Findings: PA chest radiograph shows a large paramediastinal lung opacity (A, arrow) that at first glance suggest malignancy. The clue to the diagnosis lies in identifying multiple bronchiectasis in the right and left central lung fields (A, circles).

The lateral view confirms the opacity in the posterior segment of the RUL (B, arrow) and bronchiectasis in the anterior clear space (B, circle).

Central bronchiectasis accompanied by lung opacities are typical of diseases with thick tenacious mucus and are the hallmark of cystic fibrosis o allergic bronchopulmonary aspergillosis. Coronal and axial CT confirm the presence of numerous central bronchiectasis, one of them with a large mucous impaction (C and D, arrows).

In the mediastinal window the impacted mucus is increased in density (E and F, arrows), which is a pathognomonic sign of ABPA.

Final diagnosis: ABPA with central bronchiectasis and dense pulmonary impaction
 
Congratulations to MG who was the first to answer and made a valiant effort to diagnose a difficult case.
 
Teaching point: this case looks difficult, but the diagnosis is easy if we identify basic findings. Discovering central bronchiectasis narrows the diagnosis to two entities and CT confirms one of them.