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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4538_Библиотеки_им_академика_М_И_Перельмана
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V. K. Paramasivan et al.
21.6.8 Structures Causing Airway Obstruction
Obstructive sleep apnea syndrome is caused by obstruction anywhere in the
upper airway, from the nasopharynx to the larynx. Due to obstruction at multiple
It may occur due to obstruction at multiple levels, either simultaneously or in an
alternating pattern [23, 29]. It may due to enlargement of soft-tissue structures
and alterations of craniofacial structures. Enlargement of soft tissue includes an
enlarged adenoid, the palatine tonsils, the lingual tonsils, the soft palate, and the
tongue as well as accumulation of fat in the parapharyngeal walls. Alternations
in craniofacial structures such as retroposition of maxilla and mandible and inferior positioned hyoid bone are reported in patients with OSAS (Fig. 21.7)
[30, 31].
21.6.9 Nasopharynx
Enlarged adenoids are the most typical reason for airway obstruction, especially in
children. It can also be one of the reasons for obstruction in adults. They reach a
maximum size between 2 and 10years of age and then begin to decrease in size
during puberty. The normal size of the adenoids is between 7 and 12mm. Adenoids
larger than 12mm in size are abnormally enlarged, which can be easily measured in
sleep MRI (Fig.21.8).
Fig. 21.7 Dynamic MRI
of an OSAS patient
showing soft tissues
measurements
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Fig. 21.8 Dynamic MRI
of an OSAS patient
showing adenoidal
hypertrophy
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21.6.10 Velopharynx
21.6.10.1 Enlarged andElongated Soft Palate
Typically, the soft palate is isointense to tongue musculature on T2-weighted
images. When the soft palate becomes edematous, it becomes high in signal on
T2-weighted and thickens (>1 cm). The soft palate thickens in OSA because of
microtrauma from uttering during snoring. Thickened soft palate contributes to the
worsening of OSAS by taking up more potential airway space. Criteria to consider
a soft palate to be “elongated” include when the soft palate is draped over abutting
the tongue or soft palate is posteriorly positioned abutting the adenoids and obstructing the nasopharynx, and when the soft palate hangs inferiorly, below the mid
tongue or touches the epiglottis (Fig.21.7) [23, 32].
Likewise, Drug-Induced Sleep Endoscopy, with an axial view of dynamic MRI,
we will also be able to identify the different patterns of airway collapse at the level
of velum. Figure21.9 shows a circular, anteroposterior, and lateral pattern of collapse at the level of velum, which will help the surgeon decide which technique of
surgery will improvise the surgical outcome.
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Fig. 21.9 Dynamic MRI
axial view of OSAS patient
showing different pattern
of retropalatal collapse (a)
circular collapse, (b)
anteroposterior collapse,
(c) lateral collapse
a
b
c
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21.6.11 Oropharynx
Enlarged faucial tonsils are another common cause of obstruction in both adults and
children. They have been graded as per Friedman’s classication depending upon
the size of the tonsil (Fig.21.10).
21.6.12 Enlarged Lingual Tonsils
Typically, the lingual tonsil appears as a small disk of a high T2-weighted signal at
the posterior aspect of the inferior tongue. When the lingual tonsils are enlarged,
they appear as a large high T2-signal mass posterior to the tongue, often obstructing
the velopharynx. When they enlarge, the tonsils appear as one large dumbbellshaped mass rather than 2 discrete lingual tonsils (Fig.21.11). The lingual tonsils
were noted as markedly enlarged if the anteroposterior diameter is more than 10mm
[33, 34].
21.6.13 Macroglossia
Macroglossia is dened as a resting tongue that protrudes beyond the alveolar
ridge. The posterior aspect of the tongue sits near the posterior wall of the retroglossal airway, resulting in a consistently narrowed airway (Fig. 21.12). The
Fig. 21.10 Dynamic MRI
of an OSAS patient
showing Tonsillar
hypertrophy
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Fig. 21.11 Dynamic MRI
of an OSAS patient
showing Lingual Tonsillar
hypertrophy
Fig. 21.12 Dynamic MRI
of an OSAS patient
showing tongue base
hypertrophy
V. K. Paramasivan et al.
tongue may be relatively large in patients who have a small mandible (micrognathia) (Fig.21.13), which is termed relative macroglossia. An enlarged tongue can
fall posteriorly during sleep, obstructing the retroglossal airway. Magnetic resonance imaging helps assess the size of the tongue and the degree of compression
along the retroglossal airway. It also helps in identifying secondary palatal collapse where the tongue base itself pushes the palate backward and obstructs the
retropalatal airway.
