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4 Redening Outcome Measures
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M. J. L. Ravesloot
Part II
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Diagnosis of Epiglottis Collapse
Relevant Anatomy andPhysiology
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oftheEpiglottis
MatejDelakorda
5.1 Introduction
The nutritional and respiratory paths are joined in the upper aerodigestive tract that
serves multiple functions. Due to the complex relationship between the skeletal
frame and soft tissues, accurate neurological coordination is essential for maintaining adequate patency during breathing and for exerting effective constrictions during swallowing. A comprehensive knowledge of the anatomy of this region is
fundamental for understanding pathophysiologic processes as well as performing
safe and successful surgery.
The larynx is a cartilaginous segment of the respiratory tract, which is located in
the anterior aspect of the neck. Phylogenetically, its primary function was to prevent
ingested food and liquids from entering the trachea; the function of phonation
developed with further evolution. Complete glottic closure is necessary for effective
lung cleaning (coughing, sneezing) and for generating a positive intrathoracic pressure required for defecation, lifting heavy objects, body stabilization, and childbirth. The larynx also plays an important role in breathing and is actively involved
in the regulation of respiration by a complex of sensory feedback loops. The epiglottis is a part of the supraglottic larynx and has an important function, especially
in breastfeeding newborns and infants. It is exposed to many possible diseases,
developmental anomalies, infections, and neoplasms. The role of epiglottis in
obstructive sleep apnea (OSA) has only recently been observed and elucidated.
5
M. Delakorda (*)
General Hospital Celje, Celje, Slovenia
© The Author(s), under exclusive license to Springer Nature
Switzerland AG 2023
M. Delakorda, N. de Vries (eds.), The Role of Epiglottis in Obstructive Sleep
Apnea, https://doi.org/10.1007/978-3-031-34992-8_5
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M. Delakorda
5.2 Embryology
The larynx begins to form during the third and fourth weeks of embryologic development as a morphogenetic component of the respiratory system, and by the 41st
day, its cartilage and the intrinsic muscles are already observable. Its formation
starts as a longitudinal ridge from the foregut caudal to the fourth pharyngeal pouch.
Its lower portion grows inferiorly as a diverticulum to form the trachea and lungs,
while the cephalic part forms a primitive laryngeal aditus covered by an endoderm
lining—future epithelium. As it extends toward the caudal part of the embryo, it
becomes invested by mesenchyme that gives rise to the cartilaginous and muscular
structures. Antero-superior to this ridge is a hypobranchial eminence, a midline proliferation of mesenchyme anterior to third and fourth branchial arches visible as a
swelling of the oor of the primitive hypopharynx. The epiglottis will develop from
this structure and the ventral parts of the third and fourth arches. The latter will also
give rise to the aryepiglottic folds and cuneiform cartilages. The arytenoids and
corniculate cartilages are derived from the arytenoid swellings of the sixth branchial
arches (Fig.5.1).
The lesser cornu and the upper body of the hyoid are formed by the second pharyngeal arch, while the greater cornu and the lower portion of the body derive from
the third pharyngeal arch. The process of hyoid chondrication begins in the fth
fetal week and is completed in the third and fourth months. Ossication in the
greater cornu begins toward the end of the intrauterine life, in the hyoid body shortly
before or after birth, and in the lesser cornu around puberty. The thyroid cartilage is
Fig. 5.1 The ventral part of the pharynx in the fourth week (I) and fth month (II) of fetal life. A
lateral lingual swellings, B medial lingual swelling, C1 hypobranchial eminence, C2 epiglottal
swelling, D arytenoid swellings, and * foramen cecum
5 Relevant Anatomy andPhysiology oftheEpiglottis
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derived from the fourth pharyngeal arch. The future thyroid cartilage and hyoid are
connected ventrally at the hypobranchial eminence and dorsally by a cartilaginous
bar—the hypothyroid cartilage. At the third month of fetal development, the hyoid
bone and thyroid cartilage separate, sometimes leaving a remnant of this connection
in the form of a small oval-shaped hyaline cartilage called triticeal cartilage [1].
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5.3 Developmental Anomalies
The incidence of congenital anomalies of the larynx and trachea is fairly low,
reported at 1in 10,000 to 50,000 live births, either as isolated occurrences or as
synchronous lesions, frequently seen as part of syndromes such as short rib polydactyly, or tricho-rhino-phalangeal and lacrimo–auriculo-dental-digital syndromes
[2]. The identication of such anomalies soon after birth, or prenatally, is often vital
for the survival and growth of the infant. Laryngeal anomalies are commonly related
to symptoms of aspiration and/or stridor, which can also be caused by dynamic
conditions such as laryngomalacia (see Chap. 11).
