Anomalies of vascular anatomy in the neck are well recognised and described. Tracheostomy is a surgical procedure performed to gain direct access to the airway at the level of the upper trachea. This can be performed 'open' by incising and exposing the neck or 'closed' by percutaneous dilatational methods. We present a case of an unusual aberrant artery discovered during open tracheostomy. This emphasises the importance of an accurate physical examination prior to undertaking surgery, and illustrates the potential dangers of percutaneous tracheostomy.

An 82-year old gentleman presented with sub-acute large bowel obstruction. An emergency laparotomy revealed a perforated large bowel carcinoma with faecal peritonitis, and the patient was admitted to the Intensive Care Unit (ICU) after undergoing a hemicolectomy. He developed acute renal failure requiring haemo-filtration and remained intubated for ventilatory support. On day 15 post-operation, a tracheostomy was indicated to facilitate weaning from assisted ventilation. Local ICU policy prevented consideration of percutaneous tracheostomy, so an open tracheostomy was planned by the Ear, Nose and Throat surgeons. Examination of the neck revealed no obvious abnormality.

The tracheostomy proceeded in theatre under sterile conditions with a standard horizontal approach. The strap muscles were separated by blunt dissection in the vertical plane. It became clear at this stage that a large pulsatile vessel was overlying the trachea outside the pretracheal fascia. Meticulous and cautious dissection revealed the vessel to be running obliquely across the anterior surface of the trachea from left to right, at the level of the fourth tracheal ring (Figure 1). Further examination showed the artery to be an unusual aberrant right subclavian artery, arising directly from the aortic arch as the fourth major branch. The vessel appeared to gain its usual position by passing behind the right carotid after traversing the trachea.

A decision was made to continue with placement of the tracheostomy tube as it was felt this could be performed safely in the 2^nd to 3^rd rings. The risk of late erosion of the vessel by the tracheostomy tube was felt to be small. The thyroid isthmus was divided and fixed, and the trachea exposed from the cricothyroid inferiorly. A layer of fat and fascia was fashioned to lie superior to the aberrant subclavian artery to reduce the risk of contact with the tracheostomy tube. A window was made in the trachea at the 2^nd and 3^rd rings, and the tracheostomy placement continued without incident.

Post-operatively, the patient returned to the ICU department. He made good progress leading to decannulation 16 days later and discharge from ICU to a surgical ward. His further recovery on the ward was disrupted by the development of a severe bi-basal pneumonia and despite intensive treatment over the following weeks, he succumbed to overwhelming sepsis.

The authors found no reported cases of this specific subclavian artery anomaly being discovered during surgery, although it is referred to in a standard anatomical textbook 1. Anatomical variation of the aortic arch and great vessels are well recognised with an array of anomalies described 2345. Aberrant right subclavian artery is the most common abnormality of aortic arch development. In up to 0.5% of the population, the right subclavian arises as the fourth aortic branch, as in this case, but usually from the descending thoracic aorta 6. Anomalies of this artery also include variations in its course (e.g. arteria lusoria passing dorsally between the oesophagus and spine).

The discovery of abnormal vasculature during percutaneous and open tracheostomy procedures has been previously described. Mukadam et al. (2002) recently reported a case of an aberrant brachio-cephalic artery discovered precluding a percutaneous dilatational tracheostomy 7. This was palpated in the neck and confirmed by CT scan. The procedure was abandoned and an open tracheostomy was also felt to be too risky. Jarvis (1966) discovered a similar abnormality of the brachiocephalic artery during tracheostomy 8. Nonetheless a tube was successfully placed in this case.

The discovery of anatomical variations of the aortic arch and its branches seems even more important in percutaneous dilatational tracheostomy (PDT) than open tracheostomy. PDT has gained acceptance in many centres as an alternative method to open surgical tracheostomy and was used in 78.4% of Intensive Care Units in the UK in 1998 9. Two methods of percutaneous tracheostomy are commonly employed, the guide-wire dilatational forceps technique, and the percutaneous dilatation technique first described by Ciaglia 10.

The advantages of percutaneous tracheostomy over open tracheostomy include its relative speed, simplicity, and the ability to perform it at the bedside. The major disadvantage is the increased risk of peri-operative complications including severe bleeding and damage to the posterior tracheal wall 11. There are also relative contraindications to performing the percutaneous tracheostomy such as previous surgery, known anatomical abnormalities, and the obese neck. In a study of 497 cases of PDT, Muhammad et al. found 4.8% of procedures were abandoned due to bleeding 12. The source of bleeding in four of these cases was attributed to variations in vascular anatomy. Interestingly, a case of fatality after PDT in a patient with aberrant right subclavian has previously been described 13.

This case illustrates the importance of awareness of the anatomical variability of the aortic arch branches while undertaking either open or percutaneous dilatational tracheostomy. In selected cases, a thorough neck examination can be augmented by ultrasound scan, Doppler studies, angiography or magnetic resonance scanning (in the non-emergency scenario). Therefore the rare but potentially severe risk of haemorrhage in the presence of anomalous vascular anatomy can be minimised if the surgeon maintains a high index of suspicion. In the presence of anatomical variations, open tracheostomy is safer than percutaneous dilatational tracheostomy and should be the procedure of choice.