trigones

Trigones, in anatomical usage, refers to triangular regions bounded by three landmarks within a structure. The term is applied in several contexts, with the most well known examples being the vesical trigone of the bladder and the fibrous trigones of the heart.

In the urinary bladder, the vesical trigone is a smooth triangular area on the internal floor formed by the two ureteric orifices and the internal urethral orifice. The mucosa lining the trigone is continuous with the rest of the bladder but the surface is typically smoother due to the absence of rugae. Embryologically it arises from the mesonephric ducts. Clinically, the trigone is a key landmark in urology because it marks the region through which urine exits the bladder; pathological processes such as infections or tumors can involve or affect this area and may influence symptom presentation and management.

In the heart, three fibrous trigones are described as part of the cardiac fibrous skeleton: the right fibrous trigone, the left fibrous trigone, and the posterior (or inferior) fibrous trigone. These are triangular patches of dense connective tissue that connect the annuli surrounding the atrioventricular and semilunar valves. They provide structural support for the valve rings and serve as landmarks during surgery. The cardiac trigones contribute to the electrical insulation between the atria and ventricles and are related to the location of parts of the conduction system, such as the AV node, which has clinical importance in procedures involving valve repair or catheter-based interventions.

Overall, trigones describe strategically important triangular regions across different organs, with functional and clinical relevance depending on their location.