to describe the surgical technique and initial experience with a single - port retroperitoneal renal biopsy ( sprrb ) . a single 1.5 cm incision was performed under the 12th rib at mid - axillary line , and an 11 mm trocar was inserted . after lower pole exposure , a laparoscopic biopsy forceps was introduced through the nephroscope working channel to collect a renal tissue sample . the mean operative time was 32 minutes , and mean estimated blood loss was less than 10 ml . the hospital stay of all patients was two days because they were discharged in the second postoperative day , after remaining at strict bed rest for 24 hours after the procedure . sprrb is a simple , safe and reliable alternative to open and videolaparoscopic approaches to surgical renal biopsy . image - guided percutaneous renal biopsy is the most widely used method to sample renal parenchyma for the evaluation of malignancy or diffuse renal disease . the risks of this procedure are minimal and the overall success rate of all renal biopsies varies from 70 to 100% ( 1 ) . its major indications rest on diagnosis and follow - up of several systemic and nephrological conditions that lead to glomerular damage and renal function impairment , providing useful data for treatment and prognosis . it may also be used for evaluation of solid renal masses and cystic renal lesions ( 1 ) . however , this method has absolute and relative contraindications that may hamper or preclude it , such as the presence of a solitary kidney , uncontrolled arterial hypertension , coagulation disorders , renal artery aneurysm , previous percutaneous needle biopsy failure and obesity . bleeding and inadequate amounts of renal tissue for diagnosis are not infrequent , and constitute potential disadvantages of the procedure . in addition , children may be unable to cooperate , requiring general anesthesia . in these settings , open and laparoscopic approaches are well - established alternatives and should be considered , although with a higher level of invasiveness and complexity . in search for an alternative that could minimize surgical aggressiveness of these procedures and hence spread its use , we outlined a renal biopsy technique through a single retroperitoneal laparoscopic access using standard urological instruments . the aim of this paper is to describe the technique now standardized in our institution and our initial experience with the single port retroperitoneal renal biopsy ( sprrb ) . after receiving general anaesthesia , orogastric and bladder catheterization , the patient is usually positioned in the left flank position , as the kidney is more easily accessible at the right side due to its lower position . a 1.5 cm incision is carried out just below the tip of the 12th rib , at the mid - axillary line , and is followed by blunt access to the retroperitoneum space . an initial digital dissection is done aiming to identify the lower renal pole , while also displacing the peritoneum anteriorly . during this step , care must be taken in order to avoid peritoneal tearing , as the pneumoperitoneum resulting from gas insufflation would hamper the maintenance of adequate retroperitoneal working space . next , a rubber balloon is positioned between the kidney and the posterior abdominal wall , and is filled with 300 - 400 cc of saline , creating a virtual cavity . the saline is drained after a few minutes , to achieve hemostasis , and the balloon is then removed . an 11 mm trocar is inserted and carbon dioxide is used to maintain pneumoretroperitoneum at 12 to 15mmhg . retroperitoneal inspection and identification of the psoas muscle and the lower pole of the kidney are now performed with a standard 26 french nephroscope , as shown in figure-1 . it is frequently possible to expose the renal surface bluntly , by using gentle movements of the tip of the scope to drag the perirenal fat away from the intended site of biopsy . alternatively , standard laparoscopic surgical aspirator , scissors or hooks can be inserted through the working channel of the nephroscope , and then be used to dissect , cut and coagulate nearby structures , allowing a clear renal surface to be assessed . once the biopsy site is cleared from fat , one or two samples are taken with the aid of a toothed biopsy forceps , also through the nephroscope ( figure-2 ) . bleeding is expected to be negligible , as the injury caused by the forceps is shallow ( figure-3 ) , but the parenchyma can be coagulated with the same instruments , and a cellulose hemostatic bolster can be applied , if needed . finally , the pneumoretroperitoneum is evacuated and , if no bleeding is observed , the trocar is removed and the access port is closed . figure 2sampling renal parenchyma with a toothed biopsy forceps , through the nephroscope working channel . figure 3aspect of kidney surface after a tissue sample was taken , with only minimal bleeding . at our institution , laparoscopic retroperitoneal renal biopsy is currently often performed for pediatric patients with nephrological conditions ( 2 ) . as the surgical team s experience progressed and the procedure was standardized , however , we felt that it should be even less invasive , especially for this very young population . additionally , in order to spread and popularize its execution , we devised how to use instruments that are already present in a regular urological operating room , such as the nephroscope and laparoscopic scissors and forceps , in a different fashion . a similar approach has been described previously , in pediatric surgery , for appendectomies and varicocelectomies , but with only one case of renal biopsy ( 3 ) . between january and april/2013 , five children underwent sprrb in our hospital , referred from the nephrology clinic for renal biopsy . informed consent was previously obtained from parents , respecting our institution s ethics committee recommendations and approval . the procedure was successfully performed with the technique above described , by a supervised resident in - training . the overall mean operative time was 32 minutes , and mean estimated blood loss was less than 10 ml . no open conversion was needed . the hospital stay of all patients was two days because they were kept in absolute bed rest for 24 hours after the procedure , before being discharged home . pain and analgesics use were low , and there were no significant detected complications . regarding the obtained samples , the average number of glomeruli present in the specimens was 31 , and the histopathological findings showed focal proliferative lupus glomerulonephritis in two cases , diffuse mesangial proliferative glomerulonephritis in another two , and nephritis related to henoch - schnlein purpura in one child . these results are comparable to those previously shown by us , with laparoscopic renal biopsy in children , regarding operative time , blood loss , hospital stay and success in obtaining adequate samples ( 2 ) . 
