Vatious types of bone scan hide behind the bone scan terminology.
Conventional or usual bone scan
It comprises: stereotypes “whole body” or” holo skeleton " (together of the skeleton, in former incidence and posterior incidence, realized separately or simultaneously, detectors moving at constant speed above and below the patient lengthened on the bed of examination. - stereotypes “centered” on one or several regions of interest (Region 0f Interest:ROI), left the skeleton to which the attention was drawn either by the applicant of examination, or by the visualization of the stereotypes “whole bodies” previously practised. These “centered” stereotypes are static images carried out, according to the area concerned, under various incidences: former, posterior, profile, oblique, or special incidences the such incidence “caudal” or “sat” to explore the basin (ilio-pubic branches ischio and, sacrum and coccyx).
Quantitative on a ROI
It is about a scintiscanning together with a counting of the activity detected on the whole of the ROI (the shoulder for example) and also expressed in the form of his average value by pixel constitutive of the ROI. When the ROI is a bilateral osseous or articular part, the examination must be symmetrical and comparative.
Single-photon emission computed tomographyor SPECT
Its principal indication is the exploration of the rachidian anomalies, taking into account the complexity of the explored anatomical structures and the osseous superpositions. The rebuilding of the images is carried out in the plans transverse, frontal and sagittal. The SPECT carried out on osseous parts or complex anatomical structures (rachis, carp) allows the realization of fusion of images with the tomodensitometry and the IRM (imagery multi-methods).
bone scan known as “3 times” or “3 phases "
- initial or vascular time or Vangio scintigraphic: the injection INTER-F. R.P. Is carried out the patient being positioned under the camera with scintillation centered on the ROI (shoulder, knee…) and on the area controlatérale. A recording of the local activity immediately is launched and continued over one 2 minutes period. This initial time informs, in the form of curves and possibly in the form of images, about the vascularization of the ROI considered, compared to the zone controlatérale. Its interest is to highlight the hyper vascularizations (hyper hémies) or the hypo vascularizations local, specific to certain articular pathologies ostéo (algodystrophie reflex in particular). - early or tissue time: it is about a static stereotype practised on the ROI and the zone controlatérale 5 minutes after the injection of the R.P. This early time informs about the diffusion of the R.P. since the vascular compartment towards the interstitial compartment (before it does not reach the osseous medium itself: - osteoblasts then mineral and proteinic fraction of the bone). Early time brings interesting information in the cases of increased vascular permeability (case of the ignitions, of the algodystrophie reflexes in particular.). - late or osseous time: it studies the osseous fixing itself of the R.P. and in the form of practised static stereotypes 2 H is presented after the injection, as indicated previously.
It is difficult to in a few words describe the normal aspect scintigraphic of the skeleton. Only some basic elements will be indicated here:
- the fixing of the R.P. is usually homogeneous on an osseous part considered
- the fixing of the R.P. is usually symmetrical on osseous or ostéo-articular parts symmetrical, except parts very requested in manual workers or very lateralized sportsmen
- there are zones of usual and normal hyperfixation of the R.P. Such is the case of the facial solid mass, of the large articulations (shoulders, elbows, hips, knees), of the iliaques wings and the sacro-iliaques articulations, as well as cartilages of growth in the child
- the kidneys and the bladder are usually visualized, because of urinary excretion of half of the R.P. managed.
They are of two types, compared to the normal fixing of the neighbouring healthy bone: hyperfixations and hypofixations. - images of hyperfixation, in the immense majority of the cases: they correspond to a hyperostéoblastose either pure, or reactional and peripheral with a hyperostéoclastose.
The hyperostéoblastose (increase of the local osseous renewal) is a quasi-systematic response of the bone to any organic process and the scintigraphic hyperfixation which it thus causes lack etiologic specificity. - of hypofixation, possibility infinitely rarer: they are the fact: presence of metal parts (prostheses, pacemaker ).
Principal indications of. the bone scan and aspects scintigraphigues observed
- The catalogue of the indications will be limited to essence.
