Focal Liver Lesions. Wolfgang Schima, Dow-Mu Koh, and Richard Baron Introduction MDCT Imaging Techniques

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1 Focl Liver Lesions Wolfgng Schim, Dow-Mu Koh, nd Richrd Bron 17 Lerning Ojectives To lern the optiml imging techniques nd the relevnce of differentil dignosis for liver diseses To discuss current indictions for liver-specific contrst gents To review the imging fetures of enign nd mlignnt focl liver lesions To discuss the differentil dignosis of primry nd secondry heptic tumors 17.1 Introduction Multidetector computed tomogrphy (MDCT) nd mgnetic resonnce (MR) imging provide noninvsive insights into liver ntomy nd the pthophysiology of liver diseses, which llows for etter disese dignosis, monitoring of disese evolution nd tretment response, s well s for guiding tretment decisions. Understnding the ppliction of different imging techniques is criticl for the mngement of focl liver lesions. In the current climte of chllenging helth economics, the most pproprite nd cost effective modlity should lwys e utilized. For liver imging, ultrsonogrphy (US) is widely ville, noninvsive, Author ws decesed W. Schim, M.D., M.Sc. (*) Deprtment of Rdiology, Göttlicher Heilnd Krnkenhus, Brmherzige Schwestern Krnkenhus, Snkt Josef Krnkenhus, Vinzenzgruppe, Vienn, Austri e-mil: wolfgng.schim@khgh.t D.-M. Koh Deprtment of Rdiology, Royl Mrsden Hospitl, Sutton, UK nd often used in the community for disese screening ut hs unfortuntely limited dignostic sensitivity nd specificity. Contrst- enhnced MDCT remins the modlity of choice for routine liver imging. MR imging is still used lrgely s prolem- solving tool when MDCT or US is equivocl or if there is concern for mlignncy in high-risk popultions. In this chpter, we will highlight imging of focl liver lesions, focusing on the use of MDCT nd MR imging for disese detection nd chrcteriztion. The reder should lern how to optimize CT nd MR imging in his/her own prctice, understnd how to pply nd interpret CT nd MR imging for the mngement of focl liver lesions, nd pprecite the expnding role of liver-specific MR contrst gents for lesion chrcteriztion MDCT Imging Techniques MDCT llows imging to e performed in multiple plnes. Using 64-plus-detector-row system, the entire liver cn e scnned within 1 4 s using sumillimeter detector configurtion llowing for high-qulity multiplnr reconstructions (MPR) [1]. When viewed xilly, reconstructed sections of mm thickness with n overlp of mm re usully used in clinicl prctice. Thinner slices do not improve lesion conspicuity ecuse of incresed imge noise [2] tht cn decrese dignostic specificity [3]. The mount of contrst mteril dministered cn e clculted y ptient s weight, ut 0.5 g iodine/kg.w. is typicl (i.e., 1.7 ml/kg.w. t 300 mg/ ml). The totl mount of iodine dministered determines the qulity of the portl venous imging phse, with the im of incresing the liver ttenution y 50 HU fter contrst injection [4]. To chieve good rteril phse imging, reltively high contrst medium injection rte of 4 5 ml/s is recommended [5]. On the other hnd, studies hve shown tht fixed injection durtion of 30 s (mening tht the injection rte will differ The Author(s) 2018 J. Hodler et l. (eds.), Diseses of the Adomen nd Pelvis , IDKD Springer Series, 173

2 174 ccording to ptient s weight) lso provides consistent imge qulity. The timing of the imge cquisition in reltion to contrst medi dministrtion depends on whether imging is required during erly rteril phse (for rteril ntomy only), lte rteril phse (for hypervsculr tumor detection nd chrcteriztion), or venous phse (for follow-up imging nd hypovsculr tumor detection). For the detection nd chrcteriztion of focl liver lesions, lte rteril phse imging (with dely of ortic trnsit time plus s) [6, 7] nd venous phse scn (20 30 s interscn dely or with fixed dely of ~60 70 s) re performed. However, the use of comintions of these imging phses lso depends on specific indictions [8]. Automted methods of mesuring rteril enhncement (ortic trnsit time) on CT, often termed olus trcking, hve replced the use of fixed scn-dely times ecuse it provides etter coincidence of scnning with pek enhncement of liver tumors (in the lte rteril phse) nd the liver prenchym (in the venous phse). Different techniques for dose reduction nd optimiztion of imge qulity re now widely in use: utomtic exposure control y tue current (ma) modultion, selection of lower tue potentil (kvp), nd dptive dose shielding to minimize overscnning in the z-xis, to nme few. Conventionl filtered ck projection (FBP), the stndrd CT imge reconstruction technique for mny yers, hs given wy to itertive reconstruction (IR). IR uses loop-wise rw dt correction to reduce imge noise, thus llowing imging to e performed t reduced kvp or mas, with lower rdition dose ut comprle imge qulity. All mjor mnufcturers now provide itertive reconstruction techniques (SAFIRE, ADMIRE, Siemens; idose, IMR, Philips; ASIR, MBIR, GE Helthcre; AIDR, AIDR 3D, Toshi) [9]. Stepwise IR reduces CT noise levels. However, high levels of IR my induce pixelted (plstic-like) imge texture nd my render imge qulity uncceptle [10]. A sustntil dose reduction of 38 55% is possile with IR without compromising imge qulity [11 13] (Fig. 17.1). In recent yers, dul-energy nd spectrl CT technique hs emerged, where the utiliztion of dul-source or polychromtic X-ry ems nd the differentil ttenution of such ems of different energies in tissues re pplied to improve the detection of hypervsculr heptocellulr crcinoms [14] or for the quntifiction of heptic iron content [15]. However, dul- energy CT technology is still not widely employed in clinicl prctice despite potentil merits, in prt ecuse of the post- processing time required to generte the pproprite imges MR Imging Technique W. Schim et l. MR imging of the liver cn now e performed t oth 1.5 nd 3.0 T; the ltter hs significntly improved in imge qulity due to dvncements in oth imging hrdwre nd softwre. MR exmintion of the liver should include unenhnced T1-weighted nd T2-weighted sequences, s well s contrst-enhnced sequences. Specific cquisition sequences vry y mnufcturer, ptient complince, nd the clinicl question eing ddressed. c Fig Dose reduction using itertive reconstruction techniques t MDCT. () Norml dose MDCT in the venous phse (120 kvp, ref. mas 230) reconstructed with stndrd filtered ck projection shows colorectl liver metstses. () Imge ppernce (120 kvp, ref. mas 150) using itertive reconstruction (SAFIRE level 3) is slightly different in generl, due to reduced imge noise. The lesions re shown with the sme conspicuity. Ptient dose is reduced y 36%. (c) At higher itertive reconstruction levels (SAFIRE level 5), the imge ppernce is pixelted ( plstic-like ), especilly seen t the liver prenchym nd the perirenl ft

