The Bosniak category system, introduced 17 years ago for classifying renal lesions, facilitates some quick analyses of the common cysts often discovered as incidental findings on abdominal CT scans.
But between the Bosniak Category I and II lesions that are obviously benign and the Category III and IV lesions that clearly warrant surgery, there are those that cannot be easily dismissed in either direction.
In this month’s American Journal of Roentgenology, Dr. Morton Bosniak offers further suggestions from his experience with the lesions he places in Category IIF, where F stands for follow-up (AJR, September 2003, Vol. 181:3, pp. 627-633).
"Differentiating more complex Category II lesions (nonsurgical) from some less complex Category III lesions (surgical) is important because their recommended management is different, and these cases cause the most difficulty in diagnosis and the most interobserver variation," wrote Bosniak and his co-author Dr. Gary M. Israel from the New York University Medical Center in New York City.
The researchers looked retrospectively at each of the 42 cysts evaluated at their institution that had been originally characterized as category IIF, and had been followed for at least two years. Because the cases stretched back more than 10 years, the authors noted that the exams had been performed on a variety of helical and conventional CT scanners, with varying slice collimations. Images were consistently taken before and after IV contrast, although the type and amount of contrast varied. The authors defined category IIF lesions as ones containing increased numbers of thin septa or a slightly thickened but smooth septum or wall.
"They may also contain calcification that may be thick and nodular, but they do not contain any associated enhancing soft-tissue elements," the authors wrote. "Completely intrarenal high-attenuation cysts 3 cm or larger fall into this group (category IIF) as well."
Once a lesion has been categorized as IIF, they added, it should be reexamined initially at six months, and then yearly thereafter for at least five years.
"If a lesion grows slightly, this change should not be perceived as troublesome because even benign simple cysts grow," the researchers wrote. "However, if an increase in the thickness or in the irregularity of the wall or septa is seen, surgical exploration is necessary because either finding indicates malignancy."
Patients who are young, or simply uncomfortable with the prospect of long-term follow-up, might opt for immediate surgery instead. However, given that only two of the 42 IIF lesions in their study were found to be malignant during follow-up, Bosniak and Israel expressed doubt regarding the need for immediate surgery in most IIF lesions.
"These malignant cystic lesions may represent a low-grade variant of renal cell carcinoma. They are associated with a better prognosis than other renal malignancies and have less tendency to metastasize," Israel and Bosniak stated. "Therefore, in those few cases in which a diagnosis of malignancy is delayed until follow-up examinations reveal the true nature of the lesion, the welfare of the patient does not appear to be compromised."
The authors acknowledged that the small size of their study made it impossible to determine the optimal length for follow-up, but that the average follow-up of 5.8 years in their study hinted at some useful guidelines.
"We included many cases with prolonged follow-up, not because we believe that follow-up for more than five years was needed in many of the cases, but because the data were available," the researchers wrote. "These cases support the contention that follow-up of more than five years is not generally necessary."
"In general, we think that a five-year follow-up period in patients older than 50-60 years is adequate to show that a complex cystic lesion is stable. However, in younger patients, a longer follow-up period may be necessary."
By Tracie L. ThompsonAuntminnie.com contributing writer
September 29, 2003
Related Reading
US, MRI challenge CT for classifying renal cell carcinoma, June 17, 2003
Following up incidental findings may do more harm than good, September 5, 2002
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