Author James Watts, Department of Anaesthesia and Critical Care Medicine, East Lancashire NHS Hospitals Trust, discusses a case of azygous lobe, an unusual thoracic anatomical variant.
Introduction
An elderly patient presented with recurrent pneumonia. During their stay on ITU they underwent a chest X ray which appeared to show a right upper lobe teardrop shaped mass. At first thought to be a tumour, it was later reported by a consultant radiologist to be an azygous lobe, a normal but uncommon anatomical variant.
Anatomy
The azygous (from the Greek word meaning ‘unpaired’) vein is a unilateral right sided vessel which drains deoxygenated blood from the posterior abdominal and thoracic walls into the Superior Vena Cava (SVC).
It has a variable development and anatomy, but generally it arises at about T12 from the the ascending lumbar vein and lower subcostal vein, and joins the SVC at about T4 level after passing over the apex of the right lung. The part of the vein that curves over the top of the right lung is referred to as the ‘arch of the azygous’. (1)
In approximately 0.3 to 1% of the population, the azygous vein is displaced laterally, in which case it impinges into the lung, creating what is described as an extra upper lobe. This is not a true lobe as there is no associated bronchus but instead describes the fact that the vein creates a fissure (the azygous fissure, lined by invaginated pleura and inside of which the vein itself runs) into, partially separating part of the upper lobe from the rest of the lung. This is referred to as an ‘azygous lobe’. (see figures 1 to 5) (2-4).
The Xray
