New England Section of the American Urological Association

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Renal Mass Biopsy for Cystic Renal Masses: Can We Challenge the Dogma?
Tammer Yamany, MD, Aileen O'Shea, MD, David Kuppermann, MD, Dimitar Zlatev, MD, Mukesh Harisinghani, MD, Ron Arellano, MD, Adam Feldman, MD
Massachusetts General Hospital, Boston, MA

BACKGROUND: Renal mass biopsy (RMB) has been proven as a safe and effective method for diagnostic evaluation of small solid renal masses. However, routine biopsy of cystic renal masses has been advised against due to a high rate of non-diagnostic results. Diagnostic biopsy results may benefit clinical decision making when considering treatment options such as ablative therapy. Our objective is to identify predictive tumor and patient characteristics for a diagnostic biopsy of a complex cystic renal mass.
METHODS: We performed a retrospective review of our database of 213 adult patients with cystic renal masses who underwent a RMB from 1998-2012. RMB was performed at the discretion of the urologist and patient. Any mass under consideration for ablative therapy was routinely biopsied. Core biopsies and fine needle aspirations (FNA) were performed. Non-diagnostic biopsies were considered biopsies with insufficient tissue or benign renal epithelial tissue felt not to be representative of the concerning lesion.
RESULTS: A total of 213 cystic renal masses were biopsied from 1998-2012. 137 (64.3%) biopsies were non-diagnostic and 76 (35.7%) were diagnostic with 69 (32.4%) malignant and 7 (3.3%) benign neoplasms. There was no significant difference in age, gender, biopsy modality or imaging modality for biopsy in terms of diagnostic biopsy rates. The diagnostic rate increased with an increase in mass size (0-2 cm: 18.8%, 2-4 cm: 48.0%, 4-7 cm: 37.8%, >7 cm: 50.0%; p = 0.001). Independent predictors of a diagnostic renal cystic mass biopsy included a mass diameter greater than 2 cm and differential contrast enhancement greater than 10 HU (p = 0.021 and <0.001, respectively). Inclusion of only masses larger than 2 cm with differential contrast enhancement greater than 10 HU improves the diagnostic rate to 65.7%. Among patients with a nodular component, a nodule-to-mass diameter ratio greater than 0.45 was significantly associated with a diagnostic biopsy (p = 0.027). Inclusion of only masses with a nodule-to-mass ratio greater than 0.45 improves the diagnostic rate to 85.7% from 41.9% for cystic masses with a nodular component.
CONCLUSIONS: Biopsy of cystic renal masses larger than 2 cm with differential contrast enhancement greater than 10 HU are more likely to result in a diagnostic biopsy result. Cystic masses with a larger nodule-to-mass diameter ratio are also more likely to result in diagnostic biopsy. Selective biopsy of cystic renal masses may benefit clinical decision making when considering available treatment options.


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