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A dysmorphism which is due to an intrinsic defect in the developing structure.
What is the difference between agenesis and aplasia? Give ex. of each.
- Agenesis: complete failure to form the structure. Ex. Congenital absence of a thumb
- aplasia: a tiny nubbin of tissue represents a failed attempt to from the structure. Ex. aplasia of one kidney
What is hypoplasia?
The structure is significantly smaller than normal. x. hypoplasia of another kidney
What is hyperplasia?
The structure is significantly larger than normal. Ex. Macrodactyly
What is dysplasia?
- An aberration(differ from normal) in tissue differntiation - often resembles the embryonic stage of development, sometimes with tissue which is not normally present in this location.
- also use for a premalignant condition
- ex. renal dysplasia: immature nephrons, tubule-like structures surrounded by primite mesenchye and cartilage
What is malposition (ectopia)?
- The structure is present - but in an abnormal location.
- ex. ectopic thyroid
What is fusion effect?
- structures which form by fusion may fail to do so. These expecially occur in the midline.
- ex. neural tube defect, cleft palate
- or structures which are normally unconnecte may fuse or fail to separate
- ex. horseshoe kidney
what is atresia and stenosis?
- a tubular strucutre has no lumen or a narrowed lumen.
- stenosis may also be acquired later in life.
- ex: esophagel atresia
- ex: ureteral stenosis
what is duplication?
- Two structures instead of one - the opposite of agenesis.
- ex: polydactyly
The biologic bases of normal development and of
maldevelopment are poorly understood. There is a large gap between our rapidly expanding knowledge of molecular biology genetics and our knowledge of the anatomy and clinical
features of maldevelopment. The homeobox concept and other advances are a start in filling that gap. T or F
The great majority of malformations remain idiopathic. In a minority of instances _____ or _____ has been established.
- an etiologic agent (tertatogen)
- or a specific relationship
what are the 6 known etiology?
- mother illness
Describe how genetics causes birth defects.
- Single gene defects are very uncommon causes of congenital malformation.
- Polygenic defects and the interaction of genetic “factors” with environmental factors believed to be much more common.
- Ex: congetnital heart disease occurs in 1/200 of general population
Describe how karyoptype causes birth defects.
- Specific patterns of malformations occur in association with specific karyotypic abnormalities.
- There is, however, much variation and overlap.
Ex: Trisomy 18
Describe how maternal illness causes birth defects.
- mother's gene is transfer to her children
- ex. sacral dysplasia in the offspringof mothers with diabetes mellitus
Describe how chemical causes birth defects.
- a. Some teratogenic agents show target organ specificity.
- b. There is a critical time in gestation when teratogenic agents are effective; this corresponds to the window of time when the target organ is undergoing morphogenesis.
- c. Some teratogenic agents are species-specific. Post facto experiments using rhesus monkeys resulted in the same malformations as in humans.
- d.Individual variation in susceptibility. The offspring of some mothers who took multiple pills during the critical time in gestation were normal; in other instances, the defect followed ingestion of a single pill.
- ex. thalidomide
- vitamin A congeners - isoretinoic acid
- phenytoin - nail hypoplasia
- ethanol - fethal alcohol syndrome - facial abnormalities
describe how infections can cause birth defects.
- rubella, the virus, can crosses placenta from mother to embryo
- symptoms - blindness, deafness, congenital heart disease
how does radiation affect birth defect?
- 2 types of radiation -
- induced genetic damage (which can be induced by realatively low doses and may not manifest for generations)
- direct somatic effects result in malformation (require large doses)
What is deformation?
- abnormality in the form, shape or position of a structure which is due to an external mechanical factor compressing the structure
- occurs before birth during or after the formation of the structure
- ex. facial and limb deformities associated with oligohydramnios
what is disruption?
- A defect in a structure which is due to an external
- mechanical factor which “disrupts” the
- developing or already developed structure in
- ex. amniotic band which causes a facial cleft
Deformations and disruptions are likely or unlikely to recure while malformations may be part of a situionat which is more likely to recur.
