There is a large number of morfogenesis disorders that can occur
during intrauterine development. The basic terminology is given here:
- Malformation
- Morphological defects of organs or organ parts
resulting from anomal development, which was pathologic right from the start.
Malformations can occur on a genetic or evironmental basis.
For example neural tube defects: neural tube fails to close, it
has never formed in a normal way.
- Disruption
- Secondary defect in the development of an organ or its part, which was developing
correctly at the beginning. The etiological factors are either
external or internal, but are not hereditary.
For example:
amniotic bands — as a result of a
amnion rupture during the fetal development,
strands of the amnion are released and encircle parts of the body of the
fetus, causing constrictions or even amputations.
- Deformation
- Deformations develop during later stages of intrauterine development
as a result of mechanical powers (pressure)
causing abnormal shape or position of a body part.
In these cases, the development of the fetus is not much disturbed, but
is diverted from the original course. There are many etiological factors,
for example a small or malformed uterus, leiymyomatosis,
oligoanhydramnion, abnormal positions of the fetus or multiple gravidity.
Examples: limb dislocations or pes equinovarus (clubfoot).
- Sequence
- Term used to describe the origination of secondary
congenital anomalies, which develop in cascade as
a consequence of a primary malformation.
For example Potter's sequence (oligohydramnial sequence),
which is (in more detail) described
in the congenitalia anomalies of the urogenitalia tract.
It is a pathological state caused by a lack of amniotic
fluid (for various reasons:
chronic efflux of the amniotic fluid or kidney agenesis)
leading to a sequence of secondary fetal anomalies (flattened face,
limb deformations, pulmonary hypoplasia).
- Syndrome
- Term used to describe symptoms and anomalies
present together. The collective occurence is not random,
but relates to the etiology of the process. As opposed to the
sequence, syndrome is nor not caused by any primary malformation.
Syndromes often originate from one etiologic agent,
for example some specific chromosomal aberration
(as is Down syndrome — trisomy 21,
described in more detail in
another part of the chapter)
or viral infection.
- Association
- Term used to describe a situation, where certain signs or abnormalities occur together more often
than would be expected by chance alone, but the reasons are not yet known.
The point is that if one anomaly is found, organs with an increased risk of associated anomalies
should be examined carefully. Examples: VATER association —
vertebral, anal, tracheoesophageal and radial anomalies often occur together.
- Agenesis
- complete absence of an organ and its primordia.
- Aplasia
- absence of an organ resulting from damaging its primordia.
- Atresia
- absence of an opening of mostly visceral organs.
- Hypoplasia
- a not-so-serious stage of aplasia, the organ is not
completely developed and the number of cells
in its structure is decreased.
- Hyperplasia
- organ enlargment caused by an increase in the number of its cells.
- Dysplasia
- in the malformation context, dysplasia is defined as an abnormal organisation of cells.
