Trigone

Trigone, in anatomy, denotes a triangular region bounded by three structures or openings. The term comes from the Latin trigonus, meaning three-angled. It is applied to several areas in the body, most notably the trigone of the urinary bladder and the fibrous trigones of the heart, but can be used for other triangular areas as well.

Trigone of the urinary bladder: This is a smooth, triangular patch on the interior floor of the bladder. It is bounded by the two ureteral orifices at the posterolateral corners and the internal urethral orifice at the apex. During development, the trigone forms from the incorporation of the caudal ends of the mesonephric ducts into the bladder wall. The mucosa here is relatively firm and less distensible than the rest of the bladder lining. The trigone serves as a useful anatomical landmark during cystoscopy and imaging. Infections, inflammation, or neoplasia can involve the trigone, but tumors can arise in other parts of the bladder as well.

Fibrous trigones of the heart: There are two fibrous trigones, the right and the left, which are triangular patches of dense connective tissue within the heart’s fibrous skeleton. They lie at the convergence of the valve annuli and help anchor the rings of the aortic, mitral, and tricuspid valves. By linking the valve bases, they demarcate regions of the heart and contribute to structural integrity and coordination of valvular function.

The term trigone is also used more generally for any triangular region bounded by three structures.