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The navicular fossa of urethra or fossa navicularis urethrae in Latin (‘navicular’ meaning boat-shaped) is the distal dilatation of the lumen of the spongy urethra present in the glans of the penis. It lies just before the external urethral orifice, a 6mm long sagittal slit (narrowest part of the urethra) bound by small labium on each side.
This fossa belongs to the anterior spongy portion of the male urethra. It is surrounded by erectile tissue (the corpus spongiosum) of the penis. The spongy urethra begins at the end of the membranous part of the urethra, and extends till the end of the penis, to the external urethral orifice. In the flaccid penis, it is about 15 cm long. It starts near the first urethral bend, as the bulbar urethra, the widest part of the urethra, where both the bulbourethral gland and duct open. The urethra then curves a second time downwards as the penile urethra. This part is a narrow transverse slit when empty, and 6mm in width during urinary passage. At its termination point, it expands into the navicular fossa within the glans and ends as the external urethral orifice.
Histologically, numerous small mucous urethral glands lie in the submucosa of the urethral epithelium, especially in the bulbar and distal penile portions. Moreover, various lacunae are present, the largest being the lacuna magna, which is located in the roof of the navicular fossa.
Anterior urethral strictures, including navicular fossa strictures, are a common problem faced by urologists. They are typically caused by instrumentation and prolonged catheterization, but can be secondary to infection (like in gonococcal urethritis) on rare occasions. This manifests clinically as poor urinary stream, and bladder hypertrophy in severe cases.
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