title: Lower-pole fluoroscopy-guided percutaneous renal access: which calix is posterior?
abstract: OBJECTIVE
  When obtaining fluoroscopy-guided lower-pole percutaneous renal access, knowledge of which calix is posterior is of paramount importance. Textbooks and peer-reviewed articles consistently refer to the most medial calix seen on fluoroscopy as posterior. We undertook this study to determine the orientation of the lower-pole calices to define the optimal site for lower-pole percutaneous renal access via a posterior calix.
  
  
  METHODS
  A retrospective review was performed of 101 renal units for patients who underwent routine contrast-enhanced abdomen/pelvic CT with delayed images for the workup of microscopic hematuria. Delayed images of the renal collecting system that were performed with patients in the supine position 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 calices in the lower pole (ie, two or three), the orientation of each minor calix (anterior facing, posterior facing), and the relative orientation of the minor calices (ie, which calix is most anterior, which calix is most posterior) were recorded. Exclusion criteria were: History of nephrolithiasis, history of renal surgery (open, laparoscopic, endoscopic, percutaneous), CT 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 (41.6%) renal units had two calices and 59 (58.4%) renal units had three calices. The most medial calix on coronal imaging was anterior facing in 95 (94.1%) kidneys, was the most anterior positioned calix in 84 (83.2%) kidneys, and was the most posterior positioned calix in 9 (8.9%) kidneys. Kidneys were then stratified by number of lower pole calices (two vs three). For the 42 renal units with two lower pole calices, the most medial calix on coronal imaging was anterior facing in 41 (95.2%) kidneys, was the most anterior positioned calix in 39 (92.9%) kidneys, and was the most posterior positioned calix in 2 (7.1%) kidneys. Of the 59 renal units with three lower-pole calices, the most medial calix on coronal imaging was anterior facing in 55 (93.2%) kidneys, was the most anterior positioned calix in 49 (84%) kidneys, and was the most posterior positioned calix in 4 (6.8%) kidneys.
  
  
  CONCLUSIONS
  For percutaneous lower-pole renal access, the most medial calix on coronal CT imaging and therefore retrograde opacification using fluoroscopy 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 calices because their posterior position and orientation provides optimal access to the collecting system for most cases. This anatomic understanding is critical for successful percutaneous nephrolithotomy.
authors.affiliation: Department of Urology, University of California, San Francisco, CA, USA. eisnerbh@urology.ucsf.edu
authors.forename: Brian H
authors.initials: BH
authors.lastname: Eisner
authors.forename: Jordan
authors.initials: J
authors.lastname: Cloyd
authors.forename: Marshall L
authors.initials: ML
authors.lastname: Stoller
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005471:Fluoroscopy; D006801:Humans; D007670:Kidney Calices / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009403:Nephrostomy, Percutaneous / Q000379:methods*; D012189:Retrospective Studies