COMPUTED TOMOGRAPHY IN THE DIAGNOSIS OF INTRACRANIAL MENINGIO-MA LEON A. WEISBERG Department
of Neurology (Received
and Psychiatry,
21 September
141.5 Tulane
1978: rrceitxd
for
Avenue. puhlictrtion
New Orleans,
LA 70112, U.S.A.
I I December 1978)
Abstract-The CT findings in 53 meningiomas are reported. Based upon the plain and post-contrast CT pattern and density characteristics, the diagnosis of meningioma was accurately predicted in 28 of 35 convexity, parasagittal, subfrontal. middle fossa and sphenoid wing lesions (80%). In 2 calcified nonenhancing meningioma, the diagnosis was suspected by CT findings. CT was extremely accurate in detecting 16 juxtasellar, intraventricular, tentorial and posterior fossa meningiomas, but the CT pattern was less specific such that differentiation from other neoplastic or vascular lesions was not always possible. There were only 2 false negative cases: these occurred when contrast infusion had not been performed. Meningioma
Homogeneous
enhancement
Calcification
INTRODUCTION
Computed tomography (CT) has become an important complimentary diagnostic modality to plain skull radiogram, isotope scan and angiography in evaluating patients with suspected intracranial meningioma. CT has been reported to have a high degree of sensitivity in their detection; and certain plain and post-contrast patterns and density characteristics are quite specific for establishing the diagnosis of meningioma [l, 21. The purpose of this report is to describe the CT features of intracranial meningioma and to discuss their differentiation from other neoplastic and non-neoplastic pathological conditions.
METHODS
AND
MATERIALS
Fifty patients with intracranial meningiomas as confirmed by pathological findings were evaluated with CT. In two patients, multiple meningiomas were present (two lesions in one patient and three in the other patient); therefore. the CT findings in a total of 53 meningiomas are described. In 5 patients, the meningioma represented a recurrent lesion. All patients were studied utilizing an EM1 Mark I head scanner with a 160 x 160 matrix system and a scan time of approximately 4 min. The complete examination consisted of 4 pairs of transverse tissue sections which were each 13 mm in thickness and extended from the base to the vertex region. The scan sequence was repeated following the intravenous infusion of 300 ml of meglucmine iothalamate (Conray-30) which was administered over a 5-min interval.
FINDINGS The localization of the 53 meningiomas visualized by CT is listed in Table 1. Isotope scan was positive in 24 out of 33 cases (73%). It was positive in 20 out of 24 (83%) supratentorial meningiomas, but was positive in only 4 out of 9 (44%) posterior fossa or parasellar lesions. In both cases of multiple meningiomas, isotope scan showed only single lesion. In 17 cases, isotope scan was not performed because of the previously-performed CT scan; findings were deemed conclusive enough to obviate the need for isotope scan. Plain skull radiogram was performed in 46 cases and showed hyperostosis, calcification or prominent vascular spaces in 15 cases (33%). In 8 cases (16x), there were abnormalities of the sella turcica consistent with chronic elevation of intracranial pressure. Angiography was performed in all 50 cases and was positive in 45 cases; it failed to demonstrate cerebellopontine (in 3 out of 4 cases) and parasellar meningiomas (in 2 out of 4 cases). In both cases of multiple meningioma, it was the CT findings which indicated
116
L. A. WEBBERG Table
1. Localization of 53 intracranial meningiomas visualized by CT Localization
No. of cases
Convexity Parasagittal Subfrontal Parasellar Sphenoid ridge Middle fossa Intraventricular Posterior fossa Tentorium Cerebellar Cerebellopontine-angle
15 12 2 5 6 2 1 4 2 4
the need to perform both carotid and vertebral angiogram. Air study was performed in only two cases of meningioma (intraventricular and parasellar) and this study demonstrated the lesion in both cases. In two cases, CT was reported to be negative. In one case of parasellar meningioma extending 1.5 cm in the suprasellar region, the lesion was demonstrated by isotope scan, air study and angiography. In the second case, a large falx meningioma was subsequently detected by repeat CT study. Post-contrast study was not performed in either case of these diagnostic failures. The smallest meningiomas detected by CT were 1.0 cm is size, and both lesions were clinically asymptomatic. In one case, this represented one of multiple lesions, but in the other it was a solitary meningioma. In four cases in which CT demonstrated the meningioma, the patient had no abnormal neurological findings. The CT appearance and density characteristics of meningioma on both plain and post-contrast scan is shown in Table 2. Eighteen appeared as speckled, homogeneous, sharply-marginated, ovoid or