3 17 Focl Liver Lesions In- nd opposed-phse (or out-of-phse) T1-weighted imging is recommended for mximl tumor detection nd for chrcteriztion of ft contining tumors nd the presence of stetosis. T1-weighted MRI cn e now performed using 3D DIXON technique, which cn generte in-phse, out-of-phse, wter-only, nd ft-only imges of the whole liver volume in single reth-hold cquisition. The resultnt wter-only imges hve een shown to improve the uniformity of ft suppression t 3 T, compred with conventionl spectrl ft suppression technique [16]. The use of the DIXON imges for dynmic contrst-enhnced cquisition hs lso een shown to improve the detection of heptocellulr crcinom compred with stndrd ft-suppressed sequences. Another useful recent implementtion is non-crtesin rdil T1-weighted imging, which llows 3D volume T1-weighted imging of the liver to e performed in free rething. This llows good qulity T1-weighted of the liver to e otined in ptients with poor reth holding (e.g., elderly, rethless dults, or young children) (Fig. 17.2), especilly during dynmic contrst-enhnced cquisitions [17]. T2-weighted pulse sequences with ft suppression provide etter lesion contrst thn nonft-suppressed sequences nd re lso widely used. Diffusion-weighted imging (DWI) hs ecome stndrd technique in liver imging, nd it is now ville on ll scnners. In generl, DWI depends upon the microscopic moility of wter, clled Brownin motion, in tissue. Wtermolecule diffusion (nd thus the mesured signl intensity) depends on tissue cellulrity, tissue orgniztion, integrity of cellulr memrnes, nd extrcellulr spce tortuosity. Usully, lower wter diffusion is found in most solid tumors, 175 which re ttriuted to their high cellulrity [18]. Thus, DWI is helpful for detecting liver solid focl liver lesions [19 21]. By performing diffusion-weighted imging using two or more -vlues, we cn quntify the pprent diffusion coefficient (ADC) of liver tissues. Benign focl liver lesions hve een shown to hve higher ADC vlue thn mlignnt liver lesions, lthough there is significnt overlp [22]. Nonetheless, quntittive ADC vlues my e useful to support lesion chrcteriztion nd for identifying erly tumor response to tretment, which is currently eing investigted. Imging fter the dministrtion of intrvenous contrst gents remins the cornerstone for liver MR imging. Of these, nonspecific extrcellulr gdolinium contrst medium is still most widely used. Following the intrvenous (IV) olus injection of extrcellulr gdolinium-sed contrst gents, dynmic imging (using volumetric T1-weigthed imging) is performed in chrcterizing lesion, detecting lesion, evluting tumor response to therpy, nd detecting mrginl recurrences fter tumor ltion. Liver-specific (or heptoiliry) MR contrst gents re ville nd hve specific roles in the mngement of focl liver lesions. These include gdoente dimeglumine (MultiHnce, Brcco) nd gdoxetic cid (Primovist or Eovist, Byer Helthcre). Liver-specific MR contrst gents re lso usully dministered IV s olus, s with nonspecific gdolinium cheltes for dynmic imging. However, imging is lso performed t delyed liverspecific or heptoiliry phse, the timing of this differs ccording to the contrst gent. These liver-specific gents re tken up into heptocytes to vrying extent (gdoente dimeglumine 4 5%; gdoxetic cid ~50%), resulting in vid T1 enhncement of the liver prenchym in the heptoiliry Fig Rdil cquisition technique. Colorectl liver metstses. Heptoiliry phse imging performed t 20 min fter gdoxette contrst dministrtion using () free rething rdil cquisition ftsuppressed grdient echo nd () reth-hold volume interpolted ft-suppressed grdient echo technique. Note tht the free-rething cquisition in this ptient resulted in etter delinetion of the smller liver metstses s T1 hypointense lesions ginst the enhncing liver prenchym (rrows)

4 176 phse, which is performed t 20 min for gdoxetic cid nd out 1 2 h for gdoente dimeglumine fter contrst dministrtion. Liver-specific contrst gents hve een shown to improve the detection of liver metstses [23 26], especilly when used in comintion with diffusion-weighted MR imging Benign Heptic Lesions Cysts Simple heptic cysts re common, occurring in 5 14% of the generl popultion. As they re usully symptomtic, they re detected incidentlly on US, CT, or MR imging. On CT, heptic cysts re well circumscried nd typiclly show ttenution vlues similr to wter (0 15 HU), lthough smller cysts my show higher ttenution vlues due to prtil volume effects. Cysts should not show murl thickening, nodulrity, or contrst enhncement. Smll cysts ( 3 mm in size) my pose dignostic chllenge in the cncer ptient on CT s they re too smll to fully chrcterize nd stility on follow-up imging is importnt to ressure. Nonetheless, the mjority of smll hypodense liver lesions even in the oncology ptient re usully enign. On MR imging exmintions, cysts re well-defined, homogeneous lesions tht pper hypointense on T1-weighted imges nd mrkedly hyperintense on T2-weighted imges. Their mrked hyperintensity on T2-weighted imging provides greter confidence towrd the dignosis of smll cysts on MRI Hemngiom Hemngiom is the most common enign liver tumor. On US, liver hemngiom ppers circumscried, well-defined, hyperechoic, nd ssocited with distl coustic enhncement. Smll hemngioms usully pper homogeneous, ut lrger hemngioms (>4 cm) cn show heterogeneous ppernce. On CT, hemngioms re well-defined hypodense msses. They re hypointense on T1-weighted nd mrkedly hyperintense on T2-weighted imging, sometimes with loulr contour. Hyperintensity on T2-weighted MRI helps to differentite hemngioms from other solid neoplsms [27, 28]. At reltively long T2 echo time (140 ms or longer), homogeneously right lesion is chrcteristic of enign lesion, such s cyst or hemngiom. Exceptions include cystic or mucinous metstses, gstrointestinl stroml tumor (GIST), nd neuroendocrine tumor metstses. Hemngioms show three distinctive ptterns of enhncement t CT/MRI (type I to III) [29], where there is chrcteristiclly enhncement tht closely follows the enhncement of lood pool elsewhere [30]. Smll lesions (up to ~2 cm) my show immedite nd complete enhncement in the rteril phse, with sustined enhncement in the venous nd delyed phses (type I, flsh filling ) [31] (Fig. 17.3). On delyed imging, the enhncement usully fdes to similr extent s the lood pool. The most common enhncement pttern is peripherl nodulr discontinuous enhncement, which progressively fill-in over time (type II). Lrger lesions (>5 cm) or lesions with centrl thromosis/firosis my lck centrl fill-in (type III) (Fig. 17.4). When evluted using liver-specific contrst gents, the ppernce of hemngioms in the dynmic rteril nd venous phses is similr to tht with nonspecific gdolinium cheltes. However, in the delyed phse, fter 3 min, there my e pseudowshout (hypointensity) due to erly heptocellulr enhncement of liver prenchym (Fig. 17.5). In the heptoiliry phse, hemngioms my pper hypointense to the prenchym, thus mimicking liver metstses. In this instnce, DWI my help to differentite etween hemngiom nd other solid lesions, s the pprent diffusion coefficient (ADC) of uncomplicted hemngioms is significntly higher (typiclly > s/mm 2 ) thn in mlignnt solid lesions [22, 32] Focl Nodulr Hyperplsi W. Schim et l. Focl nodulr hyperplsi (FNH) is enign lesion tht cn cuse confusion when incidentlly detected during dominl imging. On ultrsound, the lesion is usully isoechoic or slightly hypoechoic [33] to liver, ut ppers hypoechoic in ptients with diffuse heptic stetosis. Typiclly, FNH demonstrtes loulr contour, which is uncommon in mlignnt lesions. A centrl scr is present in out 67% of lrger lesions nd out 33% of smller lesions [34]. The centrl scr in FNH is usully hyperintense on T2-weighted imges, with comm-shped or spoke-wheel ppernce, which cn e distinguished from firolmellr HCC, where the centrl scr, when present, is predomintely low signl intensity on T2-weighted MR. Color/power Doppler US my show lood flow within the scr [35]. FNH is isodense or minimlly hypodense on unenhnced nd equilirium-phse post-contrst CT nd my e only suspected ecuse of the presence of mss effect on djcent vessels. On unenhnced T1- nd T2-weighted MR imges, FNH returns signl intensity similr to heptic prenchym ut is usully slightly different on either T1- or T2-weighted

