Minimally invasive options
In people, the treatment of choice is typically minimally invasive, consisting of extracorporeal shockwave lithotripsy (ESWL)
for nephroliths smaller than 2 cm and PCNL for nephroliths larger than 2 cm. Open surgery and laparoscopy are usually considered
necessary after other less invasive options have failed or have been deemed inappropriate. These and many other human studies
have shown ESWL and PCNL to have a minimal effect on the GFR of clinical stone forming patients, particularly when compared
with traditional surgical nephrotomy. These procedures, particularly PCNL, have been shown to be highly effective in removing
all stone fragments, as endoscopic calyceal inspection is superior for visualization and fragment retrieval.
In small animals, PCNL is considered if ESWL fails, ESWL is not available, cystine stones are present (which are ESWL-resistant)
or the stone is larger than 15 mm. PCNL has been performed in a handful of dogs to date, as well as in a cat. Typically, this
is done by using a combination of ultrasonographic, endoscopic and fluoroscopic guidance. Patient size is less of a factor
for PCNL than for ureteroscopy, as the smallest dog that had successful PCNL was only 3.1 kg.
Typically, for PCNL, the renal pelvis is accessed through the greater curvature of the kidney with ultrasound guidance using
a renal access needle. Subsequently, with fluoroscopic guidance, a sheath (12- to 30-Fr) and balloon dilation catheter combination
is advanced through the renal parenchyma into the renal pelvis over a guide wire and onto the offending nephrolith. A mini-PCNL
approach using an 18- or 24-Fr access kit is used.
Figure 2: An endoscopic image during intracorporeal lithotripsy for removal of a large struvite nephrolith. Note the large
yellow stone inside the renal pelvis. The lithotrite is fragmenting the stone into small pieces for removal.
Once the sheath is in the renal pelvis, a nephroscope is used to identify the stone or stones. If small enough, a stone-retrieval
basket is used to remove the stone. If the stone or stones are larger than the sheath, then intracorporeal lithotripsy is
used for stone fragmentation (ultrasonic, electrohydraulic or Hol:YAG laser) (Figure 2). This is all performed with fluoroscopic
(Figure 3) and endoscopic guidance. Once the stones are small enough to fit through the sheath, they are removed, and a locking-loop
nephrostomy tube (5- or 6-Fr) is left in place to allow the small hole to seal and form a nephropexy.
Figure 3: Fluoroscopic images during a PCNL procedure: A) A patient with sheath (black arrow) inside the kidney onto large
nephrolith (white asterisk). A safety guide wire is down the ureter (white arrows). B) A nephroscope (white arrow) inside
the renal sheath as the large nephrolith is fragmented (black arrowheads). C) Image after the nephrolith is removed. D) A
ureteral stent (white arrows) in place to protect the ureter.