Diffuse pulmonary meningotheliomatosis, primary lung adenocarcinoma

Case contributed by Liz Silverstone
Diagnosis certain


Incidental pulmonary nodules on FDG PET-CT for monoclonal gammopathy of undetermined significance (MGUS), non-Hodgkin lymphoma (NHL)

Patient Data

Age: 75 years
Gender: Female

Numerous randomly distributed low attenuation micronodules some of which are ring opacities with central lung attenuation.

A 6 mm nodule in the right lower lobe is different in character: irregular and ill-defined.

Enlarged thin slice sections from the same CT study highlight the imaging characteristics of the irregular 6 mm nodule and the background random micronodules.

3 month follow-up, coronal MIP


MIPs are useful for highlighting small lung nodules and coronal reformats help to show the random distribution.

The lung micro-nodules and right lower zone 6 mm ill-defined opacity were stable on a 3-month follow-up. 

FDG-PET, 1.5 years later.

The irregular peripheral posteromedial right lower lobe opacity had increased in diameter over 2 years from 6 mm to 12 mm and now demonstrates mild FDG-avidity, (SUV 3.3). The innumerable minute nodules are unchanged in size and do not demonstrate FDG avidity, however, they are too small to characterize.

Wedge resection of enlarging right lower lobe nodule was performed. 


"The 6 mm ill-defined dominant mildly FDG-avid nodule was an invasive mucinous lung adenocarcinoma.

Small nodular foci in the lung specimen, including one in the center of the adenocarcinoma, comprised nests of spindle cells with fibrotic septa and were EMA positive, TTF1, pan-cytokeratin and synaptophysin negative on immunohistochemistry consistent with minute pulmonary meningothelial-like nodules."

Case Discussion

Minute pulmonary meningothelial nodules are typically low attenuation and often have a ring appearance with central low attenuation giving rise to the 'cheerio sign' (US), or ‘fruit loop’ sign (Australia). Although the nodules themselves are benign, there is a higher incidence of malignant lung cancers especially adenocarcinoma in the presence of these nodules compared to the general population.

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