Anatomically speaking, a meatus, pronounced mee-AY-tus, is a naturally occurring body opening. Examples include the ear canal, the opening of the urethra and various openings in the nose. The word itself is derived from Latin and means a course or channel.
While the term "meatus" is used to refer to several kinds of natural body openings or canals, it is most commonly used in reference to an opening in a bone. The interior auditory meatus, for example, passes through the temporal bone of the skull. This opening allows nerves to pass from within the skull to the inner and middle ear.
There are three meatuses in the nasal cavity: superior, middle and inferior. These openings serve as air passageways and are connected to various sinus cavities. The sphenoid sinus drains into the superior meatus, and the maxillary sinuses empty into the middle. Ethnoid sinuses drain into both the superior and middle meatuses. During endoscopic sinus surgery, the endoscope moves into the sinuses through these openings.
The inferior meatus is the largest opening in the nasal passageways — in this case, "inferior" refers to its lower position in the anatomy rather than its size. It extends nearly the full length of the nose's lateral wall. The nasolacrimal canal, part of the system that produces tears, drains into this opening.
Meatal stenosis is a medical condition that occurs when the urinary meatus is constricted or narrowed, making passage of urine difficult. This condition occurs more often in circumcised males. It usually is caused by infection or irritation to the urinary meatus, and doctors theorize that the foreskin helps protect the opening from irritation. When the condition occurs in females, it usually is congenital, and it can cause urinary tract infections and bed-wetting.
Symptoms of this condition include blood in the urine, abnormalities in the urine stream's strength or direction, uncomfortable urination, and, in boys, a visibly narrow urethral opening. Constriction of the urinary opening is treated differently in boys and girls. With girls, a typical treatment includes local anesthetic followed by dilation of the opening. In boys, meatoplasty is more commonly used. Meatoplasty is an outpatient treatment, but it is more involved than dilation.
Because meatal stenosis in girls usually is congenital, dilating the opening is usually fairly straightforward. By contrast, stenosis in boys usually involves infection and scarring to the urinary opening. This scarring and other side effects of infection to the urinary tract makes correction somewhat more involved.