Article Text
Abstract
Congenital cystic adenomatous malformation of the lung (CCAM) is a rare lung lesion easily diagnosed on prenatal scan. The pathology of fetal lesions differs from postnatal lesion, hence the need for separate classifications during the different stages of development. Fetuses with CCAMs and hydrops have a poor prognosis and may be candidates for prenatal intervention where available. Most prenatally diagnosed CCAMs have a favourable outcome. Early surgery is required for symptomatic babies. Management of prenatally diagnosed asymptomatic lesions remains controversial, with the options of conservative management with CT scan surveillance or surgical excision. Surgical excision is favoured by many centres because of the risk of infection and malignant transformation if the CCAM remains in situ. Surgical outcomes are excellent.
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Congenital cystic adenomatous malformations of the lung (CCAMs) are rare bronchopulmonary malformations with a reported incidence of 1 in 10 000 to 1 in 35 000.1 2 They are the most common cystic lung lesions detected on routine prenatal scanning undertaken at 18–20 weeks of gestation in England and Wales. The lesions are intrapulmonary, usually unilobar with a slight predilection for the lower lobes of the lung. Both sides of the lung, both sexes and all races are equally affected. Most cases are identified prenatally. This review covers the perinatal management of CCAM, including the controversy over the surgical management of postnatal asymptomatic cases.
PATHOGENESIS
CCAM is characterised by the lack of normal alveoli and an excessive proliferation and cystic dilatation of terminal respiratory bronchioles with various types of epithelial lining. Histological examination reveals ciliated, cuboidal or columnar cells lining the cysts with a lack of architecture and usually an absence of cartilage. Bronchial atresia may be noted, and may reflect the aetiology of the lesion.3 These malformations communicate with the normal bronchial tree and have normal vascular supply. However, recent studies have shown hybrid lesions of CCAM and bronchopulmonary sequestration (BPS). BPSs are solid non-functioning congenital lung lesions, which have a blood supply originating from the aorta, rather than the pulmonary artery, and an absence of communication with the bronchial tree4–7 (fig 1). These hybrid lesions are mainly intralobar, but extralobar BPS has been described. Within these hybrid lesions, lobar emphysema and bronchial atresia is occasionally seen.
CLASSIFICATION
The accepted pathological classification is the one described by an American military pathologist, J T Stocker, based on the size of the cyst noted in resected lung specimens and at autopsy. He initially described three subtypes in 1977,8 and later included two further subtypes in 2002.9 In this classification scheme, type 0 CCAM involves all lung lobes, which is a state not compatible with life. Type 1 CCAM lesions are characterised by single or multiple cysts >2 cm in size, type 2 lesions are single or multiple cysts <2 cm in size, type 3 are predominantly solid lesions with cysts <0.5 cm, and type 4 CCAM lesions are large peripheral thin-walled cysts, often an asymptomatic incidental finding or presenting as sudden respiratory distress from spontaneous pneumothorax (table 1). However, it can be difficult to classify some adenomatoid malformations using this system, especially hybrid lesions. Although aspects of the pathogenesis remain incomplete, Langston3 places more emphasis on regarding some pulmonary cysts as part of a sequence with more than one pathology. Stocker’s classification does not accurately describe CCAMs detected antenatally. Cha et al10 identified two histological patterns of fetal CCAMs thought to represent the stage of lung development at which the arrest in pulmonary development occurred. A more appropriate classification11 introduced by Adzick et al simply differentiates antenatally detected cystic lung lesions into two types: macrocystic (type 1) and microcystic (type 2) (table 1).
MALIGNANT TRANSFORMATION
Bronchioloalveolar carcinoma and rhabdomyosarcoma in association with CCAM has been repeatedly described in children and adults.12–15 Since 1980, over 25 cases of malignancy have been reported in children as young as 1 month to 13 years of age.16–18 These malignant transformations were noted in primary CCAM lesions and those that were incompletely resected. The long-term malignant potential of in situ CCAMs is further described by MacSweeney et al18 and Robert et al19 suggesting postnatal surgical excision, rather than long-term radiological surveillance, as the preferred strategy. Thus, with increasing numbers of reports and case series of malignancy within CCAMs, together with the possibility of lung infection, surgical resection in nearly all cases of CCAM is recommended.20
PRENATAL DIAGNOSIS
The prenatal rate of detection of lung cysts at the routine 18–20-week scan is almost 100% and may be the most common mode of actual presentation. Late pregnancy diagnosis of CCAM is less sensitive. Once a cystic lung lesion is detected on ultrasound, the location, volume, size, macrocystic or microcystic classification, and blood supply should be evaluated.6 Colour Doppler ultrasound may help with the diagnosis of hybrid lesions or pure BPS. Most of these lesions are easily distinguished from congenital diaphragmatic hernias; however, sonographic features of CCAM or BPS are not sufficiently accurate and correlate poorly with histological findings.7 MRI, although not routinely used, may provide better definition for this condition; however, inaccuracies were reported in 11% of cases screened antenatally with MRI.21 Prenatal echocardiography is essential to diagnose cardiac anomalies associated with CCAM and also to establish baseline fetal cardiac function in monitoring physiological changes as the pregnancy progresses.22 Prenatally diagnosed large CCAM requires careful, serial ultrasound to monitor the development of hydrops fetalis.
