Radiography and Radiology A Foundation Manual

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1 Smple pges from BSAVA Mnul of Cnine nd Feline Rdiogrphy nd Rdiology A Foundtion Mnul Edited y Andrew Hollowy nd Frser McConnell BSAVA

2 Rdiology of the ppendiculr skeleton 7 Gwin Hmmond nd Frser McConnell Skeletl rdiology is chllenging due to the complex ntomy of the skeleton nd the lrge numer of incidentl findings nd ntomicl vrints which re encountered. Degenertive chnges re common within the joints, nd determining the significnce of lesions requires correltion with the clinicl exmintion nd history. Often it is not possile to determine the significnce of lesions sed on their rdiologicl ppernce lone. Bone hs limited response to injury, which mens there is overlp in the rdiologicl fetures of mny diseses, nd further tests (e.g. rthrocentesis nd iopsy) re often required for definitive dignosis. Key points for orthopedic rdiogrphy Low kilovoltge (kv) nd high millimpere second (mas) technique. Smll focl spot. Tle top technique, except for proximl lims in lrger dogs. Keep re of interest s prllel to the cssette s possile. Minimize film oject distnce. Minimize superimposed structures (e.g. retrct contrlterl lim). Use high detil screens (if ville) for the distl lim. Otin orthogonl views in ll cses. Otin seprte rdiogrphs for ech joint eing investigted. Accurte positioning nd centring required for relile interprettion. Lel rdiogrphs correctly. Use scler for digitl rdiogrphs (e.g. two pence coin or other oject of known size) for orthopedic templting. Use rdiogrphs of the contrlterl lim for comprison to id interprettion. High qulity rdiogrphs re required for skeletl rdiogrphy s mny significnt lesions re sutle nd my e missed on poor rdiogrphs. For the joints nd ones distl to the elows nd stifles, tle top technique using detil film screen comintion nd smll focl spot should e used to mximize sptil resolution. For the proximl joints nd long ones in lrge dogs, grid should e used, s sctter produced within the niml my e significnt. To mximize rdiogrphic contrst, low kv, high mas technique should e used, nd cre should e tken not to overexpose the rdiogrph. On properly exposed skeletl rdiogrph, the soft tissues nd treculr pttern of the one should e clerly visile. In lrge dogs, there is mrked vrition in the soft tissue thickness of the proximl lims, with significntly more muscle proximlly. With conventionl rdiogrphy, it my not e possile to otin single imge tht is correctly exposed for oth the proximl nd distl prts of the proximl lims, nd seprte exposures my e required of the proximl nd distl femur nd humerus. When tking rdiogrphs of the joints, the X-ry em must e centred on the joint of interest. Due to divergence of the X-ry em nd geometric distortion, it is essentil tht when tking rdiogrphs of multiple joints within one lim, seprte imges re otined for ech joint. Whole lim rdiogrphs should not e tken unless screening for gross lesions (e.g. one tumour or long one frcture). Orthogonl views should e otined for ll skeletl rdiogrphic studies, s pthology is often visile on only one view (Figure 7.1). In ddition, for the crpus nd trsus, lterl olique views my e required to evlute fully the extent of ny pthology (Figure 7.2). In ddition to the stndrd views, specific olique views my e required to evlute the intertuerculr groove of the humerus, trochler ridges of the trsus nd femorl trochle. As mny joint conditions re ilterl (e.g. osteochondritis dissecns (OCD), crnil crucite disese, elow dysplsi) it is dvisle to otin rdiogrphs of the contrlterl lim to detect occult pthology. In cses of suspected ligmentous injury, rdiogrphs should e otined with the joint under stress, s joint instility is often not visile on non-stressed imges (Figure 7.3). Contrst rdiogrphy is rrely performed nd hs een lrgely replced y rthroscopy, ut positive contrst rthrogrphy is occsionlly helpful in the shoulder to demonstrte the loction of OCD frgments nd lesions ffecting the iceps tendon (see Figure 7.32). 240

