Bilateral renal masses can be challenging for the urologist to manage: identifying the cause of the masses, determining best management strategies, and then educating the patient on the options and decision making process.

Bilateral renal masses can be either benign or malignant.¹ When faced with management of bilateral renal masses, there are multiple diagnoses a urologist must consider to guide appropriate management. Renal metastases are often bilateral small hypoattenuating renal masses most commonly from lung cancer followed by breast cancer, gastric cancer, and melanoma.¹ These masses are often asymptomatic and rarely present with hematuria, and should be suspected in a patient with a known malignancy. Treatment is driven by the primary malignancy.¹ Patients with lymphoma may develop extra-nodal spread to the genitourinary system manifesting as multiple poorly enhancing bilateral renal masses or nephromegaly. Given that primary renal lymphoma is rare, patients often have lymphomatous disease identified elsewhere. Patients with findings suspicious for lymphoma should undergo percutaneous biopsy and be referred to medical oncology for appropriate chemotherapy.¹

Angiomyolipomas can present as bilateral renal masses, especially in patients with tuberous sclerosis.¹ Asymptomatic masses <4 cm can be surveilled, while lesions ≥4 cm should be surgically resected or embolized due to risk of hemorrhage.² While oncocytomas, benign renal masses, are usually solitary unilateral masses, patients may develop bilateral oncocytomas, especially in those with Birt-Hogg-Dubé syndrome. Oncocytomas are indistinguishable from renal cell carcinoma (RCC) on imaging.¹

While most sporadic RCCs are unilateral, bilateral synchronous sporadic RCC has been reported in up to 4% of cases.³ Patients with bilateral synchronous tumors are also more likely to have multifocal tumors.⁴ In a review of the Surveillance, Epidemiology, and End Results database of 274 patients with bilateral synchronous renal masses, 99% of patients were found to have bilateral RCC, with 1 patient having a unilateral oncocytoma. Histological and nuclear grade concordance between renal masses was reportedly high at 93% and 85%, respectively.⁵ A single-institution study of bilateral synchronous tumors also reports a high concordance rate between tumors at 87%.⁶ Thus, the pathology of one mass is strongly predictive of the other. More recent studies demonstrate similar survival outcomes to patients with unilateral disease, although there was an insignificant increase in local recurrence.⁷

Management considerations of bilateral renal masses concerning for RCC include when to biopsy; whether or not to perform nephron sparing surgery if feasible vs ablation or active surveillance; in the case of surgical removal, which mass to remove first—the more or less complex tumor; and whether or not to perform simultaneous vs staged excisions. Maximal renal preservation with nephron sparing surgery is of the utmost importance if feasible given the higher incidence of multifocal tumors with bilateral synchronous masses and the increase in all-cause mortality associated with decreased renal function.⁸ Our approach to the surgical management of bilateral RCC stems from experience with patients with genetic renal tumor syndromes such as von Hippel-Lindau Disease, in which metastasis has not occurred in patients whose masses are observed until the largest reaches 3 cm in size.⁹ Bratslavsky and Linehan discuss their approach at the National Cancer Institute in which they obtain a percutaneous biopsy for patients presenting with bilateral renal masses without a known genetic syndrome.⁹ They use this biopsy to drive the need for further genetic workup, and the type and timing of surgical intervention. Patients with familial syndromes, clear cell RCC, papillary type 1 RCC, chromophobe RCC, and oncocytic neoplasms are observed until the largest mass is 3 cm in size.⁹ Tumors concerning for papillary type 2 RCC and hereditary leiomyomatosis and renal cell cancer-associated tumors are more aggressive and managed with early resection with wide margins.⁹ Intraoperatively, they describe their retroperitoneal approach with minimal dissection of the hilum, clamping the artery and vein en bloc to preserve the perivascular adventitia, and performing enucleations off clamp as able.⁹

The impact of staged vs simultaneous partial nephrectomy (PN) has been evaluated in several single-institution studies. Packiam et al retrospectively reviewed 107 patients undergoing bilateral vs staged PNs from 1980-2015 and found the simultaneous PN group had improved pooled length of stay (median 6 vs 8 days, P < .001), rate of urine leak (3% vs 17%, P = .018), rate of Clavien grade 3-4 complications (8% vs 23%, P = .44), and lower reduction in estimated glomerular filtration rate at 3 and 12 months postoperatively (−6% vs −24% decrease, P = .015, and −4% vs −22% decrease, P < .001).¹⁰ However, this observed difference may be due to significant selection and technical bias, though the only recorded significant differences between the 2 groups were BMI at first surgery (29 vs 32 kg/m² for simultaneous vs staged, respectively, P = .022), and number of female patients in the cohort.¹⁰ Contrary to this finding, Di Maida et al reviewed 41 patients with synchronous bilateral renal masses between 2008 and 2019 and found no difference in the reduction of estimated glomerular filtration rate at 3 months and last follow-up between simultaneous vs staged surgery (−7.3 vs −7.8, P = .31), but did find that staged procedures had a significantly higher cumulative operative time and length of stay.¹¹ Disease-free survival was also similar between the 2 approaches.¹¹ The literature demonstrates that 1- and 2-stage options are feasible and the surgeon should take into account tumor complexity and patient comorbidities to help decide the optimal management.

Whether to resect the more complex or less complex tumor first remains debatable. Surgeons who favor resection of the more complex tumor first argue it is important to optimize oncologic control in case the contralateral resection needs to be delayed due to complications.¹⁰ Those who resect the less complex tumor first prefer to ensure one side can be removed off-clamp prior to resecting the more complex tumor on-clamp if necessary to minimize the risk of acute kidney injury.¹¹ The latter group does not perform a 1-stage approach if bilateral renal artery clamping is necessary for resection.¹¹

Bilateral renal masses most always require a very active discussion with the patient about risks, benefits, treatment options, implications, complications, and concordance. Appropriate diagnosis, hereditary syndromes, maximal renal preservation, the complexity of the tumor, and patient comorbidities are all important aspects to consider. Just like many aspects of oncological urology, there is no one answer for all renal masses as they must be considered on a case-by-case basis.