Interruption before or during the embryological period during which the larynx
is formed can result in aplasia, hypoplasia, and bid epiglottis. The absence of the
epiglottis can also be accompanied by severe glottic stenosis [3]. Patients with bid
epiglottis commonly experience symptoms of respiratory compromise caused by
one or both of the cartilaginous halves being drawn into the glottic inlet with
inspiration.
5.4 Maturation: Laryngeal Descent
The anatomy and position of the larynx in infants and children differ from that in
adults [3]. From fetal to adult life, the epiglottis undergoes a considerable gradual
descent in relation to the vertebral column as well as some morphologic changes [4,
5]. These anatomic changes of the upper respiratory tract probably evolved mainly
to facilitate speech by enabling better articulation. An elevated laryngeal position
enables contact between the epiglottis and soft palate, thus supporting nutrition by
allowing breathing while sucking. It not only prevents aspiration but also makes
newborns obligatory nasal breathers. Laryngeal descent is believed to be the anatomic basis predisposing humans to OSA as a developmental extension of the
tongue backward and downward creates a compliant oropharynx prone to collapse [6–8].
At birth, the inferior margin of the cricoid cartilage is located at the level of the
upper border of the C-4 vertebra, while the tip of the epiglottis is at the level of the
C-1 vertebra. Usually, it can be visualized over the dorsum of the tongue in most
infants. From birth, the larynx starts to descend with the most obvious changes taking place during puberty when the larynx lengthens rapidly. The cricoid cartilage
descends to the level of the C-7 vertebra in men and the C-6 vertebra in women, and
the tip of the epiglottis is opposite the C-3 vertebra.
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The infant larynx has softer cartilage and laxer supporting ligaments. Epiglottis
is omega- or tubular-shaped, and hence, it is more susceptible to collapse due to
negative pressure during inspiration [9]. During maturation, the epiglottis becomes
increasingly at with the aryepiglottic folds in a more lateral position; but in most
adults, it retains its curved shape. Additionally, an angle of the thyroid cartilage’s
laminae narrows from 110–120 to 90° in men after puberty but does not change
signicantly in women.
M. Delakorda
5.5 Skeletal Framework
An adult larynx is superiorly limited by the free end of the epiglottis and inferiorly
by the lower edge of the cricoid cartilage. Its cartilaginous skeleton consists of multiple cartilage types: hyaline cartilage—specically, thyroid, cricoid, arytenoid, and
triticeal; elastic epiglottis; and broelastic corniculate (Santorini) and cuneiform
(Wrisberg) cartilage. Together with the hyoid bone, they form a complex skeletal
framework interconnected by numerous ligaments, brous membranes, and synovial joints that are moved by muscles in different directions.
The thyroid cartilage is the largest cartilage of the larynx. It is formed by two
quadrangular alae that unite anteriorly and form a thyroid notch superiorly with the
laryngeal prominence (Adam’s apple) just below it, most obvious in males. On the
lateral surface, there is an oblique line to which the sternothyroid, thyrohyoid, and
inferior pharyngeal constrictor muscles attach [9]. Posteriorly, each ala has a superior and inferior horn. The inferior horn articulates with a facet on the cricoid cartilage to form the synovial cricothyroid joint that allows rotation of the cricoid
cartilage. The superior horn attaches to the greater cornu of the hyoid bone with the
lateral thyrohyoid ligament. In about one-third of the general adult population, this
ligament contains small triticeal cartilages, which can cause symptoms such as dysphagia and odynophagia or can be mistaken for a foreign body when calcied [10–
14]. The corniculate cartilages are housed on the apex of the arytenoids. The
cuneiform cartilages, when present, are lateral to the corniculate cartilages embedded in the aryepiglottic fold. Although some feel that these cartilages are vestigial,
they do appear to add rigidity to the aryepiglottic folds.
