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Agenesis

Agenesis is a congenital condition defined as the complete or partial absence of an organ, tissue, or body structure due to its failure to form during embryonic or fetal development in utero.^[1]^[2] This malformation arises from disruptions in early organogenesis and can affect virtually any part of the body, though it most commonly involves the genitourinary, central nervous, respiratory, and skeletal systems.^[3] Notable types include renal agenesis, the absence of one (unilateral) or both (bilateral) kidneys, with unilateral cases occurring in approximately 1 in 2,000 live births and bilateral cases in 1 in 5,000; bilateral renal agenesis is typically incompatible with life without dialysis or transplantation due to lack of urine production leading to oligohydramnios and pulmonary hypoplasia.^[4]^[1] Another prominent form is agenesis of the corpus callosum (ACC), a brain anomaly involving partial or complete absence of the structure connecting the cerebral hemispheres, with a prevalence of about 1 in 4,000 live births and often associated with intellectual disability, seizures, or other neurodevelopmental issues.^[5]^[6] Müllerian agenesis (also known as vaginal agenesis or Mayer-Rokitansky-Küster-Hauser syndrome), characterized by underdevelopment or absence of the uterus and upper vagina, affects 1 in 4,500–5,000 female births and primarily impacts reproductive function, though affected individuals typically have normal ovaries and external genitalia.^[7]^[8] The etiology of agenesis is multifactorial and varies by organ, but commonly involves genetic mutations (such as those affecting developmental pathways like axon guidance or duct formation), chromosomal abnormalities, or environmental exposures including maternal diabetes, infections, or teratogens during the first trimester.^[5]^[9] Many cases are isolated, but up to 50–80% may occur as part of syndromes or with other malformations, necessitating genetic counseling and multidisciplinary management ranging from prenatal diagnosis via ultrasound to postnatal surgical reconstructions or supportive care.^[6]^[7]

Definition and Overview

Definition

Agenesis refers to the complete or partial congenital absence of an organ, tissue, or body part resulting from the failure of its development during embryogenesis. This condition arises due to the absence of primordial tissue that would normally form the structure, distinguishing it from hypoplasia, which involves underdevelopment with some residual tissue present, and aplasia, which is often used interchangeably with agenesis but may imply the presence of rudimentary elements in certain contexts, such as a blind-ending bronchus in pulmonary cases.^[3]^[10]^[11] Embryologically, agenesis occurs during the organogenesis phase, typically between weeks 3 and 8 of gestation, when precursor cells fail to proliferate, migrate, or differentiate properly, leading to non-formation of the structure rather than later degeneration as seen in atrophy. For instance, in renal agenesis, the metanephric blastema does not induce ureteric bud development, resulting in the complete absence of one or both kidneys. This failure contrasts with acquired absences and underscores agenesis as a primary developmental defect present at birth.^[12] The term "agenesis" derives from the Greek roots "a-" meaning "without" and "genesis" meaning "origin" or "birth," reflecting its connotation of failed origination. It was first introduced in medical literature in the early 19th century, appearing in pathology reports on congenital malformations around 1827, as documented in contemporary medical periodicals.^[13] Prevalence of agenesis varies widely by the affected organ. Examples include unilateral renal agenesis at about 1 in 1,000 to 2,000 births^[14] and pulmonary agenesis at roughly 1 in 15,000 live births,^[15] with rates higher in syndromic associations such as VACTERL or chromosomal disorders where multiple anomalies coexist.

Classification

Agenesis is classified primarily according to the organ system or structure affected, providing a framework for clinical evaluation and management. In the craniofacial region, it includes ocular agenesis (complete absence of the eye), dental agenesis (failure of tooth development), and auricular agenesis (absence of the external ear). Genitourinary agenesis comprises renal agenesis (absence of one or both kidneys) and Müllerian agenesis (congenital absence of the uterus and vagina). Neurological forms feature corpus callosum agenesis, characterized by missing interhemispheric brain connections. Musculoskeletal agenesis can involve limb bones, such as radial ray defects leading to absent forearms.^[5]^[16]^[17]^[18] The extent of agenesis further refines classification, distinguishing unilateral from bilateral involvement and complete from partial forms. Unilateral agenesis, affecting one side of the body, is generally viable and allows compensatory function from the contralateral structure, as seen in unilateral renal agenesis. Bilateral agenesis, involving both sides, often leads to severe complications or lethality, exemplified by bilateral renal agenesis causing oligohydramnios and pulmonary hypoplasia. Complete agenesis denotes total absence of the structure, while partial agenesis (or hypogenesis) involves rudimentary or incomplete development, such as partial corpus callosum agenesis where only the posterior portion is missing.^[16]^[5]^[14] Agenesis is also categorized as isolated or syndromic based on whether it occurs alone or as part of a multi-system disorder. Isolated agenesis involves only the affected structure without other anomalies, whereas syndromic agenesis is linked to broader conditions like VACTERL association, which features vertebral defects, anal atresia, cardiac malformations, tracheoesophageal fistula, renal agenesis, and limb abnormalities. Similarly, CHARGE syndrome includes coloboma, heart defects, choanal atresia, growth retardation, genital hypoplasia, ear anomalies, and occasionally renal agenesis. Genetic factors contribute to the syndromic forms, influencing multiple developmental pathways. Epidemiologically, isolated agenesis predominates in unilateral cases, but syndromic associations occur in approximately 30% of renal agenesis instances, underscoring the need for comprehensive evaluation.^[19]^[20]^[21]^[16]

