectomy, trans-oral tumour resection, peritonsillar abscess drainage, and tracheal intubation [2]. Glossopharyngeal nerve block could also result in stroke or inadvertent local anaesthetic injection into the ICA [3]. A case series reported retropharyngeal ICA in 15.5% of cases, with 6.3% (4 patients) demonstrating unidirectional change in ICA position on follow-up imaging. A higher grading of atherosclerosis was observed in patients with positional change in the retropharyngeal ICA [4]. A statistically significant correlation between a high body mass index and the prevalence of wandering carotid artery has been reported [5]. The suprahyoid carotid sheath may be incomplete and may explain the vascular mobility [6]. Variation in the pharyngeal wall diameter and hyoid bone position with respiratory cycle is one of the potential causes of ICA movement. A study of the motion of parapharyngeal and retropharyngeal structures has shown anteromedial displacement of the carotid artery by pharyngeal contraction during swallowing [7].

In our case, the patient had three cervical spine imaging studies; each revealed different locations of the suprahyoid ICAs over 4 years. The apparent MR signal change in the retropharyngeal space reflects flow-related artefacts and displacement of retropharyngeal fat secondary to interval ICA positional change, not to be misinterpreted as pathology. This phenomenon has not been reported in the literature to date, and if not recognised, it could potentially lead to the patient having further investigations and procedures unnecessarily.

The radiologists and clinicians need to recognise that a retropharyngeal ICA may be a transient imaging finding more often than expected to allow for more accurate informed consent and avoid false reassurance during trans-oral surgical procedures to minimise the risk of carotid injury. Preoperative imaging to localise the ICA may be less reliable for surgical planning than is often realised.

The signal changes in the retropharyngeal space on MRI should prompt the radiologist to consider the possibility that this may be related to movement artefacts of the carotid arteries and carefully review the course of the ICA flow voids. A retropharyngeal location of the ICA on preoperative imaging cannot always be relied upon for subsequent location during surgical intervention.

All patient data have been completely anonymised throughout the entire manuscript and related files.