What causes the cheerio sign on CT of the chest?
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Answer:
The cheerio sign is a small pulmonary nodule containing a central lucency, so that on the axial image it forms a ring of soft tissue around air, like the breakfast cereal. The lucency may represent a patent airway or a dilated bronchiole engulfed by the lesion, a small cavity, or preserved central airspace within a lepidic-growing tumour. It is a morphological description rather than a diagnosis and its differential is broad and clinically important. In a lung cancer screening or incidental nodule context, a persistent ring-shaped subsolid nodule raises concern for adenocarcinoma, including minimally invasive and lepidic-predominant subtypes, in which the sign carries a well-recognised association with malignancy and mandates follow-up rather than dismissal. Other causes include Langerhans cell histiocytosis, in which nodules cavitate and progress to bizarre cysts in an upper-zone distribution in a smoker; septic emboli and other necrotising infections; granulomatosis with polyangiitis; metastases from squamous, sarcomatous or gastrointestinal primaries; and organising pneumonia. Interpretation depends on number, distribution and evolution: multiple upper-zone cavitating nodules in a young smoker suggest histiocytosis, multiple peripheral nodules with feeding vessels suggest septic emboli, and a solitary persistent ring nodule with a subsolid component should be managed along adenocarcinoma lines with Fleischner or Lung-RADS follow-up.
Why is it called so?
The nodule with a hole in the middle resembles a Cheerio.
Pathophysiology
Several mechanisms converge on the same appearance. In lepidic-growing adenocarcinoma, tumour cells proliferate along intact alveolar walls without filling the airspaces, so aerated lung or a traction-dilated bronchiole persists within the lesion. In necrotising infection and vasculitis, central necrosis liquefies and drains through a communicating bronchus, leaving air in the cavity. In Langerhans cell histiocytosis, peribronchiolar granulomas destroy the bronchiolar wall and the lumen dilates and becomes cystic. Because the underlying processes are so different, the sign has no single pathological basis, and the surrounding features, wall thickness, distribution, associated ground-glass and change over time, are what carry the diagnostic weight.
Alternative names: Ring-shaped nodule; nodule with central lucency
Other associated named signs: Halo sign, the feeding vessel sign and the bubble lucency described in lepidic adenocarcinoma
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