round, soft-tissue, high-density masses. The actual measured densities on the plain scan ranged from 22 to 32 EM1 units (Fig. 1). Surgical findings showed that psammoma bodies were very prominent in 12 of these meningiomas; and that they were also present but less prominent in the other six meningiomas which showed this non-calcified, high-density pattern on plain CT. In six cases, plain scan showed non-homogeneous, mixed-density pattern without evidence of calcification (Fig. 2) and three others were seen to have mixed density with evidence of calcification (Fig. 3). The appearance of the calcification in these 6 cases was dense globular, punctate or as peripheral circular rim. In three cases, plain scan showed only high-density mass which measured entirely in the range of calcification (45-50 EM1 units). A homogeneous ovoid or triangular low-density (6-12 EM1 units), sharply-marginated lesion was seen in 16 cases (Fig. 4) on the plain scan. No abnormal density was seen in seven cases (Fig. 5). In 3 of these cases, mass effect as demonstrated by ventricular distortion or displacement was definitely visualized; but in three others, no abnormality was visualized (Fig. le). In one of these seven cases, plain scan was initially interpreted as normal, but retrospective analysis showed low-density area (Fig. 6). Four cases showed evidence of bony thickening (Fig. 7). Table
2. CT density characteristics intracranial meningiomas
(i) Plain scan findings Low density Isodense High density (non-calcified) High density (calcified) Mixed density Without calcification With calcification (ii) Post-contrast findings No enhancement Enhancement pattern Dense consolidated Speckled homogeneous Peripheral enhancing ring
in 53
No. 16 1X 3 9 6
2 51 32 16
Fig. 1. Homogeneous speckled, high-density lesion (22-26 EMI units) is seen in left parieto-occipital region. (a). Following contrast infusion, there is dense, consolidated, sharply-marginated enhancement with bowing of falx posteriorly to the right side (b). In addition, there is another enhancing supratentorial smaller enhancing lesion seen anterior to this large mass and another right infratentorial enhancing lesion (c and d) is seen which was not identified on pre-contrast study (e). 117
L. A. WEISBERG
Fig. 2. Plain scan shows mixed-density pattern in right supratentorial compartment with marked mass effect with displacement and distortion of the lateral ventricle (a). Post-contrast study shows dense, consolidated, sharply-marginated enhancement in the right middle fossa (b).
Post-contrast study was performed in all 50 cases and evidence of enhancement was seen in 51 of the 53 meningiomas. Post-contrast enhancement appeared as a densely consolidated, homogeneous, high-density (32-36 EM1 units) pattern in 32 cases (Fig. 8), or as speckled, homogeneous increased densities (3Wl2 EM1 units) in 16 cases. In 15 cases, the enhanced mass appeared multilobulated. In only three cases was there the finding of ring enhancement to suggest the presence of a cystic component, but in none of these cases was a cyst identified at operation. In only one case was there evidence of non-homogeneous enhancement as seen in other malignant neoplasms (gliomas, metastases), and this represented a most unusual case of an intracerebral men-
Fig. 3. Plain scan shows marked mass effect in the right hemisphere with single calcified area located slightly medial to right sphenoid ridge (a). Following contrast infusion, there is dense consolidated homogeneous enhancement in right middle fossa extending into the suprasellar region consistent with meningioma (b).
CT in the diagnosis
Fig. 4. Plain scan shows
of intracranial
II9
meningioma
low-density. sharply-marginated lesion in right frontal enhancement on post-contrast study (b).
region
(a) with speckled
ingioma. In all cases, the area of the enhancement was sharply differentiated from the surrounding brain parenchyma and had either round, triangular, ovoid or lenticular shape. The only two meningiomas which did not enhance initially appeared as densely calcified, globular lesions on plain scan. Mass effect was seen in 35 of the 53 meningiomas. In 13 cases. there was a surrounding lowdensity circular or semilunar rim, whereas in 22 others, there was surrounding low-density frondlike projections which were believed to represent cerebral edema. In four cases, the falx adjacent to the meningioma appeared thickened (Fig. S), and in six others the neoplasm appeared attached to the dura (falx, tentorium). Hydrocephalus was seen in 28 cases. Post-contrast study enhancement was most reliable in defining evidence of recurrent meningioma in 5 cases (Fig. 9). In the evaluation of three suspected recurrent neoplasms, the finding of bony thickening or calcification without concommitant enhancement was not indicative of recurrence as documented by negative isotope scan and angiography.
