Radiology 










45
Chapter3
Radiology
Guidelines for dental radiology 46
Dental radiography 48
Panoramic radiography 54
Facial and skull radiography 56
Ultrasonography 60
Computed tomography 62
Cone beam computed tomography 66
Magnetic resonance imaging 67
Nuclear imaging 68
Sialography 69

46
CHAPTER3 Radiology
46
Guidelines fordental radiology
Generalpoints
Guidance is provided by the Ionizing Radiation Medical Exposure
Regulations (IRMER) of 2000 and the current enforcing authority is the
Care Quality Commission(CQC).
Radiology training forms part of core continuing professional
development for GDC registrants.
Think:
Does the patient really need the radiograph?
Will it change your management?
Have you ordered the most appropriate investigation for the case? If
in doubt, talk to a radiologistrst.
Limit radiation as much as possible.
Does the request form carry all the relevant clinical information?
Do you or someone else available have the ability to interpret the
investigation?
The taking and interpretation of (dental) radiographs is part of the
dental undergraduate curriculum. This is not the case for most doctors
and you must not be tempted into taking dental radiographs unless you
are trained todoso.
Interpretation can be dicult, and do not be afraid to ask for help.
Reporting of dental radiographs should be formally completed in the
notes by a GDC registrant. Never use photocopies of radiographs for
interpretation/ reporting purposes.
Pregnant patients can have dental radiographs (the exposure of the
fetus to radiation is virtually nil), but again only if the radiograph is
necessary. Use a lead apron and if possible aim the beam away from the
abdomen.
One of the most common errors with dental radiographs is mislabelling
or wrong- siding, so always double check that you have the correct
radiograph and that it is the right way round before you act on it,
especially for irreversible procedures such as dental extractions.
Likewise, take pains to ensure that any hard- copy dental lms you
acquire are correctly labelled, sided, andled.
To avoid taking unnecessary radiographs the referring dentist may send
you their lms. This can spare the patient further radiation, so always
enquire if they are available and make eorts to obtain them, as well
as ensuring to return the lms when nished— this is always greatly
appreciated.

GUIDELINES FORDENTAL RADIOLOGY
47

48
CHAPTER3 Radiology
48
Dental radiography
Periapical radiographs
See Fig.3.1.
These show the full length of the tooth and area of bone around the
root (periapical).
Dentists tend to use term ‘PA’ for periapical while most people
in medical radiology use PA to mean posteroanterior so don’t be
confused.
Good periapical radiographs are dicult to take and few radiology
departments outside dental schools will attemptthem.
For this reason, many OMFS departments have their own intra- oral
radiology equipment. Don’t use it unless you are trained to do so. (See
E ‘Guidelines for dental radiography’, p. 46).
Periapicals can be uncomfortable, especially for lower posterior teeth,
and it is rarely possible to obtain a view of lower wisdom teeth, so
most surgeons rely on a dental panoramic tomogram (DPT) for wisdom
tooth assessment.
Upper anterior periapical views are also dicult and a standard upper
occlusal may be better.
Indications forperiapical radiographs
Apical pathology, loss of bone, cyst,etc.
Assessment of periodontal ligament width (increased with
inammation).
Looking at roots for fracture or resorption, or checking morphology
prior to extraction.
To see root canal and apex as part of endodontic treatment or to look
for resorption or foreignbody.
May show unerupted teeth and can be used in parallax.
Can be used in implantology to check position and integration.
Will show loss of the dense white line around the tooth root which
represents the compact bone (lamina dura). This will be lost if teeth are
being moved by an orthodontist or if a tooth is ankylosed. Also lost in
systemic diseases such as hyperparathyroidism.
Bitewing radiographs
‘Bitewings’ are the usual dental investigation for dental caries (see
Fig.3.2).
They show the crowns of the upper and lower molarteeth.
They do not show the apex ofteeth.
They can also be used to assess the periodontal status and bone height.
They are not much use for anything else and are rarely used inOMFS.

