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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4416_Библиотеки_им_академика_М_И_Перельмана
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Section
Normal Anatomy and Imaging
1. Imaging Modalities and Techniques
2. Sinonasal Anatomy: Structure-wise
3. Sinonasal Anatomy: Section-wise
1
1
CHAPTER
Imaging Modalities and
Techniques
Devasenathipathy Kandasamy, Chandrashekhara SH
• Introduction
• Imaging Modalities
– Radiographs
– CT Scan
INTRODUCTION
■ Paranasal sinuses (PNS) are air-lled structures located around the nasal
cavity and formed with in the bones of the skull and face. e various
functions are decreasing the weight of head, conditioning the inhaled air
with moisture and heat and increasing the resonance of speech.
■ ere are four sets of sinuses on either sides namely, maxillary, frontal,
ethmoid and sphenoid sinuses.
■ Imaging of sinonasal pathology has evolved over the last three decades
and advances in imaging have changed the way we look at diseases.
■ e unprecedented detail in which the PNS and skull base anatomy are
visualized in current generation imaging was not possible earlier.
■ Parallel growth of new techniques and approaches, such as endoscopic
and image guided surgeries have also increased the demand on imaging.
■ Sinonasal inammatory pathology is very common and usually
secondary to infection or allergy.
■ Most of them do not need imaging evaluation.
■ ere specic scenarios where imaging evaluation is indicated.
■ American Academy of Otolaryngology-Head and Neck Surgery (AAOHNS) published a consent statement in 2012 aiming to guide the choice
of imaging in the evaluation of sinonasal diseases (Table 1.1).
e consent statement also published the scenarios where imaging is
not indicated:
■ Uncomplicated sinusitis or upper respiratory tract infections.
■ Responding to medical treatment.
■ Children less than 3 years with uncomplicated acute sinusitis.
▪ Multidetector Row Computed
Tomography (MDCT)
▪ Cone Beam CT
– MRI
– F-18 FDG PET-CT
1
Section 1 Normal Anatomy and Imaging4
Table 1.1: Indications for imaging.
S. No. Indications
1.
Chronic sinusitis not responding to medical treatment
2.
Recurrent sinusitis
3.
Complication of sinusitis
4.
CSF rhinorrhea
5.
Invasive fungal sinusitis in immunocompromised individuals
6.
Tumor evaluation
7.
Preoperative planning for new or revision surgeries
8.
Complications of surgery
To prevent misuse of imaging modalities American College of Radiology
(ACR) has published its ACR appropriateness criteria in 2013, which rates the
usefulness of an imaging modality in a given situation.
2
IMAGING MODALITIES
e imaging modalities which are used to evaluate sinonasal diseases are:
■ Radiographs
■ Computed tomography (CT)
• Multidetector CT (MDCT)
• Cone-beam CT (CBCT)
■ Magnetic resonance imaging (MRI)
■ F-18 FDG positron emission tomography (PET).
Radiographs
Plain radiographs were used to evaluate PNS before the advent of CT scans.
Techniques
■ Standard four view sinus series include (Table 1.2):
• Water’s view (occipitomental) (Fig. 1.1)
• Caldwell’s view (occipitofrontal) (Fig. 1.2)
• Lateral view (Fig. 1.3)
• Submentovertical view.
■ e above standard set of views provide good assessment of PNS
(Figs. 1.4A to D). Amongst these Water’s view is most frequently employed.
■ Abnormalities manifest as opacication of sinuses, bone destruction,
soft tissue or displacement of structures.
■ However, the sensitivity and specicity of plain radiographs are poor
compared to newer modalities which make it a less favored modality.
■ In a properly exposed radiograph, PNS density is identical to orbital
density.
■ Erect or sitting position used during radiography of PNS to identify
presence or absence of uid and to dierentiate uid and thickening
caused by other pathology.
■ e recent AAO-HNS guidelines are also not in favor of using plain
radiographs for the evaluation of sinusitis.
■ Currently, the utility of radiographs is very limited.
1
Air-uid level in the sphenoid sinus
Sella turcica and nasopharynx are well seen
Best projection for examining the frontal and
ethmoid sinuses in the frontal projection
sinus
Better evaluate lower posterior sphenoid sinus
Anterior and posterior walls of the frontal sinuses
5Chapter 1 Imaging Modalities and Techniques
The lateral and medial walls of the maxillary
antrum
Frontal and anterior
ethmoidal sinuses
Maxillary sinuses Evaluation of maxillary antra, roof of orbit, frontal
Table 1.2: Various radiographic views of paranasal sinuses (PNS).
is perpendicular to the bucky
CR angled caudal 15°
OM baseline or radiographic
baseline 45° from horizontal
CR perpendicular to IR
Caldwell Radiographic baseline (OM line)
Projection Method/name Technique PNS visualized Structures visualized
Lateral R or L Head in true lateral position All paranasal sinuses Integrity of the posterior antral bony margins
PA axial 15°
(Occipitofrontal)
Closed mouth
Occipitomental Water’s
Maxillary and sphenoidal
sinuses
Ethmoidal and sphenoidal
sinuses
OM baseline or radiographic
baseline 45° from horizontal.
Open mouth
to the IR and bucky
Open mouth
Occipitomental Water’s
Submentovertical Basal view Infraorbitomeatal line is parallel
(OM line: Orbitomeatal line; CR: Central ray; IR: Image receptor).
