Generality
Agenesia is the medical term that describes the complete absence of an organ, due to an incorrect embryonic development.
The episodes of agenesis, therefore, are anatomical anomalies of a congenital nature.
Agenesis should not be confused with aplasia: while in case of agenesis, the affected organ is completely absent, in case of aplasia the organ concerned is minimally sketched.
Definition of agenesis
Agenesia is the term that, in medicine, indicates the complete absence of an organ, following an error during embryonic development
An agenesis is, in fact, an anatomical anomaly of the congenital type, where "congenital" means "present from birth".
Numerous organs of the human body can be the object of agenesis.
AGENESIA AND APLASIA ARE SYNONYMS?
Although it is a fairly widespread trend, identifying the agenesis with aplasia is a mistake.
In fact, while agenesis is the complete absence of an organ, the term aplasia indicates the failure to develop an organ or tissue, where "failure to develop" means "development not carried through".
In essence, therefore, if in the first situation (agenesis) there is not even a sketch of the organ concerned, in the second situation an attempt - albeit minimal - of development of the organ involved exists and is sometimes even visible.
ORIGIN OF THE NAME
The term "agenesis" derives from the union of two Greek words, which are: the so-called privative alpha, corresponding to the initial letter "a, " and "genesis" (γενεσις). The privative alpha denotes a lack, while "genesis" means "birth" or "generation".
Therefore, the meaning of agenesis is "lack of generation".
Types
There are various types of agenesis . The criterion of distinction for the various types is, as can be guessed, the body concerned.
The most common types of agenesis include: renal agenesis, penile agenesis, testicular agenesis, corpus callosum agenesis, Müllerian agenesis, uterine agenesis and phocomelia.
Among the less common types of agenesis, on the other hand, we note: gall bladder agenesis, ocular agenesis, ear agenesis and dental-oral agenesis.
RENAL AGENESIA
Renal agenesis is a congenital anatomical anomaly, characterized by the absence, from birth, of one or both kidneys . Specifically, the lack of a kidney only is called unilateral renal agenesis, while the lack of both kidneys is better known as bilateral renal agenesis .
Renal agenesis in its unilateral form is definitely more widespread than renal agenesis in its bilateral form; according to reliable statistical surveys, in fact, the first would affect a new born every 500, while the second would involve a new born every 4, 000.
For unknown reasons, the lack of one or both kidneys from birth (congenital deficiency) is more common in the male population.
Renal agenesis can be an isolated condition or a condition associated with pathological states, such as: trisomy 21, trisomy 22, trisomy 7, trisomy 10 or Turner syndrome.
The symptomatic picture of renal agenesis is variable: the absence of a kidney alone is an asymptomatic condition, as long as the only kidney present is healthy; on the contrary, the lack of both kidneys entails, already starting from fetal life, the presence of a condition known as oligohydramnios, from which other malformations can arise and, in the most serious cases, death at birth.
Anatomical malformations that may be associated with unilateral renal agenesis: |
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AGENESIA PENIENA
Penile agenesis is a congenital anatomical anomaly, which concerns exclusively the male population, characterized by the lack of a penis .
With an incidence equal to one case for every 5-6 million new born males, penile agenesis can be isolated or associated with testicular agenesis (which will be discussed later).
The main problem of males born with penile agenesis is the inability to eliminate urine. To remedy this problem, patients must be subjected to a specific surgical procedure, aimed at creating a functional urethra.
TESTICULAR AGENESIA
Testicular agenesis is the medical term that indicates a congenital anatomical anomaly, exclusive of the male population, which is characterized by the lack of testicles .
According to reliable studies, testicular agenesis would arise following the failure, during embryonic development, of some particular cells, called Leydig cells .
The lack of the testicles has various repercussions on the reproductive system functionalities of the concerned male: from the deficiency / absence of testosterone to the absence of spermatozoa and to the non-existent development of secondary sexual characteristics.
AGENESIA OF THE CALLOUS BODY
The agenesis of the corpus callosum is a congenital anatomical defect, marked by the absence of the so-called corpus callosum . The corpus callosum is the lamina of white substance, with a sagittal course and a curved shape, which is interposed between the two cerebral hemispheres and is composed of myelinated nerve fibers.
The agenesis of the corpus callosum depends on an error during fetal development of the brain, the latter process taking place between the third and twelfth week of gestation.
The causes of the aforementioned error are still uncertain. According to the most reliable hypotheses, they could consist of: chromosomal aberrations, hereditary genetic mutations, prenatal infections or head injuries, prenatal exposures to toxins, prenatal brain cysts or metabolic diseases.
The agenesis of the corpus callosum can determine various symptoms and clinical signs, including: visual difficulties, hypotonia, reduced motor coordination, slowing of movement, reduced perception of pain, difficulty in chewing and swallowing, cognitive deficits, attacks of epilepsy, spasticity, hearing problems, cranial malformations etc.
At the present time, there are no specific treatments for the agenesis of the corpus callosum, but only supportive treatments aimed at improving the symptomatology.
| Medical conditions to which the agenesis of the corpus callosum is very often associated: |
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Figure: the corpus callosum in the brain of the human being.
AGENESIA MULLERIANA AND AGENESIA UTERINA
Exclusive of the female population, Müllerian agenesis and uterine agenesis are two particular anatomical anomalies of congenital nature, which are characterized, respectively, by the absence of the uterus, combined with more or less severe malformations of the proximal portion of the vagina, and for the mere absence of the uterus.
In other words, while women with Müllerian agenesis lack the uterus and have an abnormal vagina, women with uterine agenesis are only deprived of the uterus.
Both Mülleriana agenesia and uterine agenesis are responsible for a condition of primary amenorrhea, in which the levels of sex hormones are normal due to the presence of functional gonads.
Sometimes associated with renal agenesis or vertebral abnormalities, Müllerian agenesis and uterine agenesis are two examples of Müllerian duct anomalies ; to be precise, they are anomalies of the Müllerian class I ducts .
phocomelia
Phocomelia is a very rare genetic disease that causes congenital anatomical anomalies of varying severity in the limbs, head and / or internal organs.
The phocomelia is included in the list of forms of agenesis, since, among the possible anatomical anomalies dependent on it, there are also the lack of upper or lower limbs and the lack of lungs.
AGENESIA OF THE CISTIFELLEA
The agenesis of the gall bladder is a congenital anatomical anomaly, which is characterized by the absence of the gall bladder.
Very often asymptomatic, this particular condition is very rare indeed; according to some statistical studies, in fact, it would have an incidence on the general population of less than 0.1%.
EYE AGENESIA
Ocular agenesis is a congenital anatomical anomaly characterized by the absence of eyeballs.
AGENESIA OF THE EARS
The agenesis of the ears is a congenital anatomical anomaly, which can be distinguished by the absence of all the components of the ears (from the external ear to the inner ear) or due to the absence of only the external portion (inner ear).
While people who lack all the components of the ears are completely deaf, the subjects lacking only the external ear still have a certain degree of hearing ability.
DENTAL-ORAL AGENESIES
Dental-oral agenesis is a group of malformations, characterized by the lack of elements that constitute the mouth.
Among the various dental-oral ageneses, they deserve a mention: anodontia, aglossia and agnatia .
Anodontia is the agenesis of teeth ; this particular condition can affect both the primary and secondary dentition.
Alloxia is the agenesis of the tongue ; therefore the interested subjects do not present the language.
Finally, agnatia is the agenesis of the mandibular bone or jaw .