3 Rdiology of the ppendiculr skeleton Chpter 7 () Mediolterl nd 7.1 () cudocrnil views of the shoulder of 4-yer-old Stffordshire Bull Terrier with cute onset lmeness fter flling from height. A lrge rticulr frcture (rrowed) is visile on the cudocrnil view of the shoulder, ut is not visile on the mediolterl view. It is essentil to otin orthogonl views when imging the joints to reduce the risk of missing significnt pthology. c d () Mediolterl, () dorsoplntr, (c) dorsolterl plntromedil olique nd (d) dorsomedil plntrolterl 7.2 olique views of the trsus of 3-yer-old White Highlnd West Terrier presented with lmeness fter eing hit y cr. There is minimlly displced rticulr frcture of the medil ridge of the tlus (rrowed); this is est seen on the dorsolterl plntromedil olique view, which skylines the dorsomedil spect of the joint. For complex joints such s the trsus nd crpus, olique views re required to llow full evlution of the joint. Dorsoplntr views of the trsus of 3-yer-old 7.3 Mine Coon ct presented for chronic trsl swelling, which occurred fter flling out of window. The rdiogrphs were otined with the joint in () neutrl position nd () stressed position. In ddition to extensive degenertive chnges, there is lxity nd suluxtion of the tiiotrsl joint, which is only visile on the stressed view. Note the widened lterl spect of the joint (rrowed) on the stressed view, indicting dmge to the lterl collterl ligment. 241

4 Chpter 7 Rdiology of the ppendiculr skeleton Restrint nd ptient preprtion Since the most common indiction for skeletl rdiogrphy is the investigtion of lmeness, generl nesthesi or hevy sedtion is required s mnipultion of the lims my e pinful. In cses of suspected skeletl trum, there my e concurrent thorcic pthology, which my ffect nesthesi nd should e ddressed prior to rdiogrphy. Accurte positioning is required for joint rdiogrphy s rotted imges my led to lesions eing missed or n erroneous dignosis (e.g. ptellr luxtion). No specific ptient preprtion is required for skeletl rdiogrphy, ut the hir cot should e dry nd free from dirt, prticulrly for rdiogrphy of the mnus or pes s dirt prticles my mimic foreign odies. Long ones Norml ntomy Long ones re essentilly modified cylinders, which hve hollow centrl diphysis (shft) with n epiphysis nd metphysis t either end (Figure 7.4). The externl surfce of the corticl one should e smoothly mrginted, ut slight roughening of the cortices occurs t the insertion of muscles nd tendons (e.g. etween the rdius nd uln t the ttchments of the interosseous ligment). Norml one is pproximtely 50 70% minerlized, with the compct corticl one eing denser thn the spongy cncellous one, which is less opque nd hs fine minerlized treculr pttern. The importnt soft tissue component of one cnnot ssessed on rdiogrphs. Within the spongy cncellous fig 2.1 one, lmelle re rrnged in plnes ccording to the loding on the one. Bone is dynmic orgn nd undergoes chnges in shpe nd rchitecture ccording to the stresses plced on it (Wolff s lw). Corticl thickness vries with the shpe nd loding of the one, with thicker cortices present in res of incresed stress nd loding within the diphysel regions. The nonrticulr surfce of ones hs n outer covering of periosteum nd n inner lyer of endosteum. These lyers re composed of connective tissue, from which the osteolsts involved in one heling re generted. The mrrow elements re contined within the centrl medullry cvity of the one. The norml periosteum is of soft tissue opcity nd is not seen s discrete structure s it hs the sme opcity s the djcent muscles. Immture ones hve n open physis etween the epiphysis nd metphysis, seen s rdiolucent line, which should not e confused with frcture. The closure times for the vrious epiphyses re shown in Figure 7.5. The physel pltes of long ones in the dog re generlly closed y 12 months of ge, lthough those of the ilic crest my remin open for longer (or occsionlly never close). In the ct, erly neutering my dely growth plte closure times nd it is not uncommon to see visile physes t 18 months of ge. In the mture niml, the