New location recommended for ovarian shielding in girls

Mar 1, 2009

Where should ovarian shielding be placed when taking x-ray exams of girls? The common medical assumption that lead ovarian shields should be placed midline of the pelvis is being challenged by researchers at Oregon Health and Science University (OHSU) in Portland.

Based on the position of ovaries relative to anatomic landmarks, OHSU radiologists are recommending that lead ovarian shields be placed in a lateral position or not used at all if relevant anatomy will be obscured.

After reviewing one too many ultrasound exams of girls younger than 18 years in which the location of ovaries was not on the midline, a research team led by Dr. Dianna Bardo, assistant professor of radiology and cardiovascular medicine, decided to analyze medical images to determine their exact location. The researchers picked MRI exams to review because ovaries aren't visible on conventional projection x-ray studies; the ovaries are very hyperintense on T2-weighted MRI studies, however, making them easily identifiable.

Bardo and colleagues retrospectively reviewed all lumbar spine and a portion of pelvic MRI exams performed on girls at OHSU over 48 months starting in 2004. Their findings are published in the March issue of Pediatric Radiology (2009, Vol. 39:3, pp. 253-259).

The researchers initially reviewed only lumbar spine MRI exams, but discovered that ovaries could not be seen in the majority of exams of girls ages 13 to 18. For this reason, they expanded their search criteria to include pelvic MRI exams for this age group only. A total of 336 exams were reviewed (274 lumbar spine MRI and 62 pelvic MRI exams). Both ovaries could be identified in 174 procedures, for a total of 307 evaluated ovaries.

Ovaries reviewed by age and location

Age group	Left	Right
Newborn to 2 years	44	42
3 years to 12 years	46	42
13 years to 18 years	66	67

Measurements of the position of each ovary in relation to anatomic landmarks of the symphysis pubis, iliac crest, and anterior superior iliac spine were taken from T1 and T2 images. The researchers measured the outermost edge of the ovary to the innermost margin of the anatomic landmark.

Distances ranged from 15.8 mm to 117.2 mm (mean, 50.4) above the symphysis pubis, 0-120 mm (mean, 49.9) below the level of the iliac crest, and 8.8-106.6 mm (mean, 48.9) medial to the anterior superior iliac spine. Because the 95% confidence intervals calculated were relatively narrow for the large sample size, the authors believe that their measurements accurately reflect the true position of ovaries in the general population.

Ovaries are almost invariably positioned in the lateral aspect of the pelvis, above the symphysis pubis, just below the iliac crests and umbilicus, and very close to the anterior superior iliac spine, Bardo and colleagues noted. For this reason, ovarian shielding techniques in girls younger than 18 have been changed at OHSU to shield the lateral pelvis rather than the midline, as long as relevant anatomy is not obscured.

Because infants have a very short distance between the diaphragm, iliac crests, and the symphysis pubis, the authors strongly recommended that the entire pelvis be shielded in infants when chest radiographs are taken to prevent radiation dose exposure through scatter.

By Cynthia E. Keen
AuntMinnie.com staff writer
March 2, 2009