accompanying a tension pneumothorax iny15% of cases. CPAM type 4 in older children may be asymptomatic and discovered incidentally on routine examination. There is an almost equal male to female ratio and no racial predilection. Other anomalies are rarely seen. Two brothers, one aged 6 weeks and the other 17 months, both exhibited CPAM type 4 lesions. The CPAM type 4 lesion can be found in any lobe (right lung more than left lung) and may involve more than one lobe iny20% of cases. Bilateral involvement has been seen in a 6-month-old male and a 3-yr-old female. Resection is usually curative, even with bilateral involvement. The lesions vary greatly in size, with mortality related to very large lesions in young infants. In two infants who died on the first day of life (the only deaths among 23 cases), the involved lobes equalled or exceeded the expected weight of the entire lung. Cysts also vary greatly in size, with some cysts exceeding 10 cm in diameter in older children. [3] The differential diagnosis of CPAM type 4 includes the other forms of CPAM (whose features are summarised below) and the purely cystic form of pleuropulmonary blastoma (PPB), which may also be seen in young infants [6]. Cystic PPB is characterised by multiple large cysts lined with cuboidal-to-ciliated columnar epithelium overlying a wall that, in areas, displays a well-formed cambium layer associated with the embryonal rhabdomyo- sarcoma component of PPB. Significant discussion has taken place in the literature in the past 8–10 yrs as regards the relationship of CPAM type 4 to cystic PPB (see below). Clinical and morphological features of the five types of CPAM CPAM type 0 CPAM type 0 was originally termed acinar dysgenesis (agenesis) by Rutledge and Jensen [5], and appears to correlate with failure of development of the lung beyond the tracheobronchial origin (fig. 1). CPAM type 0 is the least frequently occurring of the CPAM lesions, with fewer than 12 cases described in the literature [7, 8]. Clinically, infants present with cyanosis and severe respiratory distress at birth and survive only a few hours unless treated with extracorporeal membrane oxygenation, but Table 3. – Clinical features of congenital pulmonary airway malformation (CPAM) Type 0 Type 1 Type 2 Type 3 Type 4 In utero ultrasound Small lungs 1st trimester cystic mass that shrinks in 2nd–3rd trimester Normal-to-ill- defined-mass Progressively enlarging mass Normal-to-cystic mass, as with CPAM type 1 Age at presentation Birth Birth to adolescence Birth In utero to birth Birth to 4 yrs Symptoms Stillbirth severe RD Minimal-to-severe RD None-to-mild RD Stillbirth severe RD None to RD to pneumothorax Associated anomalies Rare Rare 50%, including renal agenesis Pulmonary hypoplasia of uninvolved lung Rare Treatment None Resect lobe(s) Depends on other abnormalities Resect lobe(s) Resect lobe(s) Outcome Incompatible with life Excellent following surgery Depends on severity of other abnormalities Poor: depends on severity of pulmonary hypoplasia Excellent following surgery RD: respiratory distress. CLASSIFICATION OF CHILDHOOD CYSTIC LUNG LESIONS 3