Algorithm for Bosniak 2F Cyst in Kidney Donation

Background

A renal cyst is a common finding by CT scan. The incidence in patients 50 years of age and over is between 17% and 39% [1–3]. Mean diameter of cysts is 2 cm and many cysts increase in size over time, with growth being higher in patients below as compared to above 50 years of age, with a mean of 3.9 versus 1.8 mm per year, respectively [3,4]. The Bosniak system for radiological classification of renal cysts offers a tool for surgical decision-making in clinical practice [5]. The Bosniak 2F category is composed of lesions that are thought most likely to be benign, but still must be proven to be stable over serial interval imaging. The radiology definition of Bosniak 2F cysts implies the presence of multiple hairline-thin or minimally, smoothly thick septa and/or walls that may contain perceived enhancement and/or coarse calcification but no measurable enhancement. Also included are uniformly high attenuation lesions greater than 3 cm that may be totally intrarenal [6]. Up to 5% of these cysts progress to malignancy; therefore, follow-up imaging is recommended, although there is no consensus recommendation on the appropriate interval of follow-up [7]. The American College of Radiology recommends imaging surveillance with CT or MRI without and with IV contrast material at 6 and 12 months after diagnosis and yearly thereafter for a total of 5 years [8].

Most malignant lesions in Bosniak 2F lesions are cystic clear-cell renal cell carcinomas. Histology of the remaining lesions is reported to include papillary renal cell carcinoma and a heterogeneous group of other malignancies [9]. Approximately a one-quarter of clear-cell renal cell carcinomas are classified as multilocular cystic renal cell carcinoma, a subtype of clear-cell renal cell carcinoma [9]. This entity is regarded as a ‘malignancy of low malignant potential’. Development of metastases has never been reported for this histology, irrespective of size [10,11]. No examples of metastatic progression of a Bosniak 2F lesion on surveillance has been reported in the literature.

The Dutch and UK guidelines for living kidney donation provide no information on the management of kidney donors with a Bosniak 2F cyst [12,13]. The recent Kidney Disease Improving Global Outcomes (KDIGO) clinical guideline 2015 for living kidney donation stated that use of live donor kidneys with Bosniak 2 or higher renal cysts should proceed only after careful assessment for the presence of solid components, septations, and calcifications on the preoperative CT scan (or MRI) to avoid accidental transplantation of a kidney with cystic renal cell carcinoma. Bosniak 2 or higher cysts should not be left in the donor [14]. However, a step-by-step practical guideline is missing. Here, we describe a donor with a Bosniak 2F cyst and propose a practical guideline.

Case Report

PRACTICAL GUIDELINE:

All donors suitable for donation, including donors with unilateral Bosniak 2F cyst present at CT scan, are evaluated by a multidisciplinary transplantation team, consisting of a transplant nephrologist, transplant surgeon, urologist, and anesthesiologist. Absolute contraindications for donation, such as diabetes mellitus, polycystic kidneys, and bilateral nephrolithiasis, are the same for donors without a unilateral Bosniak 2F cyst [13]. Relative contraindication for donation is the presence of a Bosniak 2F cyst in the kidney with significantly higher function as determined by nuclear renal scan.

In case of a Bosniak 2F cyst, the transplant team should address the resectability of the lesion and the collateral damage to a well-functioning kidney. Large cysts near the renal pelvis or blood vessels make it difficult to remove, and after partial nephrectomy, function should be sufficient for transplantation. Non-resectable Bosniak 2F cysts, however, can be donated to the recipient without any other donors, after agreement and written informed consent of the recipient to follow-up after kidney transplantation. These recipients should have regular imaging surveillance with CT or MRI. If the Bosniak 2F cyst is resectable, contraindications for resection should be balanced. Clinical indications for anticoagulation, such as mitral valve insufficiency, are relative contraindications to resection and transplantation. Hemorrhage risk should be discussed with the recipient. When we remove the Bosniak 2F cyst on the back-table, we precisely describe the location and aspect and ensure complete removal of all macroscopic cyst tissues, which are then sent to the pathology lab. In contrast to the case presented, we would not recommend deroofing and fulguration of the base of a Bosniak 2F cyst with the possibility of leaving positive margins behind. Closure of the parenchymal defect will be performed with running sutures and hemostatic agents if necessary.