physel scr is visile s thin rdiopque line. Delyed closure of the growth pltes, which cn e ssocited with normlities of the epiphyses, my e seen with some congenitl metolic conditions, such s congenitl hypothyroidism, ut this is rre. The mjor lood supply to the long ones is vi the nutrient formin, visile s nrrow rdiolucent chnnels running through the cortex, usully within the cudl spect of the one in the diphyses. Additionl smll rteries enter the one t the metphyses nd cross the periosteum t the sites of muscle ttchments. The smller metphysel vsculr chnnels re often not visile rdiologiclly. Epiphysis Physis Metphysis Epiphysel vessels from joint cpsule Zone of resting or germinl cells Zone of proliferting cells Zone of mturing cells nd columntion Zone of hypertrophying vcuolted cells Zone of provisionl clcifiction Zone of vsculr invsion nd ossifiction Diphysis Vessels from tendons Nutrient vessel Metphysis Epiphysel vessels from joint cpsule Epiphysis 7.4 Different regions nd lood supply in n immture (top) nd mture (ottom) long one. 242

5 Rdiology of the ppendiculr skeleton Chpter 7 Growth plte/physis Scpul: suprglenoid tuercle Proximl humerus: greter tuercle to humerl hed Proximl humerl physis Distl humerus: lterl nd medil prts of condyle Distl humerus: medil epicondyle Distl humerus: condyle to diphysis Proximl rdius Proximl uln: olecrnon Proximl uln: nconeus Distl rdius Distl uln Accessory crpl one Proximl metcrpl i Distl metcrpls ii v Phlnges Pelvis: cetulum Pelvis: ilic crest Pelvis: tuer ischii Proximl femur: neck Proximl femur: greter trochnter Proximl femur: lesser trochnter Distl femur Proximl tii: medil nd lterl condyle Proximl tii: tuerosity to condyle Proximl tii: condyle to diphysis Proximl fiul Distl tii: physis Distl tii: medil mlleolus Distl fiul Tuer clcis Approximte ge of closure 4 7 months 4 months months 6 weeks 6 months 5 8 months 5 11 months 5 10 months 3 5 months 6 12 months 6 12 months 2 5 months 6 months 5 7 months 4 6 months 4 6 months months 8 10 months 6 11 months 6 10 months 8 13 months 6 11 months 6 weeks 6 8 months 6 12 months 6 12 months 5 11 months 5 months 5 12 months 3 8 months of the one (nd not ltering the minerl content) my not e visile rdiogrphiclly. Lysis or loss of minerlized tissue (resulting in decresed opcity of one) cn only e seen rdiogrphiclly once 30 50% of the minerl content hs een lost. This usully tkes t lest 7 10 dys from the onset of chnges; therefore, percute one injury my not result in recognizle chnges. Although mny diseses crete focl re of lysis (nd so re esier to detect), some diseses (prticulrly metolic or nutritionl normlities) or chronic disuse of lim (Figure 7.6) cn result in more diffuse loss of one density, leding to diffuse osteopeni (reduction in one opcity) (Figure 7.7). This my e more difficult to recognize nd cn potentilly e mimicked y poor rdiogrphic technique (e.g. overexposure). 7.5 Growth plte closure ges for the dog. Indictions The indictions for long one rdiogrphy include: Lmeness, where pin is loclized to the long ones Assessment of norml lim ngultion or lim deformity Investigtion of hyperclcemi of unknown origin Lim swelling. Principles of skeletl rdiology Bone cn only respond to disese in two wys: loss of one (lysis) nd production of one (prolifertion). Mny diseses result in comintion of lysis nd prolifertion, nd the rdiologicl ppernce depends on the lnce etween the two processes. It should lso e rememered tht significnt one pthology cn e present with completely norml rdiogrphs, s pthology tht is predominntly within the soft tissues Mediolterl views of the trsus of Cocker 7.6 Spniel with tiil frcture treted y csting. () On the initil exmintion, the one opcity ws norml. () Rdiogrph tken 6 weeks fter csting showing severe osteopeni due to reduced weight ering nd loding of the ones. Note the thinning of the cortices (rrowed) nd reduced opcity of the one. (continues) 243

