Lacuna magna of male urethra

In male urethra the lacuna magna (also termed  Guérin's sinus) is a congenital large recess, horizontal to the urethra, located on the dorsal part of the navicular fossa of penis.The lacuna magna is separated by a fold, the valve of navicular fossa (Guérin’s valve).

The lacuna magna is a congenital anomaly present in 30% of male, resulting from an incomplete fusion between the ingrowing ectoderm at the tip of the penis and the glandular urethra.