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New York University Medical Center New York, NY 10016
The article by Dr. Harisinghani and associates in the March issue of the AJR, "Incidence of Malignancy in Complex Cystic Renal Masses (Bosniak Category III)" [1], suggests that most Bosniak category III renal cystic lesions should be biopsied to avoid unnecessary surgery on those lesions that turn out to be benign. Whereas this approach has use in selected cases, we would like to point out some important omissions in the article and correct an unfortunate misstatement.
First of all, a discussion of the Bosniak cyst classification without inclusion of category IIF is incomplete. The authors have quoted the original article written in 1986 [2] and have largely ignored the modifications to the classification that have been described many times in the past 10 years [3–6]. After the original classification was described, it became obvious that some revision was in order because there were some category II cysts that were slightly more complicated than most category II lesions but not complicated enough to place in category III. For that reason, a category IIF (F for follow-up) was introduced in 1993 [3] and has been described in a number of articles since that time [4–6].
The authors chose to ignore the existence of this category even though it is described in detail in three articles that the authors referenced many times in their article [4–6]. I suspect that some of the cases in their series might have belonged in category IIF, which describes a way that some complicated cystic lesions can be managed by follow-up studies without the need for invasive biopsy. The case shown in figure 4 in their article is such an example. Gary Israel and I have published in an article in AJR that describes our experience with 41 patients with category IIF cysts using this follow-up technique [7]. Differences of opinion can certainly arise regarding into which category a particular case should be placed— whether it be category II, IIF, or III—and the results of any review as to how many category III lesions are benign and how many are malignant is greatly influenced by the experience of the individuals interpreting the examination. If a large number of category II or IIF cysts are placed in category III, a higher percentage of category III lesions will turn out to be benign. Therefore, we can expect a wide variation in the relative number of benign and malignant category III cases in the various series reported in the literature.
Another omission in the article is a discussion regarding potential harm that biopsy can cause. No discussion of morbidity rates of the procedure is included (including their own complication rate) or the possibility of seeding of cancer in the needle track [8]. Although considered rare, needle track spread of tumor is an "underestimated risk" [9] and from my own observations is probably an underreported complication. A core biopsy of the wall of a cystic lesion (benign or malignant) can cause it to rupture and spill its contents into the surrounding tissues. Although needle biopsy is considered a relatively safe procedure, complications can occur, particularly in less experienced hands. Furthermore, the procedure is unnecessary in many of the patients in which it is performed. Certainly, renal biopsy should not be used because the imaging study (that was performed for diagnosis) is inadequate. Also, besides the complications of bleeding, infection, or needle track tumor spread, a negative biopsy result does not rule out malignancy, particularly in cystic lesions have less bulk of tissue to sample. The 18-month follow-up (median) that the authors have used to prove benignancy is hardly adequate because, as the authors themselves have written, these lesions can be slow-growing.
Finally, I want to correct a significant misstatement in the article. The authors write that "Bosniak himself has advocated placing borderline II–III lesions, especially hyperdense cysts, into category III." They reference the 1997 AJR article [4] for this statement. Although I believe in upgrading category IIF to category III (not category II to III) in borderline cases, when there is doubt, I must emphatically stress that I have never classified a hyperdense cyst into category III—not in the literature or any lecture that I have ever given. It is important that this be clearly understood because hyperdense cysts are common, and placing them and treating them as category III lesions, which in most instances indicates surgical intervention, would be totally unnecessary. Hyperdense cysts are usually category II lesions, and only if they are totally intrarenal and larger than 3 cm or are in kidneys with multiple complicated cystic lesions are they category IIF—but not category III.
Differences of opinion can arise concerning the placement of borderline cases in the Bosniak cyst classification system and the need for needle biopsy. However, the omission of category IIF in the cyst classification that uses a follow-up approach in these cysts rather than biopsy, the omission of any discussion about the possible complications associated with needle biopsy, and the misstatement concerning hyperdense cysts require that this letter be written to clarify some of these points.
References
Massachusetts General Hospital Boston, MA 02114
We thank Dr. Bosniak for his comments on our article [1]. His letter raises some important questions and concerns. In regard to the first point about category IIF lesions, we agree with him that this category constitutes an important component of the renal cyst classification system. Ours was a retrospective study. We identified cystic lesions that had already been biopsied, and the imaging features that were suspicious enough to warrant a biopsy request from a urologist. As Bosniak points out in his letter, the placement of these lesions in a category is a matter of individual preference and judgment. Our institution has seen a growing trend toward biopsy in preference to lesion follow-up, and these requests are coming from referring urologists with input from increasingly well-informed patients, but it is not a trend that we have promoted. Thus, in our experience, renal biopsy is a useful step for the so-called suspicious lesions that do not fit the classic benign category.
With reference to the potential harm of biopsy, our group has published our experience with renal biopsies [2]. Our results correlate with other published results [3]. The seeding of the needle track, although a cited theoretic risk, is exceedingly uncommon. Neither of the referenced series [2, 3] showed any incidence of needle track seeding, nor have we encountered this complication in the 5 years since preparation of the series by Wood et al. [2].
Finally, as to the point about classification of hyperdense lesions, we agree with Bosniak and regret that our article leaves this point unclear. Our intent was to indicate patients with heterogeneous hyperdense lesions and Bosniak category III lesions who could avoid surgery, at least initially, through CT-guided biopsy [1]. In conclusion, our intent is not to disparage the Bosniak system [4] for cystic renal lesion classification but to propose an alternative to surgery for complex cystic lesions that require timely characterization.
References
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  G. Ascenti, S. Mazziotti, G. Zimbaro, N. Settineri, C. Magno, D. Melloni, R. Caruso, and E. Scribano Complex Cystic Renal Masses: Characterization with Contrast-enhanced US Radiology, April 1, 2007; 243(1): 158 - 165. [Abstract] [Full Text] [PDF]
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 K. E. Maturen, H. V. Nghiem, E. M. Caoili, E. G. Higgins, J. S. Wolf Jr., and D. P. Wood Jr. Renal Mass Core Biopsy: Accuracy and Impact on Clinical Management Am. J. Roentgenol., February 1, 2007; 188(2): 563 - 570. [Abstract] [Full Text] [PDF]
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