Trigonometric Concept of Fluoroscopy-Guided Percutaneous Renal Access

Dear All

Recently the attached write up was published by Darlington et al and as requested by Dr. Venugopal Sir I am attaching a small write up on the important aspect of puncture technique in fluoroscopy guided PCNL in  prone position

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  • Gyanendra Sharma
    Gyanendra Sharma
    05 Jul 2020 04:16:35 PM

    Percutaneous renal access is a key step for a complication free PCNL. It is the step which needs a good degree of learning curve to master especially for urologists who follow the fluoroscopy guided punctured technique.

    The three main steps needed for a good access are—Determining the site of skin puncture, determining the angle  of puncture and determining the depth of puncture. The Bull’s eye technique helps to determine the site of puncture and also determines the angle of puncture. However in the Triangulation technique often the urologists decides these two aspects based on experience

    The first paper describing how to determine the site of skin puncture in fluoroscopy guided triangulation technique was published in 20091.  Later on an extension of the same concept was used to describe how to determine the angle and how to calculate the depth of puncture. These articles were basically using mathematical principles2.  A similar principle is also described in a video by ESUT3.

    A recent write up by Darlington et al also uses Trigonometric principles to determine the angle and depth of puncture.

    They have described determining the site of puncture as was described by Sharma et al and then calculated the depth using the principle that The distance BC= Sin300 which is BC=2 AB i.e the depth is twice the length of the line AB.

    Theoretically it looks appealing and as the authors have described it is more suitable in obese patients where the back is flat and the hypothetical triangle which is formed is closer to a right angled triangle. The authors have albeit not mentioned how often did they get their calculations right in the estimation of depth

    Interestingly, this concept was first described in 1998 by Dr. M.M.Bheri from Vishakhaptnam. He had described it for only the Bull’s eye technique4.

    Darlington et al have extended its use for the triangulation technique. They have even described that if you rotate the C arm to 450 towards the surgeon and determine point B then the depth will be Distance AB x 1.414. However, very few C arms used by Urologists can be rotated by 45.

    Kyriazis et al3 in their educational video have stated that the depth can be measured by the formula—(Distance AB x 12) divided by 6.28

    Though all this looks very appealing I would like to mention that it is oversimplification of a complex thing.

    ·         The back is never straight so that the chances of getting a right angle triangle are never 100%

    ·         The hydronephrosis due to stone disease will not follow fixed rules and develop in a particular way. The calyces may or may not be dilated

    ·         I always use a protractor to measure the angle of puncture(as per the Hybrid Technique) and have found the angle to vary from 50—70 degrees

    ·         The calyx which is determined as appropriate for a puncture is marked with the C arm at 0 degree and after rotating it by 30 degrees towards the surgeon. The site of puncture and the angle of puncture thus determined should be done in the same phase of respiration. If there is discrepancy here then the entire idea of forming a triangle closer to a right angled triangle is lost

    ·         The classic antero posterior orientation of calyces is seen only in the midpole (in 98% of cases). The lower pole has a very complex arrangement of calyces while  the calyces in the upper pole are always posteriorly directed and the lateral calyx of the upper pole is preferred for puncture5


    Personally I feel that knowing the site of puncture and the angle of puncture i.e the trajectory of the needle are important. Once the trajectory is known that the needle can be approached towards the target calyx in a straight line, maintaining the same phase of respiration in which the site of puncture was marked and angle determined. The feel of puncture can be definitely appreciated by the tactile feedback.

    In the initial learning phase calculating the depth can serve as a guide so that one does not overshoot the target. Another area where calculating the depth is useful is in obese patients to determine whether the standard amplatz sheath or a longer amplatz sheath will be needed

    I hope this will encourage the masters of PCNL to give their views , expert comments and guidance of the topic of Percutaneous renal access in this forum


    1.       Sharma G, Sharma A. Determining site of skin puncture for percutaneous renal access using fluoroscopy guided triangulation technique. J Endourol. 2009;23:193–5.

