Teaching Case

We present the case of a 75-year-old lady who was referred by her GP for a lateral C-spine X-ray for worsening dysphagia.

A lateral C-spine film demonstrated a heterogeneous gas and soft tissue density mass within the prevertebral soft tissue, causing increased width of the soft tissue anterior to C4-C5 with kyphosis of the vertebral segments. The diagnosis of retropharyngeal abscess was raised and the patient admitted for further evaluation. On admission, a repeat lateral neck film revealed similar appearances, however, the patient was systemically well with no evidence of sepsis and the original diagnosis of retropharyngeal abscess was questioned, fortunately surgical drainage was avoided. Nasendoscopy was unremarkable, however continuing dysphagia and sore throat prompted further investigations and a contrast-enhanced CT was performed. This clinched the diagnosis demonstrating an aberrant path of both carotid arteries, kinking posterior to the pharynx, producing a retropharyngeal pseudotumour and producing focal cervical kyphosis. Fortunately, neither aspiration nor surgical drainage had been performed prior to CT scanning or there may have been torrential haemorrhage with catastrophic results.

Background

Retropharyngeal abscess carries significant morbidity and mortality, although the incidence has decreased following the introduction of antibiotics for suppurative upper respiratory infections. Previously almost exclusively seen in children, retropharyngeal abscesses are now commonly seen in adults with a mean age of 44.5 years (1) and 70% of cases occurring in adults.

Clinical and Imaging Perspective

The retropharyngeal space extends from the base of skull to merge inferiorly with the mediastinum. This potential space, situated posterior to the pharynx and trachea is further enclosed by the prevertebral fascia posteriorly, carotid sheaths laterally and the buccopharyngeal fascia anteriorly.

The extensive craniocaudal limits of this fascial plane enable infections to spread from mouth to mediastinum and the associated morbidity and mortality is usually secondary to involvement of the adjacent structures resulting in airway obstruction, mediastinitis, epidural abscesses, jugular venous thrombosis, necrotising fasciitis and direct invasion into the carotid artery. Overall mortality is quoted at 1%, thus rapid diagnosis, usually with cross-sectional imaging and quick effective treatment with intravenous antibiotics and prompt surgical drainage where indicated is imperative to avoid these life threatening complications. [1]

Outcome

Medial transposition of the carotid arteries is a rare anomaly first described in the literature in the 1920’s. The aberrant course of the carotids is secondary to an embryological abnormality. The common carotid artery originates from the third aortic arch, the internal carotid artery from the dorsal aorta and the external carotid artery form the ventral aorta. The descent of these arches into the chest usually occurs during the eighth week. It has been postulated that incomplete descent can result in medial transposition and kinking of the carotid arteries. This phenomenon may result in minor tortuosity to complete loop-the-loops and is thought to be exaggerated in later life due to co-existent hypertension and atherosclerosis.

Aberrant carotid arteries must be considered as a differential when assessing a retropharyngeal mass. The subsequent clinical complications of these masses if misdiagnosed as retropharyngeal abscesses and surgically drained could be fatal.

Radiologists and otolaryngologists alike need to recognise this anomaly. On plain radiography, in addition to a retropharyngeal mass, there may be evidence of vascular calcification from co-existent atherosclerosis. Correlation with the clinical condition is paramount, as patients suffering from a retropharyngeal abscess would obviously be septic. If in doubt, then cross-sectional imaging should be acquired to ensure this anatomical variant is not treated inappropriately with catastrophic results.