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Fig. 21.13 Dynamic MRI
of an OSAS patient
showing micrognathia
pushing the tongue base
posteriorly
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21.6.14 Glossoptosis
Glossoptosis is dened as the posterior motion of the tongue during sleep. With
glossoptosis, the posterior border of the tongue intermittently moves posteriorly and
abuts the posterior pharyngeal wall obstructing the retroglossal airway. Glossoptosis
is associated with macroglossia, micrognathia, or decreased muscular tone. Dynamic
sagittal MR imaging demonstrates the tongue to “fall” posteriorly, abutting the
velum and the posterior wall of the pharynx, which causes upper airway obstruction. In severe glossoptosis, the tongue can also push the soft palate posteriorly,
causing intermittent obstruction of the nasopharynx. On axial images obtained at
the level of the middle portion of the tongue, the predominant motion is anterior to
the posterior motion, intermittently obstructing the retroglossal airway. In contrast,
the lateral and the posterior aspects of the retroglossal airway remain stable in position [35].
21.6.15 Hypopharyngeal Collapse
Hypopharyngeal collapse is the term given to the collapse of the retroglossal airway
that is related to decreased muscular tone. In contrast to glossoptosis, where there is
the abnormal posterior motion of the tongue during sleep, the hypopharyngeal collapse shows the tongue moving posteriorly and the posterior wall of the pharynx
moving anteriorly. Certain patients, particularly those with Down syndrome, will
have both components of glossoptosis and a oppy airway at risk for hypopharyngeal collapse [27, 28].
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21.6.16 Hypopharyngeal andLaryngeal Lesions
Vallecular cysts of the hypopharynx and other soft-tissue tumors such as lipoma in
the hypopharyngeal region have been associated with OSA.In most cases, the larynx can be involved as a site of obstruction, at the epiglottis level. Edema and granulomatous lesions of the epiglottis as scleroma may be associated with OSA [27,
29, 36].
We will be able to easily differentiate the primary from secondary epiglottic collapse in the sagittal and axial view of dynamic MRI.In primary epiglottic collapse,
vallecular air-lled space can be appreciated between epiglottis and tongue base.
However, in secondary epiglottic collapse, the tongue pushes the epiglottis back,
and an absence of air is seen between the epiglottis and the tongue base (Fig.21.14).
21.6.17 Fat Deposition inParapharyngeal Space
Excess adipose fatty tissue deposition in the parapharyngeal space may be associated with OSA [6, 8]. This is one of the most exclusive situations where sleep MRI
helps in assessing the parapharyngeal space fat deposition. In dynamic MRI, we
will also be able to evaluate large deposits of fat in the posterolateral aspect to the
oropharyngeal airspace at the level of the soft palate; fatty streaks can be noted in
the tongue, anterior to the laryngopharyngeal airspace, in the submental regions and
around the collapsible segment of the pharynx [37].
21.6.18 Retropharyngeal Lesions
Soft-tissue tumors of the retropharyngeal space such as lipoma and Schwannoma
narrow the airway with OSA.A retropharyngeal abscess associated with bacterial
or tuberculous infection may be associated with OSA.Lastly, bony tumors such as
exostosis from the cervical spine may be related with OSA [27, 38].
21.6.19 Craniofacial Abnormalities
Craniofacial abnormalities such as retrognathia, inferiorly positioned hyoid bone,
and maxillary and mandibular retroposition are associated with OSA.Cephalometry
and computed tomographic scans are essential for detecting osseous changes; however, MRI has a role but is of limited value. There is a relationship between surface
facial dimensions and upper airway structures measured at MR imaging in patients
with OSAS [39, 40].
