Sonographically, this malformation is a well-circumscribed lung mass that may appear solid and echogenic or may have one or multiple variably sized cysts (Fig. 10-24, p. 199). Lesions with cysts � 5 mm are termed macrocystic, whereas microcystic lesions have smaller cysts or appear solid (Adzick, 1985). Also called congenital pulmonary airway malformation (CPAM), it represents a hamartomatous overgrowth of terminal bronchioles. Therapy for macrocystic congenital cystic adenomatoid malformation (CCAM) is discussed later (p. 324).
Occasionally, a microcystic CCAM may demonstrate rapid growth, generally between 18 and 26 weeks' gestation. he mass may become so large that it causes mediastinal shift, which may compromise cardiac output and venous return, resulting in hydrops (Cavoretto, 2008). A CCAM-volume ratio (CVR) has been used to quantiy size and risk for hydrops in these severe cases (Crombleholme, 2002). his ratio is an estimate of the CCAM volume (length X width X height X 0.52) divided by the head circumference. In a series of 40 pregnancies with microcystic CCAM, the mean CVR was 0.5 at 20 weeks' gestation, peaking in size at 1.0 at 26 weeks, followed by a pronounced decline prior to delivery (Macardle, 2016). A third of fetuses had no increase in mass size. In the absence of a dominant cyst, a CVR exceeding 1.6 is associated with a hydrops risk as high as 60 percent. However, CCAM growth resulting in hydrops develops in fewer than 2 percent of cases if the initial CVR is below 1.6 (Ehrenberg-Buchner, 2013; Peranteau, 2016). Importantly, a CVR in the range of 1.6 indicates that the mass essentially fills the thorax, and thus it is not unexpected that ascites or hydrops may develop.
If the CVR exceeds 1.6 or if signs of hydrops develop, corticosteroid treatment has been used in an efort to improve outcome. Regimens include dexamethasone-6.25 mg every 12 hours for four doses, or betamethasone-12.5 mg intramuscularly every 24 hours for two doses. Following a single course of corticosteroids, hydrops resolved in approximately 80 percent of cases, and 90 percent of treated fetuses survived (Loh, 2012; Peranteau, 2016). Recently, multiple courses of steroids-generally twohave been advocated for fetuses with large CCAM lesions and with persistent or worsening hydrops or ascites despite a single course of medication (Derderian, 2015; Peranteau, 2016).
Identification of fetal thyroid disease is rare and usually prompted by sonographic detection of a fetal goiter. If a goiter is found, determination of fetal hyper-or hypothyroidism is essential, and thyroid hormone levels may be measured in amnionic luid or fetal blood. Traditionally, fetal blood sampling, described in Chapter 14 (p. 294), is preferred to amniocentesis for guiding treatment, although data are limited (Abuhamad, 1995; Ribault, 2009). Goals of therapy are correction of the physiological abnormality and diminished goiter size. The goiter may compress the trachea and esophagus to such a degree that severe hydramnios or neonatal airway compromise may develop. Hyperextension of the fetal neck by a goiter can create labor dystocia.