A 35-year-old woman, gravida 2 para 1, comes to the office for a routine prenatal visit. Her first child was born with a hydrocele and syndactyly of the first and second toes. The patient has no significant medical problems and takes no medications except for a multivitamin. Examination reveals clear lungs and normal first and second heart sounds. The abdomen is soft and nontender. Uterine size, fetal movements, and fetal cardiac activity are all within appropriate limits. The patient undergoes amniocentesis during the 18th week of pregnancy. Amniotic fluid analysis shows an increased level of acetylcholinesterase. This patient's amniocentesis results most likely suggest failure of which of the following processes?

Question

A 35-year-old woman, gravida 2 para 1, comes to the office for a routine prenatal visit.  Her first child was born with a hydrocele and syndactyly of the first and second toes.  The patient has no significant medical problems and takes no medications except for a multivitamin.  Examination reveals clear lungs and normal first and second heart sounds.  The abdomen is soft and nontender.  Uterine size, fetal movements, and fetal cardiac activity are all within appropriate limits.  The patient undergoes amniocentesis during the 18th week of pregnancy.  Amniotic fluid analysis shows an increased level of acetylcholinesterase.  This patient's amniocentesis results most likely suggest failure of which of the following processes?

Quizplus · Accepted Answer

11ec160b_374a_7373_9249_c5fbf78f2cfb_MD0001_00 Neural tube defects (NTDs) occur due to failure of fusion of the neural plate edges during the 4th week of fetal development. Fusion begins in the cervical region and proceeds toward the cranial and caudal ends of the neural tube (ie, the rostral and caudal neuropores). Failure of the rostral neuropore to close results in anencephaly, whereas impaired closure of the caudal neuropore causes spina bifida. If either neuropore does not fuse, an opening persists between the neural tube and the amniotic cavity that allows leakage of alpha-fetoprotein (AFP) and acetylcholinesterase (AChE) into the amniotic fluid. AFP can also cross the placenta and is detectable in the maternal serum. Detection of AFP and AChE is used for prenatal screening of NTDs (eg, spina bifida cystica, anencephaly). (Choice A) Duodenal atresia is a result of impaired recanalization of the duodenal lumen due to failure of epithelial cell apoptosis during fetal life. Although it can cause increased levels of amniotic fluid (ie, polyhydramnios), it is not associated with elevated levels of AChE. The first child's syndactyly is also an example of failed apoptosis of mesenchyme between the digits. (Choice C) Failed involution of the thyroglossal tract can lead to formation of a persistent thyroglossal duct cyst. It typically presents as a painless midline mass close to the body of the hyoid bone. Amnionic fluid AChE level is not elevated. (Choice D) Chromosomal disjunction during meiosis involves separation of 23 pairs of homologous chromosomes in anaphase I, followed by separation of 23 pairs of sister chromatids during anaphase II. Advanced maternal age is a risk factor for Down syndrome (nondisjunction of chromosome 21), which presents with low AFP and normal AChE levels in the amniotic fluid. (Choice E) Hirschsprung disease involves failure of neural crest cells to migrate into the sigmoid colon/rectum. It leads to absence of the myenteric and submucosal nervous plexuses, causing tonic constriction of the affected intestinal segments with consequent bilious emesis, abdominal distension, and failure to pass meconium. (Choice F) Failure of the processus vaginalis to obliterate can lead to congenital hydrocele or indirect inguinal hernia. Neither condition is associated with increased amniotic AChE levels. Educational objective: Neural tube defects most often occur when the neural folds fail to fuse in the region of the anterior or posterior neuropores. Persistent communication between the spinal canal and the amniotic cavity allows leakage of alpha-fetoprotein (AFP) and acetylcholinesterase (AChE) into the amnionic fluid, leading to elevated levels of AFP and AChE that can be detected on amniocentesis. __________ References: Mechanisms of tissue fusion during development. (http://www.ncbi.nlm.nih.gov/pubmed/22510983)

A 35-Year-Old Woman, Gravida 2 Para 1, Comes to the Office