Normal Presacral Space Size on Barium Enema in Children
The presacral space (also called the retrorectal space) is the soft-tissue interval between the posterior wall of the rectum and the anterior surface of the sacrum. Accurate measurement on barium enema is important because widening of this space can be an early or sole radiographic indicator of perirectal disease in the pediatric population.
Normal Reference Values
| Age | Measurement |
|---|---|
| 0-15 y/o | <5 mm |
Clinical Significance
In children aged 0–15 years, a presacral space exceeding 5 mm is considered abnormal. Because the rectum is normally held in close apposition to the sacrum, any process that displaces the rectum anteriorly — whether inflammatory, infectious, or neoplastic — will widen this interval. Early recognition prevents diagnostic delay in conditions that require prompt treatment.
Measurements should be interpreted in clinical context, as technical factors such as bowel distension and patient positioning can introduce variability. A mildly widened space in isolation warrants correlation with clinical history and, when necessary, cross-sectional imaging for further characterization.
- Granulomatous colitis (Crohn disease) — perirectal inflammation and fibrosis widen the space
- Ulcerative colitis — mural thickening and perirectal fat proliferation
- Presacral abscess or pelvic infection — fluid or phlegmon displaces the rectum
- Sacrococcygeal teratoma or presacral mass — congenital or neoplastic lesions occupying the retrorectal space
- Lymphoma or metastatic adenopathy — nodal enlargement in the perirectal region
Reference: Eklf O, Gierup J. The retrorectal soft tissue space in children: normal variations and appearances in granulomatous colitis. Am J Roentgenol Radium Ther Nucl Med. 1970;108
Imaging Notes
On barium enema, the presacral space is measured as the perpendicular distance between the posterior rectal wall and the anterior cortex of the sacrum, typically at the level of S3–S4. The bowel should be adequately distended to ensure the posterior rectal wall is clearly delineated; underdistension can artifactually simulate widening. A true lateral projection is essential to avoid obliquity-related measurement error.
Although barium enema was the historical standard for this measurement, MRI pelvis now provides superior soft-tissue characterization when a widened presacral space is detected, allowing identification of the underlying cause and extent of disease.