Congenital ear deformities can be categorized into morphological deformities and structural deformities based on the presence of cartilage developmental abnormalities. Structural ear deformities are often accompanied by malformations of the external auditory canal and middle ear, which not only affect the aesthetic appearance but may also lead to hearing impairments (1). Although fetal ear examination is not currently included in prenatal ultrasound screening guidelines, advancements in high-resolution prenatal ultrasound technology have made it possible to detect various congenital ear deformities, which is of considerable importance for prenatal counseling. At present, the literature on prenatal ultrasound screening for ear deformities consists mainly of individual case reports and retrospective reviews (2–5). Because of limitations in medical resources and a general lack of awareness among ultrasound practitioners in different hospitals, both misdiagnosis and missed diagnosis are relatively common.

In this study, we conducted a retrospective analysis of 14 fetuses with congenital auricular anomalies. The ultrasound features, associated anomalies, genetic findings, and clinical outcomes were systematically reviewed. The primary objective was to determine the diagnostic value of two-dimensional and three-dimensional prenatal ultrasound in identifying congenital auricular anomalies, with the broader aim of improving our understanding of this condition.

During the embryonic period, the development of the ear originates from the first branchial groove, the first branchial arch, and the second branchial arch. By the sixth week of embryonic development, the basic outline of the ear begins to form. Between the 13th and 14th weeks, the six auricular hillocks fuse to create the rudimentary ear, which gradually ascends above the level of the inner canthi as the mandible grows (6). By the 20th week of gestation, the anatomical features of the ear closely resemble those of an adult, and the length of both ears shows a linear correlation with gestational age (2). Between 20 and 24 weeks of gestation, the relatively larger volume of amniotic fluid results in optimal visualization of the ear structure. On ultrasound, the ear appears moderately echogenic, with a highly echogenic edge forming a characteristic “C” shape and an uneven surface. The center is concave, forming the external auditory canal, while the helix can be seen along the outer edge, gradually merging into the smoother earlobe. By the third trimester, structures such as the antihelix, scapha, cymba conchae, triangular fossa, tragus, and antitragus become increasingly distinguishable. Three-dimensional ultrasound enables multi-angle visualization of the auricle, allowing for more detailed assessment of its morphology, position, and size (7, 8). In this study, the median gestational age at which ear deformities were detected was 24 weeks and 5 days, aligning with findings from previous research (9).

The incidence of congenital ear deformities is approximately 1 in 6,000 to 1 in 6,830 births (8). During the embryonic period, pathogenic agents, drugs, or genetic factors can disrupt normal development and lead to ear malformations (10). With the advancement of high-resolution prenatal ultrasound technology, various ear deformities—such as microtia, anotia, and accessory auricles—can now be detected (3, 8). Congenital microtia is defined as an ear length that is more than two standard deviations below the mean for the corresponding gestational age (4, 11), typically accompanied by abnormal or absent ear morphology. Microtia is commonly classified into three grades: Grade I, in which most anatomical structures of the auricle are present but smaller in contour compared with the normal side; Grade II, in which the auricle is reduced to approximately half to two-thirds of normal size, with major features such as the helix absent; and Grade III, the most common type, in which most anatomical structures are unrecognizable or missing, leaving behind residual structures that appear sausage-shaped, peanut-shaped, or boat-shaped, often accompanied by atresia or absence of the external auditory canal (12). Therefore, prenatal evaluation of the fetal ear should involve not only measuring its length but also observing its morphology. In this study, of the nine microtia cases, unilateral involvement was more frequent than bilateral, with a higher prevalence on the right side—findings that are consistent with previous research (13, 14). Microtia is often associated with atresia or stenosis of the external auditory canal, and literature reports indicate that more than 90% of affected individuals suffer from conductive hearing loss. While visualizing the external auditory canal via ultrasound is generally considered difficult, some researchers have successfully identified the lateral segment using two- and three-dimensional imaging techniques (15). Beyond microtia, prenatal ultrasound can also detect other congenital ear deformities such as abnormal positioning and accessory auricles. Low-set ears are defined as ears whose upper borders lie below the line connecting the outer canthi of both eyes to the occiput (10). An accessory auricle is a vestigial remnant resulting from incomplete development of the anterior ear during embryogenesis; it can appear anywhere within the curved triangular area extending from in front of the tragus to the line between the mouth corner and ear, with the region immediately anterior to the tragus being most common (16). Question mark ear (also known as ear condyle syndrome or auriculo-condylar syndrome) is a distinct malformation marked by a cleft between the helix and earlobe in the mid-lower ear, which divides the auricle into upper and lower segments with helix discontinuity. It is attributed to developmental anomalies of the first and second pharyngeal arches and is often associated with a broad spectrum of phenotypes, including ear deformities, mandibular hypoplasia, and other craniofacial abnormalities (17).