DENTAL RADIOGRAPHY
49
Fig.3.1 Periapical of anterior teeth. Note the apical pathology on UR1. Both teeth
have amalgam retrograde root llings. The superimposed shadow is the nasaltip.
Fig.3.2 Caries visible on a bitewing radiograph; note the radiolucent (dark) areas
associated with UR5 LR6, for example. Reproduced from Boon E etal. ‘Oxford
Handbook of Dental Nursing’ (2012) with permission from Oxford UniversityPress.

50
CHAPTER3 Radiology
50
Occlusal radiographs
See Fig.3.3.
Broadly divided into upper or lower occlusal.
Lower occlusal projections are ‘true’ if the beam is at 90° to the lm, and
right/ left oblique’ or ‘standard’ if the beam is at 45° to thelm.
Upper occlusal projections can be ‘right/ left oblique’ or ‘vertex’ if the
beam is parallel to the upper incisors and ‘standard’ if at 90° to thelm.
You are unlikely to require a vertex occlusal and a lot of radiation passes
through the brain, so forgetit!
Indication forocclusal radiographs
Upper occlusal in combination with other radiographs such as DPT can
be used in parallax.
An upper standard occlusal is like having a periapical of the front four
teeth and the indications are thesame.
It is also useful for assessing the nasopalatine canal or to look for
nasomaxillarycysts.
Upper occlusals can be useful to show root fractures, which can be hard
to see with periapical if the beam is at right angles to the fracture.
Lower oblique views can show a stone in the anterior part of the
submandibularduct.
Lower occlusal views can show fractures of the anterior mandible which
sometimes do not show well on a PA of the mandible.
Fig.3.3 Occlusal showing upper right incisor region. Note the detail that this
radiograph cangive.

DENTAL RADIOGRAPHY
51
The parallax technique
See Fig.3.4.
Used when planning removal of unerupted upper canines to show if
tooth is lying on the palatal or buccal side of the jaw, which can guide
the surgical approach.
The principle is to take two radiographs of the unerupted tooth from
dierent angles in either the horizontal or verticalplane.
Then compare the two lms, thinking how the orientation of the beam
of radiation has moved from one lm to theother.
If the unerupted tooth appears to have moved from one lm to the
other in the same direction as the beam has moved from one lm to the
other, it is on palatal side (‘your pal moves withyou’).
Conversely, if the tooth moves in the opposite direction, it is buccal
(SLOB— Same Lingual, Opposite Buccal). If it does not move, it is
probably in line with the dental arch or else your radiographs have not
been taken at suciently dierent angles to show an eect!
The most common combination is a DPT and an upper occlusal. If the
canine appears to be more vertically positioned compared with, say, the
lateral incisor on the upper occlusal lm than on the DPT, it is palatally
positioned.
There are other ways to tell. You can get a lateral view or a cone beam
CT (CBCT) or you could rely on clinical signs seen ‘in clinics’ impacted
teeth and ‘in theatre’ impactedteeth.