5 17 Focl Liver Lesions 177 c d e f Fig Hemngiom type 1. Liver-specific MR contrst gent. A 45-yer-old womn with incident lesion (rrows) in the right loe of the liver. This ppers s () high signl intensity on T2-weighted imging nd () low signl intensity on T1-weighted imging nd (c e) shows uniform enhncement on dynmic T1-weighted contrst-enhnced imging, isointense to the vsculr signl t ll phses. The lesion ppers (f) hypointense in the heptoiliry phse of gdoxetic cidenhnced MRI c Fig Hemngiom type 3: nonspecific gdolinium chelte. ( c) T1-weighted dynmic enhnced T1-weighted GRE in the () rteril nd () portl venous nd (c) delyed phse shows nodulr peripherl enhncement of the lesion with centripetl filling. There is incomplete enhncement of the lesion

6 178 W. Schim et l. c d Fig Hemngiom type 3: liver-specific MR contrst gent. () T2-weighted TSE shows lrge loulted lesion of very high signl intensity. ( d) Dynmic gdoxetic cid-enhnced imging shows peripherl nodulr enhncement in the rteril () nd venous phses (c). In the heptoiliry phse (d) there is mrked hypointensity of the lesion due to lck of heptocellulr uptke in the lesion nd enhncement of surrounding liver prenchym imges. Due to the prominent rteril vsculr supply, FNH demonstrtes mrked homogenous enhncement during the rteril phse of contrst-enhnced CT/MR imging, which ecomes rpidly isodense/isointense to liver prenchym in the portl venous phse [34]. The centrl scr often showed delyed enhncement (Fig. 17.6) [33] ecuse of its vsculr component. Another key feture is tht other thn the scr, FNH re usully homogeneous in ppernce compred with the heterogeneous ppernce encountered in firolmellr HCC. Using liver-specific MR contrst gents, FNH frequently shows enhncement on delyed imges fter dministrtion of heptoiliry contrst gents (such s gdoxetic cid or gdoente dimeglumine) ecuse of the presence of norml iliry ductules within the lesion nd the expression of OATP receptors (Fig. 17.6). However, the uptke of heptoiliry contrst gents within FNH my e rrely heterogeneous or sent [36]. Nonetheless, recent met-nlysis showed tht the lesion T1 isointensity or hyperintensity t delyed heptoiliry phse MRI hs high sensitivity (91 100%) nd specificity (87 100%) for dignosing FNH [36]. This feture cn e helpful for differentiting FNH from hypervsculr metstses or heptic denoms (HCA) nd heptocellulr crcinoms (HCC) (which do not usully tke up liver- specific gents) [31, 37]. However, it should e noted tht some HCAs (prticulrly inflmmtory HCA nd et- cteninctivted HCA) nd HCC cn pper isointense or hyperintense t delyed imging fter heptoiliry contrst medi dministrtion. While differentiting FNH from vrints of HCA remins chllenging, it hs een suggested tht the presence of contrst wshout (i.e., lesion hypointensity compred to liver prenchym) of HCC in the portl venous or trnsitionl phse of dynmic contrst enhncement cn e used to distinguish etween HCC (tht shows contrst uptke in the heptoiliry phse) nd FHN nodules. The mjority of FNH tend to remin sttic in size, lthough FNH my increse in size on follow-up (3 11%), lthough orl contrceptives do not pper to stimulte FNH growth [38, 39].

7 17 Focl Liver Lesions 179 c d Fig FNH. Incidentl lesion in the left loe of the liver (rrows). () Pre-contrst T1-weighted imge shows n isointense lesion with centrl hypointense scr, which shows miniml mss effect upon djcent vsculture. () Arteril phse T1-weighted contrst-enhnced imge shows hypervsculrity of the lesion. (c) T1-weighted delyed phse imging fter contrst shows tht the lesion is now predominntly isointense to the liver ut with lte enhncement of the (vsculr) centrl scr. The enhncement pttern is typicl for FNH. (d) Heptoiliry phse imging of nother FNH: homogenous uptke of the liver- specific MR contrst gent, the spoke-wheel centrl scr is typiclly not enhnced Heptocellulr Adenom Heptocellulr denom (HCA) is uncommon, ut hs n ssocition with orl contrceptive nd nolic steroid usge. Histologiclly, HCA is composed of cells resemling norml heptocytes ut lcking ile ducts, which distinguishes them from FNH [39]. The imging fetures of HCA re heterogeneous nd vried. HCA re often hypervsculr nd my pper heterogeneous due to the presence of ft, necrosis, or hemorrhge [39, 40]. T1-weighted chemicl shift or DIXON imging is useful for detecting intrtumorl ft, while the presence of high T1-signl efore contrst dministrtion will rise the suspicion of spontneous hemorrhge. The reder should e

