Emergency MR imaging of the central nervous system

Transcription

1 Emergency Rdiology (1999) 6: 133±142 Ó Americn Society of Emergency Rdiology 1999 PICTORIAL ESSAY Dougls J.Quint Jmes Provenzle John P. Deveikis Emergency MR imging of the centrl nervous system Astrct Mgnetic resonnce (MR) of the centrl nervous system hs few, ut importnt indictions for use in the cute setting. This report reviews the few true current clinicl indictions for emergency MR imging, including ruling out spinl cord compression, vsculr dissection or durl venous sinus thromosis. Possile indictions for emergency MR, including evlution of cute stroke symptomtology, potentil meningoencephlitis or vsculitis, re lso presented. Future pplictions for MR, including MR ngiogrphy in the setting of cute surchnoid hemorrhge nd spectroscopy in cute ischemi, re mentioned. Key words Mgnetic resonnce, Mgnetic resonnce, ngiogrphy, Mgnetic resonnce, diffusion, Spinl cord, compression, Crotid rteries, dissection, Brin, ischemi Introduction While MR is clerly the imging modlity of choice for evlution of lmost ll non-trumtic CNS pthology, when MR should e performed on n emergency sis is not s cler. This hs importnt implictions with respect to MR mchine vilility (the need for 24-h service), stffing (oth technicl nd professionl) nd softwre pckges. D. J.Quint ( ) ) J. P.Deveikis B1D520, Neurordiology, Box 30, Dept of Rdiology, University of Michign Medicl Center, 1500 Est Medicl Center Drive, Ann Aror, MI , USA, Tel.: , Fx: J. Provenzle Duke University Medicl Center Durhm, North Crolin, USA In the pproprite clinicl setting, suspected spinl cord compression should definitely initilly e evluted with MR imging, nd suspected vsculr dissection or durl venous sinus thromosis re reltive indictions for initil emergency evlution with MR imging. It could e rgued tht in some clinicl settings, suspected meningoencephlitis or vsculitis my lso wrrnt emergency MR evlution. Rpid evlution of the extent of involved rin in the setting of cute cererl ischemi is lso ecoming n indiction for emergency MR imging. Non-trumtic spinl cord compression The importnce of detecting non-trumtic spinl cord compression (usully due to spred of neoplsm, ut lso occsionlly due to hemtom or scess) is tht if such compression cn e detected efore ptient loses the ility to wlk, there is 90±100 % chnce tht they will still e wlking fter the lesion is treted [1]. However, if ptient is not wlking t the time spinl cord compression is dignosed, there is significntly poorer chnce they will wlk fter tretment. Therefore, suspected spinl cord compression, prticulrly if the ptient is ecoming wek nd losing the ility to wlk, needs to e evluted urgently. MRI is well known to e the exmintion of choice to rule out spinl cord compression [2, 3] (Fig.1) due to its superior contrst resolution, multiplnr cpilities, lck of ionizing rdition, ility to detect tndem lesions (Fig. 2), voidnce of spinl needle plcement (nd the ssocited risk of decompressing the spinl cnl elow the level of spinl cord compression with excertion of ptient symptoms) nd voidnce of intrthecl instilltion of iodinted contrst mteril nd its ttendnt risk. There is no role for plin rdiogrphs in the evlution of cute spinl cord compression, s such studies cnnot show compressed spinl cord (Fig. 1). Myelogrphy, followed y high-resolution post-myelogrphy

