Dental imaging Continued »
of image interpretation, IRMER 2000 demands that all of the radiographic image should be assessed and an appropriate report documented.
Fig 3. Haemangioma in lateral mass of CV1 (atlas) noted in all three planes
So how do I report on the CBCT images? Much of the software available will make dental diagnosis very user-friendly and allow planning for implant placement straightforward, for example, ICat vision software (Imaging Sciences). There is, however, a sizeable amount of tissue data that may be missed in the FOV. This can be seen on the MPR screen on iCat vision or with better reso- lution on the Xoran software used with iCat. This author reports direct from the Xoran software, which is presented in the orthogonal planes. Currently, there are few if any
courses being run on how to report CBCT. Problem-solving begins when appearances are unusual. Is the appearance benign or does it represent an aggressive process? If so, is it malignant? Having knowledge of “normal” on an image section will help, but pattern recogni- tion may be a bit scary at first. New anatomical territory is
Fig 4. Soft tissue mass in right Prussac’s space (medial to the tympanic membrane-possible early cholesteatoma). Coronal section showing the middle and inner ear structures. Cerumen also noted in the right external auditory
now visualised: inner ear, base of skull, cervical spine, peri-oral soft tissues to name a few. A sound knowledge of what soft tissue outlines are supposed to resemble will give peace of mind that no tumours have been missed, for example, in the laryngo-pharynx (Fig 1). The old imaging maxim: “Just
compare left with right sides” has merit, assuming lesions are not bilateral in their presentation. Appreciation of the anatomical site, the relative density, outline of a lesion and access to any pre- vious imaging will all help in reaching a differential diagnosis. Getting the dissection/
radiology books out from times past may be a good way to start. However, not much cross-sec- tional anatomy was taught at dental school. The following examples are in no way comprehensive:
Some anatomy to know about on a CBCT sectional image Recently, small “neurovascular canals” have come into view on CBCT that were not appreciat- ed before2
. The “lateral lingual
canal” in the body of mandible is a good example. These neu- rovascular canals usually lie near but separate from the men- tal foramen. In the patient with an atrophic mandible, they can offer a potential surgical hazard for implant placement. They can contain nerve fibres from the nerve to myelohoid and so if impinged upon by an implant, pain can present post op. (Fig 2)
Some examples of lesions not to be missed from CBCT images A keen rugby player and diver presented for a 4cm FOV pre- implant assessment of his upper centrals. Assessment of the full field of view revealed a haemangioma of CV1. (Fig 3)
Assessment of the base of skull is imperative – ear structures should be reported on The appearance of chronic inflammatory lesions in the middle ear – an early cholesteatoma (Fig 4).
Conclusion and opinion Having a knowledge of the appropriate “ology” is the key here, for peace of mind and ongoing success in implant planning. It is for the person functioning in the IRMER oper- ator role to produce the image report. Confusingly, this may not be the person pressing the button to obtain the scan (see IRMER2000 regulations). The IRMER operator
(reporter) must report the CBCT scan and any other rele- vant images, unless that role is delegated to a suitably trained other, such as a radiologist. This author would argue that the best-placed radiologist to undertake this role should have a dental background. This obviously has cost impli- cations that must be passed on to the patient. However, in the long term, if cases come to light
where significant medical radi- ological presentations are missed, there will be medico- legal ramifications. It is also good practice to
warn the patient prior to the CBCT scan that non-dental fea- tures/lesions may become apparent on the scan, which may involve ongoing referral, and potentially give rise to a period of uncertainty until a definitive diagnosis or treat- ment can be realised. With respect to Ionising Radiation Regulations, if they are not properly implemented into practices with CBCTs, then the Scottish Government may have the right under IRMER2000 to take action which could close the imaging service down. In my opinion, the “Daddy”,
in colloquial parlance, is the wise practitioner who puts the patient’s best interests first. The “Daddy” is also someone who plays to their strengths. It may be that image acquisi- tion is more easily carried out at another site where all the above issues have been addressed. It may be that image interpretation is best carried out by a suitably qualified other. The fear of losing a patient to another operator who has “the big daddy” of dental imagers will be less if the CBCT is sited in a secondary referral centre/practice. Discussions with the owning practitioner/ specialist should ensure that we act as a family within the pro- fession, with respect for each other’s role in the team.
®
Dr Neil D C Heath, DCR, BDS, MSc, MFDS RCS, DDR RCR, Consultant and Specialist in Oral Maxillofacial Radiology, Edinburgh Dental Specialists
References 1. Heath N and Macleod R I, Dental Update 2008 (35) 353 Cone beam CT in Dental Practice
2.Trikeriotis et al 2008, Dentomaxillofac Radiol (37) 125-129. Anterior mandible canal communications: a potential portal of entry for tumour spread.
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