8 180 fmilir with the differentil dignoses of ft contining focl liver lesions on MRI, which include focl ft infiltrtion, HCA (prticulrly the HNF1A inctivting sutype), heptocellulr crcinom (usully well differentited), ngiomyolipom, lipom, tertom, nd liver metstses from ft contining mlignncies (e.g., liposrcoms). The presence of intrtumorl ft helps to nrrow the differentil dignosis of hypervsculr lesion, s hemngiom cn e excluded nd metstses nd FNH rrely contin ft. On dynmic contrst-enhnced CT or MR, denoms usully show mrked rteril-phse enhncement, with rpid trnsition to either iso- or hypottenuting/intense to heptic prenchym on portl venous phse imging. Our understnding of the moleculr errtions ssocited with HCA hs improved our understnding of HCA sutypes, which is linked to risk fctors, histologicl fetures, clinicl presenttion, nd imging ppernces [41, 42]. The ltest moleculr clssifiction ctegorizes HCA into the following six sugroups: HNF1A-inctivted HCA, inflmmtory HCA, CTNNB1-mutted HCA in exon 3, CTNNB1 mutted in exon 7 nd 8 HCA, sonic hedgehog HCA, nd unclssified HCA [43, 44]. Wht is importnt for rdiologists? Inctivting muttions of heptocyte nucler fctor 1 lph (HNF1A) re oserved in 40 50% of HCA. HNF1A-inctivted HCA usully contins ft s evidenced y diffuse nd homogenous signl loss on chemicl shift T1-weighted imging (Fig. 17.7). They return vrile T2 signl. At contrst-enhnced T1-weighted MRI, they re hypervsculr, often with contrst wshout in the portl venous or delyed phse. They re typiclly hypointense on heptoiliry-phse MRI using liver-specific contrst medium. HNF1A-inctivted HCAs hve very low risk of mlignnt trnsformtion. Inflmmtory HCA ccounts for 35 45% of HCA cses. Oesity nd history of orl contrceptives intke re risk fctors for their development. Inflmmtory HCA pper strongly hyperintense on T2-weighted MRI, which my e diffuse or rim-like in the periphery of the lesion (Atoll sign). Intrlesionl ft is uncommon nd, when present, is often ptchy or heterogeneous. On contrst-enhnced imging, there is usully intense rteril enhncement, with persistent enhncement on delyed phse imging (Figs nd 17.9). Although the mjority of inflmmtory HCA re hypointense on heptoiliry phse using liver-specific contrst medi, out 30% my pper iso- or hyperintense. Inflmmtory HCA my lso hror ctivting muttions of -ctenin in exon 3 nd re therefore t risk of mlignnt trnsformtion. Muttions of ctenin 1 (CTNNB1) in exon 3 (coding for -ctenin) re seen in 10 15% of HCA. These re ssocited with higher risk of mlignnt trnsformtion. By contrst, W. Schim et l. suset of HCA (5 10%) is ssocited with muttions of CTNNB1 in two hot spots in exon 7 nd 8, which does not confer n incresed risk of mlignncy. These vrints of HCA do not hve typicl imging fetures nd my e difficult to differentite from HCC or FNH. HCA with muttions of ctenin 1 my lso show contrst uptke in the heptoiliry phse of MRI using liver-specific contrst medi. Activtion of sonic hedgehog pthwy occurs in pproximtely 5% of HCA. As these re reltively uncommon, the spectrum of imging fetures ssocited with these is yet to e fully descried. Nonetheless, these lesions hve higher propensity to undergo spontneous hemorrhge. Aout 7% of HCA remins unclssified. These do not hve typicl clinicl or imging ppernces. Overll, the imging fetures t MRI, including their ppernces using liver-specific MR contrst gents (gdoente, gdoxetic cid) re helpful in distinguishing etween FNH nd HCA. In the heptoiliry phse of contrst enhncement, FNH typiclly show contrst uptke, wheres NHF1A-inctivted HCA nd the mjority of other HCA sutypes do not [44]. Of note is tht diffusion-weighted MRI hs little vlue in helping to distinguish etween HCA nd FNH or HCC ecuse of the sustntil overlp in the ADC vlues Biliry Hmrtoms (Von Meyenurg Complex) Bile duct hmrtoms re congenitl mlformtions of the ductl plte without connections to the ile ducts. They re usully discovered incidentlly t dominl imging. Although of no clinicl significnce, they cn mimic disseminted smll liver metstses in the ptient with cncer. Biliry hmrtoms re typiclly smll (5 10 mm in size) nd usully widely distriuted in oth loes of the liver. On ultrsound, they pper s smll hyperechoic or hypoechoic lesions nd cn demonstrte ringing rtifcts (comet til ppernce). On CT, they pper s smll cystic lesions of round, ovl, or irregulr shpe without contrst enhncement, lthough thin rim enhncement my sometimes e present, thus mimicking hypovsculr liver metstses [40]. When enhncement is present, it is usully very thin ( 2 mm) nd oserved only on equilirium-phse imges, relted to the firous component of the lesions [45]. On MRI, iliry hmrtoms pper low signl intensity on T1-weighted imging nd high signl intensity on T2-weighted imging (Fig ). They re est oserved on mximum intensity projections MRCP sequences s high signl intensity foci without connection to or ssocited normlities of the intrheptic ducts. Occsionlly, ile duct hmrtoms cn

9 17 Focl Liver Lesions 181 c d Fig Adenom (HNF1A sutype). () T1-weighted in-phse GRE imge demonstrtes very lrge mss in young womn. The mss is inhomogeneous nd shows right spots. () There is typicl signl intensity drop on the opposed-phse imge indictive of intrtumorl ft. (c) The T2-weighted TSE shows moderte hyperintensity. (d) On the gdoxetic cid-enhnced imges in the heptoiliry phse, there is little to no enhncement e very lrge, up to 20 cm, nd e symptomtic from internl hemorrhge or pressure on djcent structures [46]. Differentil dignoses of iliry hmrtoms include periiliry cysts (predominntly perihilr distriution in ptients with liver prenchyml disese), polycystic disese, nd Croli s disese (cysts communicte with ile ducts nd re ssocited with ile duct normlities). They cn lso mimic liver scesses in the pproprite clinicl setting Heptic Ascess nd Echinococcus The ppernces of heptic scesses on imging depend on etiology (periiliry scesses tend to e smll nd scttered djcent to the iliry tree; hemtogenous distriution vi the heptic rtery or vi the portl vein in ppendicitis or diverticulitis tends to led to lrger lesions diffusely spred in the liver). US revels cystic lesion with internl

