Testicular Volume

Definition The volume of the testes.

Landmarks The length and width of the testis can be measured along a vertical axis between the upper and lower pole of the testis and at the broadest width.

Position The individual should be standing upright or lying supine.

Instruments The size of the elliptical shaped testis is most easily estimated by palpation and comparison with standardized graded ellipsoid models of different volume sizes (Fig. 10.8). Since Prader developed and standardized these volume models, they are often referred to as "Prader beads." Several alternative methods for testis measurement are available, including blunt calipers, a tape-measure, or straight ruler, or the measurement may be made using ultrasonography.

Remarks Comparative palpation with the orchidometer of Prader is a quick and fairly accurate way to estimate testicular size (Fig. 10.9). The volume in milliliters is clearly printed on each of the elliptical models. At young ages, intermediate volume size models can be obtained (0.5, 1.5, and 2.5 mL size), and very large volume size models have also been developed for macro-orchidism.

Figure 10.8 Prader orchidometer.

Figure 10.8 Prader orchidometer.

The use of a tape-measure or a straight ruler to determine the longest and widest diameters is less accurate. When these linear measurements are used the testicular volume must be calculated from comparison with age-matched normals. The calculation is made using the formula for ellipsoid volume:

Testicular volume = 0.71 length2 width

If volumes are calculated or estimated, they should not be compared with the curves based on the measurements obtained from the orchidometer of Prader, because the calculation usually gives larger estimates of testicular volume. Only one method should be used to follow any individual patient over time and for comparison with other normal standards such as bone age (Fig. 10.10).

Testicular volumes for Japanese and Swiss males are compared Fig. 10.11.

Ultrasound measurements of testicular length and width have been utilized and seem to give the greatest accuracy and consistency of testicular volume.

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