Biopsy Site in Suspected Retroperitoneal Fibrosis
In suspected retroperitoneal fibrosis, perform core needle biopsy using a retroperitoneal approach, avoiding passage through the peritoneum, with ultrasound or CT guidance to access the fibrotic mass directly. 1, 2
Biopsy Technique and Approach
Core Needle Biopsy is the Standard Method
Core needle biopsy is the practical and reliable diagnostic method for retroperitoneal masses, with sensitivity of 65-96% and specificity of 81-100%. 1
The biopsy must NOT be performed through the peritoneum to avoid contamination and complications—use a retroperitoneal approach instead. 3, 1
Use ≥14-16 gauge needles to obtain adequate tissue samples for histopathological diagnosis. 3
Image Guidance Options
Ultrasound-guided biopsy can be positioned accurately, safely, and efficiently for RPF lesions, particularly when they show characteristic features (solid, irregular isoechoic masses surrounding the aorta, IVC, and ureters). 2
CT-guided biopsy is an alternative when ultrasound windows are inadequate or when more precise anatomical localization is needed. 2
Endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) may be useful in challenging cases where conventional percutaneous approaches risk injury to the IVC or ureters. 4
Target the Fibrotic Mass Directly
The biopsy should target the retroperitoneal fibrotic plaque or mass, which in typical cases appears as tissue surrounding the abdominal aorta, inferior vena cava, and ureters. 5, 2
RPF lesions are most commonly located in the lower lumbar region (60% of cases), but 40% present in atypical locations including peripancreatic, periduodenal, or pelvic sites. 5
The fibrotic tissue typically appears as solid, irregular isoechoic masses with clear borders from encapsulated structures on ultrasound, usually located below the level of the renal arteries. 2
What NOT to Do
Do NOT rely on fine-needle aspiration alone—it is insufficient for definitive diagnosis with sensitivity of only 50% and specificity of 70%. 1
Do NOT perform transperitoneal biopsy—always use a retroperitoneal approach to minimize contamination risk. 3, 1
Do NOT delay tissue diagnosis in favor of additional imaging studies—histological confirmation is essential to distinguish benign from malignant RPF. 1, 6
Alternative Approaches in Selected Cases
Laparoscopic biopsy may be considered when malignant etiology is suspected and adequate tissue sampling is needed, offering reduced morbidity compared to open laparotomy. 7
Open surgical biopsy remains an option in selected cases as decided within reference centers, particularly when core needle biopsy is technically challenging or yields inadequate tissue. 3, 6
Critical Diagnostic Distinction
Surgical biopsy remains the only definitive way to distinguish malignant from nonmalignant retroperitoneal fibrosis, which is critical because prognosis is dismal for malignant RPF but very good for idiopathic forms. 6
Histopathological diagnosis should include assessment for chronic inflammation, fibrosis pattern, and exclusion of malignancy. 5, 6