CPAM Volume and CVR
The Congenital Pulmonary Airway Malformation Volume Ratio (previously known as the Congenital Cystic Adenomatoid Malformation (CCAM) Volume Ratio) is a sonographic indicator proposed for evaluating fetuses at risk for hydrops and possible intervention. The CVR is the CPAM mass volume normalized for gestational age using head circumference.
The CPAM volume is estimated using the formula for a prolate ellipse:
- CPAM volume = (Length × Height × Width × 0.52)
The maximal length of the CPAM in sagittal view is used to measure the length. Perpendicular to this axis at the maximal width of the lesion, the width and height of the CPAM are measured.[2]
The CVR is obtained by dividing the CPAM volume by the head circumference (measured in cm):
- CVR = (Length × Height × Width × 0.52) / Head Circumference
A CVR of ≤ 1.6 at presentation suggests the risk of hydrops is low in the absence of a dominant large cyst. Lung lesions with a CVR < 1.2 may be followed on a weekly basis. Lesions with a CVR of 1.2–1.6 are often followed twice per week depending on gestational age and CVR at initial evaluation.
A CVR > 1.6 or a CPAM with a dominant large cyst increases the risk of developing hydrops. Lesions with a CVR > 1.6 may be followed 2–3 times per week. A cyst is considered dominant if it constitutes more than one-third of the CPAM size and may increase rapidly due to fluid accumulation.
The calculator on the right may be used to estimate the CVR.
References
Design by Mark Curran, MD, FACOG.
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