2 134 Fig.1 Lterl cervicl spine X-ry () demonstrtes destructive chnges of multiple lower cervicl spine verter due to metsttic rest crcinom (rrows); however, the spinl cnl invsion y tumor with spinl cord compression is seen only on the sgittl T1- weighted MR scn (). 3 C3 verterl ody, 1 T1 verterl ody Fig.2 Sgittl T1-weighted MR scns of the mid () nd upper () thorcic spine demonstrte two seprte (tndem) lung metstses (rrows) t the T3 nd T6 levels. 3 T3 verterl ody, 6 T6 verterl ody CT, remins n excellent test for detecting spinl cord compression of ny etiology. Though inferior to MR, it is still n importnt lterntive to MR in ptients with spinl internl fixtion hrdwre (Fig. 3) or when MR imging is not possile. Trumtic spinl cord compression Emergency MR imging should e performed in the setting of myelopthy following trum [2] to ssess for () frnk impingement on the spinl cord y frcture frgment (Fig. 4) (though this cn usully e inferred from CT scn), () n ssocited hernited disc cutely compressing the spinl cord or (c) spinl cnl hemtom compressing the spinl cord (Fig. 5). Ech of these findings my wrrnt cute surgicl intervention. In the setting of significnt trum, the spine lso lwys needs to e evluted for frcture with either plin rdiogrphs or preferly CT efore MR imging is performed. This is done so tht pproprite stiliztion nd monitoring of the spine cn e performed efore the ptient is trnsported to the MR re nd plced into the MR scnner. It should e noted tht in the setting of post-trumtic myelopthy, only the trumtized region of the spine needs to e evluted nd contrst-enhnced MR scns re not necessry. However, in the setting of non-trumtic myelopthy, the entire spinl cord (from the cervicomedullry junction to the conus medullris) should e evluted in two plnes. Also, contrst-enhnced scns should e otined s infectious/crcinomtous meningitis my only e detected on such scns. Vsculr dissection Dissections of vsculr structures tht supply the centrl nervous system cn e devstting, s involved vessels cn e () prtilly occluded, which cn led to ªslowflowº tht cn increse the risk of thromus formtion

3 135 Fig. 3 Recurrent chordom invding the spinl cnl nd compressing the thecl sc is oscured y internl fixtion hrdwre rtifct (smll rrows) on sgittl T1-weighted MR scn (), ut is esily dignosed on myelogrphy () (lrge rrow). A nterior, H Hrrington rod Fig. 5 Sgittl T1-weighted () nd T2-weighted () MR scns of post-trumtic epidurl hemtom (rrows); sttus following reduction of C7/T1 frcture disloction. 7 C7 verterl ody nd ultimtely result in thromoemolic strokes, nd () less commonly, completely occluded, resulting in infrction. Trum (lunt trum, spinl mnipultion) is the most common cuse of hed/neck vsculr dissection, though hypertension, migrines, vsculopthy (Mrfn's syndrome, firomusculr dysplsi), certin drugs nd phryngel infections re lso known cuses of dissection. Any ctivity which involves neck motion cn cuse vsculr dissection. Sometimes, no ntecedent cuse cn e linked to dissection. Most dissections involve the cervicl internl crotid rteries (distl to the ul region), the cervicl verterl rteries (C2 to the formen mgnum) or the petrous internl crotid region. However, dissections nywhere from the ortic rch to the intrcrnil vsculture cn Fig.4 Chnce L1 frcture demonstrted on lterl X-ry. Impingement on the conus medullris (c) is only seen on the sgittl T1-weighted MR scn. 2 L2 verterl ody

4 136 Fig. 6, Post-trumtic right verterl rtery dissection. High signl ªcrescentº sign representing hemtom in the wll of the RVA is seen (rrow) on n xil T1-weighted MR scn (). Dissection (rrows) is confirmed t forml ngiogrphy () e seen, prticulrly in the setting of mjor trum or vsculopthy. In the pst, endovsculr cererl ngiogrphy hs een the imging modlity of choice to demonstrte (smooth or irregulr) luminl nrrowing resulting in either ªstringº sign or complete occlusion of vessel in the region of dissection. As dissection is often ssocited with hemtom in the wll of the involved vessel (which cuses the vessel lumen compromise), MR imging [4, 5] is idelly suited to directly demonstrte the hemtom in the vessel wll in ddition to showing the compromised though still ptent vsculr lumen on n MR ngiogrm (MRA). When evluting for cervicl dissection, one should otin xil T1-weighted scns (with or without ft suppression) through the region of interest in the ttempt to show the clssic crescentic high-signl hemtom (Fig. 6) in the wll of the vessel. Additionl 2D TOF MR ngiogrphy through the neck to evlute vessel morphology oth for dissection nd for possile cuses of the dissection (e.g. underlying firomusculr dysplsi) cn then e performed. By first using MR/MRA, more invsive endovsculr ngiogrphy cn e voided for the evlution of mny ptients with suspected dissection. However, s () the sptil resolution of MRA remins inferior to tht of forml endovsculr ngiogrphy, () ssocited posttrumtic pseudoneurysms (Fig. 7) cn e difficult to detect with MRA nd (c) some ptients still cnnot cooperte for MRA, occsionl ptients my still require conventionl endovsculr ngiogrphy to rule out dissection. Fig.7 Post-trumtic left internl crotid (LIC) dissection with ssocited pseudoneurysm (rrows) just elow the skull se s demonstrted on 2D TOF MR ngiogrphy () nd forml endovsculr ngiogrphy ()