    2.       Sharma G, Sharma A: Determining the angle and depth of puncture for fluoroscopy-guided percutaneous renal access in the prone position. Indian J Urol. 2015, 31:38-41.

    3.       Kyriazis, Iason & Liatsikos, Evangelos & Sopilidis, Odysseas & Kallidonis, Panagiotis & Skolarikos, Andreas. (2017). ESUT educational video on fluoroscopic guided puncture in PCNL: All techniques step by step. BJU International. 120. 10.1111/bju.13894.

    4.       Bheri MM. Estimating the depth of puncture in percutaneous nephrolithotomy: an alternative approach, British Journal of Urology (1998), 81, 620–621

    5.       Sharma GR, Maheshwari PN, Sharma AG, Maheshwari RP, Heda RS, Maheshwari SP: Fluoroscopy guided percutaneous renal access in prone position. World J Clin Cases. 2015, 16:245-264. 10.12998/wjcc.v3.i3.245

  • S K PAL
    S K PAL
    06 Jul 2020 12:15:59 AM

    Dear all,

    This article has raised very relevant and pertinent issue but attempted to solve them in an oversimplified manner.  Advantages and complexity of triangulation technique are very well explained and acceptable. Various points during practical execution of this technique to be taken into consideration are -
    1. A proper puncture is not just landing into the targeted calyx from any direction. That can very well be achieved just by ultrasound guidance.First and foremost consideration is to reach to the targeted calyx in such a manner , so that further progress through the infundibulum is well aligned in a straight line. There are considerable anatomical variations in the direction and angle of infundibuli. This alignment may require some change of puncture site from the selected point on the skin.  
    2. At times , marked skin puncture site at 30 degrees ,falls on to or very close to the rib or iliac crest, which will not allow entry or free movement of the instruments. This will necessitate  change of the skin puncture site proximally or distally, and calculation of angle and depth will fall haywire. 
    3. Human body countours are not in straight lines as in geographical designs and are extremely variable.
    4. Kidneys keep moving with respiration .
    5. The puncture may get started exactly at 30 degrees as planned, but may get altered by 5 to 15 degrees while the process is in progress. This will change the depth significantly..

    Ultimately, triangulation method is certainly a better and ideal method to achieve a perfect puncture. It reduces radiation exposure to operator's hands. There is entry on the lateral aspect of renal parenchyma and there is no torque during progress of instruments, thereby producing minimal blood loss.  It is a far superior approach as compared to easy to learn short cut called -"Bull's eye technique".

    Mathematical calculations might be fair as guide lines ,But, there are so many variations and therefore no short cuts and it has to be mastered by persistence, dedication and experience. Once mastered - PCNL becomes a piece of art to enjoy. 

  • Nitesh Jain
    Nitesh Jain
    07 Jul 2020 01:24:47 PM

    there are different ways to bell the cat and no one way is full proof, when stuck people who purely does triangulation or free hand resort to bulls eye and bulls eye group when the puncture is very high resort to triangulation. the technique that suits you most, you are trained and giving you the result is the best. proponent of each will claim superiority over other with some subtle difference.  calyceal anatomy are not a fixed structure and varies from individual to individual. 

    human body cannot be equated to any mathemetical calculation as the anatomy, contour and disease burden varies from individual to individual. i feel learn all the technique, do the best what suits you and fetches you the best result ultimately what matters is the end result. 

    my take on two technique 

    Bulls eye -

    1. Easier to learn

    2. Short tract
    3. Easier manouverility
    4. Chances of supracoastal puncture more
    5. Easier to puncture any calyx
    6. Puncture depth can be assessed

    Triangulation :

    1. Most of the time puncture is subcoastal
    2. Longer tract
    3. Little more difficult to learn
    4. Manouerverility is less as tract are longer
    5. Most of the time preferred calyx is LC
    6. Once you master this than it is easier to learn supine

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