Understanding the embryological development of the nose and paranasal sinuses (PNSs) is crucial for the interpretation of morphological abnormalities. The development of the PNSs occurs via a series of complex coordinated events that start as early as the 3rd week of gestation and progress thereafter.
By the seventh week of intrauterine life, the partitioning of the oronasal membrane brings about the arrangement of the oral and nasal cavities. The nasal pits migrate anteriorly to the outside by means of the nostrils and posteriorly via the primitive choana to the nasopharynx. Congenital choanal atresia results from the failure of the oronasal membrane to rupture. By the eighth week, the lateral nasal wall and turbinate are highly developed. The cartilaginous nasal capsule gives rise to the uncinate process by 10 weeks of gestation, and by 13–14 weeks of gestation, the primitive maxillary sinuses start to develop .
The maxillary sinuses are the first sinuses to develop. At birth, the maxillary sinuses are rudimentary and have a volume of 6–8 cm. In infancy, the growth of the maxillary sinuses continues, and the final phase of pneumatization is completed after the permanent teeth erupt. Unevenness in the size and shape of the maxillary sinuses is common. Unilateral maxillary sinus hypoplasia has been reported to be present in 7% of adults, whereas bilateral maxillary sinus hypoplasia has been reported to be present in 2% of adults.
Ethmoidal air cells are pneumatized at birth, even though they achieve maturation in adulthood.
The sphenoid bone is compact at birth and harbors hematopoietic marrow; pneumatization of the sphenoidal sinuses starts as early as 2 years of age. Sinus maturation is completed by the age of 14 years. Sphenoidal sinus aplasia is very uncommon. Therefore, the lack of the pneumatization of the sphenoidal sinuses in patients less than 10 years old indicates underlying pathology . Sphenoid sinus pneumatization arrest is recognized radiologically by nonexpansile lesions with osteosclerotic margins and internal fat content (marrow fat) within the skull base [3, 4].
The frontal sinuses are the last sinuses to develop, as their growth begins after 2 years of age. Unilateral frontal sinus aplasia occurs in 15% of adults, and bilateral frontal sinus aplasia occurs in 5% of adults, as documented in the literature .
Regarding the development of the paranasal sinuses, hypoplasia is considered a delay in the pneumatization of the sinuses after 8 years of age, while aplasia is considered a total lack of pneumatization in individuals aged 10 years and older .
A wide spectrum of variations in PNS structures have been mentioned in the literature; for instance, bilateral maxillary sinus severe hypoplasia/aplasia , combined aplasia of the sphenoid, frontal, and maxillary sinuses along with ethmoid sinus hypoplasia have been reported in a 47-year-old woman with complaints of headache, nasal obstruction, and postnasal drip . Bilateral aplasia of a single sinus  and even combined aplasia of the sphenoid and frontal sinuses accompanied by bilateral maxillary and ethmoidal sinus hypoplasia were reported in a female patient aged 54 years who presented with nasal obstruction and persistent headache; bone window CT of the paranasal sinuses confirmed the diagnosis . Furthermore, total aplasia of the PNSs with normal nasal cavities has been described in a 57-year-old woman .
CT is the gold standard for the radiological workup for paranasal sinus abnormalities (developmental and acquired pathological) in pre- and postsurgical assessments, as bone window CT has the best accuracy in outlining the sinuses and provides the maximum detail of bony structural, anatomical, and architectural variations .
Numerous syndromes related to sinonasal anomalies are generally divided into those due to defects of midfacial skeletal growth and those attributed to bone dysplasia (osteosclerosis) that prevent sinus pneumatization .
Defects of midfacial skeletal growth include more than 100 forms of craniofacial dysostoses. Among the most known midfacial skeletal growth defects are Treacher-Collins syndrome (also known as mandibular dysostosis), Binder’s syndrome/maxillomandibular dysplasia, Williams syndrome, elfin facies syndrome, Apert’s syndrome, and Crouzon’s syndrome, all of which are related to bilateral paranasal sinus effects. Moreover, in Goldenhar’s syndrome (hemifacial microsomia), a unilaterally diminutive maxillary sinus is accompanied by the hyperplasia of the ipsilateral bony zygoma [10, 12]. However, none of the abovementioned conditions, alone or in combination, is associated with nasal cavity aplasia, which is the major aspect of this case report.
Among anomalies attributed to bone dysplasia (osteosclerosis) that prevent sinus pneumatization, many hereditary bony dysplasias produce changes within the skull and facial skeleton through abnormal hardening of the bone and increased bone density, leading to sinus obliteration. Examples of these anomalies include polyostotic craniofacial fibrous dysplasia, craniometaphyseal dysplasia, craniodiaphyseal dysplasia, and other skeletal hyperostosis . However, none of these features applied to the case presented here, as normal bone density was preserved in this patient.
Furthermore, Bosma syndrome is an extremely uncommon hereditary condition characterized by nasal aplasia, orbital abnormality, and sexual maturation defects. Although sinus hypoplasia can occur in Bosma syndrome, it is not generalized and commonly affects only the maxillary sinuses . In the case presented here, both eyeballs, orbits, and their contents were unremarkable, and sinus aplasia was global.
Congenital nasal cavity abnormality is a component of solitary median maxillary central incisor syndrome (SMMCI), which is also a rare, complex genetic disorder consisting of midline craniofacial structural defects, including the nose (choanal atresia and nasal pyriform aperture stenosis) and developing brain (holoprosencephaly), along with pituitary gland malfunction . Again, none of these components were observed in the case presented here; the maxillary incisors were normal, and no brain malformations were detected.
Hence, the case presented here is rare, in that it is of an individual with unique structural abnormalities that represent nasal cavity and paranasal sinus congenital/developmental defects.