The epiglottis is a thin lamella of yellow cartilage, shaped like a leaf. It projects
obliquely and vertically behind the base of the tongue and ventrally to the entrance
of the larynx. Its broad and round free end, which is occasionally notched in the
midline, is directed upward and sometimes bent anteriorly. Its lower part, called
petioles, is like a stalk, long, and narrow and connected to the back of the thyroid
cartilage. On the posterior surface of its lower half, there is a projecting part called
the tubercle that, when prominent, can obscure the view of the anterior part of the
vocal cords. The epiglottis is higher and wider in males with no signicant changes
observed with aging [15]. It can be divided into a suprahyoid and an infrahyoid portion. The suprahyoid portion protrudes into the laryngeal lumen, without any attachments, whereas on the infrahyoid part, only the posterior-laryngeal surface is
exposed. Split lines in the epiglottic cartilage reect the arrangement of its collagen
5 Relevant Anatomy andPhysiology oftheEpiglottis
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bundles. On the posterior aspect, they run primarily in a horizontal direction
throughout the upper one to two-thirds above the epiglottic tubercle and are most
pronounced between the attachments of the lateral and median hyoepiglottic ligament. This area, approximately one-third of the way from the superior margin of the
epiglottis, also referred to as the epiglottic folding plane, is important for the mechanism of epiglottic downfolding during swallowing [16]. The lower third, including
the petiolus of the epiglottis, demonstrates a vertically directed orientation of split
lines. The anterior aspect of each epiglottis shows a different, more complex orientation of split lines surrounding the holes and recesses formed by the mucous glands.
The cartilage is also perforated by the branches of the internal laryngeal nerve.
It was traditionally believed that only structures composed of hyaline cartilage
can undergo calcication (thyroid, cricoid, and arytenoid cartilages) [14, 17].
Enchondral calcication of these cartilages begins with skeletal maturity and progresses thereafter with aging. Based on macroscopic observations, the epiglottis had
been considered a permanent elastic cartilage that does not undergo ossication
[18]. However, a more detailed analysis of age-related changes in calcium deposition has shown that calcication increases with age and is more pronounced in
males [15, 19, 20]. Laryngeal cartilage calcication may affect some mechanical
properties and while it could theoretically add to its stability, it can also be a cause
of different swallowing problems, such as dysphagia, foreign body sensations, or
aspirations [21].
The hyoid bone is the central movable anatomical structure of the neck and functional part of the larynx. This U-shaped bone is located in the anterior midline and
serves as an attachment for various muscles of the oor of the mouth, tongue, and
pharynx. It is unique because in humans, unlike in other mammals, it does not articulate with any other bone or cartilage. Instead, it is suspended from the styloid
processes by the bilateral stylohyoid ligaments, brous cords extending from the tip
of the styloid processes to the lesser cornus of the hyoid bone. The hyoid position is
determined by this suspension apparatus and the activity of muscles attached to it.
Due to these connections, the hyoid position is closely related to pharyngeal airway
dimensions and associated with critical closing pressure in OSA patients [22].
During inspiration, contraction of pharyngeal dilators causes anterior movement of
the hyoid and increases the anteroposterior dimension of the retrolingual airway,
contributing to upper airway (UA) patency. In resting state, it is positioned in the
neck roughly parallel with the lower border of the mandible, and, when viewed in
lateral projection, the tip of the greater cornue partially overlaps with the cervical
spine [23].
The epiglottis has two anterior attachments. Inferiorly, at the petiolus, the epiglottis is attached to the inner surface of the laryngeal prominence of the thyroid
cartilage, just above the level of the anterior commissure and below the thyroid
notch, by the elastic thyroepiglottic ligament. At this point, bilateral vestibular ligaments and vocal ligaments are also attached, forming the Broyles’ ligament that
contains blood vessels and lymphatics [24, 25]. Superiorly, the epiglottis is attached
to the hyoid bone by the paired lateral hyoepiglottic ligaments and a single medial
hyoepiglottic ligament. The lateral hyoepiglottic ligaments are attached to the
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M. Delakorda
lateral edges of the upper portion of the epiglottis, running laterally to the tip of the
greater horns of the hyoid bone forming the pharyngoepiglottic folds (lateral glossoepiglottic folds) [16]. The medial ligament is a brous fan-shaped band of tissue
running in the midline from the upper border of the hyoid bone to the anterior surface of the epiglottis, forming the medial glossoepiglottic fold. The upper limit of
its epiglottic attachment is at the level of the lower borders of the greater cornu of
the hyoid bone and its lower attachment blends with the attachment of the thyroepiglottic ligament [26]. It had been traditionally believed that anteriorly the medial
hyoepiglottic ligament attaches only to the hyoid bone, but a more recent anatomical study revealed that the hyoepiglottic ligament also extends to one of the intrinsic
lingual muscles, most probably the genioglossus muscle [27, 28] (Fig. 5.2).