If the recipient does not agree to transplant a kidney with non-resectable Bosniak 2F cyst, the donor will be followed for 5 years. When the situation is unchanged without progression to a higher-category lesion, kidney donation can be done safely.

Bosniak cyst 3/4 or renal cell carcinoma are contraindications for donation and partial nephrectomy is recommended. Total nephrectomy and donation may be offered in exceptional cases where rescue therapy is indicated or donor and recipient are well informed and decide to accept the risk of recurrence. Some case series describe donors with incidental renal masses in living and deceased kidney donors, which were resected with clear margins on the back table and where no local recurrence or metastasis were observed in long-term follow-up [15–17].

Discussion

At present, a consensus on the management of Bosniak 2F cysts in kidney donation has not been developed. Therefore, an algorithm for kidney donors with Bosniak 2F cysts was made. This practical approach to the assessment of Bosniak 2F cyst in kidney donation is of importance in minimizing the risk of the donor and recipient and optimizing the donor pool.

The Bosniak classification system is the most widely accepted method for identifying cystic renal lesions that are potentially malignant [5]. Because Bosniak 2F renal cysts are infrequently malignant, the American College of Radiology recommends imaging surveillance with CT or MRI without and with intravenous contrast material at 6 and 12 months after diagnosis and yearly thereafter for a total of 5 years [8]. The purpose of imaging surveillance is to identify Bosniak 2F renal cysts that progress to higher-category lesions, because upward reclassification is associated with an increased malignancy rate. The malignancy rate of upward reclassification ranges from 5% to 16% and typically occurs in the first 2 years after diagnosis [18]. However, the malignancies in Bosniak 2F cysts are in general of low grade and stage and prognosis is excellent. In addition, malignancies in complex renal cysts have no tendency to metastasize [9,10], although biological behavior of Bosniak 2F cysts on immune suppression is unknown.

To remove the Bosniak 2F cyst, partial nephrectomy surgery is the preferred method, as it is the standard treatment for renal masses smaller than 4 cm in diameter [19,20]. The most frequent complications after partial nephrectomy are postoperative hemorrhage and urinary fistula. The incidence of hemorrhage varies between 4% and 8% [21,22], and the risk of postoperative hemorrhage is higher in patients with larger tumor size and central tumor location with deeper infiltration [23,24]. Other risk factors for hemorrhagic complications are high American Society of Anesthesiologists (ASA) scores and smoking [25]. The incidence of urinary fistula after partial nephrectomy has ranged from 1% to 17.4% [26]. However, more recent studies report urinary leakage rates between 0.6% and 3% [27,28]. Risk factors include hilar tumor location, tumor size, blood loss, and need for pelvicalyceal repair [26,29–31].

Additionally, some centers have even transplanted donor kidneys after a partial nephrectomy due to a small renal cell carcinoma. Penn et al. reported that when a donor renal carcinoma <2 cm was completely removed, no recurrences in 14 recipients were observed after 55–57 months follow-up [32]. It was stated that donor kidneys with renal tumors <2 cm, that have been completely removed, could be used for transplantation, with a low risk of local recurrence or metastasis. However, strict follow-up is advocated. Lugo-Baruqui et al. identified 4 donors with renal cell carcinomas [16]. All donor kidneys underwent partial nephrectomy of the tumor during the back-table preparation. After a median follow-up of 36 months, all patients remained tumor-free [32].

In consideration of the shortage of donor organs, it is important to balance the risk of tumor transmission or recurrence with the benefit associated with organ transplantation. Resection of Bosniak 2F cysts provides 2 advantages: the recipient receives a new donor kidney and will be free of dialysis, and the donor will be free of surveillance. In high-volume centers with surgical expertise, Bosniak 2F cysts should be a feasible option in expanding donor criteria. The recommendations presented here are largely based on expert experience and pragmatism and are supported where possible by published evidence. Nonetheless, a practical guideline in managing Bosniak 2F cyst in kidney donation will help healthcare professionals in daily practice.

Conclusions

We present a practical guideline for kidney donors with Bosniak 2F cysts, providing a tool to increase the donor pool without compromising the risk of the donor and recipient. Further evaluation of this algorithm by longer follow-up and more studies is needed to prove its safety.