Up to 70 percent of cystic hygromas are associated with aneuploidy. When cystic hygromas are diagnosed in the irst trimester, trisomy 21 is the most common aneuploidy, followed by 45,X and trisomy 18 (Kharrat, 2006; Malone, 2005). Firsttrimester fetuses with cystic hygromas are ive times more likely to be aneuploid than fetuses with a thickened nuchal translucency. When cystic hygromas are diagnosed in the second trimester, approximately 75 percent of aneuploid cases are 45,X-Turner syndrome Gohnson, 1993; Shulman, 1992).
Even in the absence of aneuploidy, cystic hygromas confer a significantly greater risk for other anomalies, particularly cardiac anomalies that are flow-related. These include hypoplastic let heart and coarctation of the aorta. Cystic hygromas also may be part of a genetic syndrome. One is Noonan yndrome, an autosomal dominant disorder that shares several features with Turner syndrome, including short stature, lymphedema, high-arched palate, and oten pulmonary valve stenosis.
Large cystic hygromas are usually associated with hydrops fetalis, rarely resolve,
FIGURE 10-22 Cystic hygromas. A. This 9-week fetus with a cystic hygroma (arrow) was later found to have Noonan syndrome. B. Massive multiseptated hygromas (arrowheads) in the setting of hydrops fetalis at 15 weeks' gestation.
and carry a poor prognosis. Small hygromas may undergo spontaneous resolution, and provided that fetal karyotype and echocardiography results are normal, the prognosis may be good. The likelihood of a nonanomalous liveborn neonate with normal karyotype following identiication of first-trimester hygroma is approximately 1 in 6 (Kharrat, 2006; Malone, 2005).
he lungs appear homogeneous and surround the heart. In the four-chamber view of the heart, they comprise approximately two thirds of the area, with the heart occupying the remaining third. The thoracic circumference is measured at the skin line in a transverse plane at the level of the four-chamber view. In cases of suspected pulmonary hypoplasia secondary to a small thorax, such as with severe skeletal dysplasia, comparison with a reference table may be helpul (Appendix, p. 1266). Various abnormalities may appear so no graphically as cystic or solid space-occupying lesions or as an efusion outlining the heart or lung(s). Fetal therapy for thoracic abnormalities is discussed in Chapter 16 (p. 324).