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45 Chapter3RadiologyGuidelines for dental radiology 46Dental radiography 48Panoramic radiography 54Facial and skull radiography 56Ultrasonography 60Computed tomography 62Cone beam computed tomography 66Magnetic resonance imaging 67Nuclear imaging 68Sialography 69 46CHAPTER3 Radiology46Guidelines fordental radiologyGeneralpoints• Guidance is provided by the Ionizing Radiation Medical Exposure Regulations (IRMER) of 2000 and the current enforcing authority is the Care Quality Commission(CQC).• Radiology training forms part of core continuing professional development for GDC registrants.• Think:• Does the patient really need the radiograph?• Will it change your management?• Have you ordered the most appropriate investigation for the case? If in doubt, talk to a radiologistrst.• Limit radiation as much as possible.• Does the request form carry all the relevant clinical information?• Do you or someone else available have the ability to interpret the investigation?• The taking and interpretation of (dental) radiographs is part of the dental undergraduate curriculum. This is not the case for most doctors and you must not be tempted into taking dental radiographs unless you are trained todoso.• Interpretation can be dicult, and do not be afraid to ask for help. Reporting of dental radiographs should be formally completed in the notes by a GDC registrant. Never use photocopies of radiographs for interpretation/ reporting purposes.• Pregnant patients can have dental radiographs (the exposure of the fetus to radiation is virtually nil), but again only if the radiograph is necessary. Use a lead apron and if possible aim the beam away from the abdomen.• One of the most common errors with dental radiographs is mislabelling or wrong- siding, so always double check that you have the correct radiograph and that it is the right way round before you act on it, especially for irreversible procedures such as dental extractions.• Likewise, take pains to ensure that any hard- copy dental lms you acquire are correctly labelled, sided, andled.• To avoid taking unnecessary radiographs the referring dentist may send you their lms. This can spare the patient further radiation, so always enquire if they are available and make eorts to obtain them, as well as ensuring to return the lms when nished— this is always greatly appreciated. GUIDELINES FORDENTAL RADIOLOGY47 48CHAPTER3 Radiology48Dental radiographyPeriapical radiographsSee Fig.3.1.• These show the full length of the tooth and area of bone around the root (periapical).• Dentists tend to use term ‘PA’ for periapical while most people in medical radiology use PA to mean posteroanterior so don’t be confused.• Good periapical radiographs are dicult to take and few radiology departments outside dental schools will attemptthem.• For this reason, many OMFS departments have their own intra- oral radiology equipment. Don’t use it unless you are trained to do so. (See E ‘Guidelines for dental radiography’, p. 46).• Periapicals can be uncomfortable, especially for lower posterior teeth, and it is rarely possible to obtain a view of lower wisdom teeth, so most surgeons rely on a dental panoramic tomogram (DPT) for wisdom tooth assessment.• Upper anterior periapical views are also dicult and a standard upper occlusal may be better.Indications forperiapical radiographs• Apical pathology, loss of bone, cyst,etc.• Assessment of periodontal ligament width (increased with inammation).• Looking at roots for fracture or resorption, or checking morphology prior to extraction.• To see root canal and apex as part of endodontic treatment or to look for resorption or foreignbody.• May show unerupted teeth and can be used in parallax.• Can be used in implantology to check position and integration.• Will show loss of the dense white line around the tooth root which represents the compact bone (lamina dura). This will be lost if teeth are being moved by an orthodontist or if a tooth is ankylosed. Also lost in systemic diseases such as hyperparathyroidism.Bitewing radiographs• ‘Bitewings’ are the usual dental investigation for dental caries (see Fig.3.2).• They show the crowns of the upper and lower molarteeth.• They do not show the apex ofteeth.• They can also be used to assess the periodontal status and bone height.• They are not much use for anything else and are rarely used inOMFS. DENTAL RADIOGRAPHY49 Fig.3.1 Periapical of anterior teeth. Note the apical pathology on UR1. Both teeth have amalgam retrograde root llings. The superimposed shadow is the nasaltip.Fig.3.2 Caries visible on a bitewing radiograph; note the radiolucent (dark) areas associated with UR5 LR6, for example. Reproduced from Boon E etal. ‘Oxford Handbook of Dental Nursing’ (2012) with permission from Oxford UniversityPress. 