Isotopes when written out are common nouns, and should begin with the uncapitalized element name, followed by a hyphen (not an em dash or en dash) and then the mass number. Examples are carbon-14 and uranium-235.
The central region of the kidney contains the renal pelvis, which is located in the renal sinus, and is continuous with the ureter. The renal pelvis is a large cavity that collects the urine as it is produced. The periphery of the renal pelvis is interrupted by cuplike projections called calyces.
What is an extrarenal pelvis? The renal pelvis itself is an anatomical structure normally found inside the indentation of the kidney. It is a large tubular funnel into which drains smaller tubular funnels called calyxes. The renal pelvis channels waste fluid from the kidneys to the ureter, which leads to the bladder.