Infected stones, also known as struvite calculus, are stones caused by urease-producing microbial infections, mainly composed of magnesium ammonium phosphate and carbon apatite, and account for approximately 15% of all urinary stones, and up to 38%-47% of complicated kidney stones. Infected stones grow rapidly and often fill up the renal pelvis and the calyces of the kidney rapidly. The rate of kidney function loss, stone recurrence, and patient death is high, making it a “malignant” stone disease. If left untreated, infected stones can easily lead to deterioration of renal function and fatal urogenic sepsis. The chemical composition of infected stones is magnesium ammonium phosphate hexahydrate, which is produced only by the action of microorganisms with the enzyme detoxification. Although the causes of infected stones are complex, the formation mechanism also follows the basic process of urinary supersaturation – crystal nucleation – crystal growth – crystal aggregation – crystal retention – stone formation. The prerequisite for the formation of infectious stones is the persistent urinary tract infection caused by urease microorganisms, and the necessary condition is the breakdown of urea in urine by urease produced by urease microorganisms. After urease breaks down urea, stone crystals are continuously formed as ammonia and carbon dioxide are produced and urine pH is maintained at 7.2 to 8.0. Most of the pure apatite crystals are formed within the bacteria, and the microliths formed by bacterial disintegration serve as the core of the stone. The ammonium ions produced by the decomposition of urea by detoxifying bacteria have an affinity for the charge of glucosaminoglycan, which changes the hydrophilicity of glucosaminoglycan. The mutual attraction of ammonium ions with their sulfate ions contributes to the continued enlargement of magnesium ammonium phosphate crystals, which rapidly aggregate and form stones. The crystals grown outside of the bacteria form a phosphate cover, and the bacteria enclosed within the stone become a source of recurrence of infection. Infected stones grow rapidly and usually form in 4-6 weeks, but if the urine becomes acidified, pH <6.5, the crystals will no longer form and begin to dissolve. Treatment of infected stones: Currently, it is believed that the treatment of infected stones should be mainly surgical, with the goal of complete removal of stones; drug therapy is supplementary, and only used for lithotripsy of residual stones after surgical treatment or for those who are not suitable for surgical treatment. Surgical treatment includes extracorporeal lithotripsy, intracorporeal lithotripsy and open surgery. Percutaneous nephrolithotomy (PCNL) combined with extracorporeal shock wave lithotripsy (ESWL) is indicated for the treatment of most infected stones. Most of the infected stones are treated. Open surgery should not be the first choice for treatment of cast stones, and nephrectomy may be considered when renal function is severely impaired (<20< span="">% of residual renal function). Preoperative urinary tract infection should be strictly controlled, with the goal of urinary pus cell and bacterial conversion. Nevertheless, there is still a risk of urogenital sepsis, which may be caused by the release and absorption of bacteria into the bloodstream inherent in the intraoperative stone crushing. 1. Surgical treatment: (1), ESWL: Although ESWL is the most commonly used treatment for kidney stones, ESWL is not ideal as a single treatment for deerstalker-shaped infected stones, and only 18% to 67% of stones are residue-free. Post-operatively, stone streets can form and can cause pus and sepsis due to bacterial extravasation from the stone. Nevertheless, ESWL is the least invasive surgical treatment for infected stones, and El-Assmy et al. concluded that the surface area of stones is an important factor in determining the rate of complete stone retrieval, especially for antler-shaped infected stones with a surface area of less than 380 mm2. The 2004 American Urological Association (AUA) clinical guidelines for the treatment of stone disease recommend the following protocol: when the area of cast stones is less than 500 mm2 and the collecting system of the kidney is not dilated or combined with slight dilatation, ESWL treatment alone can be used. (2), PCNL: PCNL has become the treatment of choice for infected stones, and about 90% of infected stones in clinical practice are currently treated by endoluminal surgery. In recent years, PCNL technology has been developed, and many new and improved surgical methods have been applied to clinical practice, such as multi-channel PCNL, high-power holmium laser lithotripsy, and single-incision multi-channel PCNL. The application of these techniques has led to a decrease in the overall complications after treatment of infected stones and has significantly increased the stone retrieval rate. The thermal radiation of the holmium laser, which has been used for PCNL lithotripsy in recent years, also has an antibacterial effect, which is particularly helpful in the treatment of infected stones. A recent