- primitive cancers of the bones (ostéosarcome, sarcome of Ewing): usually hyperfixants. - secondary cancers of the bones: osseous metastases of cancers ostéophiles (thyroid, prostate, centre, kidney, Lung) or not are, in the immense majority of the cases, hyperfixantes. In term of diagnosis, one can very schematically oppose two tables:
- that of many metastases, usual topography (pelvi-rachidian axis and root of the members) carrying out a typical aspect of secondary osteopathy and even, in certain cases, because of their character very hyperfixant, an aspect known as of “superscan”,
- that of rare metastases, even single, or of unusual topography: any diagnostic conclusion is random.
They are usually hyperfixantes, except contrary cases which will be specified. benign tumours of the bones, the such osseous ostéome ostéoïde.maladie of Paget: characterized by very intense hyperfixations and the possibility of visualization of typical osseous deformations (long bones out of blade of sabre). The bone scan has as an interest essential to allow a census on the whole of the skeleton of the osseous parts reached (Paget polyostotic, pauciostotic, even monoostotic) and to quantify the osseous mass reached by the affection (total pagetic osseous mass) osseous ignitions and infections (ostéites, osteomyelitides, infections on prosthesis, spondylodiscites…) : to affirm the diagnosis, the examination 3 times. and/or the coupling with a scintiscanning with polynuclear marked can be intéressant.maladies rheumatic advanced (osteoarthritides of the large articulations, rheumatic polyarthritis: PR or PCE): they are traditional indications. A particular place must be reserved for the aseptic ostéonécroses épiphysaires (ONA of the femoral head in particular) which, at the beginning, are hypofixantes (defect of vascularization) then which becomes hyperfixantes by reconstructive osteoblastic reaction of vicinity. traumatology: the cal of fractures are hyperfixants. The bone scan also makes it possible to follow the evolution of an osseous graft. rarefying osteopathies (osteoporosis): the fractures or compressing-fractures vertebral are easily identifiable and “datable” (all the more hyperfixants that they are recent). particular cases of the algodystrophie reflex (A.D.R.) and its clinical forms (capsulite retractile for example): because of its evolution in “ hot” phase (hyperhemic) and in “cold” phase, it is a good indication of the examination 3 times. particular cases of pathologies of “constraint”, “stress”, or 'tiredness ": concerning the sportsman (périostites, nonradiovisibles fractures “of tiredness”, enthésopathies), the people with important physical activity…. but also old people: the examination 3 times is of real interest, in particular in the sportsman. particular case of the paediatric indications: two elements only will be mentioned: concerning the hip: the differential diagnosis enters the primitive Legg-Perthes-Calvé disease : hypofixante with its initial phase, then hyperfixante, and the acute synovite transient or cold of hip: hyperfixante from the start, the syndrome of the “beaten children” (syndrome of Silverman) in whom the bone scan presents a medico-legal value.
Interest of the bone scan
The bone scan shows the following favorable characteristics: the scintigraphic anomalies are detectable more precociously than the corresponding radiological anomalies. This is due to the fact there is scan anomaly as soon as the osseous renewal is accelerated, whereas, radiological anomaly, appears when the local calcium load increased (condensing image) or decreased (lytic image) by approximately 30%. Classically, the scintiscanning “precedes” radiography by a time which can go up to 6 months: the bone scan is an examination of very good sensitivity, the bone scan makes it possible to carry out an assessment of extension whole body, when necessary, at the price of a reasonable irradiation of the patient. Which is not the case of the radiographic and scannographic examinations, taking into account the necessary multiplication of the stereotypes or of acquisitions, - the reasonable irradiation of the patients makes that the bone scan is a renewable examination to follow the evolution of a given pathology, - finally, the bone scan allows the fortuitous discovery of anomalies osseous, but so urinary and renal or different (cardiac amylose for example).
Limits of the bone scan
- the essential defect of the S.U. is its lack of specificity, the response of the bone being in the immense majority of case a hyperfixation. This defect of specificity is at the same time:
- physiopathological : initially osteolytic affections or osteocondensantes appear by a hyperfixation,
- etiologic: one speaks about “etiologic blindness " of the bone scan. However, best knowledge and analyzes scintigraphic characteristics of various affections must bring to moderate this criticism. irradiation delivered with the patient: it is weak and remains reasonable. The most exposed bodies are: the bone (6,81 µGy.MBq-1), the kidneys (6,94) and especially the bladder because of its role of tank (18,1). This must result making urinate the patient most often possible and in changing the layers of the infants. The problem of irradiation represents in fact the only real counter-indication of the bone scan for the pregnant woman and the woman nursing.