6 Chpter 7 Rdiology of the ppendiculr skeleton Assessment of mild ltertion in one opcity is difficult on digitl rdiogrphs which llow ltertion of rightness nd contrst of the imge during viewing. The ppernce of incresed one opcity is referred to s sclerosis (Figure 7.8) nd my e due to incresed density within one, n increse in the mount of one within the medullry cvity, incresed minerl content of one, superimposed periostel or endostel new one or superimposed ony structures (e.g. n over-riding frcture). A rre condition tht cn give rise to this ppernce is osteopetrosis (or chlk ones ), which my e idiopthic. Sclerosis of suchondrl one is useful indictor of joint pthology nd often indictes pthology in the overlying crtilge. c (continued) Mediolterl view of the trsus of 7.6 Cocker Spniel with tiil frcture treted y csting. (c) Follow-up rdiogrph tken 5 weeks fter the cst ws removed showing reminerliztion of the ones with thicker cortices nd incresed opcity. Nutritionl hyperprthyroidism in kitten. () At 7.7 presenttion, there ws diffuse osteopeni with poor contrst etween the ones nd soft tissues, nd the corticl thickness of the long ones ws reduced. A folding (pthologicl) frcture (rrowed) of one of the femurs is present. Distortion nd mlformtion of the verterl column is ssocited with the reduced one minerl content. () The sme kitten following 3 months of dietry correction. Bone density is now norml, lthough deformities resulting from the initil disese persist. () Forelim nd () hindlim of dog with 7.8 multifocl sclerosis within the medullry cvity. Differentil dignoses include one infrcts ssocited with osteosrcom or immune-medited disese nd osteopetrosis. Bone infrcts vry from stippled foci to lrge ptches of dystrophic minerliztion in the medullry cvity of the distl lims. Osteopetrosis is rre condition, resulting in polyostotic res of mrked medullry sclerosis (incresed opcity) with loss of the norml treculr pttern. Corticl thickening my e present. The chnges re usully diffuse, oliterting the medullry cvity, nd etter recognized in the ppendiculr skeleton. It my e n incidentl finding in older cts. Ptterns of osteolysis Lysis of one my occur due to vriety of mechnisms, including chronic pressure on the one (e.g. due to slowly expnding soft tissue mss), disruption of the lood supply to the one (vsculr 244

7 Rdiology of the ppendiculr skeleton Chpter 7 fig 2.18 necrosis), or destruction of the one y tumour or infection. The ppernce of focl osteolysis cn reflect the underlying disese process, in prticulr whether the disese shows ggressive or enign chrcteristics. However, lesions cn show mixture of ptterns nd in such cses the lesion is est clssified y the most ggressive pttern present (Figures 7.9 nd 7.10). Geogrphic osteolysis is single re of lysis with well defined mrgins (possily sclerotic). It is normlly found within cncellous ones nd, if lrge, my cuse distortion of the shpe of the one. This pttern is usully seen with enign diseses such s one cysts, ut lso occurs with some one tumours. The mrgintion is importnt for differentiting enign from ggressive disese, with enign lesions typiclly hving shrp, smooth, clerly defined mrgins. Moth-eten osteolysis descries multiple, often vrily sized, res of lysis with vrily defined mrgins (from shrply to poorly mrginted). Ares my colesce to form lrger res resemling geogrphic osteolysis. This pttern of lysis is indictive of more ggressive disese processes such s osteomyelitis or neoplsi (including multiple myelom). Permetive osteolysis is the presence of multiple, pinpoint, poorly defined lytic res, giving the ppernce of diffuse erosion of the one (most esily seen in the cortex) (Figure 7.11). This pttern is indictive of highly ggressive disese (rpidly progressive osteomyelitis or neoplsi). fig 2.18 Periostel rections Insult to one results in production of new one, usully from the periosteum nd endosteum. The surfce of the long ones should e crefully ssessed for the presence of periostel rections, which my e sutle, ut indicte pthology within the djcent one. As with osteolysis, the ppernce of periostel rection gives n indiction of the iologicl ehviour of lesion (enign or ggressive) nd