50CHAPTER3 Radiology50Occlusal radiographsSee Fig.3.3.• Broadly divided into upper or lower occlusal.• Lower occlusal projections are ‘true’ if the beam is at 90° to the lm, and ‘right/ left oblique’ or ‘standard’ if the beam is at 45° to thelm.• Upper occlusal projections can be ‘right/ left oblique’ or ‘vertex’ if the beam is parallel to the upper incisors and ‘standard’ if at 90° to thelm.• You are unlikely to require a vertex occlusal and a lot of radiation passes through the brain, so forgetit!Indication forocclusal radiographs• Upper occlusal in combination with other radiographs such as DPT can be used in parallax.• An upper standard occlusal is like having a periapical of the front four teeth and the indications are thesame.• It is also useful for assessing the nasopalatine canal or to look for nasomaxillarycysts.• Upper occlusals can be useful to show root fractures, which can be hard to see with periapical if the beam is at right angles to the fracture.• Lower oblique views can show a stone in the anterior part of the submandibularduct.• Lower occlusal views can show fractures of the anterior mandible which sometimes do not show well on a PA of the mandible.Fig.3.3 Occlusal showing upper right incisor region. Note the detail that this radiograph cangive. DENTAL RADIOGRAPHY51 The parallax techniqueSee Fig.3.4.• Used when planning removal of unerupted upper canines to show if tooth is lying on the palatal or buccal side of the jaw, which can guide the surgical approach.• The principle is to take two radiographs of the unerupted tooth from dierent angles in either the horizontal or verticalplane.• Then compare the two lms, thinking how the orientation of the beam of radiation has moved from one lm to theother.• If the unerupted tooth appears to have moved from one lm to the other in the same direction as the beam has moved from one lm to the other, it is on palatal side (‘your pal moves withyou’).• Conversely, if the tooth moves in the opposite direction, it is buccal (SLOB— Same Lingual, Opposite Buccal). If it does not move, it is probably in line with the dental arch or else your radiographs have not been taken at suciently dierent angles to show an eect!• The most common combination is a DPT and an upper occlusal. If the canine appears to be more vertically positioned compared with, say, the lateral incisor on the upper occlusal lm than on the DPT, it is palatally positioned.• There are other ways to tell. You can get a lateral view or a cone beam CT (CBCT) or you could rely on clinical signs seen ‘in clinics’ impacted teeth and ‘in theatre’ impactedteeth. 52CHAPTER3 Radiology52OPGUpper occlusalFig.3.4 OPG and upper occlusal views of impacted upper canines. Note that on going from OPG to upper occlusal the X- ray machine orientation moves from horizontal for the OPG to more vertical for the upper occlusal, so the position of the canine on the left moves nearer the apex of the lateral incisor, i.e. as the X- ray cone moves up, so does the tooth. Therefore it is palatal (‘your pal moves with you’). On the right there is no movement; it is in the line of the arch. These radiographs were kindly supplied by Mr Victor Crow, Consultant Orthodontist at North West London Hospitals. DENTAL RADIOGRAPHY53 54CHAPTER3 Radiology54• It involves rotating the beam and lm around the patient and imaging everything within the horseshoe- shaped ‘focal trough’.• It only shows the structures within the trough or focal section; structures outside the trough are blurred.• Ideally, the trough includes all the teeth, the whole of the mandible, and most of the maxilla.• The technique generates a lot of artefacts, especially from jewellery.• Taking a DPT requires some degree of cooperation from the patient, and rarely gives worthwhile results with the inebriated, the severely physically or mentally disabled, or the veryyoung.• The anterior region is usually poorly dened in both jaws because of superimposition of the cervical vertebrae.Indications forDPT• General dental assessment (e.g. prior to head and neck radiotherapy).• General periodontal assessment— will show boneloss.• Bone pathology, cysts, bro- osseous lesions, cancer,etc.• Bone morphology, asymmetry, hyperplasia,etc.• Fractures; in combination with another lm such as PA jaws, will show most jaw fractures and anterior mandible fractures which are dicult to see because of thespine.• Wisdom teeth— shows presence, orientation, and relationship to inferior alveolar canal but only in 2D. For a 3D view, CBCT is better.