IMAGING

Diagnostic Yield of 58 Consecutive Imaging-Guided Biopsies of Solid Renal Masses: Should We Biopsy All That Are Indeterminate?
Beland MD, Mayo-Smith WW, Dupuy DE, Cronan JJ, DeLellis RA
Department of Radiology, Diagnostic Imaging, Rhode Island Hospital, Providence, RI, USA
AJR Am J Roentgenol. 2007; 188: 792-7

• Objective: The purpose of our study was to report the diagnostic yield of 58 consecutive imaging-guided biopsies of solid renal masses.
• Materials and Methods: We retrospectively reviewed all percutaneous renal biopsies of solid masses performed at our institution over 83 consecutive months from May 1998 to March 2005 through a query of our radiology department procedure database. Fifty-five CT and three sonographic biopsies were performed at our institution during this time. A solid renal mass was documented prior to biopsy by contrast-enhanced CT (n = 48), gadolinium-enhanced MRI (n = 6), or sonography (solid noncystic masses, n = 4). The average maximal mass diameter was 3.1 cm (range, 1.0-11.0 cm). Forty-seven (81%) of the 58 biopsies were performed immediately before percutaneous ablation. Forty-four (76%) of the biopsies were performed using a coaxial technique with side-cutting automated biopsy needles (16-20 gauge), and 14 (24%) were fineneedle aspirations with a Franseen needle (20 gauge) using a tandem technique. In 19 cases, immunohistochemistry or histochemistry (Hale colloidal iron stain) was used to establish or confirm the diagnosis. Medical records and radiology and pathology reports were reviewed for all patients.
• Results: An adequate sample size was obtained in 55 (95%) of 58 renal masses and led to a definitive diagnosis in 52 (90%) of the 58. Renal cell carcinoma accounted for 36 (69%) of 52 diagnostic biopsies. The diagnosis of a benign lesion was made in 14 (27%) of 52 biopsies. Lymphoma (1/58) and metastatic disease (1/58) accounted for the remaining two diagnostic biopsies. Three biopsy samples obtained inadequate sample volumes, and an additional three samples were thought to have adequate sample volume but were not diagnostic. A single false-negative biopsy result was identified after growth was seen on follow-up imaging and subsequent nephrectomy revealed renal cell carcinoma.
• Conclusion: Imaging-guided biopsy of a solid enhancing renal mass was diagnostic in 52 (90%) of 58 consecutive biopsies. The diagnosis of a benign lesion was made in 27% of diagnostic biopsies. Because of the advances in biopsy and histology techniques, the role of imaging-guided biopsy should be reconsidered.
  
  
• Editorial Comment
  Nowadays percutaneous renal mass biopsy is indicated more frequently due to several reasons: a) increased incidental detection of malignant and benign renal masses; b) improvement on cytologic and immunohistochemistry techniques and c) the increasing role of percutaneous renal ablation. The overall sensitivity of biopsy for diagnosis for malignancy is high ranging from 80%-92%. Classically renal biopsy is indicated in patients with renal mass and primary extrarenal tumor (to exclude or confirm metastases); to confirm the radiologic findings of an unresectable renal cancer; in patients with pulmonary or cardiac comorbidity and in patients with possible primary manifestation of lymphoma in the kidneys (1). Emerging indications for renal biopsy are: presence of multiple/bilateral solid renal masses without history of cancer; prior to renal mass ablation and in patients with small (< 3 cm) solid, hyperattenuating, homogeneously enhancing renal mass. These small lesions are indistinct and may be oncocitoma, angiomyolipoma without macroscopic fat (5% of AMLs) or more rarely a papillary renal cell carcinoma. As we know, modern diagnostic imaging techniques, allows the correct diagnosis of the majority of renal mass. There is no prospective study showing the incidence of incidentally detected benign renal mass among the lesions presumably considered renal cancer. Recent studies, however, done in patients who underwent radical nephrectomy or imaging-guided tumor ablation presumably for renal cell carcinoma detected 12.8% to 37% of benign renal lesions. The authors of this study, found benignity in 27% of 58 small solid renal lesions. It would be interesting to know, how many of these lesions were part of that small group of hyperattenuating, homogeneously enhancing renal mass.
  As pointed out by the authors one important limitation of this study is that 81% of their biopsies were performed before percutaneous ablation. As we know the ideal evaluation of the biopsy specimens is made by histologic ,cytologic and immunohistochemistry evaluation. Biopsy specimens analyzed as frozen sections and hematoxylin-eosin staining, usually done prior ablation, is rapid but usually incomplete. For this reason, to establish a definitive diagnosis immunohistochemical staining was necessary, in 17 (89%) of 19 nondiagnostic samples using hematoxylin-eosin staining. This is very important information of this publication. Biopsy results are crucial in some situations where the urologist has to decide whether the lesion should be removed or clinically followed. We agree with the authors conclusion that there is a definite role for imaging-guided biopsy of small solid renal masses before intervention, particularly those hyperattenuating and homogeneous. In our opinion when surgery is contemplated, and biopsy is not performed, enucleation or partial nephrectomy should be the primary indication in this small group of lesions.

Reference
1. Silverman SG, Gan YU, Mortele KJ, Tuncali K, Cibas ES. Renal Mass Biopsy in the New Millennium: An Important Diagnostic Procedure. RSNA Categorical Course in Diagnostic Radiology:Genioutinary Radiology. 2006; 219-36.

Dr. Adilson Prando
Chief, Department of Radiology
Vera Cruz Hospital
Campinas, São Paulo, Brazil