ANATOMIC AND MORPHOLOGIC DESCRIPTION OF THE RENAL PELVIS OF THE HORSE USING MAGNETIC RESONANCE IMAGING OF POLYMER CASTS, URETEROPYELOSCOPY, AND HISTOLOGY By

ANATOMIC AND MORPHOLOGIC DESCRIPTION OF THE RENAL PELVIS OF THE HORSE USING MAGNETIC RESONANCE IMAGING OF POLYMER CASTS, URETEROPYELOSCOPY, AND HISTOLOGY By Santiago Garcia Pasquel Descriptions of the equine renal pelvis in textbooks are inconsistent and unsuitable for guiding ureteropyeloscopy. To document the anatomy of the upper urinary collecting system of the horse, specifically the renal pelvis, kidneys were harvested from 10 horses and magnetic resonance imaging was performed after distension of the renal pelvis with a polymer cast material. Transurethral ureteropyeloscopy of the upper urinary tract was also performed in four horses and followed by histological and immunohistochemical examination of the renal medulla and pelvis. The equine renal pelvis was found to be a funnel-shaped cavity, flattened dorsoventrally in the craniocaudal direction. Multiple inner medullary collecting ducts (IMCDs) from the central part of the kidney open along an ~3 cm long renal crest that protrudes into the renal pelvis while IMCDs from each pole open into two long (6-7 cm), narrow tubi maximi that terminate at either end of the renal crest. The diameter of the distended tubi maximi are narrowest (~3 mm) at their junction with the renal crest. Openings of the tubi maximi could be visualized during ureteropyeloscopy in all horses and minor anatomical variation was observed. Histological examination and immunohistochemical staining for smooth muscle actin demonstrated increased amounts in a band pattern in the outer medullary region as well as at the junction of the tubi maximi with the renal crest. This study found that currently available endoscopic equipment can be used to visualize the renal pelvis and renal crest but cannot be advanced into the tubi maximi.