• Will show if maxillary sinus is clear but is not really useful for assessing sinus pathology. It cannot rule out sinus cancer, for example, and may only show the root in the sinus if it is within the trough; if near midline, it may not show. Might show oroantral communication. CT/ CBCT may be a better choice.• Can be used to assess articular surfaces of TMJ, although CT is better. Magnetic resonance imaging (MRI) is used to assess the meniscus for internal derangement of the joint in selected casesonly!• Commonly used in implantology, although the degree of magnication can be an issue. For more accuracy, CBCT is better.• Occasionally used to show submandibular stones (90% are radio- opaque, and not all show up onDPT)Panoramic radiographyThe orthopantomogram(OPG)• Otherwise known as dental panoramic tomogram (DPT) or ortho- panoramic tomogram (OPT) (see Fig. 3.5 and Fig.3.6).• This is the most commonly used radiograph inOMFS.• In terms of radiation exposure, it is stilllow:Comparativedoses• OPG=0.016mSv (millisieverts).• Chest lm=0.1mSv=10days of background radiation. PANORAMIC RADIOGRAPHY55 Fig.3.5 Afairly typical DPT showing periodontal disease around the lower right last standing molar, impacted upper wisdom teeth, root llings, bridgework, and restorations.(a)(b)Fig.3.6 (a)Dental panoramic tomogram or orthopantomogram. Ghost shadows of the A, left hard palate; B, left lower border of mandible; C, cervical spine. True projection of D is the true left hard palate; E, the true left lower border of mandible. (b)Dental panoramic tomogram of a partially dentate patient. A, right condylar process; B, right coronoid process; C, right inferior dental canal; D, hyoid bone; E,posterior wall of the left maxillary sinus; F, zygomatic buttress; G, displaced root in maxillary antrum; H, inferior border of left maxillary antrum. Reproduced from Heath Iand Macleod I, ‘Oxford Textbook of Oral and Maxillofacial Imaging for the Anaesthetist’ (2010) with permission from Oxford UniversityPress. 56CHAPTER3 Radiology56Facial and skull radiographyGeneralpoints• The main indications for craniofacial radiographs are fractures, benign and malignant tumours, developmental anomalies, and other rare conditions.• Because these radiographs require a higher dose of radiation around the brain and eyes, it is particularly important that you order the most appropriate lm for the condition you are managing. There are likely to be protocols for most things, and there are some lms that departments will not take unless specically requested by a consultant (e.g. submentovertex view for assessing the zygomaticarch).• For assessment of craniofacial fractures you need two radiographs at dierent angles, ideally at 90° to eachother.• We will outline most common uses of craniofacial radiographs below, but if in doubt, ask before you order. You can’t un- irradiate someone! Giving unnecessary radiation could also be regarded as assault, so be warned!Occipitomental (OM)viewsSee Fig. 3.7 and Fig.3.8.• Followed by angle of beam to the horizontal, which can be 0° or30°.• If someone says ‘OM45’ they are probably referring to ‘OM0’. However, ‘45’ is the angle of the head to the vertical plate with the beam at 0°, which is confusing but is irrelevant for most of us as long as we get two OM views at dierent angles.• OM0 shows the facial skeleton and maxillary sinus without the dense bones of base of skull getting in the way, and so is used for fractures of the midface, zygomas, and orbits.• OM30 is required in combination with OM0 to ensure that fractures have not been missed, so it has the same indication as OM0 but is also useful for showing the coronoid process of the mandible.Posteroanterior view ofthejaws• Shows the posterior part of mandible, including condyles, and the complete lower border of mandible.• Useful for lesions in the mandible ramus to assess buccal– lingual expansion (e.g. cysts, ameloblastomas,etc.).• Useful in combination with DPT to show fractures of mandible, but again will not show the anterior mandiblewell.• Can help assessment of jaw asymmetry such as hyperplasia. FACIAL AND SKULL RADIOGRAPHY57 (a)(b)Fig.3.7 OM views of left zygomatic complex fracture showing step deformity at left infraorbitalrim. 58CHAPTER3 Radiology58Lateral cephalogram• Otherwise known as ‘lateralceph’.• This is a standardized and reproducible lateral view of the face and anterior skull— an earpiece localizes the skull in the sameplace.• Used by orthodontists and orthognathic surgeons to assess the PA relationships of the jaws andteeth.