Mycobacterium tuberculosis infection of an intralobar pulmonary sequestration

Abstract

Pulmonary sequestration is a rare bronchopulmonary foregut anomaly that occurs when a portion of the lung derives its blood supply from an aberrant vessel rather than the customary tracheobronchial supply. The sequestration can be classified as intralobar or extralobar. Most patients with intralobar sequestration are asymptomatic. Among symptomatic patients, presentations vary greatly, from fever, cough with expectoration, exertional dyspnea, pleuritic chest pain, and hemoptysis to eventual lung abscess or empyema. Contrast-enhanced computed tomography/computed tomography angiography is performed to determine the origin of the anomalous blood supply as well as the pathological manifestations involving the lobes. We present a patient with diagnosed intralobar sequestration who developed pulmonary tuberculosis of the sequestered lung tissue. The patient was successfully managed with long-term antitubercular therapy and left lower lobectomy with ligation of the anomalous vessel.

Pulmonary sequestration (PS) is a rare bronchopulmonary foregut malformation, comprising 0.15% to 6.4% of all congenital lung anomalies.¹ PS occurs when a portion of the lung derives its blood supply from an aberrant vessel rather than the customary tracheobronchial supply. Three-fourths of PS are intralobar sequestrations (ILS), while a quarter are extralobar, based on the presence or absence of continuity of the pleural membrane with the rest of the lung, respectively.² In this unique case, we report a patient with ILS who developed pulmonary tuberculosis confined to the sequestrated lung tissue.

CASE DESCRIPTION

A 34-year-old male farmer presented with complaints of recurrent episodes of fever, cough with expectoration, hemoptysis, and chest pain for 10 days. He had no history of comorbidities or smoking. Examination revealed significant pallor with reduced air entry and diminished breath sounds over the infraaxillary and infrascapular areas on the left side of the chest. Laboratory tests revealed a normocytic, normochromic anemia and an elevated C-reactive protein level. A tuberculin skin test, sputum nucleic acid amplification test, and sputum culture were positive for tuberculosis. Hence, antitubercular therapy was started according to the directly observed treatment, short-course regimen.

In addition, a chest x-ray revealed a left lower lobe collapse pattern. Contrast-enhanced computed tomography (CT) (Figure 1) revealed consolidation with areas of breakdown involving the posteromedial basal segment of the left lower lobe with features of volume loss and an elevated left hemidiaphragm. Moreover, multiple centrilobular nodules in a tree-bud pattern in the left lower lobe, minimal pleural effusion, focal pleural thickening, and enlarged left hilar and prevascular lymph nodes were appreciated. A prominent arterial feeding vessel was seen arising from the upper abdominal aorta, at the level of the celiac trunk, supplying the area of consolidation in the left lower lobe. The aberrant artery entered the thorax at the left cardiophrenic angle. During thoracotomy, the artery was found to have a 3 cm base and bifurcated before entering the lung. The soft, friable vessel necessitated ligation and transfixation with nonabsorbable sutures. Furthermore, a standard left lower lobectomy was done. At 2-month follow-up, the patient was asymptomatic. A repeat sputum nucleic acid amplification test was positive for tuberculosis and, therefore, antitubercular therapy was continued for another 6 months.

Figure 1.

CT scan of the chest. (a) Axial view showing lung sequestration with cavities in the left lower lobe. (b) Coronal view showing the origin of the large anomalous artery from the descending abdominal aorta. (c) Sagittal view showing a bifurcated anomalous vessel. (d) Coronal view showing the bifurcated anomalous vessel just above the diaphragm.

DISCUSSION

While an extralobar sequestration usually coexists with other malformations like diaphragmatic hernias, cardiac defects, and foregut defects,¹ ILS usually occurs as an isolated finding, suggesting that it may be an acquired anomaly. Traction by aberrant vessels, vascular insufficiency, or preceding infections could contribute to the development of ILS.² The origin of the aberrant artery supplying the nonfunctional portion of the lung is variable. The most common sources in ILS include the descending thoracic aorta (73%), abdominal aorta/celiac/splenic arteries (21%), and internal mammary/pericardiophrenic arteries.³ In contrast, the drainage of the anomalous lobe is almost always into the pulmonary veins (95%).²

Most patients with ILS are asymptomatic. However, inadequate drainage due to poor communication with normal pulmonary tissue enables optimal conditions for bacteria to proliferate.⁴ Hence, intervention is necessary, as the ILS may serve as a nidus for future recurrent infections.⁵ The most common organisms involved include Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. Although ILS can mimic primary tuberculosis as it most frequently occurs in the left lower lobe,^6,7 Mycobacterium tuberculosis infection of the sequestered lung tissue has rarely been reported.^4,8 M. tuberculosis, in particular, potentially favors colonizing sequestrated tissue due to the high arterial blood flow velocities that deliver highly oxygenated systemic blood via the anomalous artery.⁴ If tuberculosis involves only the sequestered pulmonary tissue, it is imperative to surgically remove the M. tuberculosis focus to prevent potential dissemination.⁸

Chest x-ray usually reveals a triangular-shaped mass pointing medially toward the long axis of the lung and features of complications like pneumonia or abscess.^1,3 However, CT is a better modality to visualize the ILS and anomalous blood supply. In addition, CT angiography can display homogeneous/heterogeneous opacities, cavities, cystic spaces, or calcifications.³ Alternatively, three-dimensional reconstruction by magnetic resonance angiography can be performed to visualize the origin, anatomic relations, and supply of the blood vessel.³ If these modalities fail to provide satisfactory description, conventional angiography may be done, especially if coil embolization is the desired treatment modality.^1,9

Traditionally, an open thoracotomy is performed to identify, transfix, and ligate the aberrant vessel, followed by a standard lobectomy to remove the focus of current and future infections. However, video-assisted thoracic surgery is a minimally invasive option. In fact, a 2016 cohort study reported no significant difference in the perioperative complication rate or recovery time between the two modalities but noted the reduced blood loss and greater drainage volume with video-assisted thoracic surgery.¹⁰ However, an open thoracotomy should be executed in cases involving dense adhesions, significant bleeding, or fusion to the hilum.¹⁰ A standard thoracotomy was performed in our patient due to lack of infrastructure and financial constraints of the patient.