multicenter study in Europe showed a 91% stone-free rate at 3-month follow-up after PCNL. In conclusion, PCNL is a safe, effective and minimally invasive procedure for the treatment of infected stones, with a high stone retrieval rate and few complications [14]. However, PCNL still has the problem of residual stones after surgery, and these residual stones can cause stone recurrence and are also the root cause of recurrent urinary tract infections. (3), open surgical treatment: the main open surgical approach for infected stones is anatrophic nephrolithotomy (AN), which was first introduced by Smith and Boyce in 1968. AN is currently used in patients with a stone surface area >2500m2, a severely dilated collecting system, narrowed calyces, an expected number of PCNL plus ESWL applications, obesity, and poor compliance. patients with poor compliance. (4), ureteroscopy: Although ureteroscopy is not currently advocated for the surgical treatment of infected stones, with the improvement of ureteroscopic instrumentation, this technique may even be the treatment of choice for deerstalker-shaped infected stones in strictly selected cases. establishment and correspondingly reduce surgical complications and postoperative patient discomfort. There are no reports in the literature on the use of ureteroscopy alone in the treatment of antler-shaped infected stones, but in high-risk patients with multiple comorbidities, staged ureteroscopy with PCNL may be safer and is a better alternative to PCNL. 2. Anti-infection treatment: Patients with infected stones should pay attention to the control of urinary tract infection before and after lithotripsy/stone extraction. The appropriate antibiotics should be selected according to the urine routine, urine culture and drug sensitivity test results before the operation. Since infected stones contain a large number of bacteria, the bacteria can spread to the blood through the damaged kidney tissues during surgery due to high pelvic pressure, leading to serious infection or even inducing infectious shock. Therefore, prophylactic antibiotics should be routinely administered during PCNL, while minimizing the operation time and keeping the renal pelvis as low pressure as possible. Intraoperative pelvic urine and stones should be kept for bacterial culture, and stone composition analysis should be performed if available. Complete removal of the residual stone or at least its adequate crushing is a prerequisite for effective control of urinary tract infection and stone recurrence. Because bacteria are usually present in the interstitial space inside the stone, antibiotics do not penetrate easily if the residual stone is >10 mm. A foreign study found that 78% of patients with >5mm residual stones experienced progressive stone growth even when sensitive antibiotics were applied. The bacteria that cause infectious stones are mostly Aspergillus chimaera, and penicillin and ampicillin are commonly used clinically, which can effectively control 90% of various Aspergillus species. The standard oral ampicillin regimen reduces bacterial urease production by 99%, thereby retarding stone growth and inhibiting stone recurrence. Therefore, long-term postoperative antibiotic therapy is usually used to control infection and prevent stone recurrence, typically requiring more than 3 months of use. In addition, long-term intermittent bacteriological monitoring is also necessary, which should be reviewed once a month after discontinuation of antimicrobial therapy, and changed to once a quarter after 3 months, and maintained for at least 1 year. 3. Pharmacological treatment: (1), urinary acidifier: the dissolution of infected stones is highly dependent on the pH of urine, and the solubility of stones increases when the urine is acidified with pH <6.5. Hesse et al. concluded that the goal of urinary acidification is pH 6.2, which is conducive to dissolving residual stones and preventing the formation of new stones; they treated 19 cases of active infected stones with levomefolate, and the 10-year recurrence rate was only 10% They treated 19 cases of active infected stones with levomethionine and the 10-year recurrence rate was only 10%. L-methionine is an effective acidifier, which can be metabolized to hydrogen ion and sulfate. 1500mg of L-methionine single dose treatment for 8h can significantly reduce urine pH to 6.0~6.2. (2), urease inhibitor: ammonia production after urea decomposition is the main cause of infectious stone formation. Inhibition of urease activity can stop stone growth or prevent the formation of new stones, but cannot remove the residual stones that have grown. Acetoxime acid (AHA) is one of the most studied urease inhibitors. The initial dose of AHA is 250 mg. 2 times/d for 3 to 4 weeks. It is a non-reversible, non-competitive inhibitor that prevents urea breakdown, acidifies the urine, and prevents the formation and recurrence of infectious urinary stones. Combined with antibiotics, it can improve the efficacy. The drug is administered immediately after lithotripsy or extracorporeal shock wave lithotripsy to help dissolve residual stone fragments.