Etiology

Genetic Factors

Agenesis of organs during embryonic development frequently stems from genetic disruptions that impair critical molecular pathways responsible for tissue formation and differentiation. These genetic factors encompass monogenic mutations, chromosomal anomalies, and polygenic influences, often leading to failure in organogenesis by altering transcription factor activity or signaling cascades. The contribution of genetic etiologies varies by organ type and presentation, with identifiable genetic causes implicated in 20-30% of congenital anomalies overall, and higher rates (often >70%) in syndromic cases where multiple anomalies coexist.^[22]^[6]^[23] Monogenic causes predominate in many familial and syndromic forms of agenesis, where single gene mutations disrupt key regulators of organ development. For instance, pathogenic variants in the PAX6 gene, a transcription factor essential for eye formation, cause ocular agenesis such as aniridia or severe microphthalmia by halting anterior segment development.^[24] Similarly, mutations in EYA1, which encodes a protein interacting with SIX1 in branchial arch and renal patterning, underlie branchio-oto-renal syndrome featuring renal agenesis and auricular malformations due to defective mesenchymal-epithelial signaling.^[25] In renal agenesis, HNF1B variants impair nephron induction and tubulogenesis, often resulting in cystic dysplasia or complete absence alongside diabetes risk.^[26] For Müllerian agenesis, LHX1 mutations disrupt gonad and uterine duct formation by affecting early mesodermal specification, leading to vaginal and uterine aplasia.^[27] These examples highlight how monogenic defects in transcription factors halt organ-specific embryogenesis, with over 20 such genes identified across agenesis types. Inheritance patterns of agenesis-related genetic defects vary, influencing recurrence risks in families. Autosomal dominant transmission is common in isolated dental agenesis, as seen with MSX1 or PAX9 mutations that reduce tooth bud initiation and exhibit incomplete penetrance.^[28] In contrast, autosomal recessive inheritance characterizes many bilateral renal agenesis cases, such as those involving biallelic variants in GFRA1 or GREB1L, which abolish RET-mediated ureteric budding and require both parental alleles for manifestation.^[29] Chromosomal abnormalities, including X-chromosome mosaicism, are rarely associated with Müllerian agenesis.^[30] Chromosomal abnormalities further contribute to agenesis by altering gene dosage or disrupting contiguous gene clusters. Microdeletions at 22q11.2, as in DiGeorge/velocardiofacial syndrome, are linked to corpus callosum agenesis through haploinsufficiency of TBX1 and nearby loci, impairing midline brain commissure formation.^[31] Aneuploidies like trisomy 13 and 18 elevate agenesis risk across organs; trisomy 13 frequently involves renal and ocular agenesis due to excess chromosomal material disrupting holoprosencephaly-related pathways, while trisomy 18 associates with similar multi-organ failures including gonadal agenesis.^[32] These structural variants account for about 10% of syndromic agenesis cases. Beyond monogenic and chromosomal mechanisms, polygenic and epigenetic factors drive many sporadic agenesis instances through cumulative variant effects and modifiable gene regulation. Polygenic risk, involving multiple low-penetrance loci, underlies non-syndromic forms like tooth or limb agenesis, where variants in AXIN2 or EDA interact to reduce odontogenic or appendicular signaling.^[23] Disruptions in HOX gene clusters, such as HOXD13 mutations, exemplify this by altering limb patterning and causing agenesis or brachydactyly via posterior prevalence shifts in mesenchymal condensations.^[33] Epigenetic modifications, including DNA methylation and histone acetylation at developmental loci, further modulate these risks, with aberrant silencing of HOX or WNT pathway genes contributing to organ failure in gene-environment contexts.^[34]