• It can also demonstrate the posterior airway space soft tissue shadow which may be of use in sleep apnoea patients undergoing orthognathic surgery, although it is not representative of their airway when lyingat!• Some people use it to assess the position of impacted upper canines.• It is not used for much else. The non- standardized equivalent is the lateral skull, which is not used for much except occasionally to show anterior skull fractures and maxillary posterior fracture– displacement.Lateral oblique view ofmandible• These are occasionally used to show the posterior mandible when the patient cannot have a DPT for whatever reason.• If done well they are useful for fractures of the angle of mandible or assessment of wisdom teeth or other pathology in that region.12345Fig.3.8 Campbell’s lines. Reproduced from Banks & Brown, ‘Fractures of the Facial Skeleton’ (2000), with permission from Elsevier. FACIAL AND SKULL RADIOGRAPHY59 Otherviews• Soft tissue views are occasionally used to assess foreign bodies in the lips or cheeks, although glass is not always visible— CBCT is better forthis.• There are other views of the craniofacial skeleton that are very occasionally used including reverse Townes (condyle), submentovertex (zygomatic arch), oblique PA jaws,etc.• These are only rarely useful and often radiology departments will not be happy doingthem.• If you are asked to arrange one of these unusual views, it is wise to know why beforehand, as radiology will want to know! Also, who will be able to interpret the resultingimage?• Most of these views have been superseded by CT orCBCT.Skull radiographs are rarely useful in trauma cases and will not be discussed furtherhere. 60CHAPTER3 Radiology60UltrasonographyGeneralpoints• Because there is plenty of relatively supercial soft tissue in the head and neck, ultrasonography is generally very useful.• It is only as good as the person performing and interpreting the images (operator sensitive), so it is hard to be dogmatic about its uses. Some departments get much more out of the service than others.Main indications forultrasonography inhead andneckNecklumps• Can assess size, position, number, solid or cystic, shape, blood ow, and other features.• Can be used to guide ne- needle aspiration cytology (FNAC) or core biopsy.• Can be used sequentially to monitor nodes on the borderline between benign and suspicious features with inconclusiveFNAC.• Used to distinguish solid, cystic, and single thyroid lumps from multiplelumps.Salivary gland disease• Will show tumours within major salivary glands.• Will not show parotid tumours deep to the mandible ramus, MRI is better in thesecases.• Will show salivary calculi in parotid and submandibular systems. May be dicult to see stones in submandibular duct (but often the duct is dilated in these cases which is readily visible on ultrasound(US)).• May show cysts of the major glands and can also be used forFNAC.Abscesses• Can be used to see if there is a collection of pus within a swelling.• Can be used to assess extent of neck swelling, but in the face US may be hindered by bones shielding deep areas. Contrast- enhanced CT or MRI is better.• In reality, clinical assessment alone is often adequate and US may delay progress to theatre.Otheruses• Masseteric hypertrophy.• Vascular malformations.• Oral squamous cell carcinoma (SCC) thickness using intra- oralprobe.• Duplex assessment of blood ow, looking for vessels in neck or potential free ap for reconstruction cases. For example, is there three- vessel run- o at the knee before we take the peroneal vesselout?• Lump overlying parotid— can be nice to be sure that the epidermoid cyst is actually that and not a parotid tumour. It happens! ULTRASONOGRAPHY61 62CHAPTER3 Radiology62Computed tomographyGeneralpoints• CT (and CBCT, see E ‘Cone beam computed tomography’, p. 66) is great for visualizing the dental and bony structures of the head and neck andto a lesser extent the soft tissues (see Fig. 3.9). However, radiation doses are much higher than plain lms, so their use must be justied.Comparative radiationdoses• CT head=1– 2mSv.• CBCT=0.05– 0.3 mSv (varies with equipment used and settings).• OPG=0.016mSv.• In emergency cases do not send the patient into a CT scanner if they have an impending airway crisis, uncontrolled bleeding, or other medical problem.• The more you talk to the CT sta before scanning, the better the chance of getting what youwant.• Remember that not all the information from the scan will be available for you to see, so if you cannot see what you want, talk to the radiologist/ radiographers in the CT suite and they may be able to make it available or recongure the images.