Medium Term Pulmonary Function Test After Thoracoscopic Lobectomy for Congenital Pulmonary Airway Malformation: A Comparative Study with Normal Control

Introduction

Congenital pulmonary airway malformation (CPAM) is a congenital anomaly characterized by hamartomatous proliferation of terminal respiratory bronchioles forming multicystic lung mass. Its formation has been attributed to the abnormal arrest of fetal lung development, however, the exact pathogenesis is still not known. ¹ This condition was considered an extremely rare disease with incidence estimated between 1 in 10,000 and 1 in 35,000^2,3 in the past. With more widespread use of antenatal ultrasound scanning, recent studies suggested that the actual incidence may be much higher than what was previously believed.^4,5

Despite the majority of CPAM patients were asymptomatic at birth, a significant proportion of patients develop recurrent chest infection in their later life. ⁶ Malignant transformation of CPAM into pleuropulmonary blastoma and bronchioalveolar carcinoma has also been reported. ⁷ Because of the infection risk and malignant potential, surgical resection has been advocated by some authors for complete removal. ⁸ In specialized centers, thoracoscopic lobectomy has become the standard of care with proven safety profile. ⁹

Thoracoscopic approach has demonstrated advantages over thoracotomy in terms of pain, length of hospital stay, and musculoskeletal complication in several studies.^10–12 However, to date the effect of thoracoscopic lobectomy on postoperative respiratory outcome was still poorly described. The objective of this study was therefore to evaluate the pulmonary function of CPAM patients after thoracoscopic lobectomy on a medium term basis.

Materials and Methods

All patients who underwent thoracoscopic lobectomy for CPAM between January 2006 and December 2010 were included into the study with prior approval obtained from the ethics committee. Medical and operative records were retrospectively reviewed. Patients' demographics including age, sex, body weight at operation, laterality of lesion, operative details, and postoperative outcomes were extracted from the records for statistical analysis.

Pulmonary function test (PFT) was arranged for patients 5 years after the operation. This duration was chosen to provide adequate time interval for lung to remodel and grow after operation so that the test result is more representative, and to ensure patients can cooperate with a proper PFT. Full PFT was performed in a pediatric pulmonary laboratory. Flow volume loop was performed for three times and the best result was used for analysis. Parameters measured during PFT include forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1 to FVC ratio (FEV1/FVC), total lung capacity (TLC), and alveolar volume adjusted diffusion capacity of carbon monoxide (DLCO). The measured values were then compared with the normal reference according to gender and body size. Test results less than 80% of predicted values were considered as abnormal parameters. Age-matched healthy individuals with similar body size were recruited for PFT as the control group with informed consent obtained.

Statistical analysis between the postoperative group and control group was performed using SPSS (version 17; SPSS, Chicago, IL). Continuous variables were analyzed using Student's t-test, while ordinal variables were analyzed using Mann-Whitney U test and categorical variables were analyzed using chi-square test. Data were presented as mean ± standard error of mean and range. P < .05 was considered statistically significant and all P values were two tailed.

Results

A total of 15 CPAM patients had thoracoscopic lobectomy performed during the study period, 8 men and 7 women. The mean age at operation was 11.5 ± 4.0 months (range 18 days–5 years). The mean body weight was 8.4 ± 0.9 kg (range 3.8–18.2 kg). All patients had CT thorax performed before the operation to confirm the location of the CPAM. CPAM lesions were found in left lower lobe and right lower lobe in 10 and 5 patients respectively. Thoracoscopic lobectomy was performed for these 15 consecutive patients without the need for thoracotomy conversion. No major complication was observed in this group of patients and all of them were discharged within 1 week after operation. The diagnosis of CPAM was confirmed by histological section of resected specimen. The data are summarized in Table 1.