Accordingly, two parts can be distinguished in the medial hyoepiglottic ligament:
the lingual and the hyoid part. A signicantly decreased number of elastic and collagen bers has been found in these ligaments in elderly persons, which may put
them at an increased risk of epiglottic instability [29, 30]. Taking into account the
progressive attening of epiglottis with aging, it is possible that this ligament maintains its anterior convexity.
The thyrohyoid membrane is a broad broelastic layer attached to the upper
border and superior horn of the thyroid cartilage, the upper margin of the posterior
surface of the body, and the greater horns of the hyoid bone. It thus ascends behind
the concave posterior surface of the hyoid and is separated from its body by a bursa
that facilitates the ascent of the larynx during speech and deglutition. The thickened
portion of this membrane in the midline constitutes the thyrohyoid ligament. The
aryepiglottic folds are paired structures arising from the apex and corniculate tubercle of the arytenoids and merging with the lateral margins of the epiglottis. Together
with the laryngeal surface of the epiglottis, they enclose the space referred to as the
laryngeal vestibule. The body of each aryepiglottic fold is composed of the
Fig. 5.2 Attachments of
hyoepiglottic ligament. 1
hyoepiglottic ligament (a
lingual part and b hyoid
part), E epiglottis, H hyoid
bone, and T thyroid
cartilage
5 Relevant Anatomy andPhysiology oftheEpiglottis
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aryepiglottic muscle and quadrangular membrane, with its inferior margin terminating as a thickened ligamentous tissue, forming the ventricular ligament.
Behind, the thyrohyoid membrane lies a preepiglottic space (PES), which takes
the shape of a triangular pyramid with an inferior apex and is divided into left and
right sides by a thin sagittal membrane (septum) [31]. It is bounded by the medial
hyoepiglottic ligament and valleculae superiorly; the hyoid bone, thyrohyoid membrane, and thyroid cartilage anteriorly; and the thyroepiglottic ligament and anterior
surface of the epiglottic cartilage posteroinferiorly. The PES is continuous with the
paraglottic space (PGS) that is laterally and posteriorly surrounded by the thyroid
lamina and by the mucosa of the hypopharynx (piriform sinus), respectively. At the
supraglottic level, it lies postero-inferiorly to the PES and medial to the lamina of
the thyroid cartilage. The PES and PGS are composed of adipose tissue and loose
elastic and collagen bers [32]. Preepiglottic adipose tissue, sometimes referred to
as “laryngeal fat body,” plays an important role in the process of swallowing. PES
also contains one or two lymph nodes, while the PGS is a space for the main laryngeal arteries and allows interrupted blood ow within it [33].
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5.6 Muscles
There is a large number of skeletal muscles that have to act in a coordinated way to
enable important physiological processes taking place in the larynx and pharynx
(breathing, deglutition, phonation, and articulation). Many of them inuence the
UA patency and are sometimes referred to as accessory respiratory muscles. They
can dilate and open or stiffen the airway to make it less prone to collapse by the
negative inspiratory pressure. Describing all muscles involved in pharyngeal and
laryngeal functions is beyond the scope of this work. Their characteristics and functions are presented in Table5.1. Pharyngeal dilators and muscles that affect the
distance between the thyroid cartilage and the hyoid bone, as well as their orientation, can also affect the position and shape of the epiglottis. That is why we believe
these muscles are the most relevant for the development of obstructive respiratory
events at the level of the tongue base and epiglottis.
Although many anatomic studies have evaluated the function of pharyngeal muscles during swallowing, a complete understanding of their role in sleep-disordered
breathing still needs to be established. The pharyngeal muscles are anatomically
and functionally connected and do not act as simple individual structures but rather
move and function together in a very coordinated way. It is important to realize that
a particular pharyngeal muscle can have different mechanical effects on the UA
depending on the size and shape of the airway at the time of muscle activation,
muscle ber orientation, simultaneous activation of other muscles, and the timing of
activation relative to the phase of respiration. This may help explain how pharyngeal muscles can play a role in such disparate functions as respiration, deglutition,
and phonation [34].
The pharynx is a tube-like muscular structure that comprises three external circular muscles (the superior, middle, and inferior constrictor muscles) and three
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