What is the primary characteristic of an extramural ectopic ureter?

An extramural ectopic ureter is defined by its abnormal termination outside of the bladder, specifically where the ureter bypasses the bladder and opens into the urethra. This condition typically occurs when there is a developmental anomaly during the formation of the urinary system, leading to the ureter draining urine directly into the urethra rather than the bladder. This location can result in a variety of clinical implications, including urinary incontinence, as the normal storage function of the bladder is disrupted.

In contrast to this, other options describe different anatomical relationships or conditions. The opening of the ureter into the bladder is a normal configuration, while a connection directly to the renal pelvis would represent a serious malformation that is not characteristic of an extramural ectopic ureter. Lastly, fusion of the ureter with the vaginal wall describes a different anomaly altogether, which does not fit the definition of an ectopic ureter. Thus, the correct answer accurately captures the key feature of this specific type of ureteral abnormality.