Environmental Influences

Environmental influences on agenesis primarily involve teratogenic exposures and intrauterine disruptions during early gestation, when organ primordia are forming. Maternal diabetes is a well-established risk factor for caudal dysgenesis, a spectrum of malformations that includes renal agenesis, with affected pregnancies showing up to a 200-fold increased incidence compared to the general population. Thalidomide exposure during the first trimester classically causes limb agenesis, such as amelia or phocomelia, by interfering with angiogenic processes essential for limb outgrowth. Excess retinoic acid, as seen with isotretinoin use, leads to craniofacial defects derived from neural crest cell disruptions, including ocular anomalies like microphthalmia and auricular malformations involving the external ear. Intrauterine factors, such as amniotic band syndrome, can cause disruptive agenesis through mechanical constriction, most commonly affecting limbs with transverse reductions or complete absence. Vascular disruptions during development are implicated in limb reduction defects, including agenesis, potentially due to interruptions in blood supply leading to tissue necrosis. Infections like rubella during early pregnancy contribute to ocular agenesis, with congenital rubella syndrome associated with microphthalmia or anophthalmia in affected cases. Aspects of maternal health, including smoking and alcohol consumption, elevate risks for multifactorial agenesis; for instance, prenatal alcohol exposure has been linked to bilateral renal agenesis or hypoplasia, while maternal smoking increases odds of urogenital malformations. Folate deficiency is strongly associated with neural tube defects and may contribute to other congenital anomalies through impaired DNA synthesis during embryogenesis. These environmental factors are most impactful during weeks 4-8 of gestation, coinciding with critical organogenesis phases. Overall, environmental influences account for approximately 5-10% of congenital anomalies, including non-syndromic agenesis, though they often interact with genetic predispositions to heighten susceptibility.

Specific Types

Ocular Agenesis

Ocular agenesis encompasses a spectrum of congenital malformations characterized by the absence or severe underdevelopment of the eye, primarily manifesting as anophthalmia and microphthalmia. Complete anophthalmia, also known as true anophthalmia, involves the total absence of ocular tissues, including the globe and often the orbit, resulting in an empty socket. Clinical anophthalmia refers to cases where a rudimentary globe is present but extremely small, accompanied by significant orbital hypoplasia that mimics complete absence. Microphthalmia, a less severe form, features an underdeveloped eye with reduced axial length (typically less than 20 mm) and corneal diameter (less than 10 mm), which may be simple (structurally normal) or complex (with additional anomalies). These conditions arise from a failure in the development of the optic vesicle during early embryogenesis, leading to defective ocular formation.^[35] Clinically, ocular agenesis presents with unilateral or bilateral blindness, as affected eyes lack functional vision due to the absence or malformation of key structures like the retina and optic nerve. Orbital cysts may form due to incomplete closure of the embryonic optic fissure, potentially protruding and complicating orbital development. Facial asymmetry is common, stemming from hypoplastic orbital bones and soft tissues on the affected side, which can lead to midfacial underdevelopment. Associated ocular anomalies frequently include coloboma, a gap in the iris, retina, or choroid, and congenital cataracts, which further impair any residual vision in microphthalmic eyes.^[35]^[36] Ocular agenesis is often linked to specific genetic syndromes, with approximately 30-50% of cases being syndromic rather than isolated. Mutations in the SOX2 gene are a leading cause of bilateral anophthalmia or microphthalmia, frequently accompanied by esophageal atresia, brain malformations, and developmental delays. PAX6 mutations, while more commonly associated with aniridia, can result in microphthalmia or anophthalmia, often with coloboma or foveal hypoplasia. Fraser syndrome, caused by mutations in FRAS1 or FREM2, involves ocular agenesis alongside cryptophthalmos (skin covering the eye area), syndactyly, and renal anomalies such as renal agenesis. The combined prevalence of anophthalmia and microphthalmia is estimated at 1-9 per 10,000 births, with anophthalmia occurring in about 3 per 100,000 and microphthalmia in 14 per 100,000.^[37]^[38]^[39]^[40]^[41] Prognosis for individuals with ocular agenesis is marked by severe or total visual impairment, with no potential for useful vision in anophthalmic eyes and limited function in microphthalmic ones depending on retinal integrity. Multidisciplinary management emphasizes orbital expansion to promote facial growth and cosmesis, often using conformers, ocular prosthetics, or implants starting in infancy; surgical interventions like dermis-fat grafts may be required for severe hypoplasia. Early psychological support and genetic counseling are essential, particularly in syndromic cases, to address associated systemic issues and family recurrence risks.^[35]^[42]

