Congenital pulmonary airway malformation: A case report in a 1-month-old infant

INTRODUCTION

Congenital pulmonary airway malformation (CPAM) results from abnormalities in the morphogenesis of the lung and is one of the most common and potentially life-threatening respiratory system malformations, with a mortality rate of up to 12.5% in neonates.^[1,2] Overall, CPAM is a rare disease among all other congenital anomalies, which occurs in 1 in 11,000–35,000 pregnancies and usually presents intrauterine (congenitally). CPAM is characterized by solid or cystic lesions that develop abnormally from the lower respiratory tract and are classified into five different types depending on the site of origin of the mass.^[3,4] CPAM lesions are often unilateral; however, bilateral CPAM cases have been reported and are associated with a poor prognosis.^[5,6] Postnatally, the condition usually presents with respiratory distress and can be associated with pneumonia after delivery or sometimes later in infancy.^[4]

Obstetric ultrasonography can be used to diagnose CPAM prenatally, as early as 13 weeks of gestation, with a positive predictive value of 70.3%, and subsequent ultrasound follow-up can be performed at term.^[4,7] Prenatal diagnosis is crucial to ensure appropriate prenatal management, well-planned delivery, and apposite postnatal management for favorable outcomes.^[4,8] However, prenatal diagnosis of CPAM is still very rare, as echoed in a case series from Nigeria by Ndukwu et al., in 2022.^[9] The prognosis of the CPAM depends on the CPAM classification, presence of fetal hydrops, and associated anomalies.^[10] Late postnatal diagnosis results in poor outcomes and may be fatal. Timely surgical resection (lobectomy, segmentectomy, or wedge resection) through either open chest surgery or thoracoscopic surgery is the definitive treatment of choice for symptomatic CPAM patients and often has a good prognosis.

In this case report, we present a male infant admitted at 27 days of life and diagnosed with CPAM at 1 month of life where the clinical presentation, diagnostic evaluation, surgical intervention, and subsequent outcome will be discussed. The rationale is to describe the unique clinical presentation, diagnostic work-up, treatment approach, and outcomes, whilst highlighting the diagnostic challenges and management in a resource-limited setting, and contribute to the existing knowledge on this rare condition.

CASE REPORT

A 27-day-old male infant was admitted to the neonatal unit at Muhimbili National Hospital (MNH) due to worsening difficulty breathing characterized by fast breathing and features of respiratory distress, presenting from the 1^st week of life with a negative history of cyanosis or cough. The infant remained afebrile throughout the current admission.

The infant’s mother booked for the antenatal clinic at a gestational age of 18 weeks and had a total of five focused antenatal visits every 4 weeks, during which she had 4 obstetric ultrasounds performed by a radiology technician at each monthly visit, with the exception of the second visit. All scans were performed during the second and third trimesters and were reported to have normal findings. She delivered a term, male infant weighing 3.2 kg through spontaneous vaginal delivery following a normal, uneventful pregnancy at the District Hospital in Dar es Salaam. The baby had good Apgar scores of 8 and 9 at the 1^st and 5^th min, respectively, and did not require any form of respiratory support at birth. The mother and the infant were discharged home on the 2^nd day of life. However, on the 3^rd day of life, the mother reported that her infant had fast breathing, and she returned to the same hospital on the 4^th day of life. He was seen as an outpatient; the mother was reassured that her infant’s condition was normal and allowed him to return home. The symptoms progressively worsened while at home; hence, the mother decided to take the infant to a Regional Referral Hospital (RRH) for further management. At RRH, the infant was admitted and treated with parenteral antibiotics for a preliminary diagnosis of severe pneumonia with no improvement. The clinicians had a differential diagnosis of acyanotic congenital heart disease or congenital diaphragmatic hernia and thus referred the infant to MNH for further evaluation and management.

On day 27 of life, the infant was admitted to MNH and found to be afebrile, tachypneic with signs of severe respiratory distress, and had a Silverman Anderson score of 6 with no cyanosis. He had a symmetrical chest rise, no areas of tenderness or palpable masses, and a hyper-resonant percussion was noted on the left lower half of the chest. He had equal bilateral air entry at the upper chest and the right lower chest but reduced breath sounds on the lower left chest. There were bronchovesicular breath sounds with coarse crepitations on the left and right supra-mammary and right infra-mammary regions, respectively. He was admitted to the neonatal high dependency unit and was kept on continuous positive airway pressure (CPAP) with an FiO₂ of 21%, a positive end-expiratory pressure of 6 cmH₂O, and an oxygen flow of 6 L/min and had oxygen saturations above 95% SpO₂ throughout, although the features of respiratory distress and tachycardia persisted. He was initially evaluated as a patient with severe pneumonia and acyanotic congenital heart disease. At admission, a septic work-up was performed, which included a blood culture that revealed no growth after 5 days, a C-reactive protein level of 0.2, and an initial complete blood count with a normal white blood cell count of 4.05, moderate neutropenia of 1.09, a normal absolute lymphocyte count of 2.47, and a hemoglobin level of 12.4 g/dL all suggested a non-infective process. A chest X-ray revealed coarse infiltrates in the right lower zone but, more importantly, a large cystic lesion in the left lower zone, with the mass effect shifting the heart and the mediastinum to the right side of the chest, as shown in Figure 1. An echocardiogram was also performed, which revealed that the patient had a structurally and functionally normal heart.