PFT was performed at least 5 years after the thoracoscopic lobectomy with a mean age of 9 years. All patients were aged 6 or above at the time of PFT with good general condition. No chest wall deformity was observed. A group of 15 healthy individuals, age and body size matched, were selected as control for comparison with the postoperative group. Statistical analysis showed that the age, sex ratio, and body weight were comparable between the two groups (Table 2).

The mean FVC was 99.6% predicted for postoperative patient and 97.0% for the control group (P = .56). The mean FEV1 of the two groups were 86.0% and 89.1% predicted respectively (P = .52). There was no significant difference between the mean FEV1/FVC ratio of the two groups (96.9% versus 98.7% predicted, P = .60). The mean TLC and mean DLCO were also statistically similar between the two groups (92.5% versus 94.5% predicted, P = .68 and 106% versus 100% predicted, P = .35). All participants have normal PFT results and none were diagnosed of any respiratory disease at the end of the study. Other PFT parameters were summarized in Table 3.

Discussion

Despite the discovery of CPAM can be traced back to nearly 70 years ago, it was not until the recent decade that this disease entity truly raised people's attention. ¹³ With the more popular use of routine ultrasound screening during pregnancy, most of the lesions were now detected antenatally.^4,5 Although at the extreme end large CPAM can result in fetal hydrops and death, the greater part of patients remains asymptomatic. While most surgeons advocate resection for symptomatic CPAM, the management of asymptomatic lesions is still highly controversial. The main focus of argument falls on the balance between the risks of surgery, versus the risks of recurrent chest infections and malignant potential.

The dramatic growth of minimally invasive technology had allowed surgeons to venture into the thoracic cavity. Thoracoscopic approach can now be applied to the most technically demanding procedures including esophageal atresia repair and lobectomy.^9,14 CPAM is still the main indication for thoracoscopic lobectomy in pediatric patients. Thoracoscopic lobectomy for CPAM had gained increasing popularity not only because of its better cosmetic outcome, but also because of other advantages brought about by the smaller wounds. Meta-analysis by Adams et al. showed a significantly lower wound complication rate and shorter hospitalization in 1626 patients following thoracoscopic lobectomy compared to open thoracotomy. ¹² Another study by Nasr and Bass found that both the duration of chest tube drainage and hospitalization was shorter after thoracoscopic lobectomy. ¹¹ However, any beneficial effect on pulmonary function was not yet investigated.

Possibility of impaired pulmonary function is one of the main concern following lung resection. Several studies on pulmonary function after lobectomy showed that the procedure is well tolerated by children in general, but the data are limited to open lobectomy only.^15–19 Nonetheless up to 10% of postoperative patients showed impaired PFT results to certain extent, and restrictive pattern with TLC less than 80% of predicted value was the most common finding.^15,20 In contrast, all TLC values of the postoperative group were normal in our series. Pleural adhesions, which resulted in restrictive dysfunction because of previous chest infection, was a possible reason for the restrictive pattern on PFT after open lobectomy as suggested by Nakajima et al. ¹⁵ Interestingly, this coincided with our patient group since none of them experienced any chest symptom or infection before operation. This may further add weight to the argument for early elective surgery before onset of symptom, on top of the advantages of less adhesion and thus bleeding during operation as well as the potential for compensatory lung growth. On the other hand, resection of CPAM lesions may even improve PFT result since they do not really participate in gaseous exchange, and in extreme case can cause adverse effect on respiratory function if they are sizeable.

From our study, we found that the PFT result of patients after thoracoscopic lobectomy was comparable to the control group, who were expected to have a perfectly normal lung function. Nevertheless, we were not able to compare the result with open lobectomy directly since no such patient was included into the study. The result of the study is limited by the small sample size so the conclusion may not be generalized, which also hinders the reliability of further subgroup analysis. The short follow-up time means that only medium term result can be revealed.

In conclusion, CPAM patients in our series have normal lung function after thoracoscopic lobectomy at medium term. A larger scale prospective study with longer follow-up time is necessary to confirm the long term result.