• For contrast- enhanced CT you need a recent renal function and an intravenous catheter— the radiologist will be your friend if one is already sited and viable!CT andtrauma• In cases of severe craniofacial trauma, most units have a low threshold for doing CT brain and/ or cervical spine, so get involved quickly and arrange for the patient to have a CT face done at same time. This saves them going back to the scannerlater.• For facial trauma you need ne slices and coronal reformatting. If your hospital gets a lot of facial trauma, the radiographer will know the sequences. But don’t assume that they do— it might be their rstday.• 3D reconstruction is very helpful for complex craniofacial trauma— again, ask forit.• Fractures of the orbit are very dicult to assess on plain lms and most would advocateCT.• Simple mandibular fractures rarely warrant CT, but it can be useful in comminuted fractures and/ or complex condylar injuries.• CT angiograms have a role in assessing and sometimes managing vascular injury in head and neck trauma (radiologists can embolize branches of the external carotid), but these should be ordered by a senior.• May be used for retrobulbar haemorrhage (see E ‘Retrobulbar haemorrhage’, pp. 272–4). COMPUTED TOMOGRAPHY63 CT and tumours• Most imaging requests for tumour assessment come from registrar or consultant level, but there are some basics you shouldknow.• For tumour staging, CT shows bony and cartilage invasion well, but MRI shows soft tissues better. MRI also demonstrates marrow invasion (CT is poor). Units/ MDTs tend to have specic policies for which of these scans to order for tumour staging.• Tongue and oor- of- mouth cancers are imaged well with MRI, although CT may be necessary to assess mandible invasion.• Sinonasal cancers need CT, also to assess bony invasion.• Laryngeal invasion is imaged best withCT.• Many centres use CT to stage the neck (metastases), but MRI is usually better.• Staging the chest and upper abdomen with CT is common with many head and neck cancers (up to 10% of head and neck cancers can have a synchronous primary tumour somewhere else in the aerodigestive system).CT and infections• You will need a contrast- enhanced CT which has a high sensitivity but low specicity.• Imaging should be from skull base to carina because of the risk of mediastinitis.• Usually looking for parapharyngeal, retropharyngeal, and submandibular space involvement.• The patient will have to lie at which can make a bad airway worse, so make sure they are safe to go in the machine— airway loss in the scanner is a disaster. Modern CT scans, however, are very quick, and there is good access to the patient (unlike MRI). If in doubt, check with a senior.Other uses ofCT inOMFS• CT angiograms are used for vascular malformations and assessment of vessels for potential freeaps.• Skull defect imaging prior to reconstruction with cranioplasty. Can also assess skull vault thickness and presence of diploic space prior to calvarial bone graft harvesting.• Assessment of complex craniofacial, developmental, or acquired deformity. 3D reconstruction is very helpful in these circumstances, and can be linked to a computer- assisted model, allowing the machine to visualize the problem even better.• Large thyroid to assess retrosternal extension.• For navigation- assisted surgery.• For other surgery treatment planning such as stereolithographic models of the ilium for free- ap planning.• For nding the source of a cerebrospinal uid (CSF)leak. 64CHAPTER3 Radiology64Fig.3.9 CT images of edentulous mandible fracture. COMPUTED TOMOGRAPHY65 66CHAPTER3 Radiology66Cone beam computed tomographyGeneralpoints• Over the last decade, CBCT has revolutionized imaging inOMFS.• It is a relatively aordable technique which uses a single cone of radiation to give a detailed image of small areas such as thejaws.• It uses less radiation than conventional CT (see E ‘Computed tomography’, pp. 62–5).• It is in danger of becoming over- used and exposing patients to excessive radiation to obtain an excellent image when actually a simple plain lm would do, so beware— it’s notatoy.Uses ofCBCT• Better assessment of the relationship between the lower wisdom teeth and the inferior alveolar nerve (IAN) when plain lm is suggestive of an intimate relationship (if surgery is being considered). Another option is elective coronectomy, leaving the root behind.• For planning implant placement, especially when close to the maxillary antrum or IAN. Assessment when alveolar ridge width is uncertain.• TMJ pathology, fractures, or erosion.• Intra- bony pathology, cysts/ tumours/ bro- osseous lesions.• To assess bony invasion of oral cancer.• Facial deformity— often with a stereolithographicmodel.