A 16-year-old obese primigravida girl comes to the emergency department in active labor. In an attempt to conceal the pregnancy from her family, the patient did not receive prenatal care or take prenatal vitamins. A fetal heartbeat is undetectable, and she delivers a stillborn boy via vaginal delivery. Examination of the stillborn shows several dysmorphic features including closely set eyes and a midline mass consistent with a proboscis. A fetal autopsy reveals fused cerebral hemispheres with an absent forebrain fissure and a single intracranial ventricle. Which of the following is the most likely mechanism for these findings?

Question

A 16-year-old obese primigravida girl comes to the emergency department in active labor.  In an attempt to conceal the pregnancy from her family, the patient did not receive prenatal care or take prenatal vitamins.  A fetal heartbeat is undetectable, and she delivers a stillborn boy via vaginal delivery.  Examination of the stillborn shows several dysmorphic features including closely set eyes and a midline mass consistent with a proboscis.  A fetal autopsy reveals fused cerebral hemispheres with an absent forebrain fissure and a single intracranial ventricle.  Which of the following is the most likely mechanism for these findings?

Quizplus · Accepted Answer

11ec160b_3748_779f_9249_11ac95dd5dc3_MD0001_00 The physical features of the stillborn are consistent with holoprosencephaly (HPE), which is a spectrum of structural abnormalities of the brain and face due to incomplete division of the forebrain (prosencephalon) into 2 hemispheres. Cleavage of the prosencephalon into the telencephalon and diencephalon normally occurs at 5 weeks gestation. Failure of cleavage at different points in division can result in an array of anomalies ranging from mild midline defects (eg, ocular hypotelorism, cleft lip/palate) to severe defects (eg, single midline eye, primitive nasal structure or proboscis, midfacial clefts). HPE is likely caused by a combination of genetic (eg, trisomy 13, sonic hedgehog gene mutations) and environmental (eg, maternal alcohol use) factors. It is an example of a developmental field defect, which is when an initial embryonic disturbance leads to multiple malformations by disrupting the development of adjacent tissues and structures within a particular region. (Choice A) Agenesis refers to the complete absence of an organ. Renal agenesis, the congenital absence of one or both kidneys, is an example of this type of abnormality. (Choice B) An association refers to multiple anomalies without a known unifying cause that occur together more frequently than chance alone would predict. Vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal anomalies, and limb abnormalities (VACTERL) are an example of an association of anomalies without a known common etiology. (Choice C) Deformations are fetal structural anomalies that occur due to extrinsic mechanical forces. The pressure applied by the uterus is one of the most common deforming forces. For example, uterine constraint on a fetus in breech position can cause developmental dysplasia of the hip, a condition marked by abnormal development of the femoral-acetabular junction and subsequent hip instability. (Choice D) Dysplasia describes abnormal organization of cellular architecture within a tissue. Osteogenesis imperfecta, a skeletal disorder characterized by brittle bones that fracture easily, occurs with dysplasia of connective tissue due to absent or abnormal type I collagen. Educational objective: A developmental field defect describes multiple malformations that occur secondary to an embryonic disturbance in an adjoining group of cells. Holoprosencephaly is a developmental field defect characterized by a spectrum of fetal anomalies due to incomplete division of the forebrain (prosencephalon). __________ References: Holoprosencephaly: recommendations for diagnosis and management. (http://www.ncbi.nlm.nih.gov/pubmed/20859208) Holoprosencephaly: a survey of the entity, with embryology and fetal imaging. (http://www.ncbi.nlm.nih.gov/pubmed/25590404)

A 16-Year-Old Obese Primigravida Girl Comes to the Emergency Department