L. A. WEISBERG
Fig. 5. A young woman had episodes of visual blurring and headache during pregnancy. Findings included bilateral papilledema only. Skull radiogram, electroencephalogram, isotope scan were normal; CSF was abnormal only for an elevated pressure with normal protein content. Initial CT scan without contrast infusion was normal (a) and the diagnosis of “pseudotumor cerebri” was made, but angiogram was not performed. Symptoms and papilledema resolved but recurred one year later. Repeat CT was performed; plain scan showed low-density area in right frontal region (b). Post-contrast study showed dense bifrontal, sharply-marginated, homogeneous enhancement with surrounding rim of low-density (c) consistent with meningioma, and this was surgically confirmed.
DISCUSSION In this series, CT was the most sensitive neuro-diagnostic procedure to detect meningioma. Isotope scan was positive in 73% of the cases but was less sensitive in detecting juxtasellar, tentorial and posterior fossa lesions (44%). Plain skull radiogram showed an abnormality in only 33%; this is lower than that previously reported and this was believed due to earlier diagnosis with CT [3]. Angiography was positive in 90% of meningioma but failed to detect juxtasellar and posterior fossa lesions in five cases [4]. The exquisite sensitivity of CT is demonstrated by the fact that this remarkable technique visualized an intracranial meningioma in 4 patients who had no abnormal neurological findings, negative skull radiogram and isotope scan. Based upon the
CT in the diagnosis
of intracranial
meningloma
Fig. 6. Plain scan shows vague semilunar low-density area in the right frontal parietal region (a). Following contrast infusion there is dense, consolidated, homogeneous lenticular-shaped enhancement (b). This appears contiguous with bone and bulges medially inward: these findings are consistent with parietal convexity meningioma.
of abnormal findings in these four cases, it is unlikely that angiography would have been paucity performed if the diagnosis had not been suggested by the CT findings. In addition, CT was calpable of sensitively detecting the presence of multiple meningiomas more reliably than isotope scan and angiography in two cases. The CT pattern and density characteristics of meningiomas usually reflected their patholc jgical features. On the plain scan, 33% were of homogeneous speckled, high-densities with regular contours (round, ovoid, wedge-shaped) and were sharply marginated from the surrounding parenct lyma. The actual densities were 22-32 EM1 units; this was less than the values seen in calcified le:;ions. Pathological findings confirmed the presence of prominent and widespread psammoma hod! I’formation in these neoplasms. It is postulated that the failure to measure attenuation coeffic:ients
Fig. 7. Plain
scan shows
thickening of the left petrous ridge with calcified angle consistent with petrous ridge meningioma.
mass
in the cerebellopontine
L. A. WEISBERG
Fig. 8. Plain scan shows low-density lesion in right frontal region without significant mass effect (a). Following contrast infusion there is dense right frontal homogeneous enhancement extending across the midline anteriorly. The falx appeared to be bowed. displaced to the left. and appears slightly thickened (b).
in the range of calcium in these cases represented the effect of partial volume tissue averaging with surrounding lower-density tissue in the 13-mm section. In 6 cases (1 lx), there was evidence of calcification within the meningioma. The actual densities ranged from 45-350 EMI units. This calcification was seen in several patterns, and it appeared as small punctate areas, circular rim, or as dense, globular, ovoid, sharply-marginated, calcified masses. Two meningiomas which were densely calcified on plain scan showed no evidence of contrast enhancement. Since angiographic analysis showed an abnormal vascularity in these men-
Fig. 9. Patient had cerebellar tumor removed 2 yr previously, and was then re-evaluated because of persistent neck pain. but the patient had no new neurological deficit, CT findings: plain scan showed calcified mass contiguous with bone with surrounding low-density region (a). Post-contrast scan shows dense, homogeneous, infratentorial enhancement. The fourth ventricle is not seen with lateral and third ventricle being dilated (b). Surgical findings confirmed the diagnosis of posterior fossa meningioma with no supratentorial extension.