10 182 W. Schim et l. c Fig Adenom: inflmmtory type. ( c) Arteril () venous () phse CT shows strong nd progressive contrst enhncement of the lesion, which retins enhncement in the delyed phse (c), which is typicl for peliotic chnges in inflmmtory denom c d e f Fig Adenom (inflmmtory type) in young femle presenting with vgue upper qudrnt pin. () In- nd () opposed-phse T1-weighted imging shows no significnt intrlesionl ft. The nodule is (c) mildly hyperintense on T2-weighted imging. (d f) Pre-contrst, post-contrst rteril phse, nd delyed phse imges show vid rteril enhncement, which persists. Surgicl resection confirmed n inflmmtory denom

11 17 Focl Liver Lesions Mlignnt Primry Tumors Heptocellulr Crcinom Fig Biliry hmrtoms (von Meyenurg complex). A middleged womn ws referred to MRI following n ultrsound exmintion. There re multiple foci of high T2-weighted signl within the liver, suggestive of iliry hmrtoms echoes. On CT, heptic scesses re hypodense lesions with cpsules tht my show enhncement (Fig ); cluster sign my e noted when multiple scesses re present [47]. CT ppernce of heptic scess is nonspecific nd cn e mimicked y cystic or necrotic metstses. Hence, pproprite clinicl nd lortory corroortion is vitl towrd mking the right rdiologicl dignosis. Though present in only smll minority of cses, centrl gs is highly specific for scess. On MR imging, heptic scesses re hypointense reltive to liver prenchym on T1-weighted imges nd mrkedly hyperintense on T2-weighted imges, often surrounded y locl re of slight T2 hyperintensity representing perilesionl edem, which my lso show incresed enhncement fter contrst dministrtion. Ameic liver scess is nonspecific. It usully ppers s solitry, hypodense lesion, with n enhncing wll tht my e smooth or nodulr, nd is often ssocited with n incomplete rim of edem. With MR imging, lesions re hypointense on T1-weighted imges nd heterogeneously hyperintense on T2-weighted imges [48]. On CT scn, involvement of liver y Echinococcus grnulosus (hydtid cyst) cn mnifest s uniloculr or multiloculr cysts with thin or thick wlls nd clcifictions, usully with dughter cysts seen s smller cysts, with septtions t the mrgin of or inside the mother cyst (i.e., this ppernce is quite different from usul multicystic tumor). On MR imging, the presence of hypointense rim on T1- nd T2-weighted imges nd multiloculted ppernce re dignostic fetures. HCC is the most common primry liver cncer, with the highest incidence in Asi nd the Mediterrnen. In Europen countries, HCC is found mostly in ptients with chronic liver disese (prticulrly heptitis B or C, liver cirrhosis, or hemochromtosis). At histopthology, HCC is chrcterized y norml heptocytes rrnged in treculr nd sinusoidl ptterns. Lesions my e solitry, multifocl, or diffusely infiltrting. There is wide vrying ppernces of HCC on imging. An erly HCC occurring within t risk popultion is typiclly smll (<3 cm) nd hs homogenous ppernce. By contrst, lte presenttion disese (including tumor in noncirrhotic ptients) is chrcterized y more dvnced disese, presenting s lrger heterogeneous lesion. US is frequently used for disese screening nd surveillnce of cirrhosis ptients. The ppernce of HCC on US is vrile, with iso-, hypo-, or hyperechogenicity (incresed echogenicity is often due to intrtumorl ft). Smller lesions re typiclly homogeneous nd lrger lesions heterogeneous. A surrounding firous cpsule is often present nd chrcteristic for HCC, ppering s hypoechoic rim surrounding the lesion. On unenhnced CT imges, most HCCs re hypo- or isodense (the ltter prticulrly if smll). The presence of intrtumorl ft cn lower CT ttenution nd is suggestive of primry heptocellulr tumors in the pproprite clinicl settings. Due to their ltered nd predominnt rteril supply, HCCs enhnce vidly in the rteril phse of contrst enhncement, ecoming iso- or hypodense with the liver prenchym in the portl venous phse of enhncement. Delyed phse imges show most HCC lesions s hypodense compred with surrounding liver. The wshout of contrst in these tumors is dignostic chrcteristic of HCC (Fig ). Smll HCCs my hve nodule-in-nodule ppernce on CT nd MR imges, especilly when the disese develops within regenertive or dysplstic nodule (Fig ). At MR imging, such nodule cn exhiit higher signl intensity on T2-weighted imges nd disply hypervsculrity on rteril-phse imges. Multiphse imging fter contrst dministrtion on CT helps to optimize the detection nd chrcteriztion of HCC. Lte rteril-phse imging is the most sensitive for detecting smll lesions [6, 49, 50]. A venous phse is lwys necessry for tumor detection/chrcteriztion nd

12 184 W. Schim et l. tion or fter tumor ltion. For these resons, three- to four-phsic MDCT protocol is utilized t most centers to evlute HCC. The relince on focl hypervsculrity in the rteril phse cn led to flse-positive dignosis of HCC [53]. Trnsient focl enhncement of liver prenchym during rteril phse, lso termed trnsient heptic ttenution differences (THAD), cn led to flse dignosis of HCC. In cirrhotic ptients, trnsient focl enhncement is most often cused y rteril-portl shunting, resulting in inppropri c Fig Ascesses. () Typicl lrge sucpsulr scess with n ir-fluid level nd rective pleurl effusion. (, c) Another ptient with fever nd right upper qudrnt pin. T1-weighted contrst-enhnced imges in the () rteril nd (c) portl venous phse demonstrte multiple ring-enhncing lesions in oth loes of the liver. In the rteril phse, there is lso ssocited incresed prenchym enhncement surrounding mny of the lesions. The ppernce is consistent with multiple heptic scesses ssessment of venous structures (Fig ), s well s other dominl orgns. The delyed phse imging (e.g., t 2 3 min) cn occsionlly help to detect lesion tht my e missed [51]. Much more importnt is tht it cn help to mke firm dignosis of HCC y showing typicl lesion contrst wshout, if it hd not een present in the portl venous phse [52]. Unenhnced imges re importnt for identifying hyperdense siderotic nodules nd for detecting hypodense intrtumorl ft. Unenhnced imges re lso useful for tumor follow-up fter chemoemoliz-

