Postoperative pulmonary calcification in a child with truncus arteriosus

Abstract

Pulmonary calcification is uncommon in children. It is rarely described following cardiac surgery. Here, the authors describe the case of an infant who developed extensive pulmonary calcification following the repair of truncus arteriosus.

Background

Pulmonary calcification may be divided into two main types: dystrophic and metastatic. It is associated with a number of systemic and pulmonary conditions including hyperparathyroidism, post-transplantation, renal failure and neoplasia. The aetiology is multifactorial. Clinical manifestations are variable and even widespread calcification may have a benign course. It is rarely described after cardiac surgery and has not previously been reported following the repair of truncus arteriosus.

Case presentation

A two-day-old term infant was referred for the assessment of a murmur. Initial examination revealed a non-dysmorphic female, weighing 2.9 kg. Oxygen saturations were 95% with a respiratory rate of 50 and mild indrawing. There was an active precordium, ejection click and ejection systolic and early diastolic murmurs. Chest x-ray showed cardiomegaly with right ventricular (RV) dilation and pulmonary plethora (figure 1A). Echocardiogram confirmed a diagnosis of truncus arteriosus type 1 with a short main and small branch pulmonary arteries measuring 3 mm bilaterally.

Figure 1.

(A) Preoperative chest radiograph showing cardinal features of truncus arteriosus: cardiomegaly with right ventricular dilatation and pulmonary plethora. The mediastinal contour is narrow. (B) Post-operative chest radiograph with support apparatus in situ. The heart and mediastinal structures remain central despite the opaque left hemi thorax. Towards the periphery of the left lung and posterior to the heart lung parenchymal calcification is observed.

The child underwent a repair of the truncus arteriosus on day 9 of life with a 12 mm Contegra conduit and patch reconstruction of the central branch pulmonary arteries. She had a stormy postoperative course with delayed sternal closure and multiple failed attempts at extubation. She developed a left chylothorax, which was managed with chest drain and median chain triglyceride diet and paresis of her left hemidiaphragm, which required plication on two occasions to facilitate extubation. She had a late development of sternal wound dehiscence and Escherichia coli sepsis. Several weeks into her postoperative course, she was noted to have an opaque left hemithorax on a chest radiograph, with an increase in the density of the pulmonary parenchyma, in keeping with calcification (figure 1B).

Investigations

Genetics testing confirmed a normal female karyotype and fluorescence in situ hybridization was negative for 22q11 deletion. Initial chest x-ray showed cardiomegaly with increased pulmonary vascularity for the neonatal period in keeping with truncus arteriosus. No lung lesion was noted (figure 1A). Postoperative chest x-ray, 3 weeks following surgery, demonstrated extensive changes suggestive of calcification (figure 1B). Urea and electrolytes including serum calcium, phosphate and magnesium were all normal. As were vitamin D and parathyroid hormone assays.

A CT of the chest demonstrated a small, ossified left lung with minimal remaining aerated parenchyma (figure 2). There was a thickening of the pleura in the left hemithorax and compensatory over-inflation of the right lung. Pulmonary arteries were confluent; however, the left pulmonary artery appeared to have a focal stenosis just distal to its origin. The four main pulmonary veins drained to the left atrium, but those from the left lung were small in calibre. A perfusion scan showed only minimal ventilation of the left lung—though there was some perfusion of the left lung—albeit much diminished in comparison to the right side. A CT of the brain did not show any intracranial calcification. A flexible bronchoscopy showed only mild tracheomalacia with mild left main bronchomalacia. There was no abnormal ‘material’ in bronchioalveolar lavage (BAL) washings and no growth on culture.

Figure 2.

Coronal multiplanar reconstruction from CT angiogram study. The image is windowed to show bone, which emphasises the diffuse calcification of the left lung parenchyma. Note central air bronchogram formation.

Treatment

The patient had a prolonged stay in intensive care and remained ventilator dependent. She was managed with Furosemide infusions and inotropes including Adrenaline, Milrinone and Niapride. She was treated for several episodes of generalised sepsis including necrotising enterocolitis, which was managed conservatively. Secretions grew Pseudomonas that was treated with Ciprofloxacin. Eventually, she was very gradually weaned off respiratory support. She was discharged home at 6 months weighing 4.6 kg with saturations of 98% in room air and surprisingly little increased work of breathing.

Outcome and follow-up

Despite her complex anatomy, she has remained clinically well at home. There was continuing evidence of increased right heart pressures on echo with mildly reduced RV function and tricuspid regurgitation gradient of 60 mmHg. There was a velocity of 2.8 m/s in her RV to pulmonary artery (PA) conduit with free regurgitation. A follow-up CT angiogram showed a further reduction in the calibre of the pulmonary arteries. She underwent a replacement of her RV to PA conduit with more extensive patching to her branch pulmonary arteries at 10 months of age. She made a good recovery from this and has just celebrated her first birthday. The findings in her left lung are unaltered. Her gross motor development at 1 year is delayed to an 8–10-month-old level, but she continues to make progress.

Discussion

The occurrence of pulmonary calcification following chylothorax or hemidiaphragm paresis has not been previously described to our knowledge. Pulmonary calcification postcardiac surgery is only rarely reported in the literature.¹ It has not previously been reported following the repair of truncus arteriosus. Pulmonary calcification may be divided into two main types, dystrophic and metastatic.² Dystrophic calcification occurs in the damaged lung parenchyma following an inflammatory process. It is localised and serum calcium and phosphate levels are normal.² Metastatic calcification occurs when calcium salts are deposited in previously normal tissues. Deposition can be localised or diffuse. Metastatic calcifications may be seen in the setting of neoplastic bone disease, chronic renal failure, primary hyperparathyroidism, vitamin D intoxication and excessive administration of intravenous calcium.^{3 4}

Pulmonary calcification has been described following liver and kidney transplants haematopoietic stem cell transplantation, metastatic leukaemia and haemodialysis.⁵ It is not usually associated with congenital heart disease. The pathological processes underlying this condition are not well described and are likely to be multifactorial. Mechanisms implicated include the administration of large amounts of calcium salts in the intensive care setting, extensive use of blood products, renal insufficiency and prolonged periods of mechanical ventilation. These factors may be exacerbated by disturbance in acid base balance leading to relative alkalosis in which the calcium salts are more likely to precipitate.¹ Serum calcium in this case was not reported to be abnormal; however, it may not have been monitored as frequently as other electrolytes. Closer monitoring of serum calcium and magnesium in the intensive care setting may have alerted to the risk of calcification.

Cessation of or obstruction to pulmonary artery blood flow through thromboembolism has also been postulated as contributing to pulmonary calcification by altering the microenvironment within the lung and promoting tissue alkalosis. Bloodworth and Tomashefski (1992)³ described seven patients with localised pulmonary calcification distal to pulmonary arteries obstructed by thrombus or intra-arterial tumour. In theory, a similar state might occur in the setting of severely stenosed branch pulmonary arteries as described in this case.

Clinical manifestations are variable and do not correlate with the extent of calcification. Surprisingly, the pulmonary calicification although radiologically extensive may not always be associated with increased work of breathing; many patients are asymptomatic or may be mildly breathless. Although the lesions rarely regress the clinical course is usually benign. However, there are reports of progressive calcification leading to respiratory insufficiency and death.^{1 5}

Learning points.

• This case highlights a rare postoperative complication not previously described following the repair of truncus ateriosus.

• Careful monitoring of serum calcium and magnesium with avoidance of alkalosis is important in the postoperative cardiac patient.

• Even extensive calcification may have a benign clinical course.