Discussion

The Cheerio sign was defined as the CT finding of a nodule with a hypodense centre, resembling the ring-shaped Cheerios breakfast cereal.1 Pathologically, it is caused by peribronchiolar cellular proliferation around a patent airway.2 Common causes for Cheerio sign include pulmonary Langerhans cell histiocytosis, lung adenocarcinoma, and occasionally cavitary lesions of the lung, such as fungal infections, metastatic lung cancers, lymphoma, rheumatoid nodules and granulomatosis with polyangiitis.

Cheerio sign is a rare radiographic sign, and adenocarcinoma presenting with multiple Cheerio signs, as reported in our case, is even rarer.2 It is commonly associated with invasive lepidic-predominant adenocarcinoma, as alveolar structures and bronchial patency are usually maintained in this cancer subtype.1 Although our biopsied specimen did not demonstrate a predominating lepidic component, figure 2C shows a glandular growth pattern with possible lepidic component giving rise to multiple intact airspaces. But more prominently, figure 2D shows a predominant micropapillary growth pattern with infiltrated airspaces kept patent by surrounding desmoplastic reaction. Thus, interestingly, this case demonstrates that growth patterns other than lepidic infiltration may also give rise to the Cheerio sign.

To the best of our knowledge, the usage of R-EBUS in evaluating Cheerio sign had not been described previously. R-EBUS allows visualisation of the internal structure of peripheral pulmonary lesions, such as the hyperechoic linear arcs and dots produced by air in patent alveoli and bronchioles.3 R-EBUS examination in our patient revealed these same-said multiple scattered hyperechoic linear arcs and dots, correlating with the patent airspaces seen in the CT full of Cheerios, as well as the histology of multiple intact airspaces. Kurimoto et al 3 have demonstrated the ability of R-EBUS imaging to predict malignant histology by examining the morphology of hyperechoic areas and focusing on internal echoes, vascular and bronchial patency. In the study, lesions that demonstrated hyperechoic dots and linear arcs were proven to be malignant in all cases, with 91.6% adenocarcinoma, which was consistent with our case.3

Transbronchial lung cryobiopsy is an effective tool for the diagnosis of diffuse parenchymal lung disease with a better safety profile than surgical biopsy.4 Cryobiopsy safety could be further improved with R-EBUS visualisation and avoidance of major blood vessels.5 This case highlights the rare manifestation of lung adenocarcinoma as multiple Cheerio signs, with an added perspective of its appearance from the viewpoint of R-EBUS.