Mucus plugs or mucoid impaction can mimic the appearance of lung nodules or a mass.
Sometimes differentiating mucus impaction from a lung cancer can be difficult.
Mucoid impaction is commonly seen in patients with bronchiectasis, as in cystic fibrosis (CF) and allergic bronchopulmonary aspergillosis (ABPA).
It is also seen in bronchial obstruction caused by an obstructing tumor or bronchial atresia.
The mucus in the dilated bronchi looks like the fingers in a glove (It is a common presentation).
Radiographic Features:
Plain radiograph
Mucoid impaction may appear as a branching tubular opacity that is distinct from the normal vascular shadows. This classic feature is the finger-in-glove sign, and is also seen on CT. It can sometimes prove difficult to diagnose on plain radiography.
CT
The appearance on CT can be variable, depending on where the mucous plugging occurs (central or peripheral airways).
Mucous plugs appear as fluid density material often located dependently within the bronchus, sometimes with internal gas.
The classic feature seen when plugged mucus extends along large branching airways is the finger-in-glove sign.
Depending upon the orientation of the airways with respect to the image, airway impaction will appear as circular or tubular structures that connect to more central bronchi.
Several key additional features can also occur:
Distal lung collapse: from collateral air drift; this has not yet developed in infants and young children, which is why the distal lung is rather hyperlucent in this population (congenital bronchial atresia, foreign body aspiration).
Distal airway dilatation
Double artery sign
Differential Diagnosis:
Endobronchial blood or blood clot appears similar to mucous plugging on CT.
In some situations, there can be overlap between some endobronchial tumors per se (rather than with associated mucoid impaction).
Pearls:
The appearance on CT can be variable, depending on where the mucous plugging occurs.
The classic feature seen when plugged mucus extends along large branching airways is the finger-in-glove sign.