CT in the diagnosis
of intracranial
meningioma
123
ingiomas, it is believed that the lack of visualized enhancement may be spurious in that the neoplasm was initially of such high-density, that actual contrast enhancement did not alter the observed attenuation values sufficiently to be observed [S]. Oligodendrogliomas and low-grade astrocytomas also showed dense globular calcification to simulate the appearance of meningioma, but the latter neoplasms usually had irregular edges. Intracerebral hematoma also show dense consolidated, highdensity mass but the location, irregular edges, actual density measurements, more prominent mass effect and accompanying edema usually permitted differentiation from meningioma; and the clinical presentation was also most dissimilar. The finding of a peripheral rim of calcification was also seen in aneurysm, angioma and neoplasms including craniopharyngioma; whereas punctate areas of calcification was seen in many varied neoplastic (including low-grade astrocytoma, ependymoma, medulloblastoma, pinealoma, pituitary adenoma) and certain non-neoplastic disorders. In those meningiomas with peripheral rim of calcification, dense enhancement of the peripheral rim and central region was always seen following contrast infusion. In 30% of meningiomas, plain scan showed homogeneous, non-speckled, sharply-marginated, ovoid or wedge-shaped, low-density lesion. In none of these meningiomas did pathological examination demonstrate prominent psammoma body formation, although the pathological findings were otherwise quite typical of meningioma. The homogeneous appearance was quite characteristic of meningiomas although this was seen in certain low-grade gliomas, angioma or infarction. When the meningioma appeared as a wedge-shaped, low-density lesion, this may suggest these alternative diagnoses; differentiation was then established by the post-contrast enhancement pattern. In three cases, the low-densities measure 338 EM1 units and were sharply-marginated and round in shape; this suggested cystic component but this finding was not confirmed by pathological findings. In 17% of cases, plain scan showed a mixed-density pattern; this lesion was visualized by CT to contain calcification in 33% of them. This pattern was also seen in astrocytomas and angiomas. In 13% of cases, plain scan showed no abnormal density pattern, and the diagnosis was established only on post-contrast study. In two meningiomas which appeared as isodense lesions, the failure to perform post-contrast study led to diagnostic failures of CT. The previously-described characteristic surrounding rim of low-density which is believed to represent widened subarachnoid space or edema [6] was seen in 24% of the cases. This wellcircumscribed, thin, low-density rim was more commonly seen in smaller meningiomas, whereas the larger meningiomas usually were associated with frond-like low-density regions which projected into surrounding parenchyma (41%). Since the circumscribed halo was also seen in acoustic neurinomas, pituitary adenomas, in craniopharyngiomas and in aneurysms, it was considered a non-specific finding. Bone change (hyperostosis) was specific for meningioma and was seen in 7% of cases. Following contrast infusion, enhancement was seen in 96% of cases. Meningiomas showed homogeneous pattern which was either speckled or consolidated in appearance. Ring enhancement was seen in only three cases; two were angioblastic meningioma and one was seen in an unusual intracerebral meningioma. In the latter case, the enhancement pattern was that of an irregular, complex ring which was more consistent with malignant infiltrative neoplasm than with meningioma. In those cases with ring or no evidence of enhancement, the specific diagnosis of meningioma was not possible by CT analysis alone. In the other cases, the homogeneous, speckled or dense, consolidated enhancement with sharply marginated borders was quite characteristic of meningioma. In 28 of 35 meningiomas (80%) which were located in the convexity, parasagittal, subfrontal, sphenoid ridge or middle fossa, plain and post-contrast CT scan findings were sufficiently characteristic to establish the diagnosis of meningioma, and this was confirmed by pathological findings. There were 3 cases of meningioma in which ring enhancement suggested an alternative diagnosis of glioma or metastases and diagnosis was not established by CT. In addition, there were 3 cases in which the CT pattern was believed to be characteristic of meningioma but this was not confirmed by operative findings: (i) one parasagittal glioma showed dense, homogeneous, sharply-marginated enhancement; (ii) two metastases appeared as dense, consolidated, sharply-marginated, round masses with surrounding low-density, frond-like projections. In another case, the diagnosis of angioma was made because the contiguous enhancing choroid plexus was incorrectly interpreted as a draining vein. Two false negative cases were reported. In one case, the diagnosis of juxtasellar
