due to the widespread use of imaging modalities , such as ultrasonography , computed tomography ( ct ) , and magnetic resonance imaging , the incidences of incidentally found small cortical renal masses ( srms ) and renal cell carcinoma ( rcc ) , have increased during the past years . for decades , the standard therapy for patients with clinically suspected rcc consisted of radical nephrectomy , an invasive surgical procedure with high morbidity .
however , in a recently published randomized trial of nephron - sparing surgery ( nss ) in patients with srm yielded comparable oncological outcome with radical nephrectomy . in addition
, population - based studies clearly demonstrate an overall survival benefit in patients undergoing nss as a result of preserved renal function [ 4 , 5 ] .
nephron - preserving procedures , such as partial nephrectomy and image - guided minimally invasive ablative procedures , have therefore increasingly been applied in patients with srm [ 6 , 7 ] .
initially , image - guided ablative procedures were performed in patients who were not suitable candidates for nss based on significant medical comorbidity , advanced symptomatic disease , or refusal of conventional therapy [ 6 , 8 ] .
accumulating data on follow - up and oncological safety suggest a broader indication in patients with srm .
a particular form of an image - guided ablative procedure is radiofrequency ablation ( rfa ) , which can be performed open or percutaneously . in rfa , an electric current oscillates through an electrode placed centrally in the target tissue .
this results in frictional ionic agitation and heat formation in the tissue surrounding the tip of the electrode , causing local protein coagulation and cellular death . compared with open and laparoscopic ( partial ) nephrectomy
it is a nephron - sparing therapy with low morbidity and mortality , short hospital stay , and acceptable oncologic outcome [ 8 , 10 , 12 ] .
nevertheless , rfa of the kidney can be accompanied by minor and even major complications .
several investigators have postulated the occurrence of bowel perforation as a complication of rfa of renal masses due to the close proximity of bowel [ 13 , 14 ] . to our current knowledge ,
only two articles have described such a case [ 15 , 16 ] . yet in a large series of 100 percutaneously performed renal rfas , none of the patients had colonic injuries .
the reported incidence of bowel perforation complicating renal rfa therefore ranges from 0 to 8.3% [ 8 , 15 ] . in this article
, we describe the first case of appendiceal perforation as a complication of ct - guided percutaneous rfa of an smr .
a 60-year - old male patient was referred to our outpatient clinic with an incidental mass in the right kidney , which was recently diagnosed during work - up of his microscopic hematuria .
his previous medical history consisted of kidney stone lithotripsy , hypertension treated with a beta - blocker and diuretic , and two episodes of transient ischemic attack .
abdominal ct scan showed a rapidly enhancing , exophytic mass in the lower pole of the right kidney with a maximum diameter of 2.5  cm ( fig . 
the appendix was noticed in a retrocecal position , at a 1.4-cm distance from the renal mass ( fig . 
1b , c ) . based on his mild comorbidity and on the small size of the renal mass ,
1a small , exophytic , rapidly enhancing renal mass at the lower pole of the right kidney .
b retrocecal position of the appendix on the lateral site of the right kidney in the vicinity of the renal mass ( c ) .
* appendix , renal mass a small , exophytic , rapidly enhancing renal mass at the lower pole of the right kidney .
b retrocecal position of the appendix on the lateral site of the right kidney in the vicinity of the renal mass ( c ) .
* appendix , renal mass our technique of rfa in renal masses has extensively been described in previous articles [ 17 , 18 ] . in short ,
after the patient received an antibiotic prophylaxis ( 1,500  mg cefuroxim ) and epidural analgesic before the rfa procedure , he was placed in prone position on the ct table .
a planning ct scan was performed to locate the renal mass . under fluoroscopic ct guidance ,
a 17 g cool - tip electrode ( valleylab , covidien , boulder , co ) was placed centrally into the mass .
subsequently a 20 g needle was inserted lateral in the anterior pararenal space for injection of dextrose in water to hydrodissect the renal mass from the surrounding vital tissues , such as the colon and appendix . after the hydrodissection and
the positions of the needles were checked with a ct scan of the area of interest , ablation was started .
final temperature after 15  min was  > 75c with adequate roll - offs .
the rfa procedure was performed by a highly experienced interventional radiologist ( w.p . ) who at that time had already performed  > 180 percutaneous image - guided ablative procedures ( including renal , liver , and lung ) .
a 60-year - old male patient was referred to our outpatient clinic with an incidental mass in the right kidney , which was recently diagnosed during work - up of his microscopic hematuria .
his previous medical history consisted of kidney stone lithotripsy , hypertension treated with a beta - blocker and diuretic , and two episodes of transient ischemic attack .
abdominal ct scan showed a rapidly enhancing , exophytic mass in the lower pole of the right kidney with a maximum diameter of 2.5  cm ( fig . 
the appendix was noticed in a retrocecal position , at a 1.4-cm distance from the renal mass ( fig . 
1b , c ) . based on his mild comorbidity and on the small size of the renal mass ,
1a small , exophytic , rapidly enhancing renal mass at the lower pole of the right kidney .
b retrocecal position of the appendix on the lateral site of the right kidney in the vicinity of the renal mass ( c ) .
