Muhammad Umar Amin  ( Department of Radiology, Combined Military Hospital, Bahawalpur. )
Asim Rahim  ( Department of Radiology, Combined Military Hospital, Bahawalpur. )
Muhammad Nafees  ( Department of Radiology, Combined Military Hospital, Bahawalpur. )

We present a case of congenital bronchial atresia with unique features in a twenty eight years old asymptomatic, non-smoker male who presented to our department for X -ray chest as a part of routine annual medical check up. It revealed an incidental, well defined, branching opacity in the left upper lobe close to the hilum. A differential diagnosis of vascular malformation and bronchocoele was given with advice to the patient to follow up after five months. A repeat x ray chest 5 months later revealed same branching character of the opacity. The CT scan of chest showed the detailed characteristics of the

opacity. The lesion was located in the apico-posterior segment of the left upper lobe.It was non-enhancing and had a typical branching character with paucity of vessels in the surrounding lung. Lack of symptoms and CT features of the opacity were sufficient to label this patient as a case of congenital bronchial atresia with mucocoele formation . No frank emphysematous change had yet developed around the atretic bronchial segment.

Congenital bronchial atresia (CBA) is a rare anomaly that results from a congenital focal obliteration of a proximal segmental or sub-segmental bronchus with the normal development of distal structures. The short atretic segment leads to accumulation of mucous within the distal bronchi to form a bronchocoele and under ventilation of the affected part of the lung.1 Radiologically, CBA is characterized by the presence of a branching opacity, the bronchocoele, radiating from the hilum surrounded by an area of hyperlucency.2 These features can be recognized on the chest radiograph but are more clearly defined by computed tomography. Fibreoptic bronchoscopy (FOB) is often required to exclude acquired proximal bronchial obstruction by tumour, foreign body or inflammatory stricture.3 In CBA a blind-ending bronchus may be revealed, although FOB is often normal. Bronchographic examination is generally abnormal but the appearances may be confusing and is rarely performed. Pathologically, CBA is characterized by a blind-ending bronchus associated with dilated distal bronchi containing impacted mucus. The surrounding lung parenchyma is hyperinflated due to collateral air drift. CBA can be identified accurately by imaging techniques which may make surgery unnecessary in asymptomatic cases.4

A twenty eight years old asymptomatic, non-smoker, male presented to our department for X -ray chest as a part of routine annual medical check up. It revealed a solitary, well defined, branching opacity in the left upper lobe close to the hilum (Figure 1). There was no history of bronchial asthma, pulmonary tuberculosis, malignancy or any allergic condition. A differential diagnosis of vascular malformation and bronchocoele was given for the opacity .Since the patient was asymptomatic, no intervention was considered necessary and patient was advised to follow up after 3-6 months. The patient remained asymptomatic during this period. A repeat X -ray chest on his follow up revealed no change in the size of the opacity but slight lateral shift of the opacity was seen (Figure 2). To evaluate the opacity in detail a contrast enhanced spiral CT scan of the chest with and without I/V contrast was performed and images were filmed in lung and mediastinal window. High-resolution scans were reconstructed also. The CT scan revealed a solitary V-shaped, branching tube like structure in the apico-posterior segment of left upper lobe (Figure 3) .It was hypodense, showing a density of 30 HOUNSEFIELD UNITS). It was branching 5-6 times to reach just short of pleural surface. No air fluid level was seen in the opacity. Lack of increase in the density of the lesion after I/V contrast and absence of any drainage vessel excluded vascular structure as a cause of the branching lesion. The lung surrounding the mucous filled bronchus showed paucity of blood vessels. The blood vessels in the remaining lung showed normal morphology. No other opacity was seen in the lung. No mass was seen in the hilum and there was no CT evidence of pulmonary tuberculosis or any other disease .No mediastinal pathology was seen No osseous anomaly was seen in the patient. Fibre-optic bronchoscopy was not considered as the patient was asymptomatic.

