Regarding flexible ureteroscopes the following is true:
Answer D
Most distal ureteric stones can be accessed with a rigid ureteroscope where surgical treatment is indicated. Flexible ureteroscopes facilitate the treatment of stones in the proximal ureter and pelvicalyceal system of the kidney. On the other hand, for distal ureteric stones flexible ureteroscopes are unwieldy and may easily slip out of the ureteric orifice.
Technological advances over recent years have led to the development of increasingly thin ureteroscopes that also provide exceptionally high resolution images. For example, the Stortz Flex-X® shaft is 8.5 F which tapers to 7.5 F at the tip. A single lever control allows 270° active deflection of the tip in both upwards and downwards directions. The Olympus URF-P5® has a very slender tip that measures only 5.3 F. It has a maximal upward deflection of 180° and downward deflection of 275° to aid access to the lower pole. The working channels for most flexible ureteroscopes are 3.6 F.
The new digital flexible ureteroscope incorporates a distal video sensor and LEDs for illumination and therefore do not rely on fibre optics for light and image transmission. This results in better image quality although the shaft size and tip size are relatively larger. Furthermore, because of this digital ureteroscopes have limited manoeuvrability of the distal tip compared to fibre-optic flexible ureteroscopes. Single-use flexible ureteroscopes have been on the market since 2015, and are made by a number of companies. There are digital single-use ureteroscopes available.
The following are acceptable first-line treatments for a 1.5 cm renal pelvic stone in a patient with a normal contralateral kidney, except:
Answer E
A patient with a large stone in the renal pelvis should be fully counselled regarding the treatments that are available to them. A surveillance approach is seldom appropriate for a stone of this size given the high risk of potential complications. For patients with asymptomatic renal stones smaller than 1.5 cm, observation may be appropriate if they are fully informed of the risk of experiencing a symptomatic episode and the potential need for intervention. For example, in a cohort study that included 107 patients, the cumulative 5-year incidence of a symptomatic episode was 48.5%. On the other hand, a prospective randomised controlled trial that compared surveillance with ESWL for small asymptomatic calyceal stones found no significant differences in stone-free rate, quality of life, renal function, symptoms or hospital admissions. However, surveillance was associated with a greater risk of needing more invasive treatment.
For a stone of this size (1.5 cm) located in the renal pelvis or upper or mid-zone calyces, ESWL may be effective but the patient should be advised that more than one treatment may be required. ESWL should not be considered first-line treatment for stones larger than 1.5 cm situated in lower pole calyces because of unfavourable outcomes. Similarly, stone size is inversely proportional to the effectiveness of flexible ureteroscopy and patients with large renal stones should be warned of the potential need for a staged procedure.
PCNL should be considered for stones larger than 2 cm because of reduced effectiveness of ESWL, the potential need for multiple treatments and the increased risk of complications such as colic and steinstrasse. PCNL may also be appropriate for a 1.5-cm stone in the renal pelvis for a patient who desires a single treatment and accepts the greater risk of significant morbidity compared to ESWL or URS. Laparoscopic or open endopyelotomy is not recommended for stones smaller than 2 cm and is generally reserved for special cases such as large stone burdens, previous failed PCNL, obesity or renal anatomical abnormalities.
The following are true of non-metallic ureteric stents, except:
Ureteric stents may be used to relieve ureteric obstruction or be inserted prophylactically where obstruction is anticipated; for example, prior to ESWL for large (>2 cm) renal stones or after ureteroscopy. Indications for stenting following ureteroscopy may be remembered using the acronym SPOILED (Solitary kidney, Perforated ureter, Obstructed kidney/Oedema, Infection, Large residual stone burden, Elective second procedure anticipated, Dilatation of ureteric orifice to more than 10 F).
