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Mathematical Note on CVR

CVR estimates lesion volume using the prolate ellipsoid formula: Length × Width × Height × 0.52. Because many CPAMs are irregular, multilobar, or asymmetric, this is an approximation rather than a direct measurement of true lesion volume.

CVR also divides estimated lesion volume in cm³ by head circumference in cm, so it is not a dimensionless ratio. A changing CVR may reflect true lesion growth, lesion-shape approximation, and the way fetal size is normalized.

Accordingly, CVR should be interpreted as a historical clinical risk marker used in the published literature, not as a perfect growth-normalized measurement. QLI and MSA are included as adjunctive measurements of residual lung size and mass effect.

Classic CPAM Volume Ratio (CVR)

This section preserves the original CVR calculation for compatibility with published CPAM literature and fetal-center workflows.

The CPAM volume is estimated as a prolate ellipse:

• CPAM volume = Length × Width × Height × 0.52

The classic CVR is then:

• CVR = CPAM volume / fetal head circumference

Show CPAM ultrasound illustration

A classic CVR > 1.6 has historically been used to identify fetuses at increased risk for hydrops. In a single-center series, Fabietti et al. reported CVR ≥1.25 as associated with fetal-therapy requirement; Peters et al. reported lower CVR thresholds associated with postnatal respiratory support. These thresholds should be interpreted with gestational age, lesion type, mass effect, hydrops, and center-specific practice rather than used as stand-alone directives.

Serial CPAM Volume Trend

The optional trend section compares a prior CPAM volume with the current calculated volume and reports the percent change and, when gestational ages are entered, the approximate percent change per week.

A large increase should be interpreted with CVR, MSA, hydrops, cyst type, and residual lung metrics.

Lung Compression and Mass-Effect Inputs

QLI may be entered when the right or left fetal lung area is traced at the four-chamber view. Select the lesion side so the output can identify the contralateral residual lung; for a left CPAM the contralateral lung is right, and for a right CPAM the contralateral lung is left.

• QLI-R = right lung area / (HC/10)²
• QLI-L = left lung area / (HC/12)²

Mediastinal shift angle / cardiomediastinal shift angle is included as an objective mass-effect marker. In CPAM, increasing cardiomediastinal shift angle has been associated with adverse perinatal outcomes and hydrops. A separate ultrasound MSA paper in isolated left CDH described drawing the baseline line from the posterior vertebral body midpoint to the mid-posterior sternum and a second line from the same vertebral point tangential to the lateral wall of the right atrium. In that CDH cohort, control median MSA was approximately 19°, nonsurvivors had higher MSA than survivors, and the best survival-discrimination cutoff was 43.7°. This CDH threshold should be displayed as background literature only, not as a validated CPAM cutoff.

References

Design by Mark Curran, MD, FACOG.

All calculations must be confirmed before clinical use. Results are not a substitute for clinical judgment or local fetal-treatment center protocols.