Dental and Oral Agenesis

Dental and oral agenesis refers to the congenital absence of teeth or associated oral structures, manifesting as a spectrum from mild hypodontia to complete anodontia, often impacting oral function and aesthetics. This condition arises during odontogenesis, where disruptions in tooth bud formation lead to missing permanent or primary dentition, with the most frequently affected teeth being the third molars (agenesis in 9-30% of cases), maxillary lateral incisors (2%), and mandibular second premolars (2-3%).^[43] In severe forms, it extends to oral tissues such as the palate or salivary glands, particularly within syndromic contexts like ectodermal dysplasias.^[44] Hypodontia, the most common type, involves the absence of 1 to 6 teeth (excluding third molars), while oligodontia denotes more than 6 missing teeth, and anodontia represents total tooth absence, which is exceedingly rare and often syndromic.^[45] These patterns are genetically heterogeneous, with nonsyndromic cases frequently linked to mutations in MSX1 and PAX9 genes; for instance, MSX1 alterations cause autosomal dominant hypodontia, particularly affecting premolars and molars, whereas PAX9 variants lead to oligodontia involving incisors and molars.^[46]^[47] Prevalence varies globally at 2-10%, with rates around 6.4% overall and slightly higher at 6.3% in Asian populations, showing female predominance (3:2 ratio) and ethnic variations such as elevated third molar agenesis (29.7%) in Asians.^[28]^[48] Syndromic dental agenesis commonly occurs in ectodermal dysplasias, where hypohidrotic forms feature oligodontia alongside absent or hypoplastic salivary and sweat glands, leading to xerostomia and increased caries risk.^[44] Witkop syndrome, an autosomal dominant ectodermal dysplasia caused by MSX1 mutations, presents with hypodontia or oligodontia (often mandibular incisors and second molars absent) and nail dysplasia, without significant salivary involvement.^[49] Incontinentia pigmenti, an X-linked dominant disorder, affects 50-75% of cases with dental anomalies including hypodontia, peg-shaped teeth, and delayed eruption, sometimes compounded by cleft palate in oral-facial-digital variants.^[50] These syndromes share craniofacial developmental pathways with other agenesis forms, such as ocular or auricular, via disrupted epithelial-mesenchymal interactions.^[43] The functional implications of dental agenesis include impaired mastication due to reduced occlusal support, leading to uneven chewing forces and potential temporomandibular issues, as well as speech impediments from gaps in anterior dentition affecting articulation.^[51] In severe cases with salivary gland aplasia, as seen in some ectodermal dysplasias, xerostomia exacerbates oral dryness, enamel hypoplasia, and rampant caries, further compromising oral health.^[52] Long-term management emphasizes multidisciplinary care, with orthodontic interventions to address malocclusion and space management starting in adolescence, followed by prosthetic replacements like implants or bridges to restore function and esthetics, improving quality of life metrics such as oral health-related wellbeing.^[53]

Auricular Agenesis

Auricular agenesis, also known as anotia or microtia, refers to congenital malformations of the external ear characterized by underdevelopment or complete absence of the auricle (pinna). Anotia represents the most severe form, involving total absence of the external ear structures, while microtia encompasses a spectrum of milder deformities where the pinna is small, malformed, or peanut-like in appearance, often lacking normal cartilage support. These conditions are predominantly unilateral, affecting the right ear more frequently than the left, though bilateral cases occur in approximately 10-20% of instances.^[54]^[55] The prevalence of anotia and microtia ranges from 0.8 to 4.2 per 10,000 live births globally, with variations by region and ethnicity; rates are notably higher among Hispanic populations compared to non-Hispanic whites, potentially influenced by genetic and environmental factors. Embryologically, these anomalies arise from disruptions in the development of the first and second branchial arches during the 5th to 9th weeks of gestation, where failure of the hillocks of His—mesenchymal elevations contributing to auricle formation—leads to incomplete or absent external ear structures.^[56]^[57]^[58] Auricular agenesis is frequently associated with conductive hearing loss due to malformations in the middle ear, such as ossicular chain anomalies, and atresia of the external auditory canal, which impedes sound transmission. Inner ear anomalies, including cochlear dysplasia, may also coexist, potentially leading to sensorineural hearing impairment in some cases. These auditory deficits often result in complications like delayed speech and language development, as untreated hearing loss hinders phonological acquisition and communication skills in early childhood. Additionally, anotia and microtia are linked to syndromic conditions such as Treacher Collins syndrome, characterized by mandibular hypoplasia and facial dysmorphism, and Goldenhar syndrome, involving vertebral and ocular anomalies, though isolated occurrences predominate in 60-80% of cases. Genetic mutations, such as those in the EYA1 gene underlying branchio-oto-renal syndrome, can contribute to these ear defects alongside renal and branchial anomalies.^[59]^[54]^[60] Reconstructive considerations for auricular agenesis focus on mitigating cosmetic disfigurement and improving auditory function, with interventions typically evaluated after assessing the degree of middle ear involvement and potential for hearing restoration. Early audiologic evaluation is essential to address conductive losses and prevent long-term developmental impacts.^[54]