5 137 c Fig. 8 Acute superior sgittl sinus thromosis (rrows) demonstrting the ªdeltº sign on non-contrst coronl T1-weighted MR () nd the ªempty deltº sign on contrst-enhnced coronl T1- weighted MR (). In nother ptient, sucute superior sgittl nd trnsverse durl venous sinus thromosis with sinus clot (c) demonstrting incresed signl on non-contrst coronl T1-weighted MR imging (c) Durl venous sinus thromosis Mjor durl venous thromosis refers to veno-occlusive chnges of the superior sgittl sinus, trnsverse sinus, sigmoid sinus nd/or the deeper venous system (internl cererl veins, vein of Glen, stright sinus). When these structures thromose, smller corticl or deep venous vessels cn no longer drin the rin in norml mnner, which leds to venous congestion nd ultimtely venous infrctions, which cn e ftl. As presenting symptoms in these ptients cn e non-specific (hedche, visul chnges), clinicl suspicion needs to e high. Risk fctors commonly ssocited with venous thromoses include: dehydrtion (prticulrly in infnts), pregnncy/puerperium, orl contrceptives, infection (oth locl invsion from the prnsl sinuses nd the mstoids in ddition to disseminted infection), tumor (locl invsion), cogulopthies (including the lupus nticogulnt) nd trum. As with CT, durl venous thromoses cn e suspected on non-contrst-enhnced MR imging (ªdeltº sign) nd on contrst-enhnced MR (ªempty deltº sign), ut often will need confirmtion with MR venogrphy, which hs replced endovsculr rteriogrphy nd venous digitl sutrction ngiogrphy [5]. Axil nd coronl non-contrst nd contrst-enhnced T1-weighted scns nd xil T2-weighted scns cn e performed in ptients with suspected durl venous thromosis to evlute for sucute thromus in venous sinus nd to identify ªdelt signsº (Fig. 8), nd lso to serch for ssocited venous infrctions (which re often hemorrhgic). However, s flow rtifcts cn limit evlution for thromoses on spin-echo scns, forml phse-contrst MR venogrphy to est delinete flow within the durl venous sinuses (Fig. 9) is usully lso necessry. Fig.9 Acute superior sgittl sinus thromosis (rrows) demonstrting sence of flow on midline sgittl phse contrst MR venogrphy (). A norml midline sgittl phse contrst MR venogrm () is shown for comprison. s Superior sgittl sinus

6 138 Fig.10, Tuerculous meningitis. Contrst-enhnced CT () nd contrst-enhnced T1-weighted MR () demonstrte enhncement of sl cisterns nd hydrocephlus. While the enhncement is esier to see on MR, in the emergency setting the MR did not chnge ptient mngement Fig.11 Temporl loe herpes simplex encephlitis (rrows) might e suspected on the CT scn (), ut is drmticlly demonstrted (hemorrhgic) on the non-contrst T1-weighted MR scn () As with rteril dissections, venous thromoses nd their response to therpy cn e followed with seril MR venogrms, oviting the need for more invsive endovsculr ngiogrphy. Meningoencephlitis The need for emergency MR evlution of suspected meningitis or encephlitis of ny infectious etiology is controversil, s one could rgue tht regrdless of the imging findings, suspected meningoencephlitis should e treted urgently sed on clinicl nd cererospinl fluid findings with cross-sectionl imging (usully CT) eing performed urgently solely to rule out chnges suggestive of incresing intrcrnil pressure, which would contr-indicte lumr puncture (Fig. 10). MR imging is est to define the extent of n infection or to follow the course of n infection [6]. In some cses, however, clinicl nd cererospinl fluid findings my e non-specific nd, s the risks of some of the drugs used to tret CNS infections re not insignificnt, emergency MR imging to help ªswyº clinicin either towrds or wy from dignosis of meningoencephlitis my e necessry (Fig. 11). Vsculitis The need for emergency MR imging to confirm or rule out suspected CNS vsculitis or to ssess for the ppernce of new cererl lesions in ptient with known vsculitis who is cliniclly deteriorting is not cler. Non-infectious vsculitides, including collgen vsculr disese (e. g. SLE), polyrteritis nodos, temporl rteritis, Tkysu rteritis, Wegener's grnulomtosis, cocine use, srcoidosis, primry CNS ngiitis nd others, cn often e dignosed on the sis of clinicl nd lortory findings. Some vsculitides hve predisposition to primrily involve the CNS, nd therefore MR (nd sometimes forml endovsculr ngiogrphy) is crucil for mking the dignosis. However, in this ptient popultion, MR imging on n emergency sis is proly not necessry, s cute CNS-relted symptoms

