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Address reprint requests and correspondence: Habib G. Zalzal, MD, Department of Otolaryngology, West Virginia University School of Medicine, 1 Medical Center Dr, Morgantown, WV 26506.
The sinonasal anatomy of children differs significantly when compared to the sinonasal anatomy of adults. Even within the pediatric group, the anatomy varies depending on the age of the patient, as structures reach full maturation in the teenage years. Knowledge of pediatric anatomy is important for all otolaryngologists, particularly those planning to operate within the nose of a child. This article will present the pediatric nasal and sinonasal anatomy with reference to development and related operative planning.
The anatomy of the nose and paranasal sinus develops throughout childhood, taking on different structural relationships through each stage of growth. Injury early in development, whether by trauma, infection, or other etiology, can result in deformity that would be difficult to correct if a delayed approach were preferred. Otolaryngologists should be aware of the anatomical structures and relationships of the pediatric nose and paranasal sinuses in the event a child may require surgery.
The pediatric nasal anatomy is comprised of the external nose, the internal nasal cavity (which contains the major structures of the septum and nasal turbinates), and the posterior nasopharynx. The paranasal sinuses contain the ethmoid and maxillary sinuses, which are present at birth, alongside the frontal and sphenoid sinuses, which develop throughout childhood.
Embryology
The nose and paranasal sinuses begin to develop from a combination of ectodermal, mesodermal, and neural crest cells around the fourth week of gestation (Figure 1). The ectoderm provides the outer layer and covering of the face, the mesoderm provides the precursors for the facial musculature, and the neural crest cells later mature into the vessels and nerves that will serve for facial function.
The development of the face occurs between the fourth and tenth weeks of development through the maturation of 5 prominences as the frontonasal prominence overlaying the forebrain, the paired maxillary prominences, and the paired mandibular prominences.
Figure 1Embryology of the nose and midface. (A) Embryological form of the nose and midface at week 4-5. The frontonasal, maxillary, and mandibular prominences can be appreciated on the external view. Internally, the formation of the nasal septum with palate openings can be identified. (B) During weeks 5-6, the nasal placode proliferates to form a horseshoe of tissue consisting of the nasomedial and nasolateral processes, which will become the nasal philtrum and lateral alae, respectively. (C) In the sixth week, the paired maxillary processes grow medially toward the paired nasomedial processes with fusion by week 8.
The nose takes its embryologic origin from the nasal or olfactory placode, an ectodermal outcropping in the caudal portion of the frontonasal prominence. During the fifth week of gestation, the nasal placode proliferates to form a horseshoe of tissue consisting of the nasomedial and nasolateral processes, which will become the nasal philtrum and lateral alae, respectively.
In the sixth week, the paired maxillary processes grow medially toward the paired nasomedial processes, and fuse around the eight week of gestation. Failure of the nasomedial placodes to fuse with the paired maxillary processes results in a cleft lip deformity.
During this process, the nasal and oral cavities become a common cavity posterior to the primary palate creating the primitive choana in the seventh week.
Fusion of the secondary and primary palate occurs during the ninth week of gestation, and begins posterior to the incisive foramen. Failure or incomplete fusion of the primary and secondary palate leads to clefting of the palate.
The nasal septum grows from the nasofrontal prominence and is contiguous with the primary palate. The septum will fuse with the palatal shelves of the secondary palate during the ninth week of gestation. The septum continues to grow in utero, leaving it susceptible to in-utero trauma. One of many theories regarding septal deviation is attributed to the maxillary molding theory. This hypothesis states that the tension placed upon the developing fetus via extrinsic compression causes the surrounding bony structures to grow in an altered alignment, leading to altered growth of the cartilaginous septum.
The nasal and paranasal sinuses begin to develop between the eighth and twelveth weeks of gestation. When the primitive choanae are formed, 3 soft tissue outcroppings can be found in the nasal cavity that will later become the paired inferior, middle, and superior turbinates. Between the 11th and 12th weeks, the ethmoid infundibulum begins to develop as a space lateral to the uncinate process which will run inferiorly and laterally into the developing maxillary bone beginning the maxillary sinus. Between weeks 16 and 20, the posterior aspect of the ethmoid infundibulum further grows to develop into the posterior ethmoid air cells. The anterior ethmoids originate from a superior invagination of the middle meatus around the 20th week of gestation.
