What is it:
The arcade-like sign in the lungs refers to the appearance of curvilinear or arched opacities in the peripheral lung parenchyma, forming a loop or “arcade” pattern. It represents perilobular fibrosis, often seen in organizing pneumonia or other fibrotic lung diseases.
Etymology:
Derived from “arcade,” meaning a series of arches, describing the curved arrangement of linear opacities.
AKA:
Perilobular pattern.
How does it appear on each relevant imaging modality?
Chest X-ray (CXR):
May not be clearly visible.
Peripheral opacities can suggest the presence of organizing pneumonia but lack the detail for the arcade-like pattern.
CT (Chest CT):
Parts: Curvilinear opacities outlining the secondary pulmonary lobules.
Size: Corresponds to the boundaries of the secondary pulmonary lobule.
Shape: Arched or curvilinear.
Position: Peripheral lung zones; may involve multiple lobes.
Character: Ground-glass or consolidative density, often with a perilobular distribution.
Time: Can evolve over weeks to months, either resolving or progressing to fibrosis.
Differential Diagnosis:
Cryptogenic organizing pneumonia (COP)
Chronic eosinophilic pneumonia
Fibrotic hypersensitivity pneumonitis
Idiopathic interstitial pneumonias (e.g., NSIP)
Resolving pulmonary edema
Pulmonary hemorrhage (perilobular distribution)
Recommendations:
Correlate with clinical and laboratory findings (e.g., autoimmune panels, eosinophil count).
Consider biopsy if the diagnosis remains uncertain and imaging findings are atypical.
Follow up with serial imaging to assess response to treatment.
Key Points and Pearls:
Commonly associated with cryptogenic organizing pneumonia (COP).
The arcade-like sign is often seen in cases with ill-defined linear opacities representing fibrosis along perilobular connective tissues.
Contrast with honeycombing, which represents end-stage fibrosis with clustered cystic spaces.
Timely recognition can guide treatment, often involving corticosteroids for organizing pneumonia.