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Figure 1. (A) X -ray chest showing branching opacity in lt upper lobe close to hilum (arrows). (B)Close up of the same opacity (arrows).

The laboratory investigations showed Hb 13.8g/dl, Total leukocyte count(TLC) 6.4 X 109/L, Neutrophils 57%, Lymphocytes 36%, Eosinophils 03 % and an Erythrocyte sedimentation rate(ESR) of 15 mm..
Lack of symptoms and CT features of the opacity were sufficient to label this patient as a case of mucocoele formation due to congenital bronchial atresia. No frank emphysematous change had yet developed around the atretic bronchial segment. Patient was advised to follow up regularly keeping in view the possibility of development of emphysema around the atretic segment.

Congenital bronchial atresia was first described in the radiological literature by Falor and Kyriakides in 1949. The prevalence of this disorder was estimated at 1.2 cases per 100,000 in males.5 Congenital bronchial atresia is characterized by obliteration of a localized proximal lumen of segmental bronchus. Mucous secretion distal to the point of obstruction produces the characteristic bronchocoele. Distal alveoli are ventilated by collateral drift, resulting in a region of hyperinflation. This finding was not seen in our patient. The most common site is the left upper lobe, particularly of the apical-posterior segment as was the case in our patient.

This condition is found mostly in asymptomatic young men, although the presenting ages do range from neonates to adulthood. Rarely, bronchial atresia is associated with infection or bronchial asthma. It usually occurs in isolation but can be associated with other congenital anomalies.6

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Figure 2. X -ray chest showing same opacity unchanged in size (arrows)

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Figure 3. CT scan chest shows branching mucous filled bronchus (mucocele) in apico-posterior segment of lt upper lobe (arrows).Notice the paucity of blood vessels in the involved region.

It has been postulated that in utero vascular insult plays a role in causing bronchial obliteration, leading to atresia. Whilst the exact timing of the insult is disputed, it most likely occurs after 16 weeks when the bronchial branching is complete. The unaffected distal air spaces continue to grow normally. The bronchial tree proximal to the atresia is patent.7

Congenital bronchial atresia can be seen as part of the spectrum of an agenesis-hypoplasia complex. These include interlobular sequestration, pulmonary bronchial cyst, adenomatous cystic malformation as well as congenital lobar emphysema.

Congenital bronchial atresia can occur at any bronchial segment. However, the most common site is the apico-posterior segment of the left upper lobe as was seen in our patient. The high frequency here is attributed to embryonic instability in this lobe. Almost invariably a single lung segment is affected. Involvement of multiple lung segments has been reported in very few cases only.8

CT is sensitive in demonstrating the non enhancing branching bronchocoele surrounded by regional hypertranslucency typical of congenital bronchial atresia.In addition, it can be used to exclude acquired causes of mucoid impaction. Of these, bronchial obstruction secondary to tumour or foreign body would be considered. Others include allergic bronchopulmonary aspergillosis and tuberculosis. None of these causes were present in our patient.

Vascular malformation may produce a lobulated branching opacity that resembles the appearance of a bronchocoele. Here, spiral CT with intravenous contrast would show enhancement of the vascular structures.

The diagnosis of congenital bronchial atresia should be considered in the presence of a combined appearance of a segmental bronchial mucocoele and regional hyperinflation of the lung, especially if the findings are seen in the left upper lobe in the setting of an asymptomatic young patient with no preceding history of infection or malignancy to suggest an alternative cause for the mucoid impaction.

Bronchoscopy and CT can be performed to exclude the presence of an acquired cause of mucoid impaction or a vascular malformation. The definitive diagnosis is by open lung biopsy.Recognition of this rare condition on imaging is important in facilitating appropriate management of patients

Symptoms such as fever, cough, or shortness of breath may occur due to recurrent pulmonary infection or overinflation of the involved lung parenchyma. The right lower and middle lobes are affected in only 8% of cases. The radiographic features may be highly suggestive of the diagnosis.. The recognition of this condition can prevent poor management decisions.9

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