Small renal lesions do not require close monitoring

Radiologists can breathe easier about the clinical implications of renal abnormalities that are too small to be characterized on multislice CT. Results of a retrospective multicenter outcome study performed by Dr. Erich K. Lang, director of CT at Tulane University, suggest that their pathological threat is so low that frequent follow-up is not required.

Lang reported Sunday at the ECR that he and his colleagues examined 465 renal lesions that were often initially identified as incentive findings during MSCT studies performed for other purposes. These abnormalities are typically considered too small to classify with CT; they ranged from 4 to 10 mm, with an average size of 7 mm.

Follow-up studies were performed six to 12 months later. The mean follow-up was 9.4 months. Pathological outcome was established with multiphasic CT, laparoscopy, biopsy, or surgery.

Lang and his group found that 207 lesions were no longer apparent on follow-up exams, while 120 lesions increased in size. Forty-seven lesions were inflammatory and disappeared after the patient was treated for urinary tract infection. Eleven showed some mild calyceal blunting and were also exposed to antimicrobial therapy. Four disappeared after showing cortical deformity. And 65 lesions decreased in size by more than 50%, with six showing signs of residual calyceal blunting.

Another 69 lesions were cystic and had grown to a size at least 1 cm in diameter. Fifty-one (11%) of the total grew and exhibited characteristics consistent with medullary necrosis, renal abscess, or calyceal diverticula. Follow-up CT suggested that four of these lesions were renal infarcts. Four enlarged masses were confirmed as metastatic neoplasms and two others were angiomyolipomas.

Lang concluded that untreated inflammatory renal lesions grew 80%, while untreated neoplastic lesions grew slightly less than 50%. At the same time, 22% of the inflammatory lesions developed microscopic hematuria.

Routine imaging follow-up would have benefited only 23 patients harboring inflammatory lesions, and they might eventually have developed inflammatory characteristics that would have led to their diagnosis, he said.

The detection of the four neoplastic lesions would not have affected the overall management of those cases, according to Lang. Recent studies published in Neurology showed no difference in survival among patients who underwent resection of lesions of 1 to 2.8 cm in size. The investigators determined that waiting to excise tumor that would have grown several centimeters by then would have had no effect on clinical outcome. That experience led Lang to question whether annual follow-up images of small lesions is warranted. He recommended waiting two to three years to reevaluate their status.

"The majority of these lesions that are symptomatic will be picked up on other symptomatology and will receive treatment for other diseases, particularly inflammatory disease," he said.