The anatomical structure of fused renal pyramid and its imaging findings in ultrasound and computed tomography

Objective To analyze the anatomical structure and distribution of the fused renal pyramid (FRP) in cadaveric kidney, and discuss its appearances by CT and ultrasonic examinations. Methods From June 2018 to September 2018, 108 cadaveric kidneys were proceeded for regional anatomy. The distribution and anatomical manifestations of FRP was recorded. The renal pyramid was sliced and HE stained to explore the vascular distribution in FRP. From October 2018 to January 2019, ultrasound imaging data of 112 patients with 224 kidneys were collected, including 60 males and 52 females, age (39.0±15.1), ranging from 16 to 73 years old. The renal imaging data of 89 patients and 178 patients with enhanced renal CT were collected, including 48 males and 41 females. Age (45.4±13.6), ranging from 23 to 69 years old. The imaging findings of FRP in ultrasound and enhanced CT was summarized. Results In cadaver kidneys, the proportion of FRP in upper and lower calyces was 68.6% (74/108) and 64.8% (70/108), respectively, higher than that in middle calyces 34.3% (37/108). In the middle group, the incidence of mild fusion was 39.0% (16/41) and severe fusion was 48.8% (20/41). The incidence of fusion of two renal pyramidal structures was 90.2% (37/41). HE staining showed that the boundary between the artery in FRP and the surrounding renal pyramidal was unclear, and the protection of connective tissue was lacking. In Ultrasound, the FRP presented as a large trapezoidal hypo-echoic area with red and blue color signals in doppler mode. In ultrasound, the incidence of FRP was 18.8% (42/224). In enhanced CT, the FRP presented as enhanced cord-like high density shade in large low density area in cortex phase. In enhanced CT, the incidence of FRP 27.5%(49/178). Conclusions The FRP is a common structure in human kidney. The arteries localize within the FRP and are absence of sufficient connective tissue protection which are different from normal arteries. Ultrasound and enhanced CT have recognition ability for FRP. Key words: Kidney diseases; Fused renal pyramid; Anatomical structure; Percutaneous nephrolithotomy; Ultrasound; Computed tomography