For many years, the treatment options of lower pole stones have been discussed controversially: Watchful waiting, shock wave lithotripsy, flexible ureterorenoscopy and percutaneous litholapaxy. Small lower pole stones <1 cm can be monitored actively. Shock waves can disintegrate the stones and are recommended for stones <1 cm. However, the stone-free rate is limited because of the particular anatomy of the lower pole. Modern flexible ureterorenoscopes can nowadays reach even anatomically unfavourable lower calyxes. For stones <1 cm good stone-free results can be achieved. For larger stones >2 cm percutaneous nephrolithotomy (PNL) is the standard treatment modality.

Objective To improve the efficacy of interstitial laser coagulation of tissue by causing a ‘bridging’ effect, using a sequential multiple‐probe procedure on an ex vivo kidney model, as only a limited area of tissue is destroyed with a single probe and the coagulation takes longer when multiple punctures are used. Materials and methods A laser beam was generated using a Nd:YAG laser and applied to kidney tissue by a diffuser tip (quartz glass cap 2 × 19 mm). For sequential laser application (SLA), three probes were placed through punctures into kidney tissue, at 5 or 10 mm apart. The laser energy was applied in different time‐energy combinations through the three probes. The effect of SLA was compared with that from one probe delivering the optimal PowerMode 180 protocol (Dornier, Germering, Germany), which represents the standard energy protocol for the clinical treatment of parenchymal organs using this laser device. An isolated porcine kidney was chosen for laser coagulation under different conditions of perfusion. The ablative efficacy was defined as the volume of necrosis per minute. Results Applying various time‐energy combinations to isolated unperfused porcine kidney caused extensive tissue ablation (5.6 mL). In trials with saline and blood perfusion for improved cooling, the necrotic volume was 2.5 and 3.9 mL, respectively (with no carbonization, 3.2 mL). Compared with a single‐probe procedure, the ablation efficacy was 10 times better with SLA coagulation. This improvement was initiated by the bridging effect: coagulation in neighbouring areas affects perfusion and convection to an extent that induces the formation of bridges of necrosis between the probes. Conclusion Tissue ablation is markedly improved by interstitial laser coagulation using a sequential multiple‐probe technique.

Patients with muscle-invasive clinical tumour stages and downstaging in cystectomy specimens represent a subgroup with significantly enhanced CSS rates. Further trials that integrate the parameters tumour size, stages cT2a vs cT2b and focality are required in order to define the independent prognostic signature of downstaging of tumour stages more precisely.