* appendix , renal mass a small , exophytic , rapidly enhancing renal mass at the lower pole of the right kidney .
b retrocecal position of the appendix on the lateral site of the right kidney in the vicinity of the renal mass ( c ) .
our technique of rfa in renal masses has extensively been described in previous articles [ 17 , 18 ] . in short ,
after the patient received an antibiotic prophylaxis ( 1,500  mg cefuroxim ) and epidural analgesic before the rfa procedure , he was placed in prone position on the ct table .
a planning ct scan was performed to locate the renal mass . under fluoroscopic ct guidance ,
a 17 g cool - tip electrode ( valleylab , covidien , boulder , co ) was placed centrally into the mass .
subsequently a 20 g needle was inserted lateral in the anterior pararenal space for injection of dextrose in water to hydrodissect the renal mass from the surrounding vital tissues , such as the colon and appendix .
after the hydrodissection and the positions of the needles were checked with a ct scan of the area of interest , ablation was started .
final temperature after 15  min was  > 75c with adequate roll - offs .
the rfa procedure was performed by a highly experienced interventional radiologist ( w.p . ) who at that time had already performed  > 180 percutaneous image - guided ablative procedures ( including renal , liver , and lung ) .
on the ct images performed during the procedure , the colon and appendix were considered to be a safe distance ( at least 1.0  cm ) from the ablative field as a result of the hydrodissection ( fig .  2 ) .
adequate ablation of the kidney tumor was achieved without intraprocedural complications . on the first postprocedural day
fluid collection with air configuration on the lateral and anterior side of the renal mass as a result of hydrodissection can be seen .
retrocecal appendix ( * ) is in the vicinity of the ablative field patient in left lateral decubitus position during rfa procedure .
fluid collection with air configuration on the lateral and anterior side of the renal mass as a result of hydrodissection can be seen .
retrocecal appendix ( * ) is in the vicinity of the ablative field five days after the procedure , he presented at our hospital with fever ( 39.5c ) and right lumbar pain .
3 ) showed a large retroperitoneal fluid collection with air configurations , suggesting retroperitoneal abscess formation , on the lateral side of the right kidney .
moreover , a direct connection was noticed between the cecum and fluid collection , with contrast material in the retroperitoneal abscess , suggesting perforation at the base of the appendix ( fig .  3 ) .
after ct - guided drainage of the abscess and intravenous antibiotic therapy , the patient remained septic . therefore , 2  days later laparotomy was performed .
intraoperatively , a retroperitoneally confined abscess was drained . however , due to an extensive local inflammatory reaction affecting the terminal ileum ( fig . 
4 ) , the approach had to be extended intra - abdominally to allow necessary resection of the ileocecal region followed by primary anastomosis between the ileum and ascending colon and an omental plasty . during this step ,
histopathologic examination of the resected specimen showed a perforated appendix based on ulcero - phlegmonous and gangrenous inflammation . on day 18 after the rfa
3leakage of contrast material from the perforated cecum / appendiceal base into the right anterior pararenal space suggesting appendiceal perforation . presence of air configurations in the right anterior pararenal space suggesting abscess formationfig . 
oversewn cecal perforation at the base of the necrotic appendix leakage of contrast material from the perforated cecum / appendiceal base into the right anterior pararenal space suggesting appendiceal perforation .
presence of air configurations in the right anterior pararenal space suggesting abscess formation intraoperative view after abscess drainage .
rfa of srm was first applied in 1997 and has proven to be a promising and safe technique since . in a large series of 100 patients with renal tumors treated with rfa , 11 minor and major complications were reported , of which the most common was haemorrhage .
. complications of rfa can generally be divided into two categories : ( 1 ) those related to imaging - guided electrode placement and ( 2 ) those related to thermal therapy .
the latter are more common in kidney rfa compared with other rfa indications , e.g. , hepatic rfa , as a result of the proximity of other vital structures , such as the bowel and ureter . nevertheless , only two articles so far have reported bowel perforation as a complication of renal rfa [ 15 , 16 ] .
the first step in preventing thermal complications is thorough assessment of the tumor location on preprocedural ct scans during the process of patient selection .
percutaneous renal rfa can be performed with the patient prone or in lateral decubitus position . in both positions ,
vital structures in the vicinity of the target mass will be kept away from the ablative zone by way of gravity .
third , the rfa electrodes can be used to lift the ablated tumor away from vital structures .
examples of invasive methods include hydrodissection with glucose in water or injection of carbon dioxide in between the target tissue and the tissue that needs protection . in our patient ,
a lateral dissection was performed with glucose in water to dissect the renal mass from the appendix and the colon , which was located caudolateral with respect to the renal mass .
unfortunately , in this way the appendix came even closer to the tract of the needle .
nevertheless , on the ct images performed during the procedure , the appendix was considered to be at sufficient distance from the ablative field .
eventually , this caused the appendiceal perforation . since this complication , we modified our ablative technique .
currently we start the hydrodissection before placement of the rfa electrode in the target tissue . in addition , instead of injecting 100  cm fluid during hydrodissection , we attach the needle to a continuous drip system .
in conclusion , in this article we described a case of appendiceal perforation leading to retroperitoneal abscess formation as a complication of percutaneous rfa of an srm .
although rfa of srm is generally a minimally invasive and safe procedure , one should be aware of the possibility of particular minor and major complications when performing this innovative and promising procedure .
if vital structures remain in close vicinity of the ablative field , one should consider treatment options other than rfa .
 percutaneous radiofrequency ablation ( rfa ) has gained wide acceptance as nephron - sparing therapy for small renal masses in select patients . generally , it is a safe procedure with minor morbidity and acceptable short - term oncologic outcome . 
 however , as a result of the close proximity of vital structures , such as the bowel , ureter , and large vessels , to the ablative field , complications regarding these structures may occur . 
 this is the first article describing appendiceal perforation as a complication of computed tomography - guided rfa despite hydrodissection . when performing this innovative and promising procedure one should be aware of the possibility of particular minor and even major complications 
 . 