A vaginal pessary is a device inserted into the vagina which can either be mechanical or pharmaceutical.
Strictly-speaking a pessary only refers to a medical device designed to be placed in the vagina to support the pelvic floor. Therefore stating vaginal pessary is tautologous although this form of words can still be seen in reports, especially when there is the possibility of confusion about the device's location.
A mechanical pessary is most commonly used to treat uterine prolapse. It is also used to treat stress urinary incontinence, a retroverted uterus, cystocele and rectocele. A bewildering array of shapes and sizes are available.
A pharmaceutical pessary is imbued with compounds that are active locally.
Pessaries are not a contraindication to performing an MRI (see MRI safety).
An understanding of the radiological appearance of these devices is useful to avoid misinterpreting them, and to be aware when they are malpositioned/mal-located.