Considering the diversification and popularization of minimally invasive treatment methods for renal calculi, most renal calculi can achieve good diagnosis and treatment. According to the European Association of Urology guidelines, the main treatments for renal calculi measuring < 2 cm should include extracorporeal shock wave lithotripsy (ESWL) and FURL. The main treatment for renal calculi measuring > 2 cm should include percutaneous nephrolithotomy (PCNL) [4]. If adverse effects are observed in ESWL, FURL or PCNL should be performed in patients with 1–2-cm lower pole stones. Simultaneously, we also note that not all patients with renal calculi can achieve good recovery of renal function after the removal of obstruction. Clinically, some patients’ renal functions consistently deteriorate after surgery, but these cases are rarely reported in the literature.
Pyonephrosis is a disease characterized by the pyogenic destruction of the renal parenchyma caused by the progression of infectious hydronephrosis, and in pyonephrosis, renal function is almost completely lost. Infectious hydronephrosis refers to hydronephrosis with bacterial infection. Notably, the end stage of infectious hydronephrosis can be considered as the initial stage of pyonephrosis [1]. However, there is no clear predictive model demonstrating the occurrence of pyonephrosis in patients with kidney stones. Patodia retrospectively analyzed 501 patients with kidney stones and found that some factors were closely associated with the occurrence of pyonephrosis, including larger stone volume, severe hydronephrosis, poor renal function, past history of urological surgery, and obstruction caused by other causes than stones [5]. These are considered beneficial in determining which patients with kidney stones are prone to pyonephrosis. In our study, most patients underwent more than one lithotripsy (7/8), all of whom had moderate to severe hydronephrosis, including one patient with ureteral junction stenosis due to long-term inflammatory stimulation. Therefore, for patients with these risk factors, surgery and follow-up should be performed from the initial stage of stone treatment. The patients included in this study were all diagnosed with pyonephrosis caused by stones. These patients experienced irreversible damage to the kidney due to long-term concurrent infection with stones. After several operations, the patients’ kidney functions were damaged, and the whole kidney even experienced infection, which continuously produced a chronic inflammatory response to the body. Some patients are prone to urinary tract tumors with long-term chronic stimulation of inflammation [6]. Current studies suggest that patients with long-term kidney stones are closely associated with the occurrence of urothelial carcinoma [7–9]. Therefore, for patients with complex kidney stones and a long course of calculi, attention should be paid to whether they have combined renal pelvic tumors in the course of diagnosis and treatment. In this study, a patient with pyonephrosis complicated with renal pelvic tumors was found to have suspicious lesions in the renal pelvis during first-stage PCNL operation, which is difficult to distinguish from pyonephrosis. The possible difference is that the neoplasm can bleed when the lesion is touched, while a lesion in pyonephrosis does not easily bleed. This patient was diagnosed by pathological biopsy, and laparoscopic nephrectomy was performed in a two-stage operation. Therefore, for patients with calculous pyonephrosis, specifically those with a long history, attention should be paid to the presence of combined renal pelvic tumors.
Whether pyonephrosis should be preserved is directly related to actual renal function. Regarding the judgment of renal function, most literatures take renal dynamic imaging as the basis of evaluation, and the glomerular filtration rate (GFR) is considered to be nonfunctional when it is less than 10–15 ml/min [10–12]. However, in our study, we found that 6 patients had pyonephrosis, and their GFR was between 19.4 and 35.9 ml/min. Based on the postoperative pathological analysis, calculous pyonephrosis usually has a large number of lymphocyte infiltration, severe local inflammation, a large number of renal parenchymal fibrosis, and glomerular atrophy and does not have normal filtration function. Therefore, the value of GFR alone does not reflect the real renal function of patients. Further, it cannot be used as the sole basis for kidney preservation or nephrectomy. At present, renal dynamic imaging is the most widely used method for evaluating renal function. Often, we directly focused on the final GFR values of the patients’ both kidneys, which indeed directly reflects the true renal function in nonobstructive diseases. However, when applied to the judgment of renal function in stone obstruction, renal function is usually severely impaired, and renal dynamic imaging can easily lead to the overestimation of the actual glomerular filtration function of the affected kidney [13]. At this time, we need to pay attention to the curve shape of the GFR. In general, renal dynamic imaging is divided into the perfusion phase and functional phase. When the renal blood flow function phase is not clearly developed, it is recognized as a low-level prolongation line. In fact, the kidney has no filtering function. In combination with the imaging characteristics of enhanced CT, the renal pelvis of the affected kidney is reduced, the calyx is dilated, and the cortex is thinned and resembles a bear’s footpad (Fig. 1). Hence, it is called the “bear’s paw sign” [14]. Subramanyam summarized the ultrasonographic features of 73 patients with hydronephrosis, in which the ultrasonographic diagnosis of pyonephrosis was characterized by persistent low-to-moderate internal echoes within the dilated collecting system, and concluded that ultrasonography had a sensitivity of 90% and a specificity of 97% for the diagnosis of pyonephrosis. This plays an important role in determining the occurrence of pyonephrosis based on several aspects [15].
