(1)
Surgery, University of Melbourne, Parkville, Victoria, Australia
It is essential to have a basic knowledge of renal surgical anatomy, in particular the capsule, renal parenchyma, collecting system and vasculature.
Fig. 1.1
Basic renal anatomy for PCNL
Fig. 1.2
The peripheral microvasculature of the kidney
The track for PCRS access is comprised of two components, the extrarenal (or body wall) and renal.
Fig. 1.3
The renal and extrarenal components of the PCNL track
Anatomy
Renal
The renal parenchyma is encased by a thin firm, fibrous capsule.
Fig. 1.4
Initial resistance with the capsular needle puncture of the kidney
The capsule is felt by a slight resistance and then a “give” when the kidney is punctured by the access needle.
Fig. 1.5
Perforation of the renal capsule by the needle puncture results in a sharp small advance, felt as the “give” sign
Once the needle is within the parenchyma, it will move externally with respiration.
Fig. 1.6
External movement of the hub of the puncture needle with respiration once the needle tip has entered the kidney
The collecting system begins as calyces, which coalesce to form the infundibulum, renal pelvis, pelviureteric junction and ureter (Fig. 1.1).
The upper and lower pole calyces are usually compound; the mid zone calyces are simple. The calyces are directed anteriorly and posteriorly. The posterior calyces usually point about 30° backwards, so a puncture into a posterior calyx leads directly to the infundibulum and renal pelvis. The anterior calyces are directed more forward, so when punctured from behind, the entry is at an acute angle, which may be difficult to negotiate with dilators or rigid nephroscopes.
The only portion of the collecting system that is physically attached to the renal parenchyma is the outermost tip of the calyx at the fornix (Fig. 1.1). The infundibula and pelvis are unsupported and mobile.
Fig. 1.7
The collecting system is only attached to the kidney at the fornices, elsewhere it is mobile. This is easily demonstrated on a bivalved cadaver kidney by grasping the infundibulum with dissecting forceps, as illustrated above
It is logical and confirmed experimentally that the tip of the calyx is the safest and most appropriate entry site for percutaneous puncture and renal dilatation.
Not only is this where the only portion of the collecting system is attached to the kidney, it is also the thinnest region of renal parenchyma where there are no large renal segmental vessels, only microvasculature (Fig. 1.1).
Fig. 1.8
Needle puncture entering the tip of a calyx
The renal segmental vessels are end arteries. As a result, damage to a segmental vessel can result in haemorrhage, arteriovenous fistula, pseudo-aneurysm, or segmental infarction.
Fig. 1.9
Damage to a segmental renal artery causing haemorrhage, a fistula, or segmental infarction
There is no arterial cross circulation from one segment to another.
In contrast, the renal veins do communicate across segments, so venous injuries are less damaging.
However, as the peripheral renal parenchyma is only comprised of microvasculature and no major vessels, puncture and dilatation of this region does not cause significant vascular or renal damage.
Most percutaneous endoscopic instruments are rigid. It is logical that if they enter through the thinnest region of the kidney, intrarenal manipulation of the endoscope will occur across the narrowest fulcrum, causing the least amount of renal disruption.
Fig. 1.10
Vertical (top) and transverse (bottom) sections through the site of a renal puncture
By entering the kidney through the tip of a calyx, as an instrument advances centrally, it is separated from the segmental vessels by the collecting system and so cannot cause vascular damage.
Fig. 1.11
Renal dilator entering the tip of a calyx over a guide wire
The surgeon aims to introduce instruments within and parallel to the axis of the calyx so that they do not traumatise the collecting system or the adjacent segmental vessels.
The collecting system is muscular and dynamic.
The calyces, infundibula and renal pelvis contract.
When puncturing the kidney, “irritation” of the collecting system by the needle at the tip of the calyx can induce a “spastic contraction” of the calyx. This can often be appreciated when screening as “the half moon sign”, in which a calyceal contraction or spasm will alter the distribution of contrast within the calyx, producing a crescent or “half moon” appearance.