L. A.
124
WEISBERG
meningioma was made by air study and angiography; whereas in the other the diagnosis was established by repeat CT. In both cases, contrast infusion study had not been performed: these false negative CT cases emphasize the importance of post-contrast enhancement study in the diagnosis of intracranial meningioma. CT was a highly-sensitive procedure to detect the presence of a juxtasellar meningioma but accurate differentiation from pituitary adenoma, craniopharyngioma or aneurysm was not always possible. Other studies have reported that meningiomas are eccentric and located laterally in the suprasellar cistern, appear as multilobulated, high-density enhancing masses, and contain thin, peripheral, low-density crescents [7]. In the present series, these characteristics were not helpful in accurate, pre-operative diagnosis of meningioma by CT. Meningiomas located in the cerebellopotine-angle may not always be differentiated from acoustic neurinomas as both may appear as round, densely-enhancing masses which cause displacement and distortion of the fourth ventricle and have surrounding low-density rim [S, 91. Meningioma may initially show evidence of calcification or thickening of the petrous bone which is not seen with neurinomas, and they may extend upward through the tentorial region. Based upon plain and post-contrast characteristics, gliomas and metastases involving the tentorial region were quite similar to meningiomas with the exception that only meningiomas caused thickening of the tentorium. This dural thickening was also seen in falx meningiomas. The CT pattern of the intraventricular meningioma was similar to that of other intraventricular tumors and identical to choroid plexus papillomas. The enhancement pattern seen in recurring meningiomas was identical to that seen on the initial CT scan except in one case which pathologically showed sarcomatous degeneration. In that case there was dense, irregular complex ring formation which was quite non-homogeneous. In all cases in which a recurrent meningioma was suspected, but there was no enhancement visualized by CT, there was neither isotope scan nor angiographic evidence of recurrence. REFERENCES 1. L. E. Claveria, D. Sutton and B. M. Tress, The radiological diagnosis of EM1 scanning, Br. J. Radial. 50, 15-22 (1977). 2. J. Ambrose, M. R. Gooding and A. E. Richardson, An assessment of the accuracy of computerized transverse axial scanning (EM1 scanner) in the diagnosis of intracranial tumor, Brain 98, 569582 (1975). meningiomas: a retrospective analysis of the diagnostic 3. L. H. Gold, S. A. Kieffer and H. 0. Peterson, Intracranial value of plain skull films, Neurology 19, 8733880 (1969). 4. M. Banna and A. Appleby, Some observations on the angiography of supratentorial meningiomas, C/in. Radio!. 20, 3755386 (1969). tumors, Semin. Roetg. 12, 97-110 (1977). 5. D. D. Davis, CT in the diagnosis of supratentorial the anatomic basis of the zone of diminished density surrounding 6. R. M. Sigel and A. V. Messina, Computed tomography: meningiomas, Am. J. RoentgenoL 127, 139-141 (1976). of sellar and parasellar masses by CT, Radiology 120, 9991 I1 (1976). 7. T. R. Naidich and R. S. Pinto, Evaluation and A. Passalaqua, 8 T. P. Naidich, J. P. Lin, N. E. Leeds, I. I. Kricheff, A. E. George, N. E. Chase, R. M. Pudlowski CT in the diagnosis of extra-axial posterior fossa masses, Radiology 120, 333~339 (1976). tomography of infratentorial tumors, Semin. RoentgenoL 12, 109-120 9. M. Gado. I. Huete and M. Mikhael, Computerized
(1977). About the Author-LEON ARNOLD WEISBERG received his B.A. from Yale University in 1963 and M.D. from Columbia Medical School in 1968. Dr. Weisberg completed his neurology residency at the Neurological Institute of the Columbia-Presbyterian Medical Center in 1972. He is at present an Associate Professor of Neurology at Tulane Medical Center and Charity Hospital of New Orleans. He is the senior author of the book Crrehral Computed Tomography: A Text-Atlas.
of Neurology (Received
and Psychiatry,
21 September
141.5 Tulane
1978: rrceitxd
for
Avenue. puhlictrtion
New Orleans,
LA 70112, U.S.A.
