CTICasesPseudonodule from Extrapleural Fat (Proto's Sign)
Imaging findings
A radiograph read as a possible right lung nodule shows a rounded opacity on the lateral view; CT correlation reveals no true nodule but rather extrapleural fat protruding along an anomalous, funnel-shaped fissure at the hilum, with associated soft tissue and mild stenosis at the hilum from presumed old TB unrelated to the pseudo-lesion.
Key takeaways
This is a pseudonodule caused by extrapleural fat herniating into a variant superior accessory fissure, an appearance originally described by Proto in a 1982 article, and it is being seen with increasing frequency as more patients have greater chest wall fat available to be drawn into fissures. Recognizing this fat-fissure pseudonodule prevents unnecessary workup for a presumed true pulmonary nodule.
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