Serial volumetric CT aids renal tumor staging
The use of advanced visualization software enables interpreting clinicians to determine the distribution of growth rates across different sizes and subtypes of renal cortical tumors, according to a study published in the January issue of Radiology.

Although the standard of care for renal tumors is surgical resection, because of the increased use of diagnostic imaging an increasing number of renal masses have been found incidentally. According to the authors of a retrospective study conducted in the departments of radiology, internal medicine and surgery at Sloan-Kettering Cancer Center in New York City, management of incidentally found renal tumors, especially when they are small, has been problematic.

“Better knowledge of the growth rates of renal cancer overall and in different subtypes may help in the formulation of clinical recommendations for CT observation or surgical treatment,” the authors noted.

The research team identified 53 of 2,304 patients (34 men and 19 women with a mean age of 67 years) who underwent nephrectomy from 1989 to 2006, did not receive preoperative chemotherapy or radiation therapy, and underwent at least two preoperative contrast-enhanced CT exams (at least three months apart) with identical section thickness that was no more than one-fifth of longitudinal tumor diameter.

Images from the CT exams were reviewed with a 3D multiplanar reformatting interactive mode; which allowed the reader to draw lines and regions of interest and automatically calculate the line length and the area enclosed by the region of interest.

Number of patients with renal tumors in each reciprocal of doubling time (RDT) group. Few tumors demonstrated negative growth (olive bar); most tumors demonstrated relatively slow growth (purple bar). However, some tumors demonstrated significant growth rate over time, as evidenced by large RDT values (yellow bars). Graphic and caption courtesy of the Radiological Society of North America.  
Two investigators measured and recorded the greatest axial diameters, greatest perpendicular diameters and greatest longitudinal diameters as well as the maximum diameter and volume of the renal tumors from each patient’s first and last CT exam. The tumor DT and reciprocal DT was calculated and a relationship between tumor growth and tumor volume was assessed.

“By using serial CT tumor-volume measurement, we determined that the median doubling time (DT) of renal tumors was 811 days and tumors of the same histologic subtypes and grades grew at widely varying rates,” the authors wrote.

The scientists reported that the ranges of the growth rates of renal tumors, of different sizes, subtypes and grades, are wide and overlapped substantially. In addition, they found that tumor growth rates do not correlate with initial tumor volume and the distribution of histologic subtypes and growth rates among small renal tumors is similar to that among larger tumors.

Interestingly, they also found that age at diagnosis was negatively correlated with renal tumor growth rate and that some (13.7 percent) of the pathologically proved cancers decreased in volume between the initial and final CT exam of their patient cohort.

As a result of their investigation, the researchers advised that because tumor growth rates vary widely, surveillance of small renal masses, if selected as the clinical management approach, must be vigorous.