Mandibular hypoplasia may be idiopathic but more commonly associated with
certain inherited disorders and syndromes, such as Treacher–Collins syndrome,
Nager syndrome, Goldenhar syndrome, hemifacial microsomia, trisomies 17–18
and 13–15, Cri du chat syndrome, and Pierre–Robin sequence. Magnetic resonance
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Fig. 21.14 Dynamic MRI
of an OSAS patient
showing different position
of epiglottic collapse, (a)
normal position of
epiglottis, (b) primary
epiglottic collapse, (c)
secondary epiglottic
collapse
a
b
c
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V. K. Paramasivan et al.
imaging helps in establishing the size and position of the tongue in relation to the
hypoplastic mandible and the degree of airway compromise [24, 25].
21.6.20 Associated Disorders
In Down syndrome, there is no true or absolute macroglossia but relative macroglossia in relation to the size of the oral cavity. Obstructive sleep apnea syndrome occurs
in 30–60% of patients with Down syndrome [41]. Congenital conditions affecting
craniofacial development (Fig.21.15) such as Chiari, Marfan, Down, and the Pierre–
Robin syndrome predispose to OSAS [7, 8]. Endocrinologic conditions such as acromegaly and hypothyroidism are associated with a higher prevalence of OSAS [42].
Magnetic resonance imaging is essential for the diagnosis and treatment planning of OSAS as it can detect the level, degree, and causes of the upper airway
obstruction. It also has a role in predicting treatment response and monitoring
patients with OSA after therapy. It has always been complementary to other investigations to identify the site of obstruction.
21.6.21 Neuroimaging inOSA
OSA is clinically characterized by chronically fragmented sleep and intermittent
hypoxemia, dened as repeated episodes of deoxygenation that alternate with episodes of reoxygenation. OSA-related hypoxemia is associated with an increase in
sympathetic vasoconstriction and a coinciding decrease in vascular protective
mechanisms, resulting in changes to the structure and function of the blood vessel.
Fig. 21.15 Dynamic MRI
of an OSAS patient with
craniofacial anomaly
showing airway collapse
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This imaging technique can clarify abnormalities in neural control of respiratory
function in OSA by examining the relationship between respiratory challenges and
brain function measured in the magnetic resonance imaging (MRI) scanner.
Neuroimaging can also help identify neural abnormalities associated with vascular
function in OSA.It helps identify individuals with OSA at the most signicant risk for
poor outcomes by examining relationships between brain integrity and functional
response to treatment. These results may subsequently serve as a potent clinical motivator for OSA individuals struggling with treatment adherence. There are, however,
limitations to the use of neuroimaging techniques. Some forms of neuroimaging, such
as positron emission tomography, are invasive and not easily repeated over time.
The neurological sequelae of untreated OSA have been studied by conventional
and functional imaging techniques of the brain. Moderate to severe OSA is an independent risk factor for white matter disease demonstrated by MRI because of
Transient ischemic attack or an ischemic or hemorrhagic stroke.
MRI diffusion tensor imaging (DTI) has recently been used to demonstrate evidence of a reduction in white matter ber integrity in multiple brain areas in patients
with OSA [28] and complete reversal of white matter abnormalities after 12months
of CPAP treatment [24]. Widespread changes in gray matter concentration have
been found in patients with OSA using the functional MRI technique of voxel-based
morphometry (VBM) (Fig.21.16) [43–45].
Structural MRI (sMRI) is an important tool that promotes the examination of neuroanatomic volumetric and morphometric abnormalities that may be involved in pathologic processes. sMRI also provides an essential context to consider both neurochemical
and neurofunctional ndings. The voxel-based morphometric analytic technique will
help assess regional gray matter loss in the frontal cortex, parietal cortex, temporal lobe,
anterior cingulate, hippocampus, and cerebellum of patients with OSA.The extent of
the volumetric decline was related to the severity of OSA, with patients with more
severe OSA demonstrating the most signicant amounts of gray matter volume loss.
21.6.22 Magnetic Resonance Spectroscopy
Magnetic resonance spectroscopy (MRS) is an imaging technique that permits the
investigation of neuronal cellular chemical activity by examining neurotransmitters
and amino acids. In existing MRS studies of populations with OSA, spectral
Fig. 21.16 Regional gray matter volume differences between OSA baseline and OSA follow
groups. Hot color map, OSA baseline > OSA follow; cold color map, OSA follow > OSA baseline
(corrected p < 0.05)
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