Pelvic organ prolapse (POP) refers to a condition in which one or more of the pelvic organs suffers descent from their normal position in the pelvis. It may be due to a congenital or, more often, acquired weakness or defect in the normal pelvic supporting structures. This leads to a widening of the gaps through which the pelvic organs communicate with the outside. Pregnancy and childbirth are the major contributors to this process.

Different organs may be involved in POP, including the urinary bladder, the uterus, the vagina, the intestines, and the rectum. More than one organ may descend at the same time. The classification of prolapse is done in the most comprehensive and repeatable manner using the POP-Q system.

Anatomical Classification

The anatomical classification describes which organ is primarily involved in the descent:

• Urethrocele: the anterior vaginal wall and urethra descend into the vaginal opening
• Cystocele: descent of the anterior vaginal wall and bladder
• Cystourethrocele: prolapse of the bladder and urethra along with the anterior vaginal wall
• Uterovaginal prolapse: descent of the uterus, the cervix, and the vaginal vault (the topmost part of the vagina)
• Enterocele: prolapse of the posterior uppermost part of the vagina, with loops of small intestine which have accumulated inside
• Rectocele: descent of the lower posterior wall of the vagina, with the rectum which bulges into it

It is not always possible to define which structures are contained in the bulge, however, especially if the woman has had previous vaginal surgery.

Classification by Involvement of Vaginal Wall

Pelvic organ prolapse may also be classified by which vagina wall is involved, as follows:  

• Anterior wall: Cystocele and urethrocele. The cystocele may be central, lateral, or combined.
• Apical wall prolapse: Enterocele, uterine prolapse, uterovaginal prolapse, or vaginal vault prolapse. May be associated with cystocele or rectocele.
• Posterior vaginal prolapse: Rectocele may be low, mid-vaginal, or high.
• Perineal body defects

Baden–Walker Halfway Scoring System

In this scoring system, the vagina is divided into six areas, two anterior, two superior, and two posterior. Each is assigned a score from 0 to 4 according to the degree of descent when the patient is straining maximally, using the hymen as a zero reference point. Notes may be added as to which site is prominent, or how much effort is needed to bring about demonstrable prolapse. The vagina may be mapped as well, to complete the description.

The lack of complete agreement between observers, and the possibility of a misplaced score pushing up the total stage, are among the factors that reduce the reliability of the system. However, the system is in common use.

The POP-Q System

The POP-Q system is coming into routine use because of its complete reproducibility. It measures the descent at 9 sites in the vagina which are described in terms of cm from the hymen, as in a tic-tac-toe pattern. The stage at each point is described as follows:

• Stage 0: no prolapse
• Stage 1: the leading part of the prolapse is more than 1 cm above the hymen    
• Stage 2: the leading part is 1 cm or less away from the hymen, either above or below it  
• Stage 3: the leading part is over 1 cm below the hymen but is at least 2 cm shorter than the total length of the vagina  
• Stage 4: the whole of the vagina has everted itself          

This system only in use by about 40% of specialists, although has excellent reliability in staging and allows comparison across time.

References

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3056425/
• http://www.nhs.uk/conditions/Prolapse-of-the-uterus/Pages/Introduction.aspx
• http://www.health.harvard.edu/family-health-guide/what-to-do-about-pelvic-organ-prolapse
• http://www.acog.org/Patients/Patient-Education-Videos/Pelvic-Organ-Prolapse