By the time of birth, the ethmoid sinuses, maxillary sinuses, and the turbinates are formed. The sphenoid sinus develops shortly after birth as an invagination of the posterior ethmoid sinus. The frontal sinuses will develop around the fifth year of life as an expansion of the ethmoid sinus into the frontal bone, as well as an independent invagination of the middle meatus.
Derived from cranial ectoderm, the external nose is a pyramidal structure situated in the midface. It is comprised of the nasal bones, the nasal portion of the frontal bones and the frontal processes of the maxilla.
The paired nasal bones form the external nose superiorly, whereas 2 sets of paired cartilage form the nose inferiorly. The caudal margin of the nasal bones is supported by perichondrial attachments to the underlying paired cartilage.
The lower lateral (alar) cartilage is U shaped and consists of the medial and lateral crus. The medial crura define the form of the columella, whereas the lateral crura form the shape of the nasal alae. Together, the medial and lateral crura allow for patency of the nasal vestibule, which functions as the first part of the respiratory tract.
Internally, the pyramidal shape of the external nose is supported by the nasal septum. The anterior nasal septum is mostly cartilaginous, formed by the quadrangular cartilage, and serves to provide support to the nasal tip. The posterior nasal septum is comprised of bone formed from the perpendicular plate of the ethmoid and the vomer.
Superiorly, the nasal septum and bilateral upper lateral cartilages constitute the septodorsal cartilage. Inferiorly, the thin sheet of vomer bone meshes with the vomer crest to border the cartilaginous septum.
Early growth of the cartilaginous septal wall is the predominant factor for external nose growth during infancy. The intensified development of the midfacial structures around 2 years is responsible for the craniofacial transformation toward the adult face. Around this timeframe, the cartilaginous nasal septum achieves its maximal growth rate.
Further growth of the septum is then due to the development of the perpendicular plate of the ethmoid with progressive ossification of septal cartilage.
In early childhood, the external nose maintains a soft, distensible, and squared form (Figure 2). The nostrils are angled superiorly relative to the philtrum, and the nose contains more mucosa and lymphoid tissue at this stage. Before puberty, the adolescent nose starts to thin and elongate.
The membranous nasal bones ossify as the alar cartilages continue to grow well into adulthood. The nostrils open ventrally and attain an inferior orientation relative to the philtrum during puberty.
Although growth patterns can be predicted among pediatric patients, the exact structure of the external nose at growth maturation is mostly dependent on both gender and race rather than expected adult characteristics.
Figure 2External nose and internal sinus anatomy at different ages in comparison the craniofacial shape: (A) 1 year old, (B) 5 years old, (C) 10 years old, and (D) 20 years old.
The internal nose, or nasal cavity, is divided into 2 separate compartments by the nasal septum. Each compartment connects the external environment through the nares to the nasopharynx via the posterior nasal aperture or choana. Each nasal compartment contains a roof, floor, medial wall, and a lateral wall. The roof slopes posteriorly and upwards to form the nasal bridge, whereas the floor is formed by the palatal process and horizontal palatine bone. The roof of the nasal cavity also contains olfactory nerve endings emanating from the cribriform plate, which is covered in olfactory epithelium contributing to the sense of smell.
Although the size of the internal nasal contents may change with growth, the structural architecture remains constant throughout postnatal development as long as the patient does not experience nasal trauma or recurrent infections.
The nasal vestibule formed by the medial and lateral crura of the external nose has a stratified squamous epithelium that differs from the rest of the internal nose. The respiratory epithelium of the nasal cavity is mostly composed of a mucosal epithelial layer that serves as a protective layer against inflammatory substance. This mucosal epithelium overlies a submucosal layer consisting of pseudostratified columnar epithelium that contains mucus secreting goblet cells. The nasal respiratory epithelium also contains ciliated and nonciliated columnar cells with microvilli that help with clearance of inhaled pathogens. Mast cells, eosinophils, and lymphocytes are also contained within the mucosal epithelial layer.
