Cystic hygroma presenting as an isolated malformation – case report and literature review

Nuchal translucency (NT) is the ultrasound observa­tion of subcutaneous fluid accumulation at the back of the fetal neck. When this accumulation becomes excessively enlarged, it can lead to nuchal edema, which is referred to as increased NT or cystic hygroma. Elevated NT has been demonstrated to be associated with different chromosomal anomalies or structural abnormalities and with unfavorable pregnancy outcomes⁽¹⁾.

Cystic hygroma (CH) is the result of a blockage in the lymphatic system, leading to the development of pseudocysts filled with liquid content in the fetal nuchal region that can reach significant sizes. The term “hygroma” derives from the Greek words hygros, meaning liquid, and oma, meaning tumor.

This congenital malformation occurs in approximately 1% of fetuses between 9 and 16 weeks of gestation and is associated with the occurrence of aneuploidies in 65% of cases. The incidence of CH can vary depending on the population and the specific underlying causes or risk factors, and it is generally considered to occur in approximately 1 in 268 pregnancies⁽²⁾. The reported incidence of cystic hygroma in the general population is relatively low, estimated to be around 1 in 4000 live births. An older study reported an overall incidence of approximately 1 in 1000-6000 births and 1 in 750 spontaneous abortions⁽³⁾.

However, the incidence can vary among specific populations or groups, based on various factors such as genetics, ethnicity and geographic regions. Cystic hygroma is often detected during prenatal screenings, and certain studies have reported higher incidences in populations that undergo more extensive prenatal testing and ultrasound examinations. Cystic hygromas can be associated with specific genetic conditions, and the incidence may be higher in populations where these genetic conditions are more prevalent. For example, the incidence of CH may be higher in populations with a higher prevalence of Turner syndrome or Down syndrome. The incidence of cystic hygroma can also vary by geographic region and it may be influenced by factors such as access to healthcare, prenatal screening practices, and the prevalence of genetic conditions in specific regions. More­over, advanced maternal age is associated with a higher risk of chromosomal abnormalities and, by extension, an increased risk of CH. It is essential to consult with healthcare professionals or genetic counselors for more precise information on the incidence and risk factors related to CH in a specific context or population.

When generalized, it can lead do hydrops fetalis, a condition involving abnormal accumulation of fluid in multiple fetal body compartments, such as the chest and abdomen. Hydrops fetalis can result from a variety of underlying causes, including heart, blood or immune system disorders. Historically, non-immune hydrops fetalis (NIHF) has been regarded as a fetal condition with a high risk of lethality⁽⁴⁾.

Cystic hygroma begins its development at about eight weeks of gestation, when six lymphatic sacs can be identified in the developing embryo. These lymphatic sacs are described as follows: two jugulars, two iliac, one at the base of the mesenteric root, and one dorsal to the abdominal aorta (cisterna chyli). Later, a network of lymphatics develops, allowing lymphatic communication between various regions. During the ninth week of gestation, these sacs are invaded by connective tissue as lymph nodes develop. CH arise from the sequestration of lymphatic tissue within the lymphatic-venous sacs during the aforementioned development. These sequestered tissues fail to communicate with the rest of the lymphatic or venous system. Later, dilation of the sequestered lymphatic tissues occurs as lymphatic liquid accumulates, resulting in the cystic morphology of these lesions.

Anatomical studies show that the most frequent locations of CH are the cervicofacial regions (especially the posterior cervical triangle), axilla, mediastinum, inguinal and sublingual regions. Rare locations are represented by the limbs, thoracic wall, cheeks, lumbar region, and the suprasternal area. Most frequently, it is a single and isolated location⁽⁵⁾.

The prenatal diagnosis of cystic hygroma through ultrasound is well established. The characteristic ultrasound appearance during antenatal ultrasonography is a multiseptated cystic mass with thin walls. Occasionally, the cystic mass may exhibit a more complex echogenic texture with both cystic and solid components⁽⁶⁾.

Cystic hygroma can occur isolated, but a normal karyotype can be found in only 20-50% of cases⁽⁷⁾. It can also be diagnosed in fetuses with genetic anomalies, with 62% of cases being associated with conditions such as Turner syndrome, Down syndrome (trisomy 21) or Noonan syndrome^(8-11). These genetic syndromes are known to be associated with an increased risk of CH as one of their clinical features.

The differential diagnosis can be made with posterior cervical wall anomalies, such as meningocele or encephalocele, and with anterior cervical wall anomalies, such as thyroglossal duct cyst, branchial cyst (dermoid and epidermoid cyst), bronchogenic (visceral) cyst or mandibular hamartoma and cervical thymic cyst.

The outcome of CH is in close correlation with the associated anomalies, the timing of appearance, and location. A recent study showed that, once the presence of fetal chromosomal abnormalities is ruled out, there is a significantly lower incidence of major structural fetal abnormalities, standing at only 13%, and normal fetuses exhibit a 77% survival rate⁽¹²⁾.

