Case report
A 34 year-old woman with unremarkable history was referred to our unit at 26 weeks of her pregnancy after her routine ultrasound scan had showed an anomaly inside the fetal right cardiac atrium. Her first trimester aneuploidy screening was normal with a nuchal translucency of 1.4 mm at week 12.
The finding looked like a redundant tangle going up and down across the tricuspid valve during the heart cycle. No other malformations or soft markers were seen. The finding had remained unchanged during the rest of the pregnancy. Our presumed diagnosis was Chiari"s network. No polyhydramnios nor fetal hydrops had developed and the labor was uneventful. The patient gave birth to a healthy girl (3210 g, normal Apgar score).
Postnatal echocardiography confirmed the suspected diagnosis. The baby is now one year old and thrives well.
Definition
Chiari"s network is a congenital remnant of the right valve of the sinus venosus: the septum spurium (Chiari, H. 1897) [1].
History
Described by the neurosurgeon Hans Chiari in 1897, as a network of fine fibers extending from the Thebesian to Eustachian valves in the heart. First fetal case described in 1982 [2].
Prevalence
Fetal reports of this condition are rare; a Medline search yields no results. Incidence is 2-3% in adults and usually represent a necropsy finding [3]. We do not known whether it goes unseen in fetal ultrasound scan due to small size and maybe the network experiences a slow intrauterine and neonatal progression.
Etiology and pathogenesis
Chiari’s Network is of embryologic origin. It is known to be a congenital remnant of the right valve of the sinus venosus (4). This is part of the septum spurium, a temporary partitioning that regress and does not contributes to the inter-atrial septum (thus the denotation of "spurium") It consists of a network of threads and fibers in the right atrium that originate from a region of the eustachian and thebesian valves at the orifice of the inferior vena cava, with attachments to the upper wall of the right atrium or atrial septum (3).
Sonographic findings
It resembles a “mobile cardiac tumor” or a valve anomaly. It is seen as an echogenic atrial mass that moves in and out of the right atrium into the right ventricle. Migration into left atrium during systole has been described (5). Valvular flow regurgitation and cardiac rhythm anomalies can be found (6).
Implications for targeted examinations
It is advisable to look for ascites, pericardium effusion or other signs of fetal cardiac failure. Fetal brain should be carefully screened if differential diagnosis with rhabdoyioma arises (in case of tuberous sclerosis). Fetal arrhythmia has been described (2).
Differential diagnosis
Differential diagnosis should include fetal cardiac tumors such as myxoma, rhabdomioma or primary tricuspid valve anomalies (7).
Associated anomalies
Patent foramen ovale (PFO) has been described associated to this condition (4). A large right to-left shunt was found significantly more often in patients with Chiari networks (55 versus 12 percent in the other patients). Also, PFO can occur in association with an atrial septal defect (4). Polyhydramnios has also been described (8).
Prognosis
The condition is benign and only postnatal confimation by echocardiography is needed. Neverthelss, left atrial entrapment (5) in a premature baby was reported. On the other hand, Chiari´s network was casually find in adult life in various cardiac diseases (4, 9) such as arrhytmias, sudden death or stroke secondary to PFO.
Recurrence risk
The recurrence risk in subsequent pregnancies is not known.
Management
No alteration of the prenatal management is needed since this is a normal variant. We suggest careful prenatal follow up and reassurance to the parents, and confirmation in the neonatal period.
Prenatal images and videos:
Images 1, 2: The images show transverse scans of the fetal thorax at the level of the four chamber view of the heart. An echogenic focus representing the Chiari"s network is present within the right atrium. The focus was highly movable during the heart cycle.