lung rads for cyst

A multilocular cyst seen on baseline LDCT scan of the chest is considered a Lung-RADS category 4A finding, with the recommendation to follow up in 3 months with LDCT scan (choice C is correct; choices A, B, and D are incorrect).

Lung cancer that presents as a cystic airspace lesion is not common, but up to 20% of lung cancers missed on baseline LDCT screening have been associated with cystic airspaces. Features that raise suspicion for lung cancer include thickening or nodularity of the wall of the cyst, growth of the cyst size, development of internal loculations, and increase in the solid or nodular portion associated with the cyst. Four morphologic patterns of lung cancer presenting with a cystic airspace lesion have been suggested: the first is a nodule that appears to be extending out from the wall of the cystic lesion; the second is a nodule within the cystic lesion; the third is a thickening of the wall of the cystic airspace; and the fourth is a multilocular lesion or the appearance of a cluster of cystic airspaces with soft tissue intermixed.

A meta-analysis of observational studies that included lung cancer associated with cystic airspaces summarized characteristics of these cancers. Up to one-third of these cancers occurred in individuals who never smoked. The cysts usually had nonuniform walls, over one-third of which were thick (≥2 mm) and had irregular margins, while nearly two-thirds had a nodular component. In the majority, the nodular component grew or the walls thickened over time. Growth of the cystic component was variable. Adenocarcinoma was the histopathologic diagnosis in 88% of the cancers.

The Lung-RADS nodule management system provides guidance on the management of cystic airspace lesions. Thin-walled unilocular cysts (uniform wall thickness <2 mm) are considered benign and are not classified. Cavitary nodules are distinguished from cystic airspace lesions by wall thickening as the dominant feature. These are managed as solid nodules. A fluid-containing cyst could be infectious and is not classified by Lung-RADS unless other concerning features exist. Otherwise, atypical pulmonary cysts with a growing cystic component of a thick-walled cyst are considered Lung-RADS category 3 (follow up in 6 months); a thick-walled cyst that is multilocular at baseline and a thinor thick-walled cyst that becomes multilocular are considered category 4A (follow up in 3 months); and a thick-walled cyst with growing wall thickness, a growing multilocular cyst, and a multilocular cyst with increased loculation or a new or increased opacity are considered category 4B (further evaluation recommended).

The patient in this question had follow-up imaging performed (Figures 2-4). Over time, the cystic airspace lesion was seen to develop a growing solid nodule extending from the wall. This led to a right lower lobectomy confirming T1bN0M0 adenocarcinoma of the lung.