Image-guided biopsy helps eliminate nephrectomies

Advances in CT and MR technology have led to increased detection of incidental renal masses, including very small masses. Yet it may be difficult to differentiate benign from malignant masses with imaging techniques. Researchers are finding that image-guided core-needle biopsy can make the difference between sparing a kidney and losing one.

Clinical acceptance of renal mass biopsy has been low. The reluctance on the part of referring physicians is understandable, according to Dr. Katherine Maturen, a radiologist at William Beaumont Hospital in Royal Oak, MI. Older data using the fine-needle aspiration technique showed a low rate of accurate detection of malignancy and an unacceptably high rate of nondiagnostic studies. Reports on core-needle biopsy have been much more promising, however, with accuracy ranging from 89% to 100%.

In a study by Maturen, image-guided core-needle biopsy has a sensitivity rate of almost 98%, a low incidence of complications, and a significant impact on patient management.

"There is a big need for this technique," Maturen said at the 2006 American Roentgen Ray Society meeting.

Maturen and colleagues retrospectively reviewed records of image-guided core-needle biopsies performed over five years. Renal masses ranged in size from 1 to 13 cm. Of the 153 masses, 56% were judged malignant. The majority of these were confirmed at surgery, yielding a 97.7% sensitivity rate. Just 4% of biopsies were nondiagnostic.

The technique had a significant impact in the management of 92 patients (62%), including malignant cases that went to surgery and benign findings that helped avoid surgery. The researchers estimated that as many as 75 unnecessary nephrectomies were avoided. Based on stability at follow-up imaging after one year, they suspect specificity could be as high as 100%.

Researchers at Massachusetts General Hospital also reported at the ARRS meeting similar success with the technique on 407 renal masses. Biopsy, which included combined FNA and core-needle biopsy wherever possible, influenced patient management in 80% of cases, said Dr. Anthony Samir, a clinical fellow in radiology at MGH. A high number of cases diagnosed as malignant at biopsy were confirmed at surgery. There were, however, two false-positive diagnoses at biopsy, both of which were later diagnosed as atypical benign masses. Nevertheless, image-guided biopsy had a positive predictive value for malignancy of 98%.

"Biopsy of focal renal masses has potential to decrease the rate of nephrectomy of benign renal masses," Samir said.