13 17 Focl Liver Lesions 185 Fig HCC: qudruple-phsic CT for detection nd chrcteriztion. () Non-contrst CT shows liver cirrhosis nd splenomegly. In segment 4, lesion is only fintly seen. () In the lte rteril phse, hypervsculr HCC is depicted in segment 4 (rrow). (c) In the venous phse, the lesion is not visile. (d) The delyed phse scn revels wshout of the lesion, which is now hypottenuting (rrow). The comintion of rteril hypervsculrity nd wshout is very specific sign of mlignncy tely erly focl res of portl venous distriution enhncement in the liver. THAD re usully peripherlly locted in the liver, pper wedge shped, nd my e poorly circumscried. Sucpsulr lesions tht do not exhiit mss effect or round nture should e crefully evluted efore suggesting the dignosis of HCC. THAD re not ssocited with lesion hypodensity in the portl venous or delyed phses of contrst enhncement. The comintion of hyperdensity on rteril-phse imges comined with wshout to hypodensity on venous- or delyed phse imges, lthough not sensitive (33%), is highly specific (100%) for the dignosis of HCC [54] (Fig ). However, smll proportion of HCC cn e isovsculr or hypovsculr compred with the liver, which cn e difficult to dignose. The typicl MR imging fetures of lrger HCC include firous cpsule/ pseudocpsule, intrtumorl sept, dughter nodules, nd tumor thromus (Fig ) [55]. These lesions re often heterogeneous in ppernces (mosic rchitecture) on oth CT nd MR [56]. Wheres most lrge HCC re hyperintense on T2-weighted imges, smller lesions, mesuring even 3 4 cm, cn pper isointense or hypointense. On T1-weighted imges, HCC shows vrile signl intensity reltive to heptic prenchym. A tumor cpsule/pseudocpsule my e seen on T1-weighted nd, less commonly, s hypointense on T2-weighted imging. Conventionl gdolinium contrst imging in HCC prllels the fetures descried for CT, with chrcteristic erly pek contrst enhncement nd delyed phse tumor contrst wshout of the nodulr solid components, s well s lte T1 enhncement of the cpsule/pseudocpsule. Liverspecific MR contrst gents (gdoxetic cid or gdoente

14 186 W. Schim et l. c d e Fig HCC with nodule-in-nodule ppernce. () Unenhnced CT shows siderotic (hyperttenuting) lrge nodule, which contins low-density (non-siderotic) focus (rrow). () On T1-weighted GRE opposed-phse imge, the mrginl nodule shows low signl intensity (rrow). (c) The lrge nodule shows siderosis on T2-weighted TSE imges, ut the mrginl focus displys higher SI. (d, e) Dynmic gdolinium- enhnced T1-weighted GRE imges show (d) rteril hypervsculrity of the mlignnt focus (rrow) nd (e) wshout in the equilirium phse

15 17 Focl Liver Lesions c Fig Diffuse HCC in the right loe with tumor thromus in the portl vein. () Arteril phse nd () venous phse T1-weighted GRE shows inhomogeneous enhncement nd expnsion of the portl vein. There is inhomogeneous enhncement of the right loe, ut no definite tumor is seen. (c) DWI shows solid mss in the entire intrheptic portl vein nd prt of the tumor in the right loe 187 dimeglumine) cn e dministered to provide rteril, portl venous, nd equilirium-phse imging ut hs the dded dvntge of reveling dditionl chrcteristics t the delyed heptoiliry phse of contrst enhncement. HCC typiclly do not show contrst retention of liver-specific contrst medium in the heptoiliry phse, which cn dd confidence towrd the detection nd chrcteriztion of HCC (Fig ) [57]. It hs een shown tht using gdoxetic cid-enhnced MRI cn improve the detection of smll or erly HCCs, s it is superior for detecting HCC mesuring <1 2 cm in size compred with CT [58]. In ddition, sucentimeter lesions detected y gdoxetic cid-enhnced MRI re likely to e or cn trnsform to ecome HCC within short intervl [59]. Hence, severl evolving guidelines for the imging evlution of HCC re incorporting the role of liver-specific contrst medi for the dignosis of sucentimeter HCC. Sucentimeter HCC my e treted y locoregionl therpy, thus voiding the moridity nd mortlity ssocited with rdicl surgery. However, it is importnt to note some potentil pitflls of using liver-specific contrst medi for HCC evlution. Some enign regenerting nodules my pper hypointense t the heptoiliry phse of contrst enhncement, lthough the mjority ppers isointense of the liver [60]. In ddition, some well-differentited or modertely differentited HCC my pper isointense or hyperintense on delyed imges due to higher levels of OATP1B3 nd MRP3 receptor expression. For this reson, the use of ncillry imging fetures t MRI cn improve the confidence of HCC dignosis. These include mild to high T2 signl intensity nd impeded diffusion on high -vlue DWI. The use of liver-specific contrst gents my lso help towrd the identifiction of isoenhncing or hypoenhncing HCC tht do not show typicl hypervsculrity in the rteril phse of contrst enhncement. With regrd to the use of diffusionweighted MRI for HCC evlution, higher -vlue (e.g., 800 s/mm 2 ) DWI my help in the identifiction of disese, prticulrly if the suspected nodule lso demonstrtes typicl vsculrity pttern t contrst- enhnced MRI. Becuse of ckground liver cirrhosis, higher-grde/poorly differentited HCC re more likely to show impeded diffusion nd lower ADC vlues compred with low-grde/well-differentited HCC. To summrize, mny MR chrcteristics re often ssocited with HCC (rteril-phse hyperintensity, T2 hyperintensity, venous- or equilirium-phse wshout, lck of heptoiliry MR contrst gent uptke on heptoiliry phse imges, nd restricted diffusion on high--vlue DWI). However, for ech of these findings, there is only ~60 80% sensitivity, nd enign lesions show these findings in 16 65% of cses, depending on finding, contrst gent used, nd series reported [60, 61]. Bsed on dt from numerous studies, the Americn Assocition for the Study of Liver Disese (AASLD) nd the Europen Assocition for the Study of the Liver (EASL) formed recommendtions for the noninvsive

16 188 W. Schim et l. c Fig HCC: MRI with liver-specific contrst gent (gdoxetic cid). () Axil T1-weighted GRE shows n encpsulted slightly hyperintense mss in the dome of the liver. () Gdoxetic cid-enhnced dignosis of HCC in ptients with chronic liver disese [62]. Lesions more thn 1 cm tht demonstrte rteril-phse hypervsculrity nd venous- or delyed phse wshout re triged for tretment with dignosis of HCC. If only one of the two findings re present, then the guidelines require otining different modlity with contrst imging to determine whether these findings cn e verified. If the lesion remins typicl, then iopsy is recommended. If suspected lesion is less thn 1 cm, the AASLD nd EASL guidelines recommend repeting the exmintion t 3-month imge shows strong enhncement in the rteril phse. (c) In the heptoiliry phse fter 20 min, the lesion shows hypointensity due to lck of heptocellulr uptke intervls, using the sme imging technology used to detect the lesion, to determine whether there is growth or chnging in chrcter. In following up ptients with chronic liver disese, development of new nodule with ny of the MR signl normlities discussed ove should e considered worrisome for HCC, even if they do not meet the AASLD [63] criteri for noninvsive dignosis. These criteri were developed to e specific ut re only pproximtely 70% sensitive [60]. It is essentil for rdiologists to lso document the numer nd size of ll lesions meeting criteri for HCC,

