CHEST RADIOLOGY - A CASE OF AZYGOUS LOBE

By Dr Deepu
The lungs are normally divided into five lobes by three main fissures .
 Occasionally, invaginations of the visceral pleura create accessory fissures that separate individual bronchopulmonary segments into accessory lobes .
 An azygos lobe is found in approximately 0.4% of patients . In contrast to other accessory lobes, the azygos lobe does not correspond to a distinct anatomical bronchopulmonary segment .

It forms during embryogenesis when the precursor of the azygos vein fails to migrate to its medial position in the mediastinum, where it normally arches over the origin of the right upper lobe bronchus.
 This gives rise to the following characteristics, which are visible on a standard chest x-ray

: the laterally displaced azygos vein lies between folds of parietal pleura, also referred to as the mesoazygos, where it assumes a characteristic teardrop shape ; the mesoazygos indents the right upper lobe, thereby creating the accessory (azygos) fissure, which is similar in shape to an inverted comma; the fissure delineates the azygos lobe, located superomedially ; laterally, the pleural folds of the mesoazygos separate before reaching the chest wall, resulting in a radiopaque triangular area ; and medially, the tracheobronchial angle appears empty .

 An azygos lobe may be confused with a pathological air space such as a bulla or abscess . In addition, the abnormally located azygos vein may be mistaken for a pulmonary nodule, while a consolidated azygos lobe may be confused with a mass . An understanding of the pathogenesis and characteristic x-ray features of the azygos lobe will enable an accurate diagnosis in most cases .
 If the x-ray findings are equivocal, computed tomography will be diagnostic .

CONGENITAL ANOMALIES

CONGENITAL ANOMALIES

Common congenital pulmonary anomalies are sequestration, bronchial cyst and agenesis of lung or pulmonary artery.

• These anomalies are most often recognized by serendipity from CXR obtained for other reasons. Patients with these anomalies are most often asymptomatic.
• Attention can be brought to them because of infection or rupture.

Sequestration

• Sequestration should be considered any time a lesion is noted in medial basal segment of lower lobes.
• They can present because of hemoptysis, or with infection or as CXR abnormality.
• Sequestered lung has no connection to bronchial tree or pulmonary artery .
• It is supplied by vessels from Aorta and are drained by systemic venous system.
• Bronchogram, Lung scan, Aortogram, CT Scan are useful in identifying various aspects of the anomaly.
• Aortogram is gold standard for diagnosis but CT chest in some cases can confirm the diagnosis.

Bronchial Cyst

• Bronchial Cyst can present as a mass in mediastinum or over lung fields.
• Most often they are asymptomatic.
• Occasionally they get infected or can rupture presenting as Pneumothorax.
• CT chest demonstrates cystic nature of the lesion and its close association to bronchial tree thus confirming the diagnosis.
• Surgical resection is necessary only if they are infected , the diagnosis is in doubt or the cyst has ruptured.

Agenesis of Lung

• Hemithorax and Lung fields are asymmetric and smaller than normal. Normally right Lung should be about 55% and left Lung about 45%. Hemithorax size should be symmetrical.
• Pulmonary artery segment is smaller.
• Lung scan , CT chest and Pulmonary angiograms show various aspects of the anomaly.