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Lower pole fluoroscopic-guided percutaneous renal access: which calyx is posterior?
Brian H. Eisner, MD1, Jordan Cloyd, BA2, Marshall L. Stoller, MD2.
1Massachusetts General Hospital, Boston, MA, USA, 2University of California, San Francisco, San Francisco, CA, USA.

BACKGROUND: When obtaining fluoroscopic-guided lower pole percutaneous renal access, knowledge of which calyx is posterior is of paramout importance. Textbooks and peer-reviewed articles consistently refer to the most medial calyx seen on fluoroscopy as being posterior. We undertook this study to determine the orientation of the lower pole calyces to define the optimal site for lower pole percutaneous renal access via a posterior calyx.
METHODS: A retrospective review was performed of 101 renal units for patients who underwent routine contrast-enhanced abdomen/pelvic computed tomography (CT) scan with delayed images for the workup of microscopic hematuria. Delayed images of the renal collecting system performed with patients in the supine position and were analyzed for the study. Axial and coronal CT scans were evaluated by two observers, and the anatomic details of the lower pole were collected. Specifically, the number of minor calyces in the lower pole (i.e. 2 or 3), the orientation of each minor calyx (anterior facing, posterior facing), and the relative orientation of the minor calyces (i.e. which calyx is most anterior, which calyx is most posterior) were recorded. Exclusion criteria were as follows: history of nephrolithiasis, history of renal surgery (open, laparoscopic, endoscopic, percutaneous), CT scan evidence of ipsilateral renal parenchymal or collecting system lesion.
RESULTS: CT scans were analyzed for 101 renal units (50 left, 51 right). For the lower pole, 42 renal units (41.6%) had 2 calyces and 59 renal units (58.4%) had 3 calyces. The most medial calyx on coronal imaging was anterior-facing in 95 kidneys (94.1%), was the most anterior positioned calyx in 84 kidneys (83.2%), and was the most posterior positioned calyx in 9 kidneys (8.9%). Kidneys were then stratified by number of lower pole calyces (2 versus 3). For the 42 renal units with 2 lower pole calyces, the most medial calyx on coronal imaging was anterior facing in 41 kidneys (95.2%), was the most anterior positioned calyx in 39 kidneys (92.9%), and was the most posterior positioned calyx in 2 kidneys (7.1%). Of the 59 renal units with 3 lower pole calyces, the most medial calyx on coronal imaging was anterior facing in 55 kidneys (93.2%), was the most anterior positioned calyx in 49 kidneys (84%), and was the most posterior positioned calyx in 4 kidneys (6.8%).
CONCLUSIONS: For percutaneous lower pole renal access, the most medial calyx on coronal CT imaging and therefore retrograde opacification using fluroscopy is almost always anterior-facing and is the most anterior positioned in the majority of kidneys. Percutaneous lower pole puncture should be directed at the more lateral calyces as their posterior position and orientation provides optimal access to the collecting system for most cases. This anatomic understanding is critical for successful percutaneous nephrolithotomy.


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