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Amniotic Band Syndrome by Kinsie Linman
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Abstract
Amniotic band syndrome has been studied since the time of Hippocrates and Aristotle. Speculations regarding the etiology of the syndrome over the years ranged from maternal impressions, focal development errors in the formation of limb connective tissue and finally to the rupture of the amnion and entrapment of fetal parts by the mesodermic strands that emanate from the chorionic side of the amnion. The most common triad of clinical manifestations is congenital distal ring constrictions, intrauterine amputations and acrosyndactyly.(1) The prevalence of amniotic band syndrome among live births is estimated to be around 7.7:10,000. Among abortuses it may be as high as 178:10,000. It affects males and females in the same proportion.(2) It is important for sonographers to be able to determine and evaluate the pregnancy with amniotic bands to help in care for the parent and child.
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Keywords
amniotic band syndrome, amnion, chorion, restrictions, constrictions, dissection, amputation, amniotic sheets
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Introduction
Amniotic Band Syndrome (ABS) is a group of congenital abnormalities. Many medical authors have stated that ABS is caused by bands of amnion that become attached to the fetus. Abnormalities result from attachment and or constriction that lead to webbing of the fingers and toes, amputation of limbs, severe defects of the head and the face, spine, umbilical cord and or body wall. The clinical manifestations of amniotic band syndrome vary from minor deformities to severe and even lethal anomalies.(3) The purpose of this paper is to inform and provide knowledge of this obstetric pathology.
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Body
Amniotic Band Syndrome (ABS) is a group of congenital abnormalities caused by bands of amnion that become attached to the fetus during pregnancy.(3) Amniotic Band Syndrome is a common, nonrecurrent cause of various fetal malformations involving the limbs, craniofacial region, and the trunk. The amniotic bands, or strands of fibrous tissue, can entangle or amputate fetal parts.(4) True amniotic bands are a relatively rare entity. They can freely criss-cross in the amniotic sac, can be multiple, and can be attached to fetal body parts. Entanglement of the fetus in the bands may occur, which results in a range of abnormalities ranging from band constriction to full amputation of limbs, dissection of the abdomen, or cranium, and other bizarre anomalies.(5)
The amnion and the chorion normally fuse by 14 weeks; however, separation may persist into the second trimester and may become an abnormal finding. Persistence after 16 weeks may be associated with rupture of the amnion. Rupture of the amnion without rupture of the chorion can lead to the passage of the fetus from the amniotic to the chorionic cavity.(6) Here in the chorionic cavity the fetus may adhere and fuse with the chorion.(4) Early rupture, within 45 days of gestation, leads to the most severe malformations of the fetus, particularly the central nervous system, face, and viscera. Amniotic bands may tear or disrupt previously normally developed structures leading to amputations and nonanatomic fetal facial clefts.(6)
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Etiology
The etiology for the most part is still uncertain. There have been reports associating amniotic band syndrome with early rupture of the amnion, maternal trauma, oophorectomy during pregnancy, intrauterine contraceptive devices, and amniocentesis.(1) The most widely accepted cause of ABS is the rupture of the amnion occurring early in gestation. The fibrous bands that occur from the amniotic rupture encircle the limbs, resulting in tourniquet-like defects and intrauterine amputations.(3)
The timing of the rupture is believed to occur between 28 days after conception and 18 weeks of gestation. However, late bands can occur and present at birth with multiple abnormalities of the limbs, even after a normal sonogram was performed in earlier gestation.
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Symptoms/Diagnosis
The earliest that amniotic bands have been detected was at 12 weeks gestation, by transvaginal ultrasound. Bands are often hard to detect by ultrasound, and are more often diagnosed by the effect they have on the fetal anatomy, as in the case of missing or misshapen limbs. The characteristic appearance of an aberrant sheet or band of amnion attached to the fetus with resultant deformity and restriction of motion allows a diagnosis of Amniotic Band Syndrome to be made. Ultrasound detection of bands is helpful in confirming the diagnosis of ABS as the cause of fetal deformity. However, observation of these bands without fetal abnormality is not Amniotic Band Syndrome. It is important for the sonographer to distinguish amniotic bands from other membranes or separations with the amnion.(3)
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Differential Diagnosis
Visualization of a band like structure should not be confused with amniotic band syndrome when thorough fetal anatomy survey reveals no structural anomalies. A synechia is a term meaning adhesion, or fibrous scar. Uternine synechia have also been described as “amniotic sheets” or “amniotic folds”. Most commonly, uternine synechiae are noted as an incidental finding on obstetric sonograms. In general they do not interfere with the development and growth of pregnancy, and are rarely associated with any complications. Synechia appear as a shelf-like thick band communicating along its length with the uterine wall, in other words, it has a base and a free edge unlike amniotic bands. Synechia also shows blood flow when interrogated with color Doppler, where as the vast majority of amniotic bands show no color flow. The sonographer should carefully evaluate an exam presenting with this type of anomalies and ensure all possible anatomy is seen to rule out the attachment of any fibrous bands to the fetus.(5)
Other less common types of band-like appearing structures may also be observed on an obstetric sonogram. These include: chorio-amniotic separation( which is normal finding in the first trimester up until 16 weeks), velamentous cord insertion, uterine fusion abnormalities (bicornate, septate uterus), and remaining membranes of a demised twin.(4) In these situations, correlation of ultrasound features with patient’s clinical history can be useful.
