The skin-to-calyx distance measured by renal ct scan and ultrasound

Abstract

ARTICLE INFO ______________________________________________________________ ______________________Purpose: We developed a stereotactic device to guide the puncture for percutaneous nephrolithotripsy, which uses the distance from the target calyx to its perpendicular point on skin (SCD) to calculate the needle´s entry angle. This study seeks to validate the use of measurements obtained by ultrasound (US) and computerized tomography (CT) for needle´s entry angle calculation and to study factors that may interfere in this procedure. Materials and Methods: Height, weight, abdominal circumference, CT of the urinary tract in dorsal decubitus (DD) and ventral decubitus (VD), and US of the kidneys in VD were obtained from thirty-five renal calculi patients. SCD obtained were compared and correlated with body-mass index (BMI). Results: BMI was 28.66 ± 4.6 Kg/m 2 . SCD on CT in DD was 8.40 ± 2.06cm, in VD was 8.32 ± 1.95cm, in US was 6.74 ± 1.68cm. SCD measured by US and CT were statistically different (p < 0.001), whereas between CT in DD and VD were not. SCD of the lower calyx presented moderate correlation with BMI. Conclusion: SCD obtained by CT in ventral and dorsal decubitus may be used for calculation of the needle´s entry angle. SCD obtained by US cannot be used. A rule for the correlation between BMI and the SCD could not be determined.

Use of a vegetable model as a training tool for PCNL puncture

“…measured the skin to calyx distance on dorsal CT scans to be 7.85 cm in the upper calyx and 9.25 cm in the lower calyx. [ 5 ] However, these patients had a mean body mass index of 28.66 and an abdominal girth of 100.79 cm and were, therefore, much larger than our average patients. Licheng describes mean puncture depths to be 52.54 cm on standard dose CT.[ 6 ] The flexibility of our model allows a surgeon to choose the size of the vegetable on his own.…”