Traditionally referred to as lymphangioma or if in the neck cystic hygroma, these are currently considered a form of vascular malformation of the lymphatic system characterized by localized or diffuse malformations of lymphatic channels that can be characterized as microcystic, macrocystic, or both (Christison and Fishman, 2006).

Lymphangioma is a benign type of vascular malformation composed predominantly of dilated cystic lymphatics (Isaacs, 1997). These malformations are often present at birth and are second only to hemangioma as a cause of soft tissue mass in the newborn (Potter and Craig, 1975; Isaacs, 1983, 1991, 1997). Lymphangiomas can occur in almost any location but are most commonly seen in the soft tissue of the neck, axilla, thorax, and lower extremities (Isaacs, 1997). Isaacs reported a series of 97 consecutive lymphangiomas seen at Children’s Hospital of Los Angeles in which 45 occurred in the neck, 22 in the chest wall, 12 in the extremities, and 4 in the abdominal wall. Other less common sites included the omentum, mesentery, larynx, tongue, bowel, retroperitoneum, mediastinum, conjunctiva, and mouth (Isaacs, 1991). These lesions can vary in size from tiny subepidermal skin blebs to large dilated cystic fluid filled– masses that, when presenting in the neck, are commonly referred to as cystic hygromas.

There is a disparity between lymphangiomas that are diagnosed at birth as isolated findings in otherwise healthy infants and those detected prenatally during the first or second trimester (see chapter 31). Prenatal sonographic examination in the first and second trimester identifies a group of fetuses with cystic hygroma in which 60% have associated chromosomal abnormalities and are often associated with other structural anomalies that have an extremely high mortality rate (Romero et al., 1988; Cohen et al., 1989; Welborn and Timm, 1994). In this group of fetuses, cystic hygromas are distinguished by posterior triangle location of the lymphangioma, chromosomal abnormalities, structural anomalies, hydrops fetalis, a high incidence of intrauterine death, and rare postnatal survival. In contrast, isolated cystic hygroma presenting during the third trimester, often with previously normal sonographic studies earlier in gestation, is usually located anteriorly or anterolaterally in the anterior cervical triangle. These two groups of fetuses appear to have lymphangiomas of differing origin, pathophysiology, natural history, and most importantly, prognosis (Lyngbye et al., 1986; Benacerraf and Frigoletto, 1987; Langer et al., 1990).

The lymphatic system develops at the end of the 5th week of gestation with sprouting from the six primary lymph sacs situated in the neck, iliac region, and retroperitoneum. Goetsch (1938) suggested that lymphangiomas are developmental defects secondary to sequestration of lymphatic tissue in early embryonic life. Cystic hygromas are thought to arise because of the failure of the jugular lymph sacs to join the lymphatic system. The hygroma develops fibrillike sprouts from the existing cystic spaces. These endothelial-lined cystic spaces secrete lymphlike fluid, which causes local distention and gradual enlargement of cysts. The walls may become thicker with time, with connective tissue septae separating large cysts (Chervenak et al., 1983; Isaacs, 1997).

Lymphangiomas diagnosed in utero are commonly seen in association with Turner syndrome, hydrops, oligohydramnios, single-vessel umbilical cord, Noonan syndrome, fetal alcohol syndrome, Fryns syndrome, and trisomies 18 and 21 (Stephens and Shepard, 1980; Chervenak et al., 1983; Pijpers et al., 1988; Golden et al., 1989; Welborn and Timm, 1994). Chromosomal abnormalities are found in more than 60% of fetuses with cystic hygroma. The majority have a 45,X karyotype (Romero et al., 1988; Cohen et al., 1989; Welborn and Timm, 1994), although Trisomies 13, 18, and 21 and Klinefelter syndrome have all been reported (Chervenak et al., 1983; Greenberg et al., 1983; Marchese et al., 1985; Stephens and Shepard, 1980). Conversely, fetuses with a normal karyotype appear to have a much higher incidence of consanguinity or a previous family history of abnormal fetuses (Langer et al., 1990). Cystic hygromas in these patients are more likely to be associated with familial conditions such as Noonan syndrome, multiple pterygium syndrome, polysplenia syndrome, Roberts syndrome, or an isolated autosomal recessive trait (Chen et al., 1982; Cowchock et al., 1982; Graham et al., 1983; Zarabi et al., 1983; Zelante et al., 1984).