Congenital ear deformities are often associated with craniofacial and other systemic anomalies. In this study, children with question mark ear deformities also presented with facial clefts and hearing loss on the affected side. A facial cleft results from disrupted fusion between the maxillary and mandibular processes at the corner of the mouth, leading to incomplete closure and outward displacement of the oral commissure. This condition frequently co-occurs with ear deformities, micrognathia, and other anomalies. Therefore, when ear deformities are detected during prenatal screening, careful evaluation of the jaw and corners of the mouth is warranted. Conversely, when facial clefts or micrognathia are observed, the fetal ears should be closely examined to avoid misdiagnosis. In this study, two fetuses also exhibited micrognathia. Takano et al. (18) investigated the relationship between the severity of congenital microtia and mandibular malformations, finding that patients with a coronoid process ratio (compared with the healthy side) of less than 0.85 frequently had Grade III microtia. Ear deformities are also commonly associated with cardiovascular and skeletal anomalies, which may reflect underlying syndromic conditions. In our cohort, five fetuses exhibited structural abnormalities in other systems. The likelihood of associated malformations appears to correlate with the severity of the ear deformity; more severe auricular underdevelopment is often linked to higher rates of comorbid anomalies. This may be due to teratogenic influences affecting multiple developmental pathways. As such, when anomalous ears are identified, careful examination for additional congenital anomalies—particularly those that may be subtle or easily missed, such as renal dysgenesis—is strongly recommended.

Congenital ear deformities are also frequently associated with genetic abnormalities. Previous studies have shown that microtia may be linked not only to triploid but also to non-triploid chromosomal abnormalities such as trisomy 13, trisomy 18, and trisomy 22. Growth parameters such as ear length, width, and surface area serve as useful indicators for screening chromosomal abnormalities (4, 19, 20). Beyond chromosomal abnormalities, mutations in certain genes are also closely associated with external ear malformations (21). For instance, HOXA2 is a critical transcription factor involved in ear development (22). Mutations in HOXA2 can cause microtia and preauricular tags (23). A characteristic auricular phenotype is also observed in clinical syndromes caused by specific genes. For example, CHARGE syndrome driven by CHD7, and Kabuki syndrome driven by MLL2/KMT2D/KDM6A both demonstrate fetal ear developmental abnormalities (24, 25). In our study, one fetus was found to have complete trisomy 18 syndrome. Low-set ears have also been associated with fetal chromosomal abnormalities. Therefore, prenatal ultrasound detection of ear developmental anomalies can serve as an important prompt for genetic testing and clinical decision-making (26). In this cohort, the overall prognosis for the nine children with microtia was poor; hearing impairment was observed in all three newborns who were delivered. However, it is important to note that a negative genetic testing result does not necessarily exclude an underlying genetic defect. Limitations may exist in the testing methodology or expertise, and results can also depend on the sample obtained. In Case 2, both karyotyping and WES revealed no abnormalities; nevertheless, this cannot entirely rule out underlying genetic defects. Case 4 was diagnosed with bilateral microtia and absent external auditory canals in the current pregnancy, following a history of microtia in a previous pregnancy. WES analysis of tissue in both induced deliveries detected no abnormalities.

One limitation of this study is that only one fetus underwent prenatal magnetic resonance imaging (MRI). This imaging technique holds significant diagnostic value in assessing fetal external ear deformities and serves as an effective complement to ultrasound, particularly for detecting external auditory canal atresia. The absence of a high T2-weighted imaging signal in the external auditory canal on MRI may indicate atresia. Thus, when ultrasound identifies ear deformities, further MRI evaluation is recommended to confirm the presence of associated external auditory canal abnormalities.

In conclusion, level II or advanced prenatal ultrasound, including 3D modalities, are valuable for identifying fetal ear deformities and associated craniofacial anomalies. For experienced sonographers, a thorough understanding of the sonographic features of these abnormalities is crucial for accurate prenatal diagnosis, which provide essential information for clinical management and prenatal counseling.