The IIF designation was added to include cystic lesions that are slightly more complex than category II, but that do not fulfill criteria of category III.
Based on the number or septa and their morphology, calcification patterns, lesion attenuation, and enhancement characteristics, a computed tomography evaluation of a cystic renal mass can be categorized into one of five groups: categories I, II, IIF, III, and IV (table), all of which have associated recommendations for case management. However, with further experience over the past 2 decades, the Bosniak renal cyst classification has been modified and refined (Radiology 2003; 226:47-52; AJR Am J Roentgenol 2003; 181:627-33). The purpose of this article is to present an updated (2006) version of the Bosniak renal cyst classification.
Category IIF lesions are well marginated and may contain multiple hairline-thin septa or they may have minimal smooth thickening of their walls or septa without measurable enhancement. They also may contain calcification, which can be thick, nodular, and irregular. These lesions are thought to be benign, but they have some worrisome features; therefore, follow-up computed tomography is necessary to show stability over time and to prove benignity of these lesions.
Significance of calcification
Another modification of the Bosniak classification is the role that calcification plays in the diagnosis of cystic renal masses.