17 17 Focl Liver Lesions 189 Fig Firolmellr HCC. () Arteril phse MDCT shows heterogeneously enhncing mss in the left loe (rrows) with low ttenution centrl firous scr with clcifictions (rrowheds). () T2-weighted MRI shows lrge left loe mss (rrows) with heterogeneous ppernce nd mild to modertely incresed signl intensity. Firous centrl scr is of very low signl intensity (rrowheds) s tretment for these ptients vries depending on these fctors. It is lso importnt to document whether vsculr invsion or distnt metstsis is present Firolmellr HCC Firolmellr HCC (FL-HCC) is less ggressive tumor with etter prognosis thn typicl HCC. It consists of mlignnt heptocytes seprted into cords y firous strnds. On CT, FL-HCC ppers s lrge, well-defined vsculr mss with loulted surfce nd often centrl scr nd clcifictions in up to 70% of cses [64, 65]. On MR imging, FL-HCC re typiclly hypointense on T1- nd hyperintense on T2-weighted imges, with the centrl scr eing hypointense on oth sequences (Fig ). This is in contrst to the scr of FNH, which is most often hyperintense on T2-weighted imges. The firous centrl zones of oth FNH nd FL-HCC show delyed retention of CT nd extrcellulr gdolinium MR contrst gents. By comprison with FNH, the contrst enhncement in FL-HCC is usully heterogeneous compred with the often homogeneous contrst enhncement pttern of FNH Cholngiocellulr Crcinom Cholngiocellulr crcinom (CCC) is the second most common primry mlignncy of the liver. Intrheptic CCC origintes from the intrloulr ile ducts (in contrst to hilr CCC, which rises from min heptic duct or from the ifurction). Intrheptic CCC often presents lte s lrge mss [66]. According to the growth chrcteristics, CCC is clssified s mss forming, periductl infiltrting, or intrductl growing, with the mss-forming type eing most common in intrheptic CCC [66]. At CT nd MR imging, lesions tend to e hypodense t unenhnced CT nd hypointense on T1-weighted imges, with peripherl enhncement t dynmic contrst-enhnced studies [67]. Delyed phse CT/MR imging (fter 5 15 min) my show enhncement homogeneously or in the center of the lesion due to its rich firous strom, which is suggestive of the dignosis of CCC [68]. Interestingly, the centrl firotic strom often shows signl suppression on diffusion-weighted MRI nd return reltively high ADC vlue (Fig ). Periductl infiltrtive CCC cuses erly segmentl dilttion of ile ducts in stge when the tumor itself my e difficult to discern [67]. In ddition, there re morphologic fetures tht cn suggest the dignosis of CCC. Peripherl lesions often demonstrte overlying cpsulr retrction due to their scirrhous, firous mtrix (Fig ). Dilted intrheptic ile ducts proximl to n intrheptic CCC cn lso provide clues to the dignosis, s iliry ostruction is usul with intrheptic metstses (with the exception of colorectl cncer [69] Rre Primry Liver Tumors Biliry Cystdenom/ Cystdenocrcinoms These tumors present similr ppernce nd morphology s their mucinous counterprts in the pncres nd occur usully in women. Even when enign, these tumors hve propensity for mlignnt degenertion, nd ny such tumor should e considered s potentilly mlignnt. They pper s uniloculr or multiloculr cystic msses, with the typicl nechoic nd hypoechoic US ppernce nd ner wter-like ttenution

18 190 W. Schim et l. Fig Hilr cholngiocrcinom: elderly mn with progressive jundice. () Contrst-enhnced T1-weighted imge in the rteril phse shows dilttion of the intrheptic ducts, which extend to the heptic hilum. On the () 10 mins delyed imge, the tumor demonstrtes lte enhncement, which llows etter delinetion of the tumor (rrows) from the surrounding heptic prenchym Fig Peripherl cholngiocrcinom. () Contrst-enhnced CT in the rteril phse demonstrtes multicentric hypovsculr mss with cpsulr retrction (rrow). () Delyed phse demonstrted typicl lte enhncement due to firous mtrix contents on CT, with peripherl soft tissue nodulrity nd trversing septtions. The greter presence of ppillry excrescences, soft tissue nodulrity or septtions, re ssocited with higher risk of mlignncy [70]. The cystic res show vrile signl intensity t T1-weighted MRI, including eing hyperintense to liver relted to its proteinceous content. Corse clcifictions my e oserved t US nd CT in oth cystdenom nd cystdenocrcinom nd is not sign of enignity Heptic Angiosrcom Heptic ngiosrcom is rre tumor. There is strong ssocition with prior exposure to crcinogens such s vinyl chloride nd Thorotrst, s well s in ptients with hemochromtosis. However, in the mjority, the tumor is idiopthic. Pthologiclly, ngiosrcom presents s lrge, solitry msses or with multiple tumor nodules of vrying size, which contin multiple vsculr chnnels.