The inferior turbinates are the largest of the lateral internal nasal structures, and are responsible for the majority of airflow, humidification, and air filtration during nasal inhalation. The inferior outflow tract of the nasal lacrimal duct empties underneath the inferior turbinate near the meatus. The middle turbinates are smaller and are situated above the inferior turbinates bilaterally. The middle turbinate covers the opening of the maxillary, anterior ethmoid, and middle ethmoid sinuses, ostensibly to protect each sinus from pressurized nasal airflow. Above the middle turbinate on each side is the superior turbinate, which is an even smaller structure. The superior turbinates protect the olfactory area and cover the opening to the posterior ethmoidal sinuses. In some patients, a supreme turbinate may exist superior to the superior turbinate, but this is mostly non-functional. Each turbinate consists of a spongy bone frame with overlying ciliated, pseudostratified columnar respiratory epithelium.
In patients with chronic inflammation or allergies, the posterior edge of the inferior turbinate may occasionally be hypertrophied, resulting in airflow resistance. This hypertrophy is regulated by parasympathetic innervation (trigeminal nerve) relative to venous congestion of the turbinates. Turbinate hypertrophy results in reduced airflow in the setting of environmental irritation. Importantly, the smaller nasal apertures of children are easily obstructed by turbinate hypertrophy and mucosal secretions. Nasal obstruction in turn will lead to an increased work of breathing, resulting in difficulties with nasal airway management.
The arterial supply of the internal nasal cavity is from both the internal and external branches of the carotid artery. The anterior and posterior branches of the ethmoidal artery originate from the ophthalmic artery, typically crossing the ethmoids near the skull base at the junction of the ethmoid roof through the lamina papyracea.
The sphenopalatine artery, which also arises from the external carotid artery, enters the nose through the posterior lateral inferior wall. Together, the ethmoidal and sphenopalatine arteries form a plexus with the terminal branches of the facial artery along the anterior cartilaginous septum. This area, known as Little’s Area or Kiesselbach’s plexus, is the most common site of epistaxis in children.
The venous outflow from the nasal cavity runs adjacent to the arterial supply, draining into the pterygoid and ophthalmic venous plexus, and eventually into the cavernous sinus. When patients have difficulties related to treatment of acute sinusitis or facial cellulitis, cavernous sinus inflammation causing ophthalmoplegia and subsequent sinus thrombosis is a severe complication thought may require urgent surgical intervention.
Lymphatic vessels of the nasal vestibule and preturbinate region drain toward the external nose and along the facial vessels into the submandibular lymph node region, which are palpable on physical examination. In contrast, lymphatic vessels of the nasal fossa drain toward the nasopharynx. Lymph from this region will drain into the lateral retropharyngeal lymph nodes, which lie along the vertebral body and are difficult to assess on physical examination.
Both parasympathetic and sympathetic nerves play an important role in nasal physiology, particularly in regard to regulating airflow, blood flow, and glandular secretions. The parasympathetic fibers from the sphenopalatine ganglion are distributed to the mucosal and submucosal tissues, primarily causing glandular secretions, and vasodilator effects. Sympathetic fibers, in contrast to parasympathetic fibers, do not synapse with the sphenopalatine ganglion. Instead, these fibers travel from the vidian nerve to cause vasoconstriction and decrease in nasal resistance within the internal nasal cavity.
The nasopharynx can be thought of as the superior portion of the pharynx in connection with the nasal cavity lying above the soft palate. It communicates directly with the posterior nasal aperture and the oropharynx. Present at birth, the nasopharynx will increase in depth throughout childhood to eventually produce an enlarged posterior nasal airway. Changes in the nasopharyngeal structure include remodeling of the palate and changes in the angulation of the skull base.