Renal Agenesis

Renal agenesis refers to the congenital absence of one or both kidneys due to failure of the metanephros to develop during embryogenesis. It is classified into two main types: unilateral renal agenesis (URA), where one kidney is absent and the contralateral kidney typically undergoes compensatory hypertrophy to maintain adequate renal function, and bilateral renal agenesis (BRA), where both kidneys are missing, resulting in severe oligohydramnios and the characteristic features of Potter sequence, including pulmonary hypoplasia, flattened facial features, and limb deformities.^[61]^[62]^[1] The prevalence of URA is estimated at 1 in 1,000 to 2,000 live births, while BRA occurs in approximately 1 in 5,000 to 10,000 pregnancies. URA is often associated with other congenital anomalies of the kidney and urinary tract (CAKUT), such as vesicoureteral reflux or ureteral anomalies, and may occur as part of multisystem syndromes like VACTERL association, which involves vertebral, anal, cardiac, tracheoesophageal, renal, and limb defects.^[1]^[63]^[64]^[65] In terms of presentation, URA is frequently asymptomatic in infancy and may be discovered incidentally through imaging for unrelated issues, though it can manifest with urinary tract infections or abdominal masses if associated anomalies are present. Conversely, BRA leads to profound oligohydramnios, causing Potter sequence, and results in high perinatal mortality, with nearly all affected neonates succumbing shortly after birth due to renal failure and respiratory insufficiency from pulmonary hypoplasia.^[61]^[62]^[66] For survivors of URA, long-term urological and systemic effects include an increased risk of hypertension and proteinuria due to hyperfiltration in the solitary kidney, potentially progressing to chronic kidney disease in adulthood. These outcomes underscore the need for ongoing monitoring of renal function and blood pressure in affected individuals. Renal agenesis shares developmental pathways with other genitourinary anomalies, such as Müllerian agenesis, through common embryologic origins in the intermediate mesoderm.^[64]

Müllerian Agenesis

Müllerian agenesis, also known as Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome, is a congenital condition characterized by the underdevelopment or absence of the uterus and upper two-thirds of the vagina in individuals with a 46,XX karyotype.^[67] This disorder results from the incomplete development of the Müllerian ducts during embryogenesis, leading to the absence of these reproductive structures while the ovaries remain functional.^[7] The condition affects approximately 1 in 4,500 female newborns, making it a rare but significant cause of reproductive anomalies.^[67] MRKH syndrome is classified into two main forms based on associated anomalies. Type I, also called isolated MRKH, involves only the agenesis of the uterus and vagina with normal kidneys and no other malformations.^[67] In contrast, Type II, often associated with MURCS (Müllerian duct aplasia, renal dysplasia, and cervicothoracic somite dysplasia), includes uterovaginal agenesis alongside renal anomalies (such as unilateral renal agenesis), skeletal abnormalities (like vertebral defects), and occasionally cardiac or auditory issues.^[67] The primary clinical presentation is primary amenorrhea, where menstruation does not begin by age 15-16 despite normal secondary sexual characteristics, including breast development, pubic hair growth, and typical female external genitalia.^[7] Individuals with MRKH are infertile due to the lack of a functional uterus, preventing pregnancy, although ovarian function allows for normal hormone production and the potential for egg retrieval in assisted reproduction.^[67] Genetically, MRKH syndrome is typically sporadic, with no clear inheritance pattern in most cases, though rare mutations have been identified, such as in the TBX6 gene, which may contribute to the developmental failure in a subset of patients.^[68] The psychosocial impacts of MRKH are profound, often involving grief over infertility, concerns about sexual function and intimacy, and risks of anxiety or depression due to the diagnosis.^[7] Counseling focused on infertility options, body image, and sexual health is essential to support emotional adjustment and overall well-being.^[7]