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Figure 1: Chest X-ray image taken on day-2 post-admission.

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Chest X-ray findings revealed features of pneumonia on the right lower lung and a cystic lesion occupying the left lower lobe, compressing the left upper lobe with the heart and mediastinum shifted to the right side of the chest.

A chest-computerized tomography (CT) scan was performed to further define the lesion, as shown in Figures 2a and b.

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Figure 2: Chest computed tomography scan performed on day 3 post-admission showing: (a) coronal view of the large left lower lobe cystic lesion with mediastinal shift; and (b) axial view showing the air-filled cystic lesion occupying the left lower lobe with compression of adjacent lung tissue.

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Surgical intervention

The pediatric surgery and cardiothoracic surgical teams were then consulted, and on the basis of the diagnosis of this symptomatic CPAM, the decision was made to perform a left lower lobectomy. The surgical procedure was performed with the collaboration of the MNH pediatric surgery team and the cardiothoracic team from the Jakaya Kikwete Cardiac Institute. The thorax was entered through a dorsal incision. The intraoperative findings were in accordance with the findings of the CT scan, whereby a large left lower lobe cyst compressing the left upper and lower lung lobes with a mediastinal shift to the right was found. There was mild hypoplasia with multiple severe cystic changes to the lower left lung lobe that did not respond to positive pressure ventilation. However, the left upper lung lobe was adequately re-expanded in response to positive pressure ventilation. Excision of the cyst from the left lower lobe was performed, lobectomy was also performed through dissection of the inferior pulmonary ligament, and a 16Fr chest tube was inserted and kept on underwater seal drainage. The patient tolerated the surgery well without any complications. The intraoperative findings and excised cystic lesion are shown in Figure 3.

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Figure 3: Intraoperative images showing: (a) exposure of the left lower lobe cystic lesion; (b) excised cystic lesion after lobectomy.

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Outcome

Postoperatively, the infant was admitted to the neonatal intensive care unit and was kept on a mechanical ventilator. He was successfully extubated on the 4^th day postoperatively, and the chest tube was removed on the 8^th-day post-surgery. After extubation, the infant required noninvasive respiratory support through CPAP for 2 days and was gradually weaned to low-flow oxygen through a nasal cannula for 3 more days before transitioning to room air. The infant was also kept on the intravenous antibiotic meropenem for 10 days postoperatively. The infant had complete resolution of symptoms by day 13 post-surgery, and he was discharged from the NICU to the general wards for 2 more days of observation before being discharged home.

Postoperative chest X-rays are shown in Figure 4. X-ray findings post-lobectomy showed significant re-expansion of the left upper lung with radiological improvement after surgical intervention.

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Figure 4: (a) Chest X-ray performed on day 1 post-surgery, (b) Chest X-ray performed on day 2 post-surgery, (c) Chest X-ray performed on day 3 post-surgery.

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DISCUSSION

CPAM accounts for approximately a quarter (25%) of all congenital lung lesions, making it the most common congenital lung lesion. CPAM can be diagnosed through obstetric ultrasound, which is routinely performed in most settings, including low-income countries such as Tanzania. However, prenatal diagnosis is still rare, mainly due to a low suspicion of this condition among healthcare workers.^[9] This was exemplified in our case, where despite several prenatal ultrasound scans, the CPAM was missed. An accurate obstetric ultrasound can be utilized to determine the lesion size and site of origin. Obstetric Doppler studies can also be used to establish the origin of the vascular supply to differentiate CPAM from bronchopulmonary sequestration (BPS). The BPS has the thoracic aorta as its vascular supply, whereas the vascular origin for the CPAM is from the pulmonary artery.^[11] Postnatally, CT scans and/or magnetic resonance imaging (MRI) are used to confirm the diagnosis and classify the type of CPAM, and these help to determine the appropriate plan for management.^[12,13] Nevertheless, even with the increase in antenatal obstetric ultrasound screening, the majority of CPAM cases are diagnosed postnatally. A delayed diagnosis increases the risk of developing complications such as pneumothorax, recurrent respiratory infections, and impaired postnatal lung maturation.^[6]

