Background/Purpose: Cystic adenomatoid malformation of the lung (CAM) diagnosed in utero has a variable natural history that may result in hydrops in up to 40% or regress in up to 15%, No criteria have been available to determine which lesions would grow and develop hydrops versus those whose growth would stabilize or regress. To better understand the natural history of CAM the authors developed a measure of tumor volume normalized for gestation age, the CAM volume ratio, or CVR. The results of an initial retrospective review of CVR at presentation suggested its usefulness as a predictor of outcome in CAM. The authors now report the results of prospective use of the CVR both to track tumor growth and regression during gestation and confirm its predictive value in fetuses with CAM. Methods: In the retrospective review performed between November 1998 and August 1999, 32 fetuses with CAM were reviewed and divided into those with hydrops and those in whom hydrops never developed. The CVR was determined by measuring 3 dimensions of the CAM using the formula for the volume of an ellipse and dividing by the head circumference to correct for differences in gestational age. Of the 32 fetuses in the retrospective study, the 8 that had hydrops had a significantly higher CVR (3.1+/-1.1) compared with hydropic fetuses (0.74+/-0.48; P<.001). The mean of the nonhydropic fetus's CVR plus 2 standard deviations (0.74+0.96=1.7) was used as a cutoff in the subsequent prospective study. From September 1, 1999 through March 1, 2001, the authors evaluated prospectively 58 patients with CAM by CVR measurement. These patients were followed up with serial ultrasound scans, and CVR at presentation correlated with the development of hydrops, survival, need for fetal intervention, and the need for ventilatory support or extracorporeal membrane oxygenation (ECMO), and length of hospital stay postnatally. The indication for fetal intervention was the development of hydops. Results: The fetuses with CVR≤1.6 (n=42) were considered to be at low risk for the development of hydrops, and those with CVR greater than 1.6 (n=16) were considered at increased risk for developing hydrops. Of the 42 fetuses in the low-risk group, 7 (16.7%) developed hydrops, and all but 1 had a dominant cyst. If CAMs with a dominant cyst are excluded, only 1 of 36 (2.8%) of CAMs with CVR≤1.6 developed hydrops (P<001). In fetuses with CVR at presentation more than 1.6, 12 of 16 (75%; P<.005) developed hydrops. Seventeen fetuses underwent fetal treatment (8 CVR≤1.6; 9 CVR>1.6): 7 patients required open fetal surgery (survival rate, 2 of 7), 6 patients thoracoamniotic shunting (survival rate, 6 of 6); and 4 patients cyst aspiration (survival rate, 4 of 4). All survivors of fetal intervention required at a least brief period of ventilatory support; none required ECMO. Conclusions: A CVR of greater than 1.6 at presentation accurately predicts increased risk of hydrops developing in CAM. A CVR of less than or equal to1.6 at presentation suggests that the risk of hydrops developing in the absence of a dominant cyst is less than 3%. The CVR is a useful sonographic indicator of fetuses at risk for hydrops who require close ultrasound observation and possible fetal intervention. J Pediatr Surg 37:331-338. Copyright (C) 2002 by W.B. Saunders Company.
