Excerpt from Cystic Hygroma

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Background

Cystic hygroma was first described in 1828 by Radenbacher. Cystic hygroma (meaning "moist tumor") belongs to a group of diseases now recognized as lymphatic malformations. The discovery of a cystic hygroma has a variable effect and prognosis, depending on whether it is found in the prenatal or postnatal period. This article focuses on fetal cystic hygromas, that is, cystic hygromas that are discovered prenatally.

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Cystic Hygroma [Pediatrics: Surgery]
Vascular, Lymphatic Malformations

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Lymphatic malformation.

Pathophysiology

Cystic hygromas can range from increased nuchal translucency to thin-walled cystic masses that may become larger than the fetal head.^{1, 2} The cysts may result from a lymphatic abnormality, possibly one caused by absent or inefficient connections between the lymphatic and venous systems. The concept that correct communications between these 2 systems may develop later in the gestation of some fetuses may account for cystic areas that resolve with merely a residual amount of redundant skin (pterygium colli).

Other theories for the development of cystic hygromas include the possible abnormal sequestration of embryonic lymphatic tissue that does not communicate with normal lymph-flow channels and the budding of lymphatics that canalize to form lymph-filled cysts.

Fetal cystic hygromas vary with gestational age. First-trimester findings include nuchal translucency.³ Second-trimester findings include large, thin-walled cysts with linear internal septa, especially in the setting of Turner syndrome.^{4, 5}

Frequency

United States

Cystic hygromas occur in 1 of 200 aborted fetuses with a crown-rump length of greater than 30 mm. In pregnancies carried to term, the frequency is 1 case per 6000 births.

Mortality/Morbidity

Morbidity and mortality appear to be more common among fetuses with multilocularity or septa in their cystic hygromas than they are among fetuses that do not.⁶ This observation may be more indicative of true cystic hygromas than it is of simulators. Bronshtein and colleagues indicated that nonseptate cystic hygromas were transient in 98% of cases and that septate cystic hygromas were transient in only 44% of cases.⁷ In this same series, 72% of fetuses with septate cystic hygromas had aneuploidy. Other characteristics of cystic hygromas are as follows:

• When associated with fetal hydrops, patients with cystic hygromas have a mortality rate of almost 100%. These patients typically have karyotype abnormalities.
• Hygromas with a volume of more than 75 mm³ tend to persist. These are associated with more abnormal outcomes and chromosomal abnormalities than are smaller hygromas and hygromas discovered later in pregnancy.
• Cystic hygromas that are found in a purely anterior location on the neck are usually not related to cystic hygromas that are associated with aneuploidy and death. They have a better prognosis, and many resolve spontaneously.

Related eMedicine topics:
Hydrops Fetalis [Pediatrics: Cardiac Disease and Critical Care Medicine]
Hydrops Fetalis [Radiology]

Sex

Cystic hygromas are strongly associated with Turner syndrome (usually 45 XO), which causes an abnormal phenotype in affected girls.⁵

Age

Cystic hygromas can be discovered before birth or in the neonatal period. Occasionally, the cystic hygroma may not be discovered until the patient is older.

Related Medscape topic:
Resource Center Neonatal Medicine

Anatomy

In cystic hygroma, cavernous lymphatic spaces communicate and grow to form large cysts that can infiltrate the surrounding tissue.

Clinical Details

Fetal cystic hygromas have almost a 50% association with chromosomal disorders, such as aneuploidy. Cystic hygroma is strongly associated with Turner syndrome (predominantly a 45 XO karyotype), trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and Noonan syndrome.^{1, 4, 5, 8, 9, 10} Some cystic hygromas can occur in otherwise healthy fetuses and babies. In such patients, postnatal treatment is aimed at improved cosmesis or the alleviation of mechanical complications. Occasionally, cystic hygromas can become large and extend into the mediastinum, axillae, mouth, and chest. Occasionally, they occur exclusively in those areas. As with other fetal anomalies, larger hygromas may be detected at an earlier point in gestation.¹¹

Some suggest that the prenatal diagnosis of cystic hygromas is particularly aided by transvaginal ultrasonography (US). In fact, the condition is most often diagnosed by using prenatal US, and the findings can be striking and unmistakable. Findings include large cystic structures, usually with multiple septa related to the back of the neck of the fetus. Cystic hygromas have been associated with oligohydramnios, but this is not a typical finding. Some patients can have features of hydrops.

Fetal cystic hygroma is a part of a continuum of pathology, and varying degrees of involvement are described, each with its own incidence of chromosomal involvement. The stages, and their risk of chromosomal abnormality, are as follows:

• Localized nuchal fluid - 12% risk
• Diffuse nuchal translucency - 23% risk
• Cystic hygroma - 50% risk
• Fetal hydrops - 78% risk

Although most hygromas (75%) involve the neck, they can also affect other sites, including the axillae (20%), mediastinum, retroperitoneum, abdominal viscera, groin, bones, and scrotum (5%).

First-trimester findings can be subtle, and only increased nuchal translucency may be evident.³ These masses may continue to grow into typical hygromas. Rarely, lymphatic-venous communications can develop later in the prenatal period, and the hygromas then resolve. Many believe that the webbed neck of patients with Turner syndrome is the residual material from a resorbed cystic hygroma.

Morbidity and mortality appear to be more common among those fetuses with multilocularity or septa in their cystic hygromas. This observation may be indicative of true cystic hygromas rather than of simulators. In one report, the authors indicated that nonseptate cystic hygromas were transient in 98% of cases, whereas septate cystic hygromas were transient in only 44% of cases. In this same series, 72% of fetuses with septate cystic hygromas had aneuploidy.⁷

Cystic hygromas found in a purely anterior location on the neck are usually not related to cystic hygromas associated with aneuploidy and death. They have a better prognosis, and many resolve spontaneously.

Preferred Examination

US is the modality of choice for diagnosing fetal cystic hygromas.¹² US is readily available, noninvasive, and used extensively in pregnancy for fetal monitoring and diagnosis.

Magnetic resonance imaging (MRI) requires a long acquisition time, making it impractical unless special protocols are used. MRI is also expensive and not readily available in all settings.

Computed tomography (CT) scanning uses ionizing radiation and is contraindicated in pregnancy unless overriding considerations are involved.

Plain radiography also uses ionizing radiation and is contraindicated. If plain radiographs are used, the findings are not helpful because this condition affects the soft tissue, and the image is unlikely to have good contrast.

Limitations of Techniques

In the diagnosis of fetal cystic hygromas, US is considered the modality of choice. Fetal positioning, maternal body habitus, and operator dependence can make the diagnosis difficult at times. The diagnosis can be missed, even with large fetal cystic hygromas, when severe oligohydramnios is present; the hygromas can be mistaken for pockets of amniotic fluid.

Plain radiography is contraindicated because it uses ionizing radiation. In addition, because the pathology is limited to the soft tissue, it is not expected that radiographs would be helpful.

CT scanning also involves ionizing radiation, but this modality can provide better resolution in select patients.

MRI can be used to assess the extent of infiltration of the cysts into the surrounding structures, but special fast MRI sequences must be used to overcome normal fetal movement, which obviously cannot be controlled.

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