Infarct versus Neoplasm on CT: Four Helpful Signs

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Infarct versus Neoplasm on CT: Four Helpful Signs

Joseph C. Masdeu 1

In a search for distinguishing features, the computed tomographic (CT) findings in 35 patients with recent cerebral infarction and 65 patients with cerebral neoplasms were compared. Gray-matter enhancement and sparing of the thalamus characterized infarcts; white-matter edema and ring enhancement located in the white matter favored the diagnosis of neoplasm.

On computed tomography (CT), malignant brain neoplasms often exhibit mass effect and contrast enhancement. These features , however, are common in recent cerebral infarction . The reliability of other radiologic signs that distinguish these two types of cerebral lesions is reported .

mas) and in one (4%) metastasis. Thus, a CT scan with this pattern was six times more likely to belong to an infarct th an to a glioblastoma and 11 times more likely to belong to an infarct than to a metastasis. The difference between the infarct and neoplasm

groups was statistically significant (p < 0.001).

Among the infarcts, timing of CT weighed heavily regarding th e presence of this sign: it occurred in only two of the 17 scanned in the first 5 days, whereas 13 of the 18 infarcts scanned 5-15 days after the stroke had gray-matter enhancement, most often confined to the cortical ribbon .

Pathologically, infarcts with gray-matter enhancement showed

Materials and Methods

The CT scans of 35 patients with cerebral infarction were compared with the CT scans of 65 patients with cerebral neoplasms (39 gliomas and 26 metastases). All lesions were confirmed histologically, either through biopsy or autopsy. All the scans were obtained with an EMI 1005, a Syntex Sys 60, or an EMI 6000 before and after the infusion of 100 ml of 60 % iothalamate meglumine .

Only recent infarcts, regardless of their vascular distribution, were included in the study. Seventeen cases were scanned within 5 days after the stroke and the other 18 had CT 5-1 5 days after the ischemic episode. Of the 35 infarcts, 26 were confined to the territory of the middle cerebral artery, two involved the anterior cerebral territory, and three were in the distribution of the posterior cerebral artery. The other four straddled several arterial territories.

Each scan was evaluated for the presence of each of the following radiologic signs (figs. 1 and 2): (1) gray-matter enhancement, considered to be present when an area clearly identifiable as the co rtical ribbon or deep nuclei underwent an abnormal increase in attenuation value after the infusion of contrast material; (2) thalamic sparing, when , at a midthalamic level, a lesion with low attenuation involved the structures located anterolateral to the thalamus, but spared the thalamus itself; (3) white-matter edema, evidenced, in more than one CT cut, by a subcortical area of low attenuation that spared the cortical ribbon, thus outlined as bands of isodense tissue by the abnormal white matter; (4) ring enhancement of the white matter, when areas of abnormal enhancement, shaped as a ring, were located, at least in part, outside the gray matter. The chisquare test was used to calculate the significance of the findings.

Results

Gray-matter enhancement was present in 15 (43%) of the infarcts, but in only three (7%) of the gliomas (all of them gliosarco-

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Fig . 1.-Neoplastic white-matter edema (A and B) spares cortex. By contra st . low attenuation due to infarction (C and 0) reaches inner table and does not spare cortex. Thalamus is spared by infarct in C and 0 , which stops sharply at level of internal capsule .

I Neurology Service, Hines Veterans Administration Hospital, Hines, IL 60141, and Departm ents of Neurology and Pathology, Loyola University Medical Center, Maywood. IL 60153 . Present address: Departments o f Neurology and Medicine, Montefiore Medical Center, Albert Ein stein College of Medicine . Send reprint requests to Departm ent of Neurology, Montefiore Hospital and Medical Center, 111 E. 210 St., Bronx , NY 10467.

