Anatomical Terminology: Mid Inferior Pole vs. Lower Pole of the Kidney
The "mid inferior pole" and "lower pole" are NOT the same anatomical regions of the kidney. The lower pole (also called inferior pole) refers to the caudal end of the kidney, while "mid inferior pole" would refer to the middle portion of that lower pole region.
Kidney Anatomical Divisions
The kidney is divided into distinct anatomical zones that are clinically relevant for imaging and surgical planning:
The inferior pole (lower pole) represents the entire caudal portion of the kidney, positioned anterior and lateral to the superior pole 1.
The mid-renal zone (kidney midzone) is a separate anatomical region between the superior and inferior poles, which can be drained by various caliceal configurations 2, 3.
Images caudad to the renal hilum represent the inferior pole, while images cephalad represent the superior pole 1.
Clinical Significance of the Distinction
The lower pole is a complete anatomical unit with its own collecting system, typically drained by 4 or more minor calices in approximately 49% of cases 2. This region has specific clinical implications:
The lower pole collecting system has distinct anatomical features including the infundibulum-pelvic angle, infundibulum length, and number of calices that affect stone treatment outcomes 4.
Lower pole stones have significantly worse stone-free rates (25%) compared to non-lower pole locations (40%) after shock wave lithotripsy 5.
The mid-renal zone classification (groups A1, A2, B1, B2) specifically describes how the middle region of the kidney drains, which is anatomically separate from the lower pole proper 2, 3.
Ultrasound Imaging Considerations
During renal ultrasound, separate views of the superior and inferior poles are often required to adequately image the entire kidney in its longitudinal plane 1. The inferior pole specifically refers to the region visualized when angling the transducer inferiorly and laterally from the renal hilum 1.
If someone refers to the "mid inferior pole," they are likely describing the middle portion of the lower pole region, not using standard anatomical terminology. Standard nomenclature uses "upper pole," "mid-pole" (or mid-renal zone), and "lower pole" as the three primary divisions 5.