Purpose or Case Report: To characterize the sonographic appearances of lower extremity peripherally inserted central catheter (PICC)–associated thrombus and fibrin sheath in infants, and to identify imaging features that can aid differentiation between these two commonly overlapping entities.
Differentiating these on ultrasound is essential for accurate diagnosis, guidance of clinical management, and avoiding unnecessary anticoagulation or catheter removal. However, sonographic differentiation in this population remains challenging due to small vessel size, technical limitations, and limited published data.
Methods & Materials: This ongoing retrospective study includes lower extremity venous Doppler ultrasound examinations performed in infants from 2008 to the present at a tertiary pediatric hospital. Studies with indwelling or recently removed lower extremity PICCs were identified by pediatric residents. Each study was reviewed for echogenicity (hyperechoic or not) and shape (linear vs. round). Fibrin sheath was defined as a uniformly hyperechoic, thin, linear structure conforming to the catheter contour, while thrombus was identified as a more irregular or rounded intraluminal echogenic or hypoechoic focus. Epidemiological parameters, catheter size, anticoagulation status and follow up ultrasound findings (when available) were recorded for correlation. Each case was initially reviewed by a pediatric radiology fellow and independently by two attending pediatric radiologists; discrepancies were resolved by consensus. The diagnosis based on these imaging features was compared with the original report to assess diagnostic concordance.
Results: Preliminary analysis demonstrates that fibrin sheath appears as a consistently hyperechoic, linear structure enveloping the catheter. Thrombosis, in contrast, appears more irregular or rounded. Consensus review reduced interobserver variability and helped reclassify several indeterminate cases, highlighting the diagnostic value of systematic evaluation of echogenicity and morphology.
Conclusions: Specific ultrasound characteristics—particularly echogenicity and shape—can help distinguish fibrin sheath from thrombus in lower extremity PICCs in infants. Incorporating these objective imaging criteria, along with clinical and procedural factors, can enhance diagnostic confidence and potentially prevent unnecessary anticoagulation or catheter removal. Ongoing data collection aims to refine these criteria and establish standardized sonographic guidelines for this common clinical dilemma.