7 139 Fig.12 Acute (less thn 6 h) ischemic chnges (rrows) in the left temporo-prietl region, well seen on diffusion imging (), ut poorly seen on T2-weighted (2500/80) imging () cn e dequtely evluted with CT (ruling out cute hemorrhge or mss effect) nd MR cn then e performed on more routine sis to evlute definitively for vsculitis-relted ischemic chnges [7]. In some cses of vsculitis, however, the rgument cn e mde tht therpeutic regimens my e chnged immeditely in deteriorting ptient if new lesions cn e demonstrted on MR imging. Cererl ischemi At the end of the 1990s, emergency MR imging for the evlution of cute cererl ischemi is rpidly evolving field. While hemorrhge ssocited with cererl Fig. 13 Acute (less thn 24 h) ischemic chnges (rrows) in the left prieto-occipitl region (rrow) esily identified on diffusion imging (), poorly seen on FLAIR imging () nd not seen on T2- weighted imging (c). Also note the chronic ischemic chnges (i) on the FLAIR nd T2-weighted scns which re poorly seen on the diffusion imging ischemi nd non-vsculr cuses of stroke symptoms (such s mss effect nd/or edem ssocited with infection nd neoplsm) cn usully e comfortly ruled out with CT in the cute setting, diffusion nd perfusion MR re much more sensitive techniques for detecting the erliest chnges of cererl ischemi. Diffusion-weighted (DW) MR imging hs lredy proven to e vlule in the emergency room setting for the evlution of suspected cererl infrction. DW MR imging llows chrcteriztion of tissues ccording to rtes of microscopic diffusionl motion of wter [8] nd is therefore sustntilly more sensitive thn CT or even conventionl spin-echo MR imging for the detection of cererl infrction in its erliest phse (i.e., within the first few hours fter stroke onset). On DW imges, res of hypercute infrction re seen s regions of hyperintense signl (Figs. 12, 13, 14, 15) due to restricted wter diffusion within these regions, in contrst to the intermedite signl intensity of norml rin tissue [8]. At the sme point in time, little or no signl normlity will e seen on T2- weighted imges or fluid-ttenuted inversion recovery c

8 140 Fig. 14 ±e An 11-yer-old ptient with cute onset of left hemipresis. Diffusion MR () otined severl hours fter presenttion demonstrtes gyriform normlity in the posterior right frontl region (rrowheds). This region ppers essentilly norml on the T2-weighted study (). Motiondegrded MR ngiogrphy including reformtted imge (c) nd skull se ªsourceº imge (d) demonstrtes sence of the right internl crotid rtery (rrows, norml left internl crotid rtery). Forml endovsculr ngiogrphy (e) confirmed complete occlusion of the right internl crotid rtery due to dissection (curved rrow) c d e (FLAIR) imges (Figs.12, 13, c, 14, 15). One further dvntge of DW imging is its ility to discriminte hypercute nd cute res of infrction from older infrctions, which pper isointense or only slightly hyperintense to norml rin tissue on DW imges (Fig. 13). Perfusion-weighted (PW) MR imging llows for evlution of cererl lood flow to the rin sed on signl chnges reflecting either lood oxygention levels or the mount of intrvsculr contrst gent delivered to portion of the rin [9]. If perfusion deficit on MR imging is more extensive thn corresponding diffusion normlity, the re of perfusion normlity without diffusion normlity my represent the ªischemic penumrº of rin ªt riskº for dditionl injury in the cute period. Identifiction of such penumr my eventully prove to e n indiction for ggressive therpy. Finlly, in the setting of cute ischemi, emergency MR ngiogrphy my sometimes e le to define the etiology of ptient's symptoms, such s vsculr dissection (Fig. 14) or n emolus (Fig. 15). As erly interventions imed t reversing or minimizing the effects of cute cererl ischemi continue to ecome more widely ville, such sensitive imging techniques s DW nd PW MR imging, s well s MRA, will ply n incresingly importnt role in the emergency evlution of the stroke ptient. The future In the future, dditionl roles for emergency MR evlution my include evluting for intrcrnil neurysms nd further evlution of cute cererl ischemi. In the setting of cute surchnoid hemorrhge, ruling out neurysms with high-resolution MR ngiogrphy my ecome fesile. Currently however, the sptil resolution, the time required to cquire MR ngiogrphic imges, nd the ptient coopertion tht is ne-