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Sonographic Appearance
Sonographically the bands may be observed while a real time obstetric study is being performed. The sonographer may observe where the bands are attached to the uterine wall and what, if any, constriction is placed on the fetus. Careful observation with real time scanning will allow the sonographer to determine if the fetus is free from the band or if movement is restricted.(4) Usually thin membrane like strands criss crossing the amniotic sac and attaching to fetal body parts are seen. The most common findings are constriction rings, which can be demonstrated on entangled body parts and are often associated with distal lymphedema.(5) The most common constriction rings are found on the fingers and toes.(1) Associated fetal anomalies are usually present, and may be severe. These include: asymmetric craniofacial clefts, abdominal wall disruptions, and limb deformities. Any body area may be involved and the characteristic anomalies can be described as: restrictions, constrictions, dissection, and amputations.(5)
Cranial involvement may be detected as anencephaly and facial clefts.(4) In classic anencephaly the calvarial bones are symmetrically absent, while in anencephaly caused by ABS there is some portion of the calvarium present. Spinal deformity associated with an abdominal wall defect is particularly suggestive of ABS. While the typical appearance of an omphalaocele is possible, the more common defect is a large slash like defect of both the thoracic and abdominal cavities.(3)
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Treatment/Prognosis
Prognosis varies depending on the associated anomalies. It can be quite good for infants with only minor constriction rings and lymphedema of the digits. Children with limb amputations require reconstructive or plastic surgery and prosthesis. The syndrome is lethal for the severe forms with multiple associated anomalies.(1)
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Conclusion
As a sonographer this paper should help you to recognize and present this process of pathology. Also it should reinterate how carefully one should scan when performing an obstetric exam to ensure all aspects of the anomalies are discovered and interrogated. Amniotic Band Syndrome can be lethal to the fetus or the child can develop and live a relatively normal lifestyle with plastic surgery and prosthesis, if needed. It is a rare pathology to discover, but each sonographer should be skilled in using the knowledge acquired to differentiate the type of fibrous adhesions in the uterus. Correlations of ultrasound imaging and patient history and symptoms can be useful in the diagnosis of the fetal pathology, Amniotic Band Syndrome.
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References
• Prenatal Sonographic Diagnosis of Focal Musculoskeletal Anomalies: Korean Journal of Diagnostic Radiology. December 2003 Volume 4 Issue 4: Jung Ryu, MD , Jeong Cho, MD , Long Choi, MD
• Amniotic Band Syndrome: Department of Radiology Sonographer’s Fetal Course 2006 www.thefetus.net. Luis Flavio Goncalves, MD , Philippee Jeanty, MD, PhD
• The Fetus With Amniotic Band Syndrome: Fetal Care Center of Cincinnati
www.fetalcarecenter.org.
• Textbook of Diagnostic Ultrasonography: Sandra L Hagen-Ansert 5th Edition
• Recognizing Intra-Amniotic Band-Like Structures on Obstetric Ultrasound
September 1999 www.obgyn.net Martin Necas, RDMS, RVT, Terry DuBose, MS, RDMS, Joseph Worrall, MD, RDMS
http://www.obgyn.net/us/cotm/9909/bands.htm
• Ultrasound Abnormalities of Amniotic Fluid, Membranes, Umbilical Cord, & Placenta: Obstetrics & Gynecology Clinic of North America: Tersea Marino, MD
Volume 31 Number 3 March 2004
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Copyright CVTC 2003-2006. All Rights Reserved.