• Assessment of unerupted teeth, probably only in complexcases.• Assessment of airway space in obstructive sleep apnoea.• Its role in trauma has yet to be fully established, but it is probably useful for zygomatic, complex, and orbital fractures as well as condylar neck fractures.• It may also be useful for nding foreign bodies in the head andneck. MAGNETIC RESONANCE IMAGING67 Fig.3.10 MRI of the right temporomandibular joint. Reproduced from Kerawala and Newlands, ‘Oral and Maxillofacial Surgery 2e’ (2014) with permission from Oxford UniversityPress.Magnetic resonance imagingMRI andOMFS• Uses strong magnetic elds to excite and then re- equilibrate protons in water containing tissues to give contrasting radio frequency signals• Good for imaging soft tissues. Can be combined with IV contrast.• No ionizing radiation involved.• Contraindications— cochlea implants, pacemakers, shrapnel, and metallic objects inorbit.• The most common use of MRI in OMFS is tumour staging. Good for tongue and oor- of- mouth tumours and for assessing bone marrow invasion. It is slightly better than CT for imaging necknodes.• It is useful for parotid tumours where US cannot show the deep extent of a tumour because of the ramus of the mandible.• MR sialograms are becoming a useful alternative to conventional sialography. They demonstrate more of the gland structure and do not use any radiation, but they have no therapeutic eect.• For TMJ disc displacement/ internal derangement, MRI can be used to assess whether the disc is irreducibly displaced, and some experts believe that they can assess disc morphology. (See Fig.3.10.)• MR angiography can be used in the same way as CT angiography for vascular lesions and assessing blood ow for free- ap planning.• In looking for causes of facial pain, it may be used to screen for space- occupying lesions or demyelinating disease in brain, skull base, or infratemporal fossa (seriously consider if patient >50yearsold).• MRI is very sensitive for diagnosis of osteomyelitis and also for assessing marrow involvement in tumour staging. 68CHAPTER3 Radiology68Nuclear imagingPET andOMFS• Positron emission tomography (PET) of the head and neck region is usually used in combination with CT (PET- CT). This uses uorodeoxyglucose (FDG) which is taken up by metabolically active cells. This unstable substance is made in a cyclotron, usually at the site of PET- CT or couriered in when needed. Therefore it is expensive!• PET can show recurrent malignant disease in areas where it is dicult to examine such as the skull base, under aps, or the tonguebase.• PET has a high false- positive rate but is very sensitive (low false-negative rate).• After radiation you must wait about 3months as the inammation from the radiotherapy creates a false hotspot.• Most PET- CTs are requested at senior level/ through MDTs in special cases or for research. Few units use them routinely.SPECT• Single photon- emission computed tomography (SPECT) uses a gamma- emitting radioisotope, or radionuclide (such as technetium 99m) which can bind to certain types of tissue and be detected with a gamma camera.• The advantage is that the resultant SPECT ‘scintigram’ can give excellent 3D information (see Fig.3.11).• Used in bone scintigraphy— as a functional bone scan— to look for metastases, or abnormal areas of bone metabolism or remodelling• Increasingly used for sentinel node biopsy— for cutaneous or mucosal head and neck cancer (see E pp. 160–1)• Newer indications include infection (as a leucocytescan).• Senior-level request required!Fig.3.11 3D SPECT imaging of a sentinelnode. SIALOGRAPHY69 SialographyGeneralpoints• Involves cannulation and subsequent injection of contrast medium into the gland ductal system and lms taken at intervals thereafter.• Three phases of sialography:• Preoperative phase:‘scout lm’ looking for radio- opaquestone.• Filling phase:contrast injected and lmstaken.• Emptying phase:after 75 minutes a nal lm is taken of the gauge rate of emptying.• Can be used with plain lms, CT, orMRI.• Shows internal structure of the parotid or submandibular glandular systems.• Can show strictures, stones (sialoliths), and dilatations (sialectasia).• Some inference can be made about the dynamics of the system from the rate of emptying.• The ‘pruned tree’ appearance of the internal structure of the parotid gland as seen on the sialogram can point towards Sjögren’s disease.• Occasionally a salivary gland tumour may be apparent as rarely the rst sign of the tumour is obstruction.• The injection of a contrast agent may have a therapeutic eect, especially in patients with mucus plugging. 70

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