CLINICAL TOOL
CPAM Volume Ratio (CVR) Calculator
Calculate the CPAM Volume Ratio (CVR) to assess the risk of fetal hydrops and determine the need for prenatal intervention in Congenital Pulmonary Airway Malformations.
About this page
This is a clinician-reviewed evidence brief, not an interactive calculator. It summarises the guideline logic our subspecialists apply when managing these cases every day. For a case-specific assessment, request a consultation or refer your patient.
Clinical Purpose
To quantify the size of a fetal lung mass (CPAM/CCAM) relative to fetal size (head circumference) to predict the risk of hydrops fetalis and guide management decisions (e.g., steroids, shunting, or ex utero intrapartum treatment).
Inputs
- Mass Length (cm)
- Mass Height (cm)
- Mass Width (cm)
- Fetal Head Circumference (cm)
Formula & Guideline Source
Crombleholme et al. (2002), Journal of Pediatric Surgery.
Limitations
The CVR is a surrogate marker for mass effect. Measurements must be taken carefully using orthogonal planes. The traditional threshold of CVR > 1.6 predicts a high risk of hydrops, but some fetuses with lower CVRs may still develop complications.
FAQ
How is the CVR calculated?
CVR = (Length × Height × Width × 0.52) / Head Circumference. The mass dimensions represent an ellipsoid volume, and dividing by HC normalizes for gestational age.
What is the clinical significance of a CVR > 1.6?
A CVR greater than 1.6 at initial presentation is associated with a significantly increased risk (approximately 80%) of developing fetal hydrops, necessitating close surveillance and possible fetal intervention.
References
- Crombleholme TM, et al. Cystic adenomatoid malformation volume ratio predicts outcome in prenatally diagnosed cystic adenomatoid malformation of the lung. J Pediatr Surg. 2002.