Bilateral disease and hydrops fetalis are indicators of poor outcome,6 23 24 whereas mediastinal shift, polyhydramnios and early detection are not poor prognostic signs.24–27 In the absence of termination, the natural fetal demise of antenatally diagnosed cystic lung disease in fetuses is 28%.25 It is well documented that spontaneous involution of cystic lung lesions can occur,28–30 but complete postnatal resolution is rare,7 and apparent spontaneous “disappearance” of antenatally diagnosed lesions should be interpreted with care, as nearly half of these cases subsequently require surgery.7 25 Patients with stable or regressing lesions could be delivered at the referring hospital.
PRENATAL MANAGEMENT
In only 10% of cases does the need for fetal intervention arise.20 23 Selection criteria for fetal intervention include normal karyotype and absence of other detected anomalies. The spectrum of interventions includes simple centesis of amniotic fluid,31 thoracoamniotic shunt placement,32 percutaneous laser ablation,25 and open fetal surgical resection.33 Prenatal interventions are not without risk. Simple thoracocentesis may work as a temporary measure, but is ineffective as definitive therapy, as reaccumulation of fluid is inevitable. With thoracoamniotic shunts, there is the risk of premature labour, displacement of the shunt, or sepsis. Maternal steroid administration has been reported to have a beneficial effect on some CCAMs, although the mechanism is unclear.34 A large cystic mass and hydrops fetalis in isolated cystic lung lesions are the only two real indications for fetal intervention.6 20 24 25 In hydrops fetalis, prenatal intervention versus the exact age cut-off for delivery and postnatal resection has not been established. Mann et al6 suggest that, in fetuses with isolated lung lesions in whom hydrops develops after 30–32 weeks, administration of steroid with early delivery and immediate postnatal resection results in improved survival.
POSTNATAL DIAGNOSIS
Normal vaginal delivery is recommended unless the maternal condition indicates otherwise. Large lesions are predicted to become symptomatic shortly after birth (prevalence as high as 45% in some series),7 20 35 thus delivery at a specialised centre would be appropriate. However, smaller lesions are less likely to be symptomatic at birth, and the infants could be delivered at the referring institution with follow-up in a specialist clinic.35
POSTNATAL MANAGEMENT
Postnatal management is dictated by clinical status at birth. Symptomatic lesions require urgent radiological evaluation with chest radiography and ideally a CT scan (fig 2), followed by surgical excision. In asymptomatic cases, postnatal investigation consists of a chest CT scan within 1 month of birth, even if regression or resolution is noted on prenatal scanning.7 25 35 Plain radiography should not be relied upon, as it will miss and underestimate many lesions35 (fig 3). Outside the neonatal age group, CCAM can act as a focus for infection or malignancy, resulting in recurrent pneumonia, lung abscess, empyema or a lung mass. The management of the symptomatic lesions carries a higher morbidity.20 35
Surgical excision of postnatal asymptomatic lesions remains controversial, with some centres opting for conservative management.36 37 The approach to treating this asymptomatic group has evolved in some centres, where a CT scan is performed within 1 month postnatally, followed by surgery before 6 months of age, because of the inherent risk of infection and malignant transformation.20 29 30 35 Small lesions (<1 cm) may be managed expectantly, bearing in mind that true resolution of these lesions is exceptional.29 30 35 Successful outcomes greater than 90% have been reported for surgically managed, asymptomatic lung lesions.30 35
SURGICAL APPROACH
The surgical approach to removing CCAMs is either by open thoracotomy20 or, more recently, using the minimally invasive video-assisted thoracoscopic approach.35 38 39 The two techniques offer similar results, but a better cosmetic result is achieved with video-assisted thoracoscopy.38 Excision of the cystic lesion is accomplished by lobectomy20 35 to ensure complete resection and avoid postoperative air leaks. However, some surgeons prefer a limited resection by means of segmentectomy in asymptomatic CCAMs.30 39
Early postoperative complications include pneumothorax, prolonged air-leaks, sepsis and bronchopleural fistula.29 30 Late sequelae such as wheezing, recurrent pneumonia, incomplete resection or recurrence have been reported.39 Better outcomes are described in patients who undergo early surgery for asymptomatic lesions.20 29 35
Acknowledgments
I thank Dr A Chakraborty and Dr K Platt for help with the images, and Dr Georgina Hall for reviewing the manuscript for medical readership.
REFERENCES
Footnotes
Competing interests: None.