9 141 c Fig. 15 ±c A 30-yer-old ptient 3 dys fter repir of n ASD with cute onset of left hemipresis. Diffusion MR otined severl hours fter presenttion demonstrtes normlity in the nterior right middle cererl rtery territory. This region is only minimlly norml on the T2-weighted study. c MR ngiogrphy including reformtted imge demonstrtes occlusion of the right middle cererl rtery t its origin (rrow) due to susequently demonstrted emolus cessry to perform MR ngiogrphy do not permit relile ruling out of intrcrnil neurysms, prticulrly those distnt from the circle of Willis region. Similrly, smll intrcrnil rteriovenous mlformtions nd fistuls (dditionl though less common cuses of surchnoid hemorrhge) will currently e missed on MR ngiogrphy. Assessing for slvgele rin in the setting of cute stroke with MR spectroscopy (in ddition to diffusion nd/or perfusion MR imging) to further determine whether ptient is cndidte for ggressive therpy my eventully ecome the stndrd. Currently, however, such spectroscopy, like functionl imging, remins non-existent or t est experimentl t most imging fcilities. In summry, s with essentilly everything in medicine, the ptient's clinicl condition determines whether ny procedure/intervention is wrrnted nd whether tht study should e performed on n emergent sis. If one performs MR imging nd one's ptient referrl pttern wrrnts it, such service should proly e ville 24 h/dy for those times when true emergency MR imging is indicted. References 1. Bch F, Lrsen BH, Rohde K, Borgesen SE, Gjerris F, Boge- Rsmussen T, Agerlin N, Rsmusson B, Stjernholm P, Sorensen PS (1990) Metsttic spinl cord compression. Occurrence, symptoms, clinicl presenttions nd prognosis in 398 ptients with spinl cord compression. Act Neurochir 107: 37±43 2. el-khoury GY, Kthol MH, Dniel WW (1995) Imging of cute injuries of the cervicl spine: Vlue of plin rdiogrphy, CT, nd MR imging. AJR 164: 43±50 3. Bnnn PE, Johnston RA (1992) Neoplstic disese of the spine. Curr Opin Neurol Neurosurg 5: 540± Klufs RA, Hsu L, Brnes PD, Ptel MR, Schwrtz RB (1995) Dissection of the crotid nd verterl rteries: imging with MR ngiogrphy. AJR 164: 673± Ptel MR, Edelmn RR (1996) MR ngiogrphy of the hed nd neck. Top Mgn Reson Imging 8: 345± Demerel P, Wilms G, Roerecht W, Johnnik K, Vn Hecke P, Crton H, Bert AL (1992) MRI of herpes simplex encephlitis. Neurordiology 34: 490± Hurst RW, Grossmn RI (1994) Neurordiology of centrl nervous system vsculitis. Semin Neurol 14: 320± Lovld KO, Luch HJ, Bird AE, Curtin F, Schlug G, Edelmn RR, Wrch S (1998) Clinicl experience with diffusionweighted MR in ptients with cute stroke. Am J Neurordiol 19: 1061± Moseley ME, Glover GH (1995) Functionl MR imging. Cpilities nd limittions. In: Kuchrczyk J, Moseley M, Roerts T, Orrison W (eds) Neuroimging Clinics of North Americ. Sunders, Phildelphi, pp 161±193 Commentry Roert A. Novelline Quint nd collegues review the current indictions for emergency MR exmintions of the centrl nervous system (CNS). The uthors stte tht ªwhile MR is clerly the imging modlity of choice for evlution of lmost ll non-trumtic CNS pthology, when MR should e performed on n emergency sis is not s clerº. However, they conclude tht MR imging hs ªfew, ut importnt indictions for use in the cute settingº. Their cse mterils include excellent exmples of ptients with cute non-trumtic spinl cord compression, trumtic spinl cord compression, vsculr dissection, durl venous sinus thromosis, meningoencephlitis, cererl vsculitis nd cererl ischemi which were dignosed on n emergency sis with MR imging. The uthors further propose tht future, dditionl roles for