The classification of CPAM has evolved over time, and currently, there are five categories according to the site of origin, size, and associated cysts. Initially, congenital cystic adenomatoid malformation (CCAM), which includes only 3 types, occurred because of abnormal proliferation of the bronchial tree of the lung, resulting from failure of bronchoalveolar development, with a gland-like pattern (adenomatoid) impairing alveolar formation, resulting in cystic or mass-like lesion(s). In 2002, it was determined that CPAM can have another origin in addition to those of cystic and adenomatoid origin previously included in the 1977 Stocker classification. To include the other two types of CPAM, the type 0 and type 4 CCAM were changed to the current CPAM.^[6,14] The five types of CPAM, which are based on clinical, gross, and microscopic criteria, include the following:

Type I CPAM is the most common type and accounts for approximately 70% of CPAM cases where the more dominant cyst size measures 2–10 cm in diameter and arises from the distal bronchus or the proximal bronchiole.

Type II CPAM accounts for approximately 5–20% of CPAM cases where the more dominant cyst size measures <2 cm in diameter, affects terminal bronchioles, and is associated with other abnormalities, renal agenesis or dysgenesis, pulmonary sequestration, and congenital cardiac anomalies.

Type III – This comprises approximately 5–10% of CPAM cases with microcysts: Those <5 mm in diameter typically involves an entire lobe arising from the alveolus. It is rare and often fatal.

Type IV – Unlined cysts typically affect a unilateral lobe. This subtype is difficult to distinguish from types I and II radiologically and is associated with malignancy.

Type 0 - A very rare subtype of CPAM is caused by arrest of lung development postnatally, with acinar dysgenesis or dysplasia, which is usually lethal.

This case report highlights the successful management of a type I CPAM in a 1-month-old infant despite a delayed diagnosis. The infant was managed by left lower lung lobectomy, as the lesion occupied more than 20% of the left hemithorax, and the infant was symptomatic. This patient’s management is in accordance with current management recommendations for symptomatic CPAM.^[15] Lobectomy involves the removal of the affected lobe of the lung to eliminate the cystic lesion and restore normal lung function in the remaining lung. In the absence of hydrops fetalis, infants with type I CPAM have a good prognosis of up to 95% survival.^[12,15] Therefore, in our case with isolated type I CPAM, once the definitive diagnosis was reached and surgery was performed, the infant showed remarkable improvement. In contrast, infants with bilateral CPAM and/or multiple cystic lesions or with associated anomalies rarely survive beyond 1 month of postnatal age, and surgery is often unsuccessful.^[6]

Prenatal diagnosis for congenital anomalies has improved over the years, facilitating the planning of neonatal deliveries and management. Antenatal screening through high-resolution ultrasound during the second trimester can detect echogenic lung lesions with reproducible results. This imaging tool is safe, cost-effective, and widely available for fetal anomaly screening, including the CPAM.^[16] Ultrasound results dictate the frequency of follow-up scans, the need for intrauterine intervention, and the planning of delivery at a tertiary neonatal care center.^[11] In our case, prenatal ultrasound scans were performed by a radiology technician at gestation ages of 18, 26, 30, and 34 weeks. However, the diagnosis was missed. This is not uncommon in many limited-resource settings, where CPAM is often diagnosed postnatally.^[9,17] Neonates with a prenatal diagnosis of CPAM are flagged for immediate postnatal screening for features of respiratory distress, which, if present, may warrant early evaluation and management. However, if the infant remains stable and asymptomatic, they can be referred for pulmonology follow-up.^[15,18] These patients subsequently undergo a chest CT scan or MRI to determine if the CPAM has undergone involution or if surgery is still needed. MRI has been shown to accurately detect 95.6% of CPAM cases as a non-ionizing radiation option; although it is costly, it also requires highly technical staff to perform and is not readily available.^[13] Future developments are therefore looking further at machine learning algorithms to enhance fetal anomaly detection.^[19]

An early diagnosis of CPAM in the first trimester may often indicate a more severe and rapidly progressive form, whereas late-occurring CPAMs detected in the second trimester tend to have a better prognosis.^[7] In our case, the antenatal diagnosis was missed; hence, it was difficult to determine the onset; however, given the favorable outcome, it may have been the late-onset form of CPAM.

CONCLUSION

A low index of suspicion among healthcare practitioners can lead to significant morbidity in infants with a delayed diagnosis of CPAM. Postnatal chest X-ray and CT scans play crucial roles in confirming the diagnosis, assessing the extent of the lesion, and guiding the surgical approach, resulting in a favorable outcome in our case. Prenatal diagnosis is still the cornerstone for early detection and early intervention; therefore, training on fetal anomaly detection among radiology technicians and obstetricians working in limited resource settings is highly recommended.