I I December 1978)
Abstract-The CT findings in 53 meningiomas are reported. Based upon the plain and post-contrast CT pattern and density characteristics, the diagnosis of meningioma was accurately predicted in 28 of 35 convexity, parasagittal, subfrontal. middle fossa and sphenoid wing lesions (80%). In 2 calcified nonenhancing meningioma, the diagnosis was suspected by CT findings. CT was extremely accurate in detecting 16 juxtasellar, intraventricular, tentorial and posterior fossa meningiomas, but the CT pattern was less specific such that differentiation from other neoplastic or vascular lesions was not always possible. There were only 2 false negative cases: these occurred when contrast infusion had not been performed. Meningioma
Homogeneous
enhancement
Calcification
INTRODUCTION
Computed tomography (CT) has become an important complimentary diagnostic modality to plain skull radiogram, isotope scan and angiography in evaluating patients with suspected intracranial meningioma. CT has been reported to have a high degree of sensitivity in their detection; and certain plain and post-contrast patterns and density characteristics are quite specific for establishing the diagnosis of meningioma [l, 21. The purpose of this report is to describe the CT features of intracranial meningioma and to discuss their differentiation from other neoplastic and non-neoplastic pathological conditions.
METHODS
AND
MATERIALS
Fifty patients with intracranial meningiomas as confirmed by pathological findings were evaluated with CT. In two patients, multiple meningiomas were present (two lesions in one patient and three in the other patient); therefore. the CT findings in a total of 53 meningiomas are described. In 5 patients, the meningioma represented a recurrent lesion. All patients were studied utilizing an EM1 Mark I head scanner with a 160 x 160 matrix system and a scan time of approximately 4 min. The complete examination consisted of 4 pairs of transverse tissue sections which were each 13 mm in thickness and extended from the base to the vertex region. The scan sequence was repeated following the intravenous infusion of 300 ml of meglucmine iothalamate (Conray-30) which was administered over a 5-min interval.
FINDINGS The localization of the 53 meningiomas visualized by CT is listed in Table 1. Isotope scan was positive in 24 out of 33 cases (73%). It was positive in 20 out of 24 (83%) supratentorial meningiomas, but was positive in only 4 out of 9 (44%) posterior fossa or parasellar lesions. In both cases of multiple meningiomas, isotope scan showed only single lesion. In 17 cases, isotope scan was not performed because of the previously-performed CT scan; findings were deemed conclusive enough to obviate the need for isotope scan. Plain skull radiogram was performed in 46 cases and showed hyperostosis, calcification or prominent vascular spaces in 15 cases (33%). In 8 cases (16x), there were abnormalities of the sella turcica consistent with chronic elevation of intracranial pressure. Angiography was performed in all 50 cases and was positive in 45 cases; it failed to demonstrate cerebellopontine (in 3 out of 4 cases) and parasellar meningiomas (in 2 out of 4 cases). In both cases of multiple meningioma, it was the CT findings which indicated
116
L. A. WEBBERG Table
1. Localization of 53 intracranial meningiomas visualized by CT Localization
No. of cases
Convexity Parasagittal Subfrontal Parasellar Sphenoid ridge Middle fossa Intraventricular Posterior fossa Tentorium Cerebellar Cerebellopontine-angle
15 12 2 5 6 2 1 4 2 4
the need to perform both carotid and vertebral angiogram. Air study was performed in only two cases of meningioma (intraventricular and parasellar) and this study demonstrated the lesion in both cases. In two cases, CT was reported to be negative. In one case of parasellar meningioma extending 1.5 cm in the suprasellar region, the lesion was demonstrated by isotope scan, air study and angiography. In the second case, a large falx meningioma was subsequently detected by repeat CT study. Post-contrast study was not performed in either case of these diagnostic failures. The smallest meningiomas detected by CT were 1.0 cm is size, and both lesions were clinically asymptomatic. In one case, this represented one of multiple lesions, but in the other it was a solitary meningioma. In four cases in which CT demonstrated the meningioma, the patient had no abnormal neurological findings. The CT appearance and density characteristics of meningioma on both plain and post-contrast scan is shown in Table 2. Eighteen appeared as speckled, homogeneous, sharply-marginated, ovoid or round, soft-tissue, high-density masses. The actual measured densities on the plain scan ranged from 22 to 32 EM1 units (Fig. 1). Surgical findings showed that psammoma bodies were very prominent in 12 of these meningiomas; and