CONGENITAL PULMONARY AIRWAY MALFORMATION

CASE REPORT

A 58-year-old female patient presented to the OPD with complaints of persistent cough and expectoration since past 3 months. There was a history of intermittent episodes of hemoptysis associated with low grade fever. She also had a history of dyspnoea on exertion. There was history of recurrent episodes of similar illness for the past 10 years. She used to get cough, scanty sputum, haemoptysis and fever, 2-3 times every year. CT Thorax done in 2014 reported it as bronchiectasis. She was under follow up treatment as a case of bronchiectasis for the past 4 years. She also gave history of antituberculous treatment (ATT) twenty-five years back, details of which were not available. She is a known hypothyroid patient on thyroid replacement therapy. X-ray chest showed few cystic lesions in the right mid and upper zone. HRCT thorax showed a large cyst in the right upper lobe surrounded by a bunch of small cysts. Surgery was advised which the patient refused. She was put on conservative medical management and regular follow up.

DISCUSSION

Congenital pulmonary airway malformations (CPAM) are multicystic masses of segmental lung tissue with abnormal bronchial proliferation. This entity was first described by Chin and Tang in 1949 as congenital cystic adenomatoid malformation (CCAM). Later in 2002, Stocker proposed the name CPAM and classified in to 5 types.

CPAM Type 0-Acinar dysplasia/agenesis is a rare malformation largely incompatible with life. Lungs are small, firm with diffusely granular surface. Microscopically, it shows bronchus like structures with muscle, glands and numerous cartilage plates and loose, vascular mesenchymal tissue.

CPAM Type I-It accounts for nearly 60-65% of cases. Lesion is predominantly cystic type (measuring 3-10 cm in diameter) surrounded by smaller cysts. Microscopically, the large, thin walled cysts are lined by ciliated pseudostratified columnar epithelium with some mucin producing cells. The wall composed of fibromuscular and elastic tissue It is operable and has a good prognosis.

CPAM Type II-it accounts for 10%-15% of cases and mainly seen in first year of life. It has poor prognosis because it is frequently associated with other congenital anomalies. Grossly lesion is composed of medium sized cysts measuring 0.5 to 2.0 cm in diameter that are evenly distributed and blend with the adjacent normal parenchyma. CPAM Type 2 has been noted in nearly 50% cases of extralobar sequestration.

CPAM Type III- It is infrequent and accounts only about 5% of cases. It is small cystic or solid type, exclusively seen in first few days to months of life with characteristic male preponderance. It is commonly associated with maternal polyhydramnios or foetal anasarca. It has high mortality rate. Cysts are small measuring less than 0.2 cm in diameter, forming large bulky mass involving an entire lobe or even an entire lung. Microscopically the lesion resembles an immature lung devoid of bronchi.

CPAM Type IV-It accounts for 10%-15% of cases and presents as hamartomatous malformation of the distal acinus. It is seen in age range of newborn to 4 years. This lesion involves a single lobe. Grossly large, thin walled cysts are lined by flattened epithelium-alveolar lining cells with underlying loose, fibrovascular mesenchymal tissue.

The reported incidence of CPAM ranges from 1 in 11,000 to 1 in 35,000 live births. The accepted pathogenesis for CPAM is that an abnormal airway patterning and branching during lung morphogenesis results in the appearance of lung cysts. This condition results from the failure of normal bronchoalveolar development with a hamartomatous proliferation of terminal respiratory units in a gland-like pattern (adenomatoid) without proper alveolar formation. Histologically, they are characterized by adenomatoid proliferation of bronchiole-like structures and macro- or microcysts lined by columnar or cuboidal epithelium, presence of mucus secreting cells and absence of cartilage

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The microscopic features that distinguish CPAM from normal lung include the following:(i) Proliferation of the terminal respiratory structures forming cysts (ii) Polypoid projections of the mucosa (iii) Increased smooth muscle and elastic tissue within cyst walls (iv) The absence of cartilage (v) The presence of mucous-secreting cells and (vi) The absence of inflammation. The diagnosis is usually made either on antenatal ultrasound or in the neonatal period during the investigation of progressive respiratory distress. If large, they may cause pulmonary hypoplasia, with resultant poor prognosis. In cases where the abnormality is small, the diagnosis may not be made for many years or even until adulthood. When it does become apparent, it is usually as a result of recurrent chest infection.

CPAM in adults is very rare. Enuh et al. reported CPAM with aspergillosis in a 59-year-old male who died secondary to massive hemoptysis and development of disseminated intravascular coagulation during lobectomy. Morelli et al. described CPAM in a 38-year-old male with persistent cough and hemoptysis who did well after lobectomy. A case of CPAM in a 56-year old female was reported in 2018 which remains the second oldest case of CPAM so far reported. Because of the higher percentage of asymptomatic cases of CPAM and various degrees of lung involvement, it might be difficult to determine the prognosis in adults. Late-onset CPAM in adults may be more complicated on radiographic images due to recurrent infections. CPAM usually involve a single lobe. The lesion involving bilateral lobes of the lung is also uncommonly encountered. In CPAM associated literatures, a few bilateral CPAM cases in adult patients have been reported. Bilateral CPAM may appear like interstitial pneumonia because of similar CT scan presentations showing grid-like opacity through the entire lung fields. The extensive involvement of the lesion increases the risk of surgery. Therefore, most patients with such lesions are treated with conservative treatment once diagnosis is confirmed by lung biopsy.