Section 1 Normal Anatomy and Imaging6
Fig. 1.1: Radiograph of paranasal sinuses (PNS)—Water’s view.
Fig. 1.2: Radiograph of paranasal sinuses (PNS)—Caldwell’s view.
Fig. 1.3: Radiograph of paranasal sinuses (PNS)—Lateral view.
7Chapter 1 Imaging Modalities and Techniques
A
C
Figs. 1.4A to D: Schematic diagram of various radiographic views of paranasal sinuses
(PNS).
B
D
Section 1 Normal Anatomy and Imaging8
CT Scan (Figs. 1.5A to C and Table 1.3)
■ CT scan is the modality of choice and the workhorse for the evaluation
of sinonasal diseases.
■ e ability of CT scan to show the sinuses in much better detail coupled
with good spatial resolution has practically replaced plain radiographs.
■ Findings, such as sinus opacication, bone destruction, mucoperiosteal
thickening and normal variations in the anatomy are not only valuable
in the diagnostic point of view but also for the preoperative planning in
these patients.
A B
Figs. 1.5A to C: Computed tomography
(CT) of paranasal sinuses (PNS). (A)
Coronal soft tissue window; (B) Coronal
C
Table 1.3: Computed tomography (CT) techniques.
1. Axial plane: parallel to the infraorbitomeatal plane
2. Craniocaudal: Frontal sinus to hard palate
3. Tube current: 120 kVp, tube current modulation with quality reference mAs of 80
4. 0.6 mm acquisition with reconstruction of data into 1–3 mm sections in axial, coronal
and sagittal planes
5. Bone windows: Width 3500, center 300
6. Soft tissue windows: Width 270, center 70
7. Sinus windows: Width 2000, center 400
bone window; and (C) Sagittal bone window
sections used for PNS evaluation.
Multidetector Row Computed Tomography (MDCT)
■ Role of MDCT
• Axial scanning avoids the extension of head
• Lack of obscuration of important anatomy by spray artifact from
dental restoration
• Allow more rened reconstructions in other plane than the primary
scan plane.
■ Role of Coronal Reconstructions
• Primary imaging orientation
• Best shows osteomeatal unit
• Relationship of ethmoid roof to brain
• Correlate with surgical orientation.
■ Role of Sagittal Reconstructions
• Better visualization of frontal recess and frontal sinus, these are areas
of persistent and recurrent sinus disease
• Better show sphenoid sinus and basal lamella and agger nasi cell,
contributing the safer and accurate endoscopic procedure.
■ Whenever CT scan images are reviewed, it is best to visualize all three
planes simultaneously and they must be linked. So that when the cursor
is kept on any plane the other two planes will align accordingly to the
same point of interest (Figs. 1.6A to D).
9Chapter 1 Imaging Modalities and Techniques
A
C
Figs. 1.6A to D: Reviewing method of CT images. Images are viewed in all three planes
simultaneously and they are linked to each other. Wherever cursor or cross-hair is placed on
an image the other planes align to that point automatically.
B
D
Section 1 Normal Anatomy and Imaging10
■ Noncontrast CT (NCCT) is usually done for sinonasal inammatory
diseases unless there is a suspicion of extrasinus involvement. Contrastenhanced CT (CECT) is generally recommended for the evaluation of
tumors.
■ Demonstration of the pathology or the normal structures in multiple
planes, such as coronal (most important), axial and sometimes sagittal is
crucial for the surgical point of view.
■ Multiplanar reformations (MPR) were not possible in older CT scanners,
hence direct acquisition of images in both axial and coronal planes were
performed. e axial acquisition is done in supine position and coronal
acquisition is usually done in prone position with hyperextension at neck.
is doubled the radiation dose and increased artifacts due to motion
(patient discomfort due to awkward positioning) and dental implants.
■ With the advent of MDCT, scenario changed and with the capability of
rapid thin section acquisition it is now possible to acquire the entire
sinonasal region in seconds. Once the volume data is acquired images
can be reformatted in any plane. is technique negates the limitations
of older scans.
■ e volume data can be post processed to generate various types of
3D images such as volume rendering technique (VRT), surface shaded
display (SSD), etc.
■ e major limitation of CT scan is the radiation dose involved in the
process. Roughly a standard dose CT PNS gives four times radiation dose
than a standard three set plain radiographs.3 ere are various methods
available to reduce the radiation dose by maintaining the diagnostic
quality. Two most important techniques which are widely used to reduce
the radiation dose are—(1) tube current modulation, and (2) iterative
reconstruction.
■ Tube current modulation is a type of automatic exposure control in
which the radiation dose is adjusted in accordance with the patient
habitus, attenuation of body part and the desired image quality. e
implementation of this technique varies with the vendors and it can
bring down the radiation dose up to 60%.
■ Iterative reconstruction is actually an older technique but the advances
in computing have made it feasible only recently. Generally, it is added
on to the existing ltered back projection method. It has the potential to
bring down the radiation dose up to 85%.
Cone Beam CT
■ CBCT is getting wide acceptance as a point of care imaging tool and it
is compact, portable and cheap compared to main stream CT scanners.
■ ey use area detectors in contrast to multiple thin rows of detectors in
conventional CT. e scanning of area of interest is completed in single
rotation as compared to multiple rotations in conventional CT scanners
(Table 1.4).
■ Major advantages of CBCT compared to conventional CT are superior
spatial resolution and lesser radiation dose.
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