Corpus Callosum Agenesis

Agenesis of the corpus callosum (ACC) refers to the congenital absence or malformation of the corpus callosum, the primary white matter tract connecting the two cerebral hemispheres, which plays a crucial role in interhemispheric communication. This condition arises during early fetal brain development, typically between weeks 8 and 20 of gestation, when axons fail to cross the midline. Types of ACC include complete agenesis, characterized by the total absence of the corpus callosum, and partial agenesis (also known as hypoplasia or dysgenesis), where segments such as the splenium or posterior body are missing or underdeveloped, often leading to the formation of Probst bundles—longitudinal axonal tracts that do not cross the midline.^[5] In partial cases, the anterior portions like the rostrum and genu may be preserved, resulting in varying degrees of connectivity disruption.^[5] The prevalence of ACC is estimated at 1 in 4,000 to 5,000 live births, though it is detected in 2% to 3% of individuals evaluated for neurodevelopmental disabilities.^[6] Approximately 30% to 45% of cases are syndromic, meaning they occur as part of broader genetic or congenital syndromes, while 20% to 35% involve identifiable monogenic causes.^[6] Chromosomal abnormalities, such as trisomies 13 and 18, account for about 20% of instances.^[5] Isolated ACC, without additional malformations, represents the remainder and is more likely to be asymptomatic, highlighting the heterogeneity of clinical outcomes.^[6] Neurological symptoms in ACC vary widely depending on whether the condition is isolated or associated with other brain anomalies, but common manifestations include seizures (affecting about 25% of cases), developmental delays (in 60%), and hydrocephalus due to ventricular enlargement like colpocephaly.^[5] Cognitive effects often involve impaired interhemispheric transfer, leading to deficits in complex reasoning, social cognition, and bimanual coordination, though many individuals with isolated ACC exhibit normal intelligence and function well into adulthood.^[5] Other frequent issues encompass speech delays (29%), vision impairments (33%), and behavioral challenges such as attention-deficit/hyperactivity disorder (ADHD).^[5] If isolated, up to 70% of cases may remain asymptomatic, underscoring the importance of distinguishing isolated from complex forms for prognosis.^[6] ACC is frequently associated with specific syndromes and environmental factors. Notable genetic associations include Aicardi syndrome, an X-linked disorder featuring ACC alongside chorioretinal lacunae and infantile spasms, predominantly affecting females.^[5] Environmental influences, such as prenatal exposure to alcohol, link ACC to fetal alcohol spectrum disorders (FASD), where corpus callosum defects serve as a marker of teratogenic impact, occurring in approximately 6.8% of FASD cases. Other linked conditions encompass Joubert syndrome, Apert syndrome, and chromosomal anomalies like trisomy 18.^[5] These associations emphasize the multifactorial etiology, involving disruptions in axon guidance, cell adhesion, and ciliary function pathways.^[6]

Diagnosis

Prenatal Diagnosis

Prenatal diagnosis of agenesis relies primarily on imaging modalities and genetic testing to detect the absence of organs or structures during fetal development. Ultrasound serves as the cornerstone for initial screening, with the first-trimester nuchal translucency scan identifying potential soft markers associated with chromosomal anomalies that may underlie certain forms of agenesis, such as increased nuchal translucency in cases linked to trisomies.^[69] The second-trimester anomaly scan, typically performed between 18 and 22 weeks' gestation, is crucial for visualizing structural absences, including empty renal fossae indicative of renal agenesis or absent long bones suggesting limb agenesis; for instance, bilateral renal agenesis often presents with severe oligohydramnios, facilitating earlier detection as early as 12-14 weeks.^[70] In cases of suspected corpus callosum agenesis, ultrasound may reveal indirect signs like ventriculomegaly or absence of the cavum septi pellucidi, though confirmation often requires advanced imaging.^[71] Non-invasive prenatal testing (NIPT), using cell-free fetal DNA, can screen for common chromosomal anomalies like trisomy 13 or 18 associated with multiple organ agenesis, offering high sensitivity (>99% for trisomy 21, 95-99% for others) with no miscarriage risk, though it requires confirmatory invasive testing for positives.^[72] Invasive diagnostic procedures, such as amniocentesis, are recommended when ultrasound or NIPT findings suggest agenesis, particularly to evaluate for underlying chromosomal or genetic etiologies. Performed typically after 15 weeks' gestation, amniocentesis allows for karyotyping to detect aneuploidies like trisomy 18 or 13, which can be associated with multiple organ agenesis, and array comparative genomic hybridization (array CGH) to identify microdeletions or duplications not visible on standard karyotype, such as those in 22q11.2 deletion syndrome linked to conotruncal anomalies or renal issues.^[73] These tests carry a low risk of procedure-related miscarriage, approximately 0.1-0.3%, and provide results within 1-2 weeks for karyotyping or faster for array CGH.^[74] Fetal magnetic resonance imaging (MRI) complements ultrasound for detailed assessment, especially in complex cases involving the central nervous system or craniofacial structures. Conducted after 18 weeks when fetal anatomy is more defined, MRI offers superior soft tissue resolution, confirming corpus callosum agenesis by directly visualizing the absent structure and associated brain anomalies like gray matter heterotopias, with a diagnostic sensitivity of 89-93% for central nervous system malformations compared to 67-68% for ultrasound alone.^[75] For craniofacial agenesis, such as ocular or auricular variants, MRI delineates subtle midline defects or orbital absences not fully appreciated on ultrasound.^[76] The sensitivity of prenatal detection varies by organ type; ultrasound is more effective for renal agenesis, particularly bilateral forms due to pronounced oligohydramnios, but less so for unilateral renal agenesis, and prenatal detection of dental or oral agenesis is challenging and uncommon, often not feasible with standard imaging. For müllerian agenesis, prenatal diagnosis is challenging and less common, often limited to second-trimester ultrasound in high-risk cases showing absent uterine structures, with MRI providing confirmatory detail in suspected female genital malformations.^[77] Upon confirmation of agenesis, multidisciplinary prenatal counseling is essential, involving fetal medicine specialists, geneticists, neonatologists, and psychologists to discuss prognosis, potential associated anomalies, and options for pregnancy management.^[6] Counseling emphasizes variability in outcomes—for example, isolated renal agenesis may allow for compensatory hypertrophy of the contralateral kidney, while corpus callosum agenesis carries risks of neurodevelopmental delays in 30-50% of cases—tailored to genetic testing results indicating etiology, such as syndromic versus isolated forms.^[78] This approach supports informed parental decision-making regarding continuation of pregnancy and postnatal planning.^[79]

