The Spiderweb Sign: A Pulmonary CT Finding After Intranodal Lymphangiography.

This case series describes an imaging finding seen in patients following lymphangiography-lace-like hyperdensities outlining the pulmonic lymphatic pathways-termed the spiderweb sign. In a retrospective review of patients who underwent lymphangiograms at a large tertiary care hospital from January 2022 to December 2025, 11 patients had CT thorax images within 1 week of the procedure, and 4 of these patients demonstrated the spiderweb sign. Specifically, the spiderweb sign manifests as hyperdense linear opacities outlining the interlobular septa, peribronchovascular interstitium, and visceral pleura. We present the 4 representative cases illustrating the imaging findings. For the cohort, procedural parameters were collected to assess associations with the presence or absence of the imaging finding, but no definitive association was found. While the exact mechanism remains unclear, these findings parallel patterns seen in prior studies and appear clinically benign. An additional literature review of pulmonary findings following lymphangiography was conducted to contextualize the spiderweb sign. Awareness of these postprocedural imaging findings as expected findings rather than developing pathology is essential to prevent misinterpretation. Larger multicenter studies are needed to clarify procedural factors and the underlying pathophysiology.