that they were also present but less prominent in the other six meningiomas which showed this non-calcified, high-density pattern on plain CT. In six cases, plain scan showed non-homogeneous, mixed-density pattern without evidence of calcification (Fig. 2) and three others were seen to have mixed density with evidence of calcification (Fig. 3). The appearance of the calcification in these 6 cases was dense globular, punctate or as peripheral circular rim. In three cases, plain scan showed only high-density mass which measured entirely in the range of calcification (45-50 EM1 units). A homogeneous ovoid or triangular low-density (6-12 EM1 units), sharply-marginated lesion was seen in 16 cases (Fig. 4) on the plain scan. No abnormal density was seen in seven cases (Fig. 5). In 3 of these cases, mass effect as demonstrated by ventricular distortion or displacement was definitely visualized; but in three others, no abnormality was visualized (Fig. le). In one of these seven cases, plain scan was initially interpreted as normal, but retrospective analysis showed low-density area (Fig. 6). Four cases showed evidence of bony thickening (Fig. 7). Table
2. CT density characteristics intracranial meningiomas
(i) Plain scan findings Low density Isodense High density (non-calcified) High density (calcified) Mixed density Without calcification With calcification (ii) Post-contrast findings No enhancement Enhancement pattern Dense consolidated Speckled homogeneous Peripheral enhancing ring
in 53
No. 16 1X 3 9 6
2 51 32 16
Fig. 1. Homogeneous speckled, high-density lesion (22-26 EMI units) is seen in left parieto-occipital region. (a). Following contrast infusion, there is dense, consolidated, sharply-marginated enhancement with bowing of falx posteriorly to the right side (b). In addition, there is another enhancing supratentorial smaller enhancing lesion seen anterior to this large mass and another right infratentorial enhancing lesion (c and d) is seen which was not identified on pre-contrast study (e). 117
L. A. WEISBERG
Fig. 2. Plain scan shows mixed-density pattern in right supratentorial compartment with marked mass effect with displacement and distortion of the lateral ventricle (a). Post-contrast study shows dense, consolidated, sharply-marginated enhancement in the right middle fossa (b).
Post-contrast study was performed in all 50 cases and evidence of enhancement was seen in 51 of the 53 meningiomas. Post-contrast enhancement appeared as a densely consolidated, homogeneous, high-density (32-36 EM1 units) pattern in 32 cases (Fig. 8), or as speckled, homogeneous increased densities (3Wl2 EM1 units) in 16 cases. In 15 cases, the enhanced mass appeared multilobulated. In only three cases was there the finding of ring enhancement to suggest the presence of a cystic component, but in none of these cases was a cyst identified at operation. In only one case was there evidence of non-homogeneous enhancement as seen in other malignant neoplasms (gliomas, metastases), and this represented a most unusual case of an intracerebral men-
Fig. 3. Plain scan shows marked mass effect in the right hemisphere with single calcified area located slightly medial to right sphenoid ridge (a). Following contrast infusion, there is dense consolidated homogeneous enhancement in right middle fossa extending into the suprasellar region consistent with meningioma (b).
CT in the diagnosis
Fig. 4. Plain scan shows
of intracranial
II9
meningioma
low-density. sharply-marginated lesion in right frontal enhancement on post-contrast study (b).
region
(a) with speckled
ingioma. In all cases, the area of the enhancement was sharply differentiated from the surrounding brain parenchyma and had either round, triangular, ovoid or lenticular shape. The only two meningiomas which did not enhance initially appeared as densely calcified, globular lesions on plain scan. Mass effect was seen in 35 of the 53 meningiomas. In 13 cases. there was a surrounding lowdensity circular or semilunar rim, whereas in 22 others, there was surrounding low-density frondlike projections which were believed to represent cerebral edema. In four cases, the falx adjacent to the meningioma appeared thickened (Fig. S), and in six others the neoplasm appeared attached to the dura (falx, tentorium). Hydrocephalus was seen in 28 cases. Post-contrast study enhancement was most reliable in defining evidence of recurrent meningioma in 5 cases (Fig. 9). In the evaluation of three suspected recurrent neoplasms, the finding of bony thickening or calcification without concommitant enhancement was not indicative of recurrence as documented by negative isotope scan and angiography.
L. A. WEISBERG
Fig. 5. A young woman had episodes of visual blurring and headache during pregnancy. Findings included bilateral papilledema only. Skull radiogram, electroencephalogram, isotope scan were normal; