Flexible ureteroscopy has replaced Extracorporeal Shock Wave Lithotripsy (ESWL) as the most commonly performed surgical treatment of renal stones. Ureteroscopy is being adopted by a higher percentage of urologists, and this continues to rise every year worldwide. The reasons for the successful adoption of ureteroscopy include
- Excellent maneuverability
- Superb visualization with digital scopes
- Near 100% success rate of stone breakage using Holmium laser
- Being a less technically complex procedure when compared to percutaneous nephrolithotomy (PCNL)
- More definitive
- Entails wider indications than ESWL
- Has fewer contraindications
There are at last 3 known potential pathways of stone creation in humans. In the first pathway – it is suggested that there is overgrowth of stones on an interstitial plaque, most commonly calcium oxalate. Most probably these grow on Randall's plaque, which are a microscopic plaque of calcium deposited in the interstitial tissue of the renal papilla. These plaques are most probably a nidus for urinary stone formation. Large amounts of Randall's plaque are unique to idiopathic calcium oxalate stone formers. When looking at the idiopathic calcium oxalate stone formers (ICSF), all stones are most probably attached to the renal papilla, and all stones have an apatite core. As seen in figure 1.1 If this hypothesis is correct, Randall’s plaques are critical for stone formation. As plaque coverage increase, stone formation may eventually be expected to increase as well.
The second pathway suggests that plugging of the ducts of Bellini and inner medullary collecting ducts (IMCD) causes the growth of stones on the plugs or the stones grow out of expelled plugs in free solution. Growth on plugs occurs in Brushite (calcium phosphate) stones (figure 2), distal renal tubular acidosis, ileostomy and hyperparathyroidism. In cystinuria and medullary sponge kidney disease (a congenital disorder of the kidneys characterized by cystic dilatation of the collecting tubules in one or both kidneys), the plugs are mobile, and therefore, unattached stones forming in the free fluid, are the overwhelming rule.
Figure 1 – The plaque is necessary for the attached calcium oxalate stones:
Figure 2 – Endoscopic view of renal papilla from a brushite patient:
The third and last pathway supports the idea of formation in free solution. This mainly occurs in gastric bypass patients, cystinuria, ileostomy, uric acid stones, and struvite (Figure 3).
Figure 3 - Formation in free solution:
Dr. Lingeman moved on to discuss the topic of nephrocalcinosis. Nephrocalcinosis was once known as Albright's calcinosis and is a term originally used to describe deposition of calcium salts in the renal parenchyma due to various conditions. These include primary hyperparathyroidism, distal renal tubular acidosis, and medullary sponge kidney disease. This disease entity can be best identified using the ureteroscope, more than any other method.
Lastly, Dr. Lingeman discussed the topic of the need in a grading system of papillary injury. Ureteroscopy is the most sensitive method for identification of stones. The known imaging modalities, abdominal X-ray [KUB], ultrasound and non-contrast CT scan, have a sensitivity of detecting nephrolithiasis of 58-62%, 70%, and 95-100% respectively. Ureteroscopy was found to be more accurate in identifying all kidney stones when compared to non-contrast CT scans. In contrast to CT scans, ureteroscopy enables you to detail the stone appearance, including color, crystals, see whether the mechanism of formation is through the plaque or plug theory, ascertain the papillary appearance and marked heterogeneity. Therefore, there is a need for a papillary grading system, so that it can be correlated to stone composition, enable us to understand the risk of renal injury, stone recurrence, and association of this to metabolic disease. The newly formed grading system will enable the involved urologists to have a standardized common language, and will enable us to improve the collaboration between researchers. The final score of the grading system should be able to risk stratify stone formers. This score will be consist of four gradable parameters and will range between 0 to 8:
- Randall’s plaque score – grade 0 –minimal, grade 1 – moderate, grade 2 - severe
- Loss of contour – Global loss of papillary architecture. Grade 0 –mountain/hill. Grade 1 – plateau, grade 2 – valley/plain
- Pitting – This means a crater like erosion of the papillary tip. Grade 0 – no pitting, grade 1 – pitting involving <25% of the surface, grade 2 – pitting involves >25% of the surface
- Plugging score – the presence of yellow suburethral plugs, protruding from dilated Bellini duct. There will be 3 grades: 0 – no plugs, 1- 1-5 plugs, 3 – more than 5 plugs.
Presented by: James E. Lingeman, MD, Professor of Urology, Indiana University School of Medicine
References:
1. Miller N et al. BJU Int. 2009
Written by: Hanan Goldberg, MD, Urologic Oncology Fellow (SUO), University of Toronto, Princess Margaret Cancer Centre, @GoldbergHanan at the 70th Northeastern Section of the American Urological Association (NSAUA) - October 11-13, 2018 - Fairmont Royal York Toronto, ON Canada