AJNR 4:522-524, May/ June 1983 0195-6108 / 83 / 0403-0522 $00 .00 ? American Roentgen Ray Society

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Fig . 2. -Gray-matter en hancement. A, Precontrast scan 7 days after stroke . Mild inc rease in atte nuation of infarcted corti cal ribbon (arrowheads), which enhanced marked ly after contrast infusion (B). C, Gross pathologic specimen 10 days after st roke shows hemorrh ag ic infa rction of cortex . (Courtesy of Dr. Em anuel Ross, Departm ent of Path ology, Loyola Medical SchooL)

CT OF THE HEAD

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infarcti on of the co rti ca l ribbon and , in most cases, un derly ing white matter. However, only th e co rtex showed multiple petechial hemorrhages. Under the mi c ro scope, th e nec roti c co rtex had, in add ition to neuron al and glial loss, ball hemorrh ages around cap ill ari es with reactive endotheli al cell s. In man y cases diapedesis of red and white blood ce lls was pronounced . Capillary engorg ement and proliferation characterized areas of co ntrast enh ance ment. Am ong th e neoplasms, three gliosarcomas and a malign ant melanom a th at infiltrated th e co rte x and leptomeninges showed enh ancemen t of the co rtical ribbon . Neovascular proliferation was prominent in th e areas of enhancement.

Thalamic sparing was present in 11 (3 8%) of the 29 infarcts th at occurred in the di stribution of the middl e ce rebral artery. Since th ese infarcts were larg e, when scanned early they showed pronounced mass effect, th ereby mimi c king neoplasms. However, onl y five (7 %) of th e 65 tumors had a similar pattern on CT scan. The difference between th e number of infarcts and th e number of

neoplasms showing thi s feature was significan t, with p < 0.005 .

Only massive infarcts in the carotid territory presented thi s CT sign . In addition to the frontoparietal operculum , the superolateral part of the lenticular nucleus had undergone infarction, which extended to the lateral part of the internal capsule but stopped abruptly at th e capsular level in all 11 infarcts th at had shown thi s finding on CT. Th e th alamu s, fed by branches of th e vertebrobasilar system, had been spared . Neverth eless, when th e patient died 6 or more month s after a large hemisph eri c infarct, th e ipsil ateral th alamu s was atrophied and showed neuronal loss due to transynapti c degeneration .

White-matter edema or a CT pattern similar to it was present in only five (14 %) of the 3 5 infarcts but in 29 (74 %) of the 39 gliomas and in 19 (73 %) of the 26 metastases . Thus when thi s sign was present the lesion was five times more likely to be a neoplasm th an

an infarct (p < 0 .001). Moreover, all of the infarcts that showed

this pattern also had gray-matter enhancement. Th e co rtex that stood out against a background of hypodense white matter was enhanced by contrast infusion.

Ring enchancement of th e white matter was absent in th e group of recent infarcts, but it was ve ry co mm on in th e gli ob lastoma and metastasis group . Th e sa me ca n be sa id of nodu lar enh anceme nt. On scans obtain ed at least 3 week s after the stroke, two infarcts showed inco mpl ete rin g enh ance ment in th e margin s of the infarcted ti ssue.

Patholog ica ll y , the area of enh ancement in tumors co rresponded to viable tum or ti ssue, with mark ed neovasc ularizati on. Thi s tissue usuall y surrounded a necroti c co re . In th e case of infarc ts, it corresponded to granul ati on ti ss ue at th e margin o f th e infarcted area.

Discussion

Th e CT features di sc ussed above have been mentio ned in previou s reports. The originality of thi s stud y stems from th e attempt to

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evalu ate th eir relative freq uency in a group of neoplasms and in a group of recent infarc ts, w here all th e diagnoses we re verified hi stologica ll y.

Th e multiple-n od ule appearance of metastati c tum ors, or even a large ring-shaped enh anc in g lesion, in dica ti ve of a malignant primary or meta stati c brain tum or, poses no d iagnosti c prob lem even in th e face of a c linica l hi story o f strok e. Howeve r, recent in farcts w ith apparentl y biz arre enh anc ing pattern s and mass effect may be mi staken for neopl asms. Occasionally , th e diag nosti c difficu lties are co mpound ed by th e coexistence in th e sa me patient o f a brain tum or and of areas of infarcti on. Thi s was the case in some report ed cases [1 , 2] and in four of our patients , not in c luded in thi s stu dy, two of whom presented with a neurolog ic defi c it attri butable to the infarc t rath er th an to th e tum or. Inc reased in trac rani al pressure ca used by th e neopl asm may have been in strum ental in produc in g these isc hemi c lesion s. In any event , based on th e signs described above, th e diagnosis was accurately made on CT and sub seq uentl y con firm ed by hi stology.