 table 1clinical features of patients submitted to single - port retroperitoneal renal biopsy.patientgenderage ( years)bmi ( kg / m)ot ( min.)bl ( ml)gndiagnosiscomplications1m0723.625423diffuse mesangial proliferative glomerulonephritisnone2f0924.5371338nephritis related to henoch - schnlein purpuranone3f1121.827530focal proliferative lupus glomerulonephritisnone4m1024.0401743diffuse mesangial proliferative glomerulonephritissmall skin ecchymosis5f1232.031621focal proliferative lupus glomerulonephritisnoneaverage-9.825.1832931 - - 
 bmi = body mass index ( kg / m ) ; ot = operative time ( minutes ) ; bl = blood loss ( milliliters ) ; gn = number of glomeruli per biopsy . bmi = body mass index ( kg / m ) ; ot = operative time ( minutes ) ; bl = blood loss ( milliliters ) ; gn = number of glomeruli per biopsy . although it is likely that the same approach could be used in adult patients as well . our experience with this very initial group was composed entirely of children , and sprrb has been shown to be a very simple , safe and reliable alternative to other laparoscopic approaches . the use of a nephroscope , instead of a regular laparoscope , obviates the need to place an additional trocar for using an auxiliary instrument to dissect the perirenal fat , as is the standard practice ( 4 , 5 ) . its working channel finely substitutes that , sparing one incision , the cost of another trocar and also surgical time to place it . because a second trocar traditionally would be only 5 mm wide , it may seem that the benefit here is not strongly relevant in terms of postoperative pain or cosmetic results , but it is our understanding that no technical difficulty was added whatsoever , by using only one access . moreover , especially children could benefit the most even of a small effect , and coincidently they constitute the majority of patients requiring a surgical renal biopsy in our hospital . mini - perc nephroscopes are not available at our institution at this time , but its use could be a step forward , in this regard , and further decrease the required size of the access port incision . additionally , the ease for urologists in using regular urological equipment , and the possibility that the surgeon simultaneously controls both the camera and laparoscopic scissor / biopsy forceps , are other advantages of this alternative method . in our hospital , retroperitoneal laparoscopy is the procedure of choice for renal biopsy in children and the sprrb is an even less invasive option for these patients , performed through a single incision and with very satisfactory results and only minor pain .
objective to describe the surgical technique and initial experience with a single - port retroperitoneal renal biopsy ( sprrb).materials and methods between january and april 2013 , five children underwent sprrb in our hospital . 
 a single 1.5 cm incision was performed under the 12th rib at mid - axillary line , and an 11 mm trocar was inserted . 
 a nephroscope was used to identify the kidney and dissect the perirenal fat . 
 after lower pole exposure , a laparoscopic biopsy forceps was introduced through the nephroscope working channel to collect a renal tissue sample.results sprrb was successfully performed in five children . 
 the mean operative time was 32 minutes , and mean estimated blood loss was less than 10 ml . 
 the hospital stay of all patients was two days because they were discharged in the second postoperative day , after remaining at strict bed rest for 24 hours after the procedure . 
 the average number of glomeruli present in the specimen was 31.conclusion sprrb is a simple , safe and reliable alternative to open and videolaparoscopic approaches to surgical renal biopsy .