Reporting of Perirenal Hematoma Size After Ultrasound-Guided Renal Biopsy in Adults: A Scoping Review.

Introduction: Percutaneous renal biopsy (PRB) is the gold standard for diagnosing nephropathies, but it carries a risk of bleeding complications, mainly perinephric hematomas (PHs). While PH incidence is often reported, the significance of PH size remains insufficiently explored. This scoping review systematically mapped the evidence on PH size after ultrasound-guided PRB in adults, focusing on imaging modalities, measurement methods, the definition of 'large' PH, factors influencing PH size, and its clinical implications. Materials and Methods: Following the Joanna Briggs Institute methodology, we searched PubMed/MEDLINE, Embase, Cochrane CENTRAL, and Scopus through 27 August 2025. Eligible studies included at least 50 adult subjects undergoing ultrasound-guided PRB with quantitative, imaging-based assessment of PH size. Results: Fifty-one studies met the inclusion criteria. Almost all relied on ultrasound, with only one using computed tomography. PH size was measured using heterogeneous methods, most often one-dimensional diameters, less frequently surface area or volumetry, with no standardization. Reported PH frequencies varied substantially across studies (1.1-85%), likely reflecting differences in imaging protocols, timing, and reporting thresholds. Several studies proposed PH size thresholds (e.g., diameter ≥ 2-3 cm, volume ≥ 40-85 mL) linked to adverse outcomes such as transfusion or hemodynamic instability. Factors associated with larger PHs included needle gauge, number of passes, impaired kidney function, coagulopathy, and certain histopathologies. Conclusions: PH size has prognostic value beyond incidence alone. Standardized measurement and reporting are needed to clarify its clinical relevance after PRB.