]> 2026-07-31T12:14:21+00:00 WBR0885 0 en Agenesis Ageneis refers to absent organ development due to absent primordial tissue Malformation Malformation refers to an error that occurs anywhere during the embryonic period between 3 to 8 weeks of embryogenesis. Deformation Deformation is an enbryologic defect that occurs after 8 weeks. Aplasia Aplasia is absent organ development despite the presence of primordial tissue. Migration defect Migration defects are classically seen with neural crest cells. Examples include aotricopulmonary septum formation defects and Hirschprung disease. Several embryologic anomalies in organ development and maturation can be encountered. Typically the anomalies are classified according to either the presence or absence of primordial tissue or the time period during which they most likely occur. In general, 5 common error can be described. Malformation refers to an error that occurs anywhere during the embryonic period between 3 to 8 weeks of embryogenesis. A deformation is anything that occurs after 8 weeks. Before 3 weeks defects are usually fatal. In terms of primordial tissue, agenesis refers to absent organ development due to absent primordial tissue, while aplasia is absent organ development despite the presence of primordial tissue. Hypoplasia refers to incomplete organ development. Spina bifida is a neural tube defect by which the bony spinal canal fails to close completely due to the failure of the neuropores to close at 4 weeks of development. It usually presents with a tuft of hair on the lumbar area. Spina bifida is a classical example of a malformation.<br/> '''Educational Objective:''' Spina bifida is an example of malformation that occurs usually around 4 weeks of gestation.<br/> '''References:''' Spranger J, Benirschke K, Hall JG, et al. Errors of morphogenesis: concepts and terms. Recommendations of an international working group. J Pediatr. 1982;100(1):160-5. Embryology A child born to a 28-year-old homeless woman is transferred to the neonatal intensive care unit directly after birth for treatment of respiratory distress. Although the mother had several personal difficulties in the past months, she reports that the pregnancy was smooth and she was always followed up at community healthcare facility. After the infant is stabilized, the physician proceeds with an initial physical examination. Although the physical exam is mostly unremarkable, the physician notices a small tuft of hair of the infant's lower back. What is the most likely congenital anomaly in this patient an example of? B General Principles 2020-10-28T01:59:28Z 2459150.582963 WBR0885