Disclosure
Background: Radenbacher first described cystic hygroma in 1828. The term means a moist tumor. Cystic hygroma 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 antenatal period or the postnatal period. This article is focused on the discussion of fetal cystic hygromas, that is, cystic hygromas discovered antenatally. Pathophysiology: Cystic hygromas can range from increased nuchal translucency to thin-walled cystic masses that can become larger than the fetal head. The cysts may result from a lymphatic abnormality, possibly from absent or inefficient connections between the lymphatic and venous systems. The concept that correct communications between these two systems may develop later in the gestation of some fetuses may account for cystic areas that resolve with merely a residual 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. Second-trimester findings include large thin-walled cysts with linear internal septa, especially in the setting of Turner syndrome. Frequency:
Mortality/Morbidity: Morbidity and mortality appear to be more common among fetuses with multilocularity or septa in their cystic hygromas than among others. This observation may be more indicative of true cystic hygromas than simulators. Bronshtein et al indicated that nonseptate cystic hygromas were transient in 98% of cases and septate cystic hygromas were transient in only 44% of cases. In this same series, 72% of fetuses with septate cystic hygromas had aneuploidy
Sex: Cystic hygromas are strongly associated with Turner syndrome (usually 45 XO), which causes an abnormal phenotype in affected girls. Age: Cystic hygromas can be discovered before birth or in the neonatal period. Occasionally, cystic hygroma may not be discovered until the patient is older. Anatomy: 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. 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. Some suggest that prenatal diagnosis is particularly aided by transvaginal ultrasonography (US). In fact, the condition is most often diagnosed by using antenatal 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 the continuum of pathology, and varying degrees of involvement are described, each with its own incidence of chromosomal involvement. The stages include localized nuchal fluid (12% risk of chromosomal abnormality), diffuse nuchal translucency (23% risk), cystic hygroma (50% risk), and 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. These masses may continue to grow into typical hygromas. Rarely, lymphatic-venous communications can develop later in the antenatal period, and the hygromas then resolve. Many believe that the webbed neck of patients with Turner syndrome is the residual of 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 compared with 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%. In this same series, 72% of fetuses with septate cystic hygromas had aneuploidy (Bronshtein, 1993). 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. US is readily available, noninvasive, and used extensively in pregnancy for fetal monitoring and diagnosis. MRI requires a long acquisition time, making it impractical unless special protocols are used. MRI is expensive and not readily available in all settings. CT uses ionizing radiation and is contraindicated in pregnancy unless overriding considerations are involved. Plain radiography 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: US is 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 of the ionizing radiation. In addition, because the pathology is limited to the soft tissue, radiographs are not expected to be helpful. CT also involves ionizing radiation, but it 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.
Branchial Cleft Cysts
Anterior cystic hygroma
Findings: Plain radiography is not typically used because of ionizing radiation and because of its inability to depict the internal contents of the soft-tissue mass in the neck. |
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Findings: CT scanning is avoided because of its use of ionizing radiation. However, if the reasons to use CT are overwhelming, the extent of pathology can be assessed with CT.
Findings: Long acquisition times inherent to most acquisition sequences make the use of MRI impractical unless special fast sequences are performed. In optimal settings, MRI can provide exquisite anatomic detail, and it can be especially helpful in identifying additional pathology and in determining the extent of the disease. Degree of Confidence: MRI can be used with a high degree of confidence. Usually, further imaging modalities are not needed if good-quality MRI studies are obtained.
Findings: US is the modality of choice in the diagnosis of fetal cystic hygroma. The classic finding is a cystic mass with multiple septa appearing as multiple, asymmetric, thin-walled cysts related to the posterior aspect of the neck. These masses are associated with aneuploidies. The cysts can extend to the lateral or even the anterior aspects of the neck if the hygroma is large. The presence of a nuchal ligament, which is demonstrated as a posterior midline band extending through the cyst, is a characteristic finding. Oligohydramnios can occur. When it does, it can limit the discovery of additional cardiac or other visceral abnormalities that can coexist with cystic hygroma. These abnormalities should be investigated. Hydrops may be diagnosed by identifying body wall edema, pleural effusions, and/or fetal ascites. Degree of Confidence: US remains an operator-dependent modality and must be performed by a trained individual skilled in evaluating fetal anomalies. A thorough fetal examination results in a high confidence level. Most often, US is the only technique necessary for antenatal diagnosis. False Positives/Negatives: Fetal cystic hygromas should be differentiated from posterior encephaloceles, in which an underlying skull defect is present, and cervical myelomeningoceles, in which an underlying vertebral defect is present. A common artifact is caused by the presence of loops of umbilical cord near the cervical spine of the fetus. On occasion, these loops can simulate cervical cysts. Doppler evaluation demonstrates characteristic umbilical flow signals from this area. Fetal cystic hygroma must also be differentiated from other neck masses and cysts such as anterior cystic hygromas, goiters, and cervical teratomas. Compared with other masses, purely anterior cystic masses in the fetal neck have a different and better prognosis, and many resolve spontaneously.
Intervention: Amniocentesis and karyotyping are necessary to diagnose the chromosomal abnormalities commonly associated with fetal cystic hygroma. Once fetal cystic hygroma is diagnosed, all efforts should be aimed at identifying the associated anomalies and following up the patient to assess the development of fetal hydrops. Genetic counseling is necessary to discuss the diagnosis, other diagnostic possibilities, the possible need for karyotyping, and the potential risks to the fetus or child. The patient's family should be appropriately counseled regarding the risks in subsequent pregnancies. Medical/Legal Pitfalls:
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