Pulmonary sequestration with tuberculous infection of the sequestrated lung

An eight-month-old female child presented with fever, left anterior chest wall swelling and discharging abscess in the left supraclavicular region since one month of age. On physical examination, there was decreased air entry on the left side. Her white blood cell counts were elevated (44,000/µL).

The chest radiograph showed a large homogenous soft tissue opacity in the left lung field (Figure 1). A contrast-enhanced CT of the chest was done. There was a large soft tissue lesion occupying the left hemithorax in the upper and mid portions. Within the lesion, there were fluid-filled dilated bronchi which showed no communication with the bronchial tree of the residual aerated lung (Figure 2 a, b).

The lesion had its arterial supply via a branch from the left subclavian artery and the venous drainage was into the left brachiocephalic vein (Figure 3 a, b).

There was a fistulous tract opening on the skin surface communicating with one of the dilated fluid-filled bronchus in the lesion suggestive of broncho cutaneous fistula (Figure 4).

Background

Pulmonary sequestration (PS) is dysplastic lung tissue without any communication with the tracheobronchial tree. The arterial feeder is mostly through the aorta and variable venous drainage. This was initially described by Pryce et al in 1946 and divided into intralobar and extralobar types. In 2008 Lee et al classified pulmonary sequestration under bronchopulmonary vascular malformations which includes concurrent abnormalities of the airway, arteries, veins and associated gastrointestinal tract and diaphragmatic anomalies. [1] The incidence of PS is 0.29% accounting for 0.15–6.4% of all congenital pulmonary malformations.[2]

Clinical Perspective

Intralobar sequestration is more common (75-85%) and presents in late childhood or adolescence with recurrent pulmonary infections, whereas extralobar sequestration presents in newborns or infants as respiratory distress, cyanosis and feeding difficulty. [3]

Imaging Perspective

The left lower lobe is the most common location of PS.

Intralobar type does not have a separate pleura and the venous drainage is usually to the pulmonary circulation. Extralobar type has a separate visceral pleura and can sometimes be extra thoracic with venous drainage usually into the systemic circulation.

On Chest radiographs,

• The lesion is seen as triangular opacity in the affected bronchopulmonary segment.

On Ultrasonography,

• The lesion appears as a solid well-defined triangular intra-thoracic or extra-thoracic echogenic mass
• In-utero cases may show a feeding vessel from the aorta on colour Doppler [4]

On CT,

• The lesion is seen as a focal enhancing area of consolidation.
• CT Angiography study shows arterial blood supply mostly from the aorta but less frequently, it can be from intercostal, subclavian, internal thoracic or pericardial arteries
• Fluid or air bronchograms are seen within if the lesion is infected or as a part of a hybrid lesion with a foregut communication [5]

DSA Angiography is the gold standard procedure for the diagnosis of PS [6]

Outcome

Surgery with thoracotomy or video-assisted thoracoscopic surgery (VATS) approach is the standard care for these patients. [7] In our case, VATS with lobectomy of left lung sequestration was performed. The sequestered lung was broken into pieces with a harmonic scalpel and tissue was sent for histopathology.

Histopathology revealed necrotizing granulomatous inflammation suggestive of tuberculosis involving the sequestered lung.

Take Home Message / Teaching Points

The differential diagnosis of pulmonary sequestration must be kept in mind when evaluating non-resolving consolidation in children. CT angiography is the mainstay in the diagnosis of pulmonary sequestration.

After the diagnosis of the sequestrated lung is confirmed, the possibility of superadded infection like tuberculosis should be considered.