CTICasesExcipient Lung Disease with Left Lower Lobe Sparing due to Thromboembolic Occlusion
Imaging findings
Chest CT shows diffuse, highly defined, sharp centrilobular nodules throughout both lungs with complete sparing of the left lower lobe and lingula. The corresponding pulmonary arterial branches to the left lower lobe are completely occluded by old, infected thrombi. Pulmonary angiography confirms microvascular obstruction with gaps in the distal capillary blush, except in the occluded segments where no drug material could deposit. Histopathology under polarized light reveals extensive crystalline cellulose structures within the pulmonary arterial lumens.
Key takeaways
This classic presentation of excipient lung disease (secondary to intravenous injection of crushed methylcellulose-containing pills) highlights a unique 'sparing sign.' Sparing of the left lower lobe occurs because chronic thromboembolic occlusion of the lobar artery prevented the injected pill material from traveling to and depositing in that specific lung region, confirming the vascular-embolic mechanism of the disease.
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