Arhinia is an extremely rare congenital condition defined by the complete absence of the external nose, nasal passages, and olfactory structures from birth. This anomaly is present at birth. Its profound rarity means only a limited number of cases have been documented globally.
Understanding Arhinia
Arhinia involves the complete absence of the external nose, including nasal bones and cartilage, and internal nasal passages. It also means the absence of the olfactory bulbs and tracts, which are responsible for the sense of smell. This condition differs from other nasal anomalies where some nasal structures might be present or underdeveloped, as arhinia denotes a total lack of these components. Fewer than 100 cases have been reported worldwide. The absence of these structures results in a flat midfacial profile, often with only a depression where the nose would normally be, making arhinia immediately apparent at birth.
The Genetic and Developmental Roots
Arhinia originates from a failure in the development of nasal placodes during early embryonic stages, typically around 4 to 6 weeks of gestation. These placodes are thickened areas of embryonic ectoderm that normally invaginate to form the nasal pits, which then develop into the nose and associated structures. A disruption in this process can lead to the complete absence of nasal formation.
While many instances of arhinia occur sporadically, genetic factors are increasingly recognized in some cases. Research has implicated mutations in the SMCHD1 gene as a cause of congenital arhinia. This gene plays a role in craniofacial development, and its variants can lead to this rare condition, sometimes even with variable expression within families.
Broader Health Considerations
Arhinia is seldom an isolated anomaly and frequently presents alongside other significant health challenges. Newborns with arhinia are obligate mouth breathers, meaning they cannot breathe through their nose, which leads to immediate respiratory distress at birth. This can cause severe airway obstruction and necessitates prompt intervention to ensure adequate breathing.
Individuals with arhinia experience complete anosmia, the total loss of the sense of smell, due to the absence of olfactory structures. Feeding can also be difficult for affected infants, as coordinating sucking and breathing simultaneously is impaired. Specialized feeding techniques, such as orogastric tubes, are often required.
Associated craniofacial anomalies are common, affecting various parts of the head and face. These can include eye abnormalities such as microphthalmia (abnormally small eyes) or anophthalmia (absent eyes), and coloboma (a defect in the eye structure). Brain anomalies like holoprosencephaly, where the forebrain fails to divide properly, or hypoplasia of the olfactory bulbs, are also observed. Other midline defects, including a high arched palate or an underdeveloped upper jaw, may also be present. While intelligence is generally normal if there are no brain abnormalities, chronic health issues and neurological involvement can contribute to developmental delays.
Navigating Diagnosis and Care
Arhinia is typically diagnosed prenatally through detailed ultrasound examinations, which can identify the absence of nasal structures, or immediately at birth due to obvious physical characteristics and respiratory difficulties. Early prenatal diagnosis allows for comprehensive counseling and preparation for specialized care at delivery.
Immediate management at birth focuses on establishing a stable airway, often requiring endotracheal intubation or a tracheostomy to bypass obstructed nasal passages. Feeding support is also initiated promptly, frequently through orogastric tubes, as infants cannot coordinate feeding and breathing simultaneously. This initial stabilization is critical for the newborn’s survival.
Managing arhinia necessitates a multidisciplinary team approach. This team commonly includes:
Neonatologists
Otolaryngologists
Craniofacial surgeons
Geneticists
Ophthalmologists
Neurologists
Speech and feeding specialists
Psychologists are also involved to provide support for the individual and their family. Reconstructive surgery is a complex, multi-staged process that typically begins in childhood and continues through adolescence. These surgeries aim to create functional nasal passages and improve facial aesthetics, often involving techniques such as maxillary osteotomy to create space and the use of rib cartilage and forehead flaps to construct a nose. These surgical interventions do not restore the sense of smell. Ongoing medical, developmental, and psychosocial support is essential throughout the individual’s life to address the unique challenges associated with arhinia.