Which procedure involves the introduction of a catheter into a body cavity or organ to inject or remove fluid?

The procedure that involves the introduction of a catheter into a body cavity or organ to inject or remove fluid is catheterization. This technique is commonly used in medical situations to either drain fluids from certain areas of the body or to deliver medications directly into the body. For example, urinary catheterization allows for the drainage of urine from the bladder, which can be critical in patients who are unable to void on their own.

While cystoscopy is a specific procedure that involves inserting a scope into the bladder for diagnostic or treatment purposes, it does not specifically refer to the use of a catheter for fluid manipulation. Hemodialysis involves using a machine to filter waste from the blood, typically through a vascular access but does not primarily focus on the introduction of a catheter for fluid removal in the same way. Hydronephrosis, on the other hand, refers to a condition where urine builds up in the kidneys due to an obstruction and is not a procedure. Therefore, catheterization is the most fitting choice in this context.