10 142 emergency MR evlution my include the detection of suspected intrcrnil neurysms in ptients presenting surchnoid hemorrhge nd the ssessment of slvgele rin in cute stroke with MR spectroscopy. In recent yers severl other reports hve identified cute non-cns medicl nd surgicl conditions which re est evluted y emergency MR exmintions [1]. Mny involve the musculoskeletl system [2±6]. Feldmn et l. [7] reported on the role of emergency MR in the detection of occult frctures. In series of 30 ptients, MR imging llowed identifiction of cute frctures in n emergency room setting, s well s sutle sucute or chronic frctures in the context of strong clinicl suspicion despite negtive or inconclusive rdiogrphs or other susequently indecisive imging studies. And mgnetic resonnce imging my prove more cost effective thn trditionl techniques. Ruin et l. [8] compred the cost effectiveness of MR imging compred to rdionuclide one scnning in the evlution of ptients with cliniclly suspected hip frctures nd negtive or equivocl plin films. In their series the time to surgery ws longer in ptients undergoing one scnning nd consequently erly MR imging proved more cost effective. Mny ortic emergency conditions such s suspected ortic dissection [9, 10] nd suspected ortic trum [11] cn e ccurtely dignosed y MR imging, which my e the est procedure in ptients with renl filure or history of prior serious rection to intrvenous contrst medium. MR imging hs lso proven eneficil in vriety of thorcic nd dominl emergency conditions. Wht is ovious to the rdiologist in emergency imging prctice is tht, s the indictions for emergency MR exmintions ecome incresingly recognized, so does the need for: (1) n MR scnner tht is instlled conveniently close to the emergency deprtment nd (2) full-time emergency MR support stff. A low-field mgnet would proly not e the est choice to fill this need s so mny currently recognized indictions for emergency MR imging involve the centrl nervous system, which is est evluted with high-field units. Consequently, the plnning of future emergency rdiology divisions or units should include considertion of n on-site or closely ville MR scnner. Also, the plns for stffing should include n in-house or on-cll MR technologist 24 h per dy, 7 dys per week. This stffing need further emphsizes the enefits of cross-trining of off-hours rdiology technologists who re trined to do not only rdiogrphy, ut lso CT, ultrsound or MR imging. References 1. Bogost GA, Crues III JV, Moser FG (1994) MR imging in the evlution of trum. Emerg Rdiol 1: 1±14 2. Linklter J, Potter HG (1998) Emergent musculoskeletl mgnetic resonnce imging. Top Mgn Reson Imging 9: 238± el-khoury GY, Kthol MH, Dniel WW (1995) Imging of cute injuries of the cervicl spine: vlue of plin rdiogrphy, CT nd MR imging. AJR 164: 43±50 4. Mesgrzdeh M, Schneck CD, Tehrnzdeh J, Chndnni VP, Bonkdrpour A (1994) Mgnetic resonnce imging of nkle ligments. Emphsis on ntomy nd injuries to lterl collterl ligments. Mgn Reson Imging 2: 39±58 5. Turner DA, Prodromos CC, Petsnick JP, Clrk JW (1985) Acute injury of the ligments of the knee: mgnetic resonnce evlution. 154: 717± Crotty JM, Snow RD, Brogdn BC, DeMouy EH (1998) Mgnetic resonnce imging of trum ptterns in the knee. Emerg Rdiol 5: 237± Feldmn F, Stron R, Zwss A, Ruin S, Hrmti N (1994) MR imging: its role in detecting cute frctures. Skeletl Rdiol 6: 439± Ruin SJ, Mrqurdt JD, Gottlie RH, Meyers SP, Tottermn SM, O'Mr RE (1998) Mgnetic resonnce imging: cost-effective lterntive to one scintigrphy in the evlution of ptients with suspected hip frctures. Skeletl Rdiol 27: 199± Hnsen ME (1994) Angiogrphy nd mgnetic resonnce imging of ortic dissection. Emerg Rdiol 1: 292± Fisher ER, Stern EJ, Godwin JD, Otto CM, Johnson JA (1994) Acute ortic dissection: typicl nd typicl fetures. Rdiogrphics 14: 1263± Fttori R, Celletti F, Bertccini P, Glli R, Pcini D, Pierngeli A, Gvelli G (1996) Delyed surgery of trumtic ortic rupture. Role of mgnetic resonnce imging. Circultion 84: 2865±2870