Contained within the nasopharynx are the Eustachian tubes lying on the lateral walls of the cavity. These connect the nasopharynx to the middle ear, allowing for equalization of barometric pressure within the middle ear. The nasopharyngeal tonsil, or adenoid, lies on the roof and posterior wall of the nasopharynx in children. The adenoid typically atrophies by age 13, although enlargement in childhood can cause nasal obstruction, chronic rhinitis, and sleep apnea symptoms. Sensory innervation of the nasopharynx is produced by the trigeminal and glossopharyngeal nerves.
Within the nasal cavity exist several out-pouches during development that form the paranasal sinuses. These sinuses are comprised of the ethmoidal, maxillary, frontal, and sphenoid sinuses. The ethmoidal sinuses are the first to be fully developed, followed by the maxillary sinuses. Both the ethmoid and maxillary sinuses are radiologically present at birth (Figure 3). The frontal sinuses develop afterwards, followed by the sphenoid sinus which matures late in adolescence.
Figure 3Internal nasal and sinus development of the maxillary, ethmoid, and frontal sinuses via coronal view. Maxillary, ethmoid, and frontal sinus growth at different stages (right) in comparison to final adult development (left).
The ethmoidal sinuses are central structures of the nose, with numerous anatomical landmarks for surgical planning. The lateral wall of the ethmoid sinus, or lamina papyracea, is shared as the boundary for the medial wall of the orbit. The midline vertex of the ethmoid sinus is formed by the crista galli, from the anterior cranial fossa, and perpendicular plate of the ethmoid, from the superior nasal septum. The roof of the ethmoid sinus is composed of thin bone from the medial cribriform plate and thicker bone of the lateral ethmoid roof.
The ethmoid sinuses themselves are separated by a series of recesses originating from 5 bony lamellae. These include the uncinate process, bulla ethmoidalis, basal lamella, superior turbinate, and supreme turbinate. Among these 5 bony lamellae are 4 recesses as the frontal recess, the infundibulum, the sinus lateralis, and the sphenoethmoidal recess. Upon birth and throughout childhood, these partitions will allow for aeration during development of the ethmoid air cells.
The ethmoids are divided into anterior and posterior air cells by the basal lamellae of the middle turbinate. In turn, these anterior and posterior divisions will drain inferiorly to the middle turbinate and superior turbinate, respectively.
The bulla ethmoidalis usually gives rise to the largest anterior ethmoid air cell, which can reach the roof of the ethmoid sinus to form the posterior wall of the frontal recess. The most anterior ethmoid air cell is termed the agger nasi cell when it develops anterior to the head of the middle turbinate.
Posterior ethmoid cells, although fewer, are generally larger. These posterior cells can pneumatize laterally and superiorly toward the sphenoid sinus, a variant termed the Onodi cell, which can lead to potential complications during surgery, related to its close proximity to the optic nerve and internal carotid artery.
By the time of birth, the ethmoid sinuses are present in 90% of patients and structurally grow along with the midface of the child continuously until 16-18 years of age, when they reach a mean volume of 4.51 mL.
The most developmentally significant portion of ethmoid air cell formation occurs in the first 5 years of postnatal life, although no significant benchmark has been established for formation of a particular structure.
The largest of the paranasal sinuses, the maxillary sinus is also present at birth with the ethmoid sinuses. Contained within the maxillary bone, the boundaries of the maxillary sinus include the facial surface of the maxillary bone (anterolateral), the anterior wall of the pterygopalatine fossa (posterior), the lateral wall of the nasal cavity (medial), the alveolar process (inferior), and the orbital floor (superior).
At this point, the maxillary sinus is parallel to the nasal floor. By 15 years, the maxillary sinus should be nearing its maximum dimensions with a reported average volume of 14.8 mL.
Typically, growth can no longer be achieved once the sinus expands into the alveolar crest.
The medial wall of the maxillary sinus forms part of the lateral nasal wall, which includes the uncinate process. Although the primary maxillary os lies within the ethmoid infundibulum, accessary sinus ostia are found within the medial maxillary wall.
These ostia are rarely identified in fetal specimens, and are thought to be due to developmental phenomenon in childhood. Infectious processes are theorized to be involved with these accessory ostia, to allow for further drainage of maxillary sinus contents.
