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I. Human malformations occur in 2-3% of births. Some examples of these are

 A. SINGLE MONSTERS

1. Phocomelia: limb anomaly spontaneously create Seen in

1/100,000 births

a. A typical lesion of thalidomide: 10% of the women whotook t he drug during the critical period had babies with

this anomaly

2. Coelosomy: a defect of closure of the abdominal wall whereby

the normally developed abdominal viscera are found in an

extra-abdominal position

3. Craniorrhachischisis: complet e failure of the neural tube to

close

a. There are angiomatous degeneration of nervous tissue,

absence of t he cranial vault, and absence of the

posterior arches of the vertebra

B. DOUBLE MONSTERS OR DOUBLE-TYPE MALFORMATIONS can be

considered as nonseparated twins with the degree and type of fusion

being variable

1. Janus-type (janiceps) cephalothoracopagus (pagus, meaning

something fastened)2. Asymmetric thoracopagus

3. Acardia is one of a pair of monozygot ic twins which has

degenerated after a failure of vascularization. Structures

already present regress, ending in the formation of what looks

like an amorphous mass with no organization

C. EXPERIMENTAL MALFORMATIONS: the mammalian embryo, despite its

apparent protect ion, is very sensitive t o t he influence of various

exte rnal teratogenic agent s. Most of the malformations, seen in

humans clinically, have been reproduced experimentally

1. Classification of te ratogenic factors: usually described in 5 major

groups

2. Physical facto rs: x-rays, radiation, et

3. Chemical factors: hypoglycemia, antitumor drugs,

neurepileptics, et

4. Nutritional factors: hyper- or hypovitaminosis, mineral excess, ordeficiencies, vitamin imbalance, et

5. Hormonal factors: use of androgens, synthet ic progesterones,

cortisone, et

6. Infect ious facto rs: toxoplasmosis, ricket tsioses, Asian flue, and

viruses

7. Viruses: especially rubella or German measles, cytomegalovirus,

herpes simplex virus, measles, mumps, hepatits, poliomyelitis,

chickenpox, syphilis, ECHO virus, and Coxsackie virus. A number

have been implicated but not all cause malformations

Mode of action of teratogenic factors: the effect dependspredominantly on the stage of intervention of the agent(chronologic factor) and the genetic constitution(constitutional factor). Several types of sensitivity are listed

Time or stage of sensitivity

32. Congenital Malformations And Their Causes: Human Malformations

Review of MEDICAL EMBRYOLOGY Book by BEN PANSKY, Ph.D, M.D.

PREV NEXTTABLE OF CONTENT31. Congenital Malformations And Their Causes 33. The Fetal Membranes

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Before implantation: exte rnal agents, according to theirintensity, provoke either completely rreversible lesions ordefinitive mortal lesions

 Aft er implantation and during the ent ire period of activemorphogenesis: this is the principle teratogenic period becausea primordium is most sensitive to teratogenic actions at thetime of its appearance

a) The same substance can produce different malformations if given at different stages o f morphogenesis

b) When more than 1 primordium develop simultaneously, thesame agent can result in multiple malformations

Species sensitivity: an agent teratogenic for 1 species may not

be so for another

Strain sensitivity: even in the same species, t he pe rcentage of malformations seen with any substance can vary according tostrain and even the line

Individual sensitivity: even in the same animal litter subjectedto a teratogenic influence, certain individuals react differentlyand may be free of any malformations. Even those malformedare not so to the same de gree necessarily. Different metabolicpeculiarities may explain t hese individual variations and alsothose seen between strains

PREV NEXTTABLE OF CONTENT31. Congenital Malformations And Their Causes 33. The Fetal Membranes

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