Postnatal Evaluation

Postnatal evaluation of agenesis begins immediately after birth for suspected cases, focusing on confirming the congenital absence of organs or structures through targeted clinical assessments and diagnostic tests. This process verifies prenatal suspicions and identifies any associated anomalies, guiding further management. Physical examination is the initial step, allowing for non-invasive detection of key features across various types of agenesis.^[80] During the newborn physical exam, clinicians palpate the abdomen to assess for absent kidneys in renal agenesis, where the lack of palpable renal masses on one or both flanks may suggest unilateral or bilateral involvement. For auricular agenesis, or microtia, otoscopy evaluates the external ear canal and pinna for hypoplasia or complete absence, often graded by severity from mild deformity to anotia. Ophthalmoscopy is performed to inspect the orbits in ocular agenesis, revealing anophthalmia (complete absence of the eye) or microphthalmia through the lack of visible ocular structures or orbital depth. In dental agenesis, oral examination in infancy may note delayed eruption or spacing, though full assessment typically awaits later childhood. These exams are conducted routinely in the neonatal period to establish baseline findings.^[1]^[54]^[81] Imaging modalities are selected based on the affected organ to provide definitive visualization. Renal ultrasound is the first-line postnatal tool for confirming agenesis, demonstrating the absence of renal parenchyma and compensatory hypertrophy of the contralateral kidney if unilateral; computed tomography (CT) or magnetic resonance imaging (MRI) may follow for complex cases or associated anomalies. For corpus callosum agenesis, brain MRI is the gold standard, clearly delineating the absent midline structure on sagittal views and identifying any concurrent brain malformations. Dental panoramic X-rays or cone-beam computed tomography are used post-eruption (around age 6-7 years) to quantify missing teeth in oligodontia or anodontia. In auricular cases, high-resolution CT assesses middle ear and canal patency. For Müllerian agenesis, evaluation typically occurs in adolescence with pelvic ultrasound or MRI to confirm uterine and vaginal absence, prompted by primary amenorrhea. Prenatal findings, if present, direct the urgency and scope of these studies.^[14]^[82]^[43] Genetic testing is recommended when syndromic features or multiple anomalies raise suspicion for an underlying genetic etiology, involving targeted panel sequencing or whole-exome analysis on blood samples to identify mutations in genes associated with specific agenesis types, such as PAX6 for ocular or MSX1 for dental. A multidisciplinary team, including neonatologists, geneticists, otolaryngologists (ENT), ophthalmologists, and pediatric surgeons, collaborates for comprehensive assessment, ensuring coordinated evaluations and family counseling. Timing varies by severity: immediate imaging and intervention planning for life-threatening bilateral renal agenesis to address oligohydramnios sequelae, whereas cosmetic or functional concerns like auricular agenesis allow delayed assessment until stable.^[83]^[84]^[1]

Management

General Approaches

Supportive care for individuals with agenesis focuses on addressing immediate physiological needs and promoting overall well-being across various types of congenital absence. Nutritional support is essential to mitigate growth delays often associated with these conditions, involving tailored caloric and protein intake to support development, particularly in cases linked to renal or gastrointestinal involvement.^[85] Respiratory assistance, such as mechanical ventilation and oxygenation targeting 90-95% saturation, is critical for infants experiencing Potter sequence due to pulmonary hypoplasia from oligohydramnios in bilateral renal agenesis.^[62] Psychological counseling plays a key role in managing body image concerns and emotional distress, especially in visible or reproductive-related agenesis like müllerian or auricular types, with peer support groups recommended to foster self-acceptance and reduce anxiety.^[7] Management of agenesis requires a multidisciplinary team approach to coordinate holistic care, integrating geneticists for etiology assessment, surgeons for potential interventions, and therapists for functional support. Early intervention programs, including physical, occupational, and speech therapy, are vital for addressing developmental delays common in syndromic or central nervous system-related cases like corpus callosum agenesis.^[86] This collaborative framework ensures comprehensive evaluation and timely referrals, improving outcomes through integrated prenatal and postnatal planning.^[84] Prognosis in agenesis varies significantly based on whether the condition is isolated or syndromic, as well as unilateral or bilateral; isolated cases, such as unilateral renal agenesis, generally carry a favorable outlook with normal life expectancy, while syndromic or bilateral forms, like complete corpus callosum agenesis with additional anomalies, often lead to neurodevelopmental challenges.^[87] Overall survival has improved with neonatal intensive care unit support, including dialysis for bilateral renal agenesis, where up to 82% of live-born infants achieve short-term survival beyond 14 days post-dialysis access placement.^[66] Ethical considerations in managing agenesis emphasize palliative care for lethal forms, such as bilateral renal agenesis, to prioritize comfort and quality of life when curative options are limited. Family support resources, including counseling and hospice services, are integral to help parents navigate grief and decision-making in life-limiting diagnoses.^[88] Long-term monitoring involves regular follow-ups to detect complications like infections, renal injury, or increased malignancy risk, particularly in unilateral renal agenesis where hypertension and proteinuria may emerge over decades.^[89] Organ-specific surgeries may complement these broader strategies in select cases to enhance function.^[7]