The anatomical relationship of the maxillary sinus and maxillary dentition also changes over the course of sinus development. Because the alveolar cortical bone thins with time, the roots of the maxillary dentition that initially developed in the thick alveolar bone of childhood can erupt into the inferior floor of the maxillary sinus. The incisors, canines, and premolars are typically not associated with the maxillary sinus.
Other variations of maxillary sinus development range from total absence to hyperpneumatization, although other developmental abnormalities maybe associated with craniofacial defects such as choanal atresia, cleft palate, and mandibulofacial dysostoses.
At 12 months of age, aeration of the sinus begins to occur. At 4 years, the frontal sinus starts to pneumatize such that by 6 years, nearly 20%-30% of children will have radiographic evidence of a pneumatized frontal sinus.
Nearly 85% of children at 12 years will have a pneumatized frontal sinus depending on whether they had undergone a growth spurt. By 25 years, the final size of the frontal sinus is achieved dependent on the degree of bone resorption.
Upon reaching full maturation, the anterior wall of the frontal sinus is twice as thick as the posterior wall covering the dural intracranial layer. The floor of the frontal sinus serves as the superior border of the orbit as well.
The outflow tract of the frontal sinus is dependent on the developmental aeration of the ethmoidal cells inferiorly. Markedly, pneumatized agger nasi or ethmoidal bulla cells will narrow the frontal recess and obstruct frontal sinus drainage. The frontal sinus drains under the middle meatus medial to the uncinate process in 88% of adult patients, and drains lateral to the uncinate in the remaining 12%.
Presence of the frontal sinus is quite variable in patients, as it can range from total absence to extended pneumatization of the sphenoid wings, parietal bone, and temporal bone (4). Total absence has been documented in 4% of patients, whereas unilateral absence has been noted in 5%.
The sphenoid sinus is the last of the paranasal sinuses to mature during childhood development (Figure 4). Although the sphenoid sinus is present as a protuberance of the sphenoethmoidal recess at birth, the sinus does not truly develop until late childhood.
The primordial capsule of the sphenoid sinus will first develop in-utero, but slowly ossify and grow posteriorly and inferiorly during infancy. At about 4 years of age, the primordium will invade the presphenoid to pneumatize the sphenoid bone.
At age 7, the sphenoid sinus starts growing in a dorsal direction reaching the sella turcica before starting a growth spurt that ends at the age of 15.
The degree of pneumatization is categorized into 3 types as sellar (86%), presellar (11%), and conchal (3%) type. The sellar type is the most pneumatized, reaching beyond the floor of the sella turcica and completely exposing the sella. The presellar type only reaches up to the vertical plane of the sella turcica, whereas the conchal type is rudimentary and typically seen during the preteenage years.
Figure 4Internal nasal and sinus development of the sphenoid sinus via sagittal view. Seen through the middle turbinate, laying underneath the concha, are the ostia of the ethmoid, frontal, and maxillary sinuses.
At maturation, the sphenoid sinus has several important neurovascular relationships. The internal carotid artery, as it courses through the cavernous sinus, produces a prominence in the lateral sphenoid wall in 65% of individuals. However, up to 25% of patients may have a sphenoid cavity dehiscence which makes it important to identify any pulsations in the surgical area while operating within the sphenoid sinus.
The outflow tract of the sphenoid sinus drains into the sphenoethmoidal recess. Variations in sphenoid size are typically the norm rather than exception. Complete absence of the sphenoid is apparent in 1% of adult patients.
There are many details to be aware of when performing surgery upon the pediatric nose or within the paranasal sinuses. One must not only take into account the narrow anatomical conditions, but also the surgical landmarks that may not yet be apparent in the developing patient. Although some otolaryngologists may wait to perform nasal surgeries, such as endoscopic sinus surgery or functional septorhinoplasty, until after childhood, particularly attention must be paid to the nuances of pediatric anatomy if surgery is necessary before puberty.
Disclosure/Conflicts of Interest
The authors report no proprietary or commercial interest in any product mentioned or concept discussed in this article.
References
Neskey D.
Eloy J.A.
Casiano R.R.
Nasal, septal, and turbinate anatomy and embryology.
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