NOSE, MOUTH AND PHARYNX
The nose is the main entrance of the respiratory system: its external
portion is particularly showy, projecting anteriorly between the orbits,
but its internal portion is notably wider, starting at the nares and
ending in the nasopharynx. The inner part of the nose is divided by the
nasal septum into two irregularly shaped air chambers known as the nasal
cavities, which communicate with the sinuses of the ethmoid, sphenoid,
frontal, and maxillary bones through small orifices called ostia and are
also connected with the orbits through the lachrymal canals and with the
anterior cranial fossa through the olfactory foramina. In a
well-conducted study, Xi et al. described the development of the nasal
cavities and larynx as well as their air-flow dynamics and aerosol
deposition, employing models based on computed tomography (CT) images of
4 children aged 10 days, 7 months, 3 years, and 5 years and comparing
the models to a model from a 53-year-old adult (2): the study showed
that the nasal cavities rapidly increase in space over the first 5 years
of life, when the volume included between the nares and the larynx
reaches 40.3% of that of the adult. In this study, the turbinate
region, including the 3 turbinate bones located in the lateral walls of
the nose, experienced the most noticeable growth during childhood and
was undeveloped in both the 10-day-old and 7-month-old models. Moreover,
the nostrils were described as smaller and their shape as more circular
in the newborn, becoming more oval during infancy and childhood and
wedge-shaped in adulthood (2), as shown in previous studies (3). Smaller
nares and nasal cavities unavoidably limit the inflow of air, so it is
estimated that the nose contributes up to 50% of total airway
resistance in younger children. Unsurprisingly, even a mild nasal
obstruction due to swelling or mucus production increases the work of
breathing in infants and may cause respiratory distress. As far as the
paranasal sinuses are concerned, the ethmoidal and maxillary sinuses are
already present at birth, while the frontal and sphenoidal sinuses
develop later, being radiologically demonstrated by the age of 5-6 years
and adolescence, respectively (4). The main feature of the oral cavity
in newborns and infants is a larger tongue, which completely occupies a
much smaller oral cavity than in subsequent ages (Figure 1 - 2).
Moreover, the base of the tongue is in strict connection with the
epiglottis, which extends towards the velum. Infants also have a shorter
neck, larger head relative to body size and a prominent occiput; as a
result, when lying supine, the alignment of the oral, laryngeal and
tracheal axes is hampered due to excessive neck flexion,
with a high risk of upper airway
obstruction and/or difficult visualization of the glottic opening during
laryngoscopy. Placing a folded towel roll under the shoulders allows
neutral positioning of the neck, improving airway alignment (4, 5). The
pharynx belongs to both the respiratory and gastrointestinal tracts and
is conventionally subdivided into the nasopharynx, oropharynx and
hypopharynx/laryngopharynx. The paediatric pharynx is shorter and has
shorter cross-sectional diameters than the adult pharynx. Moreover, the
nasopharynx and oropharynx house Waldeyer’s ring, which is composed of
the adenoids and the lingual, tubal and palatine tonsils; these
lymphatic structures are commonly enlarged in children, since they grow
quickly until the age of 5-7 years and then undergo physiological
atrophy (4). Studies with magnetic resonance (MR) imaging have shown
that this increased mass of lymphoid tissue may contribute to airway
obstruction in children (6). Last but not least, the Eustachian tubes
open on the lateral wall of the nasopharynx: these structures,
connecting the middle ear to the pharynx, are shorter, floppier and more
horizontal at birth, facilitating mucus stagnation, and they undergo
rapid growth in the first year of life (7, 8).