Cystic Renal Masses

Approximately 10% of cases of RCC present as a fluid-filled, cystic mass [24-26]. Simple, uncomplicated cysts can be accurately diagnosed by US, Ct or MRI. Although uncommon, these simple cysts may be complicated by hemorrhage, infection, or ischemia. As part of the reparative process, complicated cysts demonstrate acute and chronic inflammatory changes with granulation tissue that may include neovascularity and calcification (Fig. 3). On gross examination, a complicated cyst is often indistinguishable from cystic RCC. The precise differentiation of cystic renal carcinoma from complicated cyst is performed by microscope. RCC is best treated by surgical excision or by ablation. A cyst is not simple if it has any of the following: calcification, hy-perdensity/high signal, septations, multiple locules, en hancement, nodularity or wall thickening (Fig. 4). Although microscopic evaluation is required for precise diagnosis, there are certain radiological findings that are reliable for differentiation of a complicated cyst from a cystic RCC. The goal of the radiologist is to categorize each cystic renal mass as nonsurgical (i.e. benign) or as surgical. Although most cystic renal masses can thus be appropriately classified and correctly managed, there is a subset of cystic masses that are probably benign but do not fulfill either the benign or the surgical criteria and thus should be followed.

When following cystic lesions that are probably benign, surgery can be avoided in many patients [25]. When a lesion is to be followed, it is important to communicate to the referring physician and to the patient the importance of complying with the follow-up recommendations. Follow-up time for these lesions has not been definitively determined, but an initial re-examination after three to six months, followed by an annual examination is reasonable. The total time for follow-up is also subjective. Five year follow-up is probably adequate in older patients, whereas a longer follow-up is prudent in younger patients. When evaluating for changes, it is important to compare the current study to the earliest images, not on

Fig.4. Patterns of septation within a cystic mass. (a) Thin (arrow). (b) Thick (arrow). (c) Irregular and enhancing (arrow). Fig. 4a. Reprinted with permission from [26]

ly the most recent. Change is often slow and only recognized by comparing the oldest and current images.

Table 1 presents the guidelines for cystic renal masses: ignore, excise or follow. When evaluating cystic renal masses, it is always important to consider the patient's pretest probability for disease (e.g. Von Hippel Lindau disease) and the patient's ability to tolerate uncertainty, especially if a lesion is to be followed.

Percutaneous biopsy of indeterminate cystic renal masses remains controversial at best. Indeterminate cystic renal masses that are benign usually represent complicated cysts that contain inflammatory changes [27]. As a result, biopsy specimens obtained from the cyst's wall or fluid typically contains only renal epithelial cells, inflammatory cells, and fibrous tissue, material which cannot be used for a specific benign diagnosis [28]. Retrieving no malignant cells still leaves the radiologist, referring physician, and patient with the possibility that the lesion was improperly sampled or missed. Therefore, complete surgical resection is the only procedure that allows a definitive tissue diagnosis to be obtaineid. However, follow-up is not definitive because there is no known period of follow-up that can result in a confirmation of the benign diagnosis based on the lack of growth or change in appearance of the mass. As many indeterminate cystic renal masses are benign, proceeding directly to surgery would result in unnecessary surgery in many patients. Furthermore, some patients have co-morbidities that place the patient at risk for surgery. Recently it was shown that biopsy was avoided in 39% of patients with co-morbid disease and an indeterminate cystic renal mass [29]. Therefore, biopsy may be helpful in selected circumstances, such as patients who have co-morbidities that increase the risk of surgical exploration. In these patients, biopsy results serve as additional data that can be combined with imaging data to render a probable clinical diagnosis. However, it should be emphasized to the patient and referring physician that cystic renal mass biopsy results, particularly in the absence of malignant cells, are typically not definitive alone.

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