lso the chronicity of the pthology. In generl, smooth, shrply mrginted periostel rections indicte chronicity nd enign disese, wheres poorly mrginted, irregulr new one indictes more ctive pthology. The more ill defined nd irregulr the periostel rection, the more ggressive the lesion. With very ggressive disese such s primry mlignnt one tumours the new one produced is often wispy in ppernce with ill defined mrgintion. The mount of periostel new one produced vries with the ge of the ptient nd should e tken into ccount when interpreting periostel rections. Skeletlly immture nimls produce much more exuernt new one thn ged nimls. Periostel rections cn e divided into two rod groups (Figure 7.12): Continuous periostel rections Interrupted periostel rections. Continuous rections: A continuous periostel rection tends to suggest slower nd more enign disese process (lthough these rections cn e seen towrds the mrgins of more ggressive lesion). Smooth, shrply mrginted periostel new one is feture of chronic, enign lesions, e.g. heling frcture. Continuous ptterns tht require more gurded prognosis include those with rush order or plisding lock-like ppernce, which re frequently seen with either more ggressive diseses Geogrphic or with systemic lysis disese Geogrphic such s hypertrophic lysis osteodystrophy, lest ggressive A further continuous more ggressive pttern, the Codmn s tringle (indicting new one filling underneth n re of periostel elevtion), is commonly ssocited with primry one neoplsi, lthough ny elevtion of the periosteum (e.g. ssocited with trumtic disese) cn result in this pttern. Interrupted rections: These typiclly indicte more ggressive disese (see Figure 7.10) nd frequently resemle sunurst with multiple spurs of new one extending into the surrounding soft tissues. Geogrphic lysis lest ggressive Geogrphic lysis more ggressive Moth-eten lysis Permetive lysis most ggressive Permetive lysis 7.9 Moth-eten Focl one lysis destruction from lest (left) to most (right) ggressive. most ggressive 245

8 Chpter 7 Rdiology of the ppendiculr skeleton fig 2.22 c d e fig Primry osteosrcom ffecting the long ones. The rdiogrphic fetures vry ut re chrcteristic of n ggressive one lesion nd include extensive one destruction, corticl thinning or disruption, ggressive periostel rection (plisding or spiculted) nd poorly defi ned trnsition to norml one. The metphysel loction is typicl for primry one tumour. () The lesion is chrcterized y moth-eten osteolysis, plisding periostel rection long the crnil cortex nd Codmn s tringle t the cudl cortex (rrowed), long with some lysis of oth the crnil nd cudl cortices. () The lesion is predomintely Endostel lytic with res of moth-eten nd Superiostel permetive sclloping sclloping lysis. (c) The lesion is mixed lytic prolifertive with centrl mixed geogrphic/moth-eten re of lysis nd cudl ill defi ned spiculted periostel rection, indicting rpid deposition of new one. (d e) Mediolterl nd crniocudl rdiogrphs of n osteosrcom rising in the distl rdil metphysis. The mixed lytic prolifertive lesion hs moth-eten nd permetive res of lysis, with n irregulr spiculted periostel rection (with Codmn s tringle seen on the medil spect of the rdius) nd mrked soft tissue swelling round the lesion. Although in close proximity to the uln nd crpus, the lesion in the rdius is monosttic (i.e. only involves the rdius). This is typicl of primry mlignnt one tumours nd helps differentite them from soft tissue tumours nd secondry one tumours. Endostel sclloping Superiostel sclloping c Lysis loction in corticl one destruction (e.g. moth-eten or permetive) nd sclloping () Lterl view of long one diphysis. The lytic res pper to e in the medull ut re in the superimposed cortex. () Cross-section of the one in (). The lytic res re ctully in the cortex ut re superimposed on the medull. It should e orne in mind tht opcity is infl uenced y tissue thickness. Thus, distnces nd comined re out hlf the distnce of c (rdiologiclly seen cortex), so they pper reltively rdiolucent on the lterl view. 246