Isolated cystic hygromas presenting late in gestation appear to be a completely different entity (Lyngbye et al., 1986; Benacerraf and Frigoletto, 1987; Langer et al., 1990; Fujita et al., 2001; Tanriverdi et al., 2005; Gedikbasi, 2007). These cases had cystic hygromas located in the anterior and lateral location and were not generally associated with other anomalies or hydrops. Langer et al. suggested that in these cases lymphangioma developed much later in gestation. In one of his cases, the fetus had a normal sonographic examination at 17 weeks of gestation (Langer et al., 1990). If this is true, it is unlikely that the mechanism would be similar in the late presenting group of cystic hygromas and the early gestation group. Cystic hygromas may also regress in utero, presumably due to development of collateral lymphatic and venous connections. Webbing of the neck and puffiness of the hands and feet are characteristic features of Turner syndrome, which is thought to be due to fetal cystic hygromas that spontaneously resolve.

Precise estimates of the incidence of cystic hygroma and lymphangioma are difficult to come by and depend on whether prenatal or postnatal data are evaluated. Fonkalsrud estimated the incidence of cystic hygroma to be 1 in 12,000 births, with 50% to 65% of cases presenting at birth, and 80% to 90% presenting by the second year of life (Bill and Sumner, 1965; Fonkalsrud, 1980). A total of 52 confirmed diagnoses of cystic hygroma were reported to the South East Thames Regional Congenital Malformation Registry in a region with an annual birth rate of 52,000, yielding an incidence of 1 in 1000 births. This series included terminations, intrauterine fetal death, stillbirths, and postnatal deaths to give a more accurate account of the incidence of cystic hygroma (Fisher et al., 1996). The incidence of cystic hygroma was as high as 1 in 300 among spontaneous abortuses reported by Byrne et al. (1984).

The sonographic features of cystic hygroma include fluid-filled cystic spaces divided by fine septae commonly observed in the nuchal region and anterior and posterior triangles of the neck (Figure 32-1). They often have a dense midline posterior septum extending from the fetal neck across the full width of the hygroma. This septum is the sonographic equivalent of the nuchal ligament (Chervenak et al., 1985). In order to differentiate cystic hygroma from other diagnoses, it is important to exclude a bony defect in the skull or vertebral column as would be seen with encephalocele. Solid components should be excluded to distinguish cystic hygroma from a cystic teratoma. Cysts separated by septae are helpful in distinguishing nuchal edema from cystic hygroma.

Lymphatic malformations may be diagnosed in the chest, abdomen, retroperitoneum or inguinal region. Rasidaki et al. (2005) have reported a chest wall lymphatic malformation in which MRI in addition to ultrasound was used to make the diagnosis. Similarly, there have been several reports of prenatal diagnoses of axillary lymphatic malformations (Song et al., 2002; Zanotti et al., 2001).

Once cystic hygroma has been detected, a search for other potential associated signs of nonimmune hydrops such as fetal skin edema, ascites, and pleural or pericardial effusions should be sought. In addition, structured anomalies seen in association with cystic hygroma should be sought, including cardiac, facial, vertebral, and genitourinary anomalies and diaphragmatic hernia (Bulas et al., 1992) (Table 32-1).

The differential diagnosis of cystic neck masses includes nuchal edema, encephalocele or other neural tube defects, cystic teratoma, and twin sac of a blighted ovum. The approach to each of these conditions differs, highlighting the importance of accurate prenatal diagnosis. The presence of skull or vertebral column defects suggests the diagnosis of encephalocele, especially if associated with hydrocephalus. The distinction between cystic hygroma and cervical teratoma can be extremely difficult. Teratomas usually have a more complex sonographic appearance, with solid as well as cystic components. Calcifications within the mass are thought to be diagnostic of teratoma (see Chapter 110). Fetal magnetic resonance imaging (MRI) may be very helpful in distinguishing cystic hygroma from cervical teratoma (Liechty et al., 1997; Hubbard et al., 1998) (Figures 32-2A and 32-2B). Nuchal edema is usually without septae except the midline nuchal ligament and is a few millimeters in thickness (see Chapter 31).