19 17 Focl Liver Lesions The imging ppernce of ngiosrcom is often nonspecific, ppering hypodense on unenhnced CT, hypointense on T1-weighted MR imging, nd mildly hyperintense on T2-weighted imging (lthough if prominent sinusoidl vsculr spces re present, these cn pper of homogeneous nd very high T2-weighted signl intensity). Following iodinted or gdolinium-sed contrst dministrtion, most lesions show nonspecific heterogeneous enhncement. Potentilly prolemtic, however, re those tumors with prominent sinusoidl vsculr spces, ecuse they cn mimic the ppernce of enign hemngiom on CT nd MRI. The high MR T2-weighted signl in such lesions further compounds this prolem. In most such cses, however, creful evlution will show tht the tumorl enhncement does not follow chrcteristics of lood pool t ll phses or tht there re other fetures, such s multiple lesions, tht mke the dignosis of hemngiom unlikely [71, 72] Epithelioid Hemngioendotheliom Epithelioid hemngioendotheliom (EHE) is rre tumor of vsculr origin, not to e confused with infntile hemngioendotheliom, which is very different tumor. These heptic tumors re chrcterized y multiple, peripherl-sed lesions tht progressively ecome confluent msses. In ddition to the unusul peripherl liver distriution, key chrcteristic feture is the presence of overlying cpsulr retrction, due to the presence of firosis nd scrring [73]. The CT ttenution or MR signl intensity chrcteristics re nonspecific, lthough occsionl tumorl clcifictions my e seen. Contrst enhncement with CT or MR gdolinium cheltes often shows centrl zone of decresed enhncement with mrked peripherl enhncement (Fig ). The reverse pttern hs lso een oserved with centrl re of incresed enhncement nd peripherl decresed enhncement. Concentric zones of mrked enhncement hve lso een reported. A visile rnch of the portl or heptic vein terminting t the periphery of these lesions t (lollipop sign) hs lso een descried, lthough this is not pthognomonic of the disese [74]. Lesions often ecome confluent nd my grow lrge enough to replce nerly the entire liver prenchym Heptic Metstses At US, liver metstses cn pper hypoechoic, isoechoic, or hyperechoic. On dynmic contrst-enhnced CT, most metstses pper hypovsculr nd hypodense reltive to liver prenchym on the portl venous phse (Fig ). Hypervsculr metstses re most commonly seen in renl cell crcinom, neuroendocrine tumors, srcoms, 191 Fig Epithelioid hemngioendotheliom. Contrst CT (portl venous phse) shows multiple predominntly peripherl-sed hypodense lesions. Note tht some of the lesions show lminted ppernce (rrows). Erly development of cpsulr retrction is present with flttening of the cpsule overlying some of the lesions (rrowheds) nd rest tumor ptients (Fig ). These tumors re est seen in the rteril phse nd my ecome isodense nd difficult to detect t the lter phses of contrst enhncement. At MR, metstses re usully hypointense on T1-weighted nd hyperintense on T2-weighted imges [75]. Peritumorl edem mkes lesions pper lrger on T2-weighted imges nd is highly suggestive of mlignnt mss [76]. High signl intensity on T1-weighted sequences is typicl for melnom metstses due to the prmgnetic nture of melnin. Some lesions my hve centrl re of hyperintensity (trget sign) on T2-weighted imges, which corresponds to centrl necrosis. DWI with high -vlues (e.g., ) is very helpful for detecting smll liver metstses, which my otherwise escpe detection (Fig ). On dynmic contrst- enhnced MR imging, metstses demonstrte enhncement chrcteristics similr to those descried for CT. Metstses my demonstrte hypointense rim compred with the center of the lesion on delyed imges (peripherl wshout sign), which is highly specific for mlignncy. It hs een shown in colorectl cncer tht the comintion of using DWI, together with liver-specific contrst medi, enhnced MRI results in the highest dignostic ccurcy for the detection of liver metstses (Fig ) [77] Differentil Dignosis of Focl Liver Lesions The pproch to chrcterizing focl liver lesion seen on CT egins with determining its density. If the lesion shows ner wter density, is homogenous in chrcter, nd hs

20 192 W. Schim et l. Fig Metstses. () Contrst-enhnced MDCT in the rteril phse demonstrtes severl predominntly hypervsculr liver metstses of neuroendocrine cncer of the pncres. () Contrst-enhnced MDCT in the venous phse shows typicl hypovsculr colorectl metstses Fig Vlue of diffusion-weighted MRI for detection of smll metstses. () Contrst-enhnced MRI shows one smll metstsis in the right loe (rrow). There is sutle hypointensity in the right loe in sucpsulr loction. () DWI clerly shows tht there is n dditionl metstsis (rrows) shrp mrgins, then cyst should e considered nd cn e confirmed with US, equilirium-phse CT, or even MR imging (T2 right nd non-enhncing post-gdolinium), which cn ensure there re no solid components or murl wll lesions. However, the rdiologist should e fmilir with the imging fetures of other cystic lesions tht cn mimic simple cysts. When evluting solid focl liver lesions, disese chrcteriztion is lrgely relint on oserving the rte nd pttern of contrst enhncement. If lesion shows peripherl nd nodulr enhncement, with the density of enhncing portions showing the sme generl levels of lood vessels in the rteril, venous, nd delyed phses, hemngiom cn e confidently dignosed. Arterilly hypervsculr enhncing

21 17 Focl Liver Lesions 193 lesions include FNH, HCA, HCC, nd metstses from neuroendocrine tumors, melnom, renl cell crcinom, nd rest cncer. In generl, HCC is considered in setting of cirrhosis or chronic liver disese. FNH is most likely in young women with non-cirrhotic liver nd if the lesion is homogeneous nd ner-isodense/ner-isointense on unenhnced CT/MR imging with centrl T2-weighted hyperintense scr. By comprison, thick, irregulr, heterogeneous enhncement or the presence of peripherl wshout t the delyed phse suggests mlignnt mss, such s metstses, CCC, or even HCC. In prticulr, delyed enhncement is feture of CC due to is firotic strom. Liver-specific MR contrst hs een shown to improve the chrcteriztion of FNH nd HCA, increse the detection of suspicious focl lesions in ptients with liver cirrhosis, s well s the identifiction of smll focl liver lesions. DWI is lso now routinely performed in liver imging. Its min clinicl enefit is the detection of focl liver lesions, which my e missed on conventionl nd contrst-enhnced imging sequences. Quntittive ADC mesurements cn support the chrcteriztion of focl liver lesions, with higher ADC vlues (e.g., > mm 2 /s) fvoring enign lesions [22]. However, the use of ADC vlue should e mde with the knowledge of the scnner ADC repetility, s well s in collortion with ll other imging findings ecuse of the significnt overlp of ADC vlues etween enign nd mlignnt lesions. c Fig Colorectl liver metstses t gdoxetic cid-enhnced MRI. () Unenhnced T1-weighted MRI shows two hypointense lesions in segments 6/7 nd 4. () The T2-weighted TSE imge shows the lesions to e modertely hyperintense. (c) The gdoxetic-enhnced T1-weighted GRE imge in the heptoiliry phse shows two dditionl smll sucpsulr metstses (rrows) not seen on unenhnced MRI or MDCT (not shown) Tke-Home Messges Contrst-enhnced liver MDCT for detection nd chrcteriztion of focl msses should e t lest iphsic, with qudruple-phsic protocol eing recommended for HCC detection nd chrcteriztion in cirrhotic ptients. MRI protocol should routinely include dynmic contrst- enhnced pulse sequences nd DWI. Liver-specific MR contrst gents re recommended for evlution of ptients with potentilly resectle colorectl liver metstses. Liver-specific MR contrst gents re helpful for chrcteriztion of FNH nd denom nd my increse the reder confidence in HCC chrcteriztion.