What is multiple malformations and give example.
- Consider the possibility of a hereditary disorder, karyotypic abnormality, or exposure to a teratogenic agent.
- ex. A stillborn fetus has polydactyly, cephalocele and bilateral renal dysplasia. This is an autosomal recessive disorder.
What is a syndrome and give ex?
A characteristic pattern of dysmorphisms. The pattern cited in the first example above is characteristic of Meckel’s syndrome
What is association and give example?
- A more-than-chance occurrence of multiple dysmorphisms - but “softer” than that of a syndrome.
- Example: VATER association -
- Vertebral/Anal/Tracheo-Esophageal fistula/Radial and/or Renal malformations. Highly variable.
What is a sequence and give example?
- One or more congenital dysmorphisms leading to other dysmorphisms.
- Example: Dr. Potter described a syndrome of bilateral renal agenesis, facial flattening, limb deformities and bilateral pulmonary hypoplasia. These pregnancies are associated with oligohydramnios. Facial flattening, limb deformities and pulmonary hypoplasia also occur in other situations in which there is oligohydramnios. Oligohydramnios can occur as the result of lack of amniotic fluid formation (urine is the major component of amniotic fluid and bilateral renal aplasia or severe dysplasia will result in oligohydramnios) or as the result of amniotic fluid loss (rupture of placental membranes). Potter syndrome is now known as Potter sequence.
Describe the reasons why perinatal autopsies should be done.
- Perinatal was defined as "from 20 weeks gestation to 1 month after birth"
- autopsy was essential in determining the "cause of death" in 26% of the cases
- essential in about 50% of cases in which genetic counseling was done
- perinatal autopsies contributes useful information in early all cases
- important info for areas like intrauterine growth retardation, immaturity vs. dysmaturity...
- contributed to pioneer studies in prenatal medicine. amniocentesis for intrauterine diagnosis and intrauterine "surgery" was used to treat fetal hydrocephalus
Define and describe the major features of SIDS.
- the sudden unexpected death of an infant under 2 year of age which remains unexplained after a complete postmortem examination
- An apparently well baby is put down in the evening - and found dead the next morning
- The death is unobserved. The baby is found in a prone position.
- The largest single “cause” of post-neonatal infant death.
- Peak frequency is at 2 - 3 months of age.
- Very uncommon before 1 month and less than
- 10% after 6 months of age
- 20% of SIDS are explained at autopsy - finding of previously unknown congenital heart disease, meningitis, trauma
- other 80% of SIDS, no explanation with autopsy. Findings that is not specific to SIDS: petechiae on surface of throacic organs or minor degrees of inflammation in upper respiratory tract
- Risk factors: premature brith, low socioeconomic status, a young mother, and cigarrette smoking
- many theories to explain SIDS: acute or chronic hypoxemic mechanism and avoiding sleeping prone position
What is the spectrum of effects on the host?
- 1. no effect (abnormal but not pathologic)
- 2. compatible with a normal lifespan - but with impairment
- 3. shortened lifespan
- 4. compatible with intrauterine life - but lethal after birth
- 5. incompatible with intrauterine life
What is incidence of birth defects?
- difficult to determine
- major congentital dysmorphisms are said to occur in up to 3% of liveborn individuals
- minor in up to 7-10%
Distinguish between abnormal vs. pathologic, congenital vs. heredity, and "present at birth" vs. "manifest at birth"
Describe the major pathologic feature of "shaken baby syndrome" and given an example of a cause of mistaken diagnosis of child abuse.
- features: tearing of bridging veins resulting in subdural hematoma, retinal hemorrhage is possible
- conditions that can be confused with child abus are in the following 4
- 1. multiple fractures due to previously undiagnosed osteogenesis imperfecta
- 2. welts of a "bating" can be simulated by photoxic dermatitis
- 3. glutaric acidemia, Type I may be associated with subdural hematomas
- 4. coagulopathies and increased capillary fragility disease
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