Pyonephrosis may be relieved with either a ureteric stent or percutaneous nephrostomy (PCN). One of the advantages of PCN is that it may be inserted under local anaesthesia thereby obviating the need for general anaesthesia in a patient who may be unstable due to sepsis or hyperkalaemia. That said, some clinicians will place stents without a GA, especially in women. Furthermore, a PCN may require less instrumentation of the urinary tract and reduce the risk of exacerbating sepsis. On the other hand, PCN requires the skills of an experienced interventional radiologist and where this expertise is not available a retrograde stent inserted by an experienced urologist may be a better option. The literature to date supports both methods of decompression.
Pearle randomised 42 patients with obstructing ureteric calculi to either PCN or retrograde ureteric stent. There were no significant differences in time to resolution of fever or white cell count. There was one failed PCN which was salvaged with a retrograde stent. Length of stay was longer for PCN but ureteric stent was twice as expensive. In another randomised controlled trial Mokhmalji found that PCN was superior to retrograde ureteric stent insertion. Failure rate was lower (0% vs. 20%), need for prolonged antibiotic therapy was reduced and PCN dwell time was less than for retrograde stents.
Ureteric stents may encrust rapidly in susceptible individuals but some may be left in-situ for one year; for example, the Percuflex® stent.
A systematic review and meta-analysis of five randomised placebo-controlled trials that included 461 patients suggested that administration of alpha-blockers reduced urinary symptom and body pain scores in patients with ureteric stents.
Enteric (secondary) hyperoxaluria can occur as a result of the following, except:
Answer C
Hyperoxaluria may be classified as primary, enteric or idiopathic. Primary hyperoxaluria (Types I and II) is inherited as an autosomal recessive condition that causes defective metabolism of glyoxalate in the liver and excess levels of endogenous oxalate. Enteric hyperoxaluria may occur in patients with functionally or anatomically abnormal small bowel. Oxalate normally complexes with calcium to form an insoluble salt that is excreted in the faeces. However, in conditions such as inflammatory bowel disease or after small bowel resection, the malabsorption of fatty acids leads to the saponification of calcium resulting in increased oxalate absorption from the colon. Similarly, a low-calcium diet encourages the absorption of oxalate from the bowel and should not be recommended to patients who form calcium oxalate stones.
Ethylene glycol (anti-freeze) induces hyperoxaluria and is commonly used in experimental animal studies to investigate calcium oxalate urolithiasis. Ascorbic acid (vitamin C) is converted to oxalate in the liver and may cause hyperoxaluria.
Oxalobacter formigenes is an anaerobic bacterium which colonises the large intestine of humans and causes the degradation of oxalate. It is important in the metabolism of calcium oxalate and its absence in the intestine following treatment with broad spectrum antibiotics such as quinolones may increase the risk of calcium stone formation.
The following are true of extracorporeal shock wave lithotriptors, except:
Answer B
The HM1 (Human Machine 1) lithotriptor was developed in 1980 by the German aerospace company Dornier following research into the effects of shock waves on metal parts of supersonic aircraft. Four years later, the HM3 lithotriptor was introduced into clinical practice and remains amongst the most effective devices to fragment renal calculi. Its main drawback is that it requires general anaesthesia and immersion of the patient in a water bath. The shock waves are generated when a high-voltage electrical current passes across an underwater spark-gap electrode, creating a vaporisation bubble, which then rapidly collapses. The shock waves are focussed by an elliptical dish, angulated to avoid interference of the bubbles with transmission of the shock wave energy through the water to the patient.
Second-generation lithotriptors commonly use piezoelectric or electromagnetic generators as the energy source. These devices are more portable that the electrohydraulic lithotriptors such as the HM3 machine. In electromagnetic lithotriptors, such as the Stortz Modulith®, electrical energy applied to a magnetic coil results in the generation of a shock wave. Shock waves are focussed to a small focal zone (F2), which has the advantage of minimising collateral damage but may compromise fragmentation rates as the kidney and stone move with respiration. Shock wave generation in piezoelectric lithotriptors, for example the Wolf Piezolith 3000®, is achieved through the application of electricity to multiple ceramic crystals arranged around a hemispherical dish.
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