What is diameter?

Diameter are:

  • - 1. A straight line passing through the center of any circular anatomic structure or space; frequently used to specify certain dimensions of the female pelvis and fetal head
  • - 2. The distance along such a line
  • - 3. The thickness or width of any structure or opening.

anteroposterior d. of midpelvis The distance between the pubic symphysis and sacrum at the junction of the fourth and fifth vertebrae; it is on the plane of least pelvic dimensions.
anteroposterior d. of pelvic inlet See diagonal conjugate and true conjugate, under conjugate.
anteroposterior d. of pelvic outlet The distance between the lower rim of the pubic
symphysis and the sacrococcygeal junction. Sometimes the tip of the coccyx is used for the posterior point.
biparietal d. The greatest transverse diameter of a skull; it extends from one parietal
bone to the other; in the fetus at term it usually measures 9.25 cm.
bitemporal d. The distance between the two temporal sutures of the fetal skull at term, usually around 8 cm.
interspinous d. The transverse diameter of the midpelvis between the two ischial
spines; usually the smallest diameter of the pelvis.
oblique d.’s of pelvis Of the inlet: two diameters, each measured from one sacroiliac joint to the opposite junction of the ischial and pubic rami. Of the outlet: the distance from the midpoint of the sacrotuberous ligament to the opposite junction of the ischial and pubic rami.
occipitof rontal d. The diameter of a skull from thefrontal bone between the eyebrows to the prominent portion of the occipital bone.
occipitomental d. The distance of a skull from the chin to the most prominent portion of the occipital bone.
suboccipitobregmatic d. The diameter of a fetal skull at term from the middle of the large fontanel to the under surface of the occipital bone, just where it joins the neck.
transverse d. of pelvic inlet The greatest distance between opposite sides of the pelvic
brim.
transverse d. of pelvic outlet The distance between the two ischial tuberosities.

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