The therapeutic management varies widely, from expectant management to termination of pregnancy, depending on the severity of the CH and the associated anomalies. The expectant management approach is suitable for cystic hygromas that develop in fetuses without associated chromosomal abnormalities. Close ultrasound monitoring is recommended to assess dynamic changes, such as growth, reduction in size, or even the complete resolution of the fluid accumulation. On the other hand, in severe cases of CH, termination of pregnancy may be recommended, especially when there are severe associated chromosomal abnormalities. In cases with moderate involvement, surgical intervention after birth is recommended, as antenatal drainage of the cystic hygroma has proven to be ineffective. In such cases, it is advisable to transfer the pregnant individual to a specialized neonatal care center (the respiratory complications are most common) and have access to a pediatric surgery center. It is important to acknowledge that the management approach should be tailored to each individual case, and decisions should be made in consultation with healthcare professionals and specialists, based on the specific circumstances and risks involved.

It is generally considered that the recurrence risk of CH depends on its association with fetal aneuploidies. In cases where cystic hygroma is associated with genetic syndromes, the risk of recurrence in future pregnan­cies is low. Chromosomal abnormalities typically occur sporadically, and the likelihood of them appearing in subsequent pregnancies is small.

However, in cases where the karyotype (chromosome pattern) is normal, the risk of recurrence is increased. This means that, if a previous pregnancy with CH had a normal chromosome pattern, there is a higher chance of cystic hygroma occurring in future pregnancies. It is important to consult with a healthcare provider or genetic counselor for personalized guidance and risk assessment in specific situations.

Regarding the situations in which cystic hygroma has a spontaneous resolution, a retrospective study took into account 68 fetuses diagnosed with simple nuchal hygromas between 10 and 14 weeks of gestation who underwent ultrasound evaluation and karyotyping. Those with normal chromosomal complements were monitored by ultrasound throughout the pregnancy to track the resolution of their hygromas. Twenty-three out of 27 fetuses with normal karyotypes spontaneously resolved their hygromas within four weeks of diagnosis and were phenotypically normal at birth. Forty-one fetuses had abnormal karyotypes, with trisomy 21 being the most frequent anomaly⁽¹³⁾.

A more recent retrospective study on 185 cases with cystic hygroma showed that 34.1% of the fetuses had a normal karyotype, of which 56% had a major congenital anomaly⁽¹⁴⁾. The authors suggest that an adverse outcome in pregnancies where first-trimester CH and a normal karyotype are present can be anticipated in the presence of structural anomalies or hydrops fetalis, while normally structured fetuses have a better prognosis.

To clinically illustrate this condition, we have chosen to present the case of a 30-year-old primiparous patient with no significant medical history. At 13 weeks of pregnancy, a diagnosis of cystic hygroma was made, measuring 4.8 mm. No other associated malformations were observed at the first-trimester morphology scan (Figures 1 and 2).

Despite the non-reassuring ultrasound findings, the patient decided to continue the pregnancy, and she underwent non-invasive prenatal testing (NIPD) at 13 weeks of gestation. No numerical chromosomal abnormalities analyzed were identified, the analyzed microdeletion syndromes were not detected, and no monogenic diseases from the analyzed panel were identified (Figure 3).

The patient returned for an ultrasound at 16 weeks of pregnancy, when the nuchal anomaly has regressed, with normal growth of the fetus. The second-trimester morphology scan did not reveal any pathological changes, and a nuchal fold measurement of 7 mm was described.

Amniocentesis was performed at 16 weeks of gesta­tion, molecular prenatal karyotype from amniotic fluid was performed, and the microarray analysis identified a normal male profile without clinically significant microdeletions or microduplications in the analyzed chromosomal regions.

At 22 weeks of gestation, the fetus showed normal morphological development, without any pathological signs (Figures 4 and 5). There was no evidence of cystic hygroma, and there were no other associated ultrasound abnormalities. The fetus was following a typical growth curve. At present, the fetus is 31 weeks, showing a normal development, normal nuchal fold and the absence of other structural anomalies.

Cases of spontaneously regressed cystic hygroma, unassociated with other congenital malformations, with a favorable prognosis at birth, have been reported in the literature. In 2008, a case was presented in the literature, involving a patient in her third pregnancy, with no previous obstetric history⁽¹⁵⁾. At nine weeks of gestation, the fetus exhibited CH, which spontaneously resolved at 12 weeks of gestation. The patient declined further investigations for karyotyping. At 24 weeks of gestation, an abdominal cystic formation was detected on ultrasound, which also spontaneously resolved at 26 weeks of gestation. At birth, the newborn had a normal karyotype and showed no developmental defects. Thus, it is emphasized that fetal anomalies such as cystic hygroma, when associated with a normal karyotype, have a favorable prognosis regarding spontaneous resolution.

Conclusions

When counseling individuals facing first-trimester septate cystic hygroma, the initial focus is often on the high probability of an abnormal karyotype, which is observed in 61% of cases⁽¹²⁾.

Nevertheless, comprehending the underlying pathophysiological processes has resulted in the conceptualiza­tion of diagnostic protocols, enhanced comprehension of the root causes and, consequently, advances in fetal or neonatal treatments. Collaborative counseling is pivotal in assisting families in navigating choices during pregnancy, considering potential therapeutic interventions for the fetus, making decisions about neonatal management and, when necessary, embracing or transitioning to palliative care. Recent studies that prove the possibility of normal chromosomal fetuses with high survival rates highlight that such counseling can be more optimistic than previously anticipated once chromosomal abnormalities have been ruled out.

 

Conflict of interest: none declared  
Financial support: none declared
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