Th alamic sparing had th e lowest degree of spec ific ity . Thi s sign appears only with large infarcts in th e territory of th e mid dle ce rebral artery, most often due to carotid artery occlu sion. Alth ough far from rare, suc h massive infarcts are not as co mm on as lateral watershed infarcts or as th ose involving th e territory of branches of th e middl e cere bral artery. Large infarc ts, however, are accompani ed by pronounced mass effec t and acutely may not show gray-matter enhance ment. Thu s, at an ea rl y stage of ce rebral infarcti on, th alam ic sparing may be helpful to rul e out a neoplasm as th e ca use of th e pronounced mass effect.

Th e CT pattern of w hite-m atter edema proved to be highl y specific for neoplasms [3 ]. Thi s pattern accompanies nonneoplasti c lesions also, suc h as abscesses, radiation necrosis, and large demyelinating lesions. A somewhat simil ar pattern , w ith low-atten uati on white matter outlining th e co rti ca l ribbon, may appear some weeks after an infarct restri cted to th e white matt er of th e hemisph eres [4] (M asdeu JC, Naheedy MH , unpubli shed observat ion s). However, thi s CT finding seldom accompanies acu te infarc ts, beca use not on ly th e white matt er but the co rtex as well is affected by cytotox ic edema.

A roun d th e second week after infarcti o n, co rti cos ubcort ical infarc ts may show an isodense co rti ca l ribbon outlined by the low attenu ati on of th e underl ying wh ite matter [5]. In thi s stud y this occ urred in fi ve infarcts. Helpfull y, all of th ese infarcts showed also co ntrast enh ance ment of th e corti cal ri bbon; gyral enh ancemen t occurs infreq uentl y w ith neoplasms [6] . Gli ob lastomas, parti c ularl y when th ey have a pronounced desmoplastic component , and medullobl astomas may appear w ith gyral enh anceme nt. Thi s occ urred in three of our cases. A simil ar pattern may be caused by metastatic tumors th at tend to infiltrate along th e leptomeninges and co rtex . A metastatic melanoma exemplifi ed thi s occurrence in th e present se ri es , but breast and lu ng ca rc in omas and lymp homas occas ion all y show gyral en hanceme nt.

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Infarcts se ldom show rin g enh ance ment in vo lving th e w hite matter [7, 8). Wh en present , thi s pattern usuall y appears several wee k s after th e stroke. Enh ance ment of th e gray matter may ad opt rin glike co nfigurati ons, parti c ularl y in th e basal ganglia and where th e co rti ca l gyri present a co nvo luted appearance on axial secti on, suc h as at th e dorsa l ex tent o f th e sylvian fi ssure. Th ese pattern s should not be mi staken fo r neopl asti c rin g enh ance ment , oftentimes c learly located in th e white matter [9). Th e stand ard procedure for co ntrast enh ance ment was used in th e present stud y. Wh en an infarci is scanned after a hi gh dose of iod in e, or delayed scannin g is used, th e white matter may show co ntrast enhance ment [10).

Althoug h thi s stud y dealt w ith images obtained by CT scannin g, Ihe desc ribed signs refl ect th e hi stolog ic c hanges c haracteri sti c of suc h co mm on lesions as infarcts and mali gnant neopl asms of th e brain . Improved im ag ing tec hniques, suc h as nuc lear magn eti c resonance, should di splay th em even more c lea rl y.

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8. Weisberg LA . Computeri zed tomographi c enh ance ment pattern s in ce rebral infarcti on. Arc h Neuro /1980 ;37 : 2 1 - 2 4

9. Lilj a A, Berg strom K , Spann are B , Ol sson Y. Reli ability of co mputed tomog raph y in assessin g hi stopath ologica l features of mali gnant supratentori al g li omas. J Comput Assist Tomogr 1981 ;5: 625-636

10 . Haym an LA , Evans RA , Basti on FO, Hinc k VC. Delayed high dose co ntrast CT: identifying pati ents at ri sk of massive hemorrh agic infarcti on. AJNR 1981 ;2: 1 3 9-147 , AJR 1981 ; 136 :1151-1159

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