For calculous obstructive pyonephrosis, the indication of surgical resection, besides the above judgment of renal function, we considered that the following factors should be considered equally: (A) recurrent stones and poor control of infection; (B) multiple calyx neck atresia or stenosis in the kidney, which cannot be effectively treated by endoscopy; and (C) thickening of the long ureteral wall or iatrogenic long-segment ureteral stenosis. Therefore, when the treatment effect of pyonephrosis due to calculi is not satisfactory and the infection control of the affected kidney is insufficient, PCNL or FURL should be performed again. Focusing solely on the GFR value of the affected kidney to judge renal function should be avoided. A correct surgical plan should be taken into consideration in combination with the dynamic phase curve of kidney function, kidney stones, infection, and contralateral kidney function. Retaining the affected kidney blindly may cause the patient’s condition to be delayed, increase the cost of medical treatment, and negatively affect the patient’s quality of life.
Laparoscopic treatment of pyonephrosis after multiple PCNL or FURL operations should first determine the correct timing of surgery. In the stage of acute infection, internal or external drainage should be performed first, and surgical treatment should be started at least 6 weeks after adequate drainage. In the anti-infection treatment stage, attention should be paid to the patient’s renal function and drainage of the affected kidney. For urologists, nonfunctional pyonephrectomy after endoscopic interventions remains a challenging procedure, with Duarte reporting a 72% success rate for laparoscopic resection of nonfunctional pyonephrosis alone [16].
Regarding the laparoscopic approach, although the transperitoneal approach is easy to establish, has a large operative space and evident anatomical markers, and is conveniently performed when dealing with intraoperative complications, for pyonephrosis after endoscopic interventions, considering that there may be severe adhesion between the kidney and psoas major muscle, the transperitoneal approach may be more difficult in dealing with renal hilar vessels. One patient in this group underwent a transperitoneal approach, but when dealing with renal hilar vessels, the patient was forced to undergo open surgery because of excessive bleeding. The retroperitoneal laparoscopic approach is mostly used in our center. We believe that the retroperitoneal approach has significant advantages including the following. First, with the retroperitoneal laparoscopic treatment of pyonephrosis, the abdominal cavity cannot be accessed; hence, intraoperative renal rupture can be avoided and the risk of abdominal infection is reduced. Second, when isolating the renal artery, the retroperitoneal approach is simpler than the abdominal approach due to its anatomical relationship with the renal artery. Third, in our review of 8 patients, 4 were treated after PCNL with fistula tract purulence, and with the retroperitoneal approach, it can debride the fistula tract immediately after the resection of the kidney and reduce the patient’s trauma.
It should be noted that the establishment of the retroperitoneal space is more difficult compared to the conventional retroperitoneal laparoscopic surgery because repeated endoscopy and inflammatory stimulation of pyonephrosis and inflammatory adhesion of the retroperitoneal space are often severe, and the establishment of the retroperitoneal space can easily cause unclear layers and wound bleeding, different from the establishment of pneumoperitoneum in the conventional retroperitoneal space, where we usually establish the first puncture passage by puncture expansion above the iliac crest, where there is usually a thick extraperitoneal fat as a liner, and where the inflammatory adhesion is mild. Because of the long-term and repeated inflammatory stimulation around the renal artery, it is difficult to detect the renal artery directly from the separated renal hilum, and the surgical field is unclear. Our study aimed to detect the psoas major muscle plane first, along with the psoas major muscle plane, from the lower pole of the kidney to the renal hilum for freeing, to clearly dissect the renal artery after the renal artery is disconnected. In the process of handling the renal vein, the position of the renal portal is relatively fixed, and the space is insufficient. At this time, the upper and lower poles of the kidney need to be dissected freely. After the whole kidney has a certain range of activity, the renal vein should be clearly exposed and subsequently severed. If the adhesion between the ventral and upper poles of the patient is serious, subcapsular resection can be performed.
Considering the data from our center, the operation time of pyonephrosis is generally longer than that of retroperitoneal laparoscopic radical nephrectomy, which is closely associated with repeated inflammatory stimulus, adhesions of renal hilum structure, and unclear layers caused by multiple surgical disturbances. Therefore, surgeons should have sufficient experience in performing retroperitoneal laparoscopic surgery.