Organ-Specific Treatments

For ocular agenesis, such as anophthalmia, treatment focuses on orbital expansion to promote symmetric facial growth and prosthetic fitting, as biological vision restoration is not possible due to the absence of ocular structures. Orbital expanders, including hydrogel implants or saline-filled devices, are implanted shortly after birth to stimulate bony and soft tissue development, often combined with serial conformers—clear plastic shells that maintain socket depth and eyelid expansion. These interventions, initiated in infancy, aim to minimize facial asymmetry, with regular prosthetic ocular fitting following expansion to achieve cosmetic outcomes.^[90]^[91]^[92] In dental and oral agenesis, or hypodontia, prosthetic and surgical restorations address missing teeth to restore function and aesthetics, particularly when associated with clefts. Dental implants provide a fixed, long-term solution for edentulous areas once skeletal maturity is reached, offering high stability and success rates comparable to non-agenesis cases, while resin-bonded bridges serve as less invasive interim options for single-tooth gaps without requiring bone grafting. If hypodontia co-occurs with cleft lip or palate, multidisciplinary repair integrates orthodontic alignment prior to implant or bridge placement to optimize occlusion.^[93]^[94]^[95] Auricular agenesis, often manifesting as microtia, involves reconstructive surgery or prosthetics to improve appearance and, if needed, hearing function. Autologous rib cartilage frameworks, harvested from the costal region, form the basis of staged reconstruction starting around age 6-10 years, achieving natural contour and projection with satisfaction rates of 80-90% among patients and families. Osseointegrated prosthetic ears, anchored via titanium implants, offer an alternative for those unsuitable for autografting, with low complication rates under 7%. For associated conductive hearing loss, bone-anchored hearing aids or cochlear implants address auditory deficits independently of external ear reconstruction.^[96]^[97]^[98] Renal agenesis management varies by unilaterality or bilaterality, emphasizing renal support and complication prevention. Unilateral cases typically require lifelong monitoring of the solitary kidney through blood pressure control, renal function tests, and imaging to detect compensatory hypertrophy or injury risks, as most individuals maintain adequate function without intervention. Bilateral renal agenesis, historically lethal due to oligohydramnios-induced pulmonary hypoplasia, may allow survival with prenatal amnioinfusion; recent advances include serial amnioinfusion therapy to further mitigate pulmonary hypoplasia, as reported in 2025 studies.^[99] Postnatal care then involves dialysis initiation in neonates and eventual kidney transplantation, which offers over 90% one-year graft survival in pediatric recipients.^[100]^[101]^[102] For Müllerian agenesis, or Mayer-Rokitansky-Küster-Hauser syndrome, neovaginal creation enables sexual function, while fertility options leverage preserved ovarian tissue. Non-surgical vaginal dilation using progressive dilators (Frank method) achieves functional patency in 75-85% of cases with consistent patient compliance, avoiding operative risks. Surgical neovaginoplasty, such as the laparoscopic Vecchietti procedure involving traction on an intra-abdominal olive, yields anatomic success in over 90% of patients with 7-8 cm depth, though long-term patency requires dilation and reaches about 70% without stenosis recurrence. Since uterine absence precludes gestation, fertility proceeds via in vitro fertilization of the patient's oocytes followed by surrogacy, with live birth rates mirroring standard IVF outcomes at referral centers.^[103]^[104]^[103] Agenesis of the corpus callosum lacks direct structural repair due to its congenital nature, with management targeting associated neurological symptoms through symptomatic and rehabilitative measures. Antiepileptic medications, such as levetiracetam or carbamazepine, are used to manage seizures when present, selected based on electroencephalogram findings and avoiding teratogenic agents in reproductive-age patients.^[5] Neurorehabilitation, including physical, occupational, and speech therapies from early childhood, supports motor coordination, cognitive development, and adaptive skills, often leading to favorable long-term outcomes including greater independence in cases of isolated agenesis, as reported in follow-up studies (e.g., 88% favorable prognosis as of 2022).^[105]^[106] General supportive care, such as multidisciplinary monitoring, enhances outcomes across these organ-specific interventions.^[107]

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