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2009-05-09-09 Answer to the case of the week #245 © Alvarez www.TheFetus.net


Answer to the case of the week #245

June 11 - June 25, 2009

Margarita Alvarez de la Rosa Rodriguez, MD, PhD*; Ana I. Padilla, MD, PhD*; Marta Coloma, MD*; César Perera, MD, PhD**; Juan M. Troyano MD, PhD*.

*  Obstetrics and Gynecology Departement. Canary Islands University Hospital. La Laguna University. La Laguna 38320. Tenerife. Canary Islands. Spain.
** Pediatric Cardiology Department. Canary Islands University Hospital. La Laguna University. La Laguna 38320. Tenerife. Canary Islands. Spain.

 

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.

 

Videos 1, 2: The videos 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 moves within the right atrium.

 

Postanatal images and videos:

Images 3, 4, 5, 6, 7, and 8: The images show transverse scan at the level of the right ventricle (RV) and the right atrium (RA) 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.

 

 

 

Video 3: The video shows transverse scan at the level of the right ventricle and the right atrium of the heart. The echogenic membrane representing the Chiari"s network is vigorously moving within the right atrium.

Images 9, 10: The following images were taken from another case from our website (Rugerro Trevisan, 2006, Chiari network) just to explain the position of the Chiari"s network within the right atrium of the heart. The image 9 shows transverse scan of the fetal thorax at the level of the four chamber view. The arrow points at the echogenic structure within the right atrium, representing the Chiari"s network. The image 10 shows a fusion of the image 9 with a drawing explaining the structures visible on the image 9. 

 

Images 11, 12: The image 11 represents a drawing of the heart development at the 31st day of gestational age. The orifices of the superior and inferior vena cava and of coronary sinus are formed as a process of intussusception of the right, and partially of the left, sinus venosus horns. Initially common opening of these structures into the atrial part of the heart is bordered by so called venous valves, which join superiorly to form a transient septum called septum spurium. An abnormal resorption of the right valve of the sinus venosus (which serves to direct the blood in embryonic life from the inferior vena cava to the fossa ovalis) results in Chiari"s network within the right atrium. The image 12 represents a drawing of the transverse plane of the fetal thorax at the level of the four chamber view. Position of the Chiari"s network is visible within the right atrium (Chiari"s network may have variable appearance ranging from the a few thin fibers to a membrane-like structure). RA - right atrium, RV - right ventricle, LV - left ventricle, LA - left atrium, Ao - descending aorta).

 

References

1. Cloez JL, Neimann JL, Chivoret G, Danchin N, Bruntz JF, Godenir JP, et al. [Echographic rediscovery of an anatomical structure: the Chiari network. Apropos of 16 cases]. Arch Mal Coeur Vaiss. 1983 Nov;76(11):1284-92.
2. Clements J, Sobotka-Plojhar M, Exalto N, van Geijn HP. A connective tissue membrane in the right atrium (Chiari"s network) as a cause of fetal cardiac arrhythmia. Am J Obstet Gynecol. 1982 Mar 15;142(6 Pt 1):709-12.
3. Schneider B, Hofmann T, Justen MH, Meinertz T. Chiari"s network: normal anatomic variant or risk factor for arterial embolic events? J Am Coll Cardiol. 1995 Jul;26(1):203-10.
4. Hara H, Schwartz RS. Patent foramen ovale. Journal [serial on the Internet]. 2008 Date: Available from: http://www.uptodate.com/
5. el-Khouri H, Putman D, Rutkowski M. Unusual case of prominent Chiari network trapped in the left atrium. J Am Soc Echocardiogr. 1998 Jan;11(1):71-3.
6. Prajapat L, Ariyarajah V, Spodick DH. Abnormal atrial depolarization associated with Chiari network? Cardiology. 2007;108(3):214-6.
7. Gonzalez A, Rodriguez JM, Meliá E, Alvarez M, Herrero F, Charines E, et al. Malformaciones y arritimias cardiacas fetales. Diagnóstico ecográfico y resultados perinatales. Actualidad obstétrico-ginecológica. [Review]. 1996;XIII:3.
8. Chiari network [database on the Internet]. Jeanty, P. 2006 [cited 28th March 2009]. Available from: www.thefetus.net.
9. Kerut EK, Norfleet WT, Plotnick GD, Giles TD. Patent foramen ovale: a review of associated conditions and the impact of physiological size. J Am Coll Cardiol. 2001 Sep;38(3):613-23.
10. Schneider B, Hofmann T, Justen MH, Meinertz T. Chiari"s network: normal anatomic variant or risk factor for arterial embolic events? J Am Coll Cardiol. 1995 Jul;26(1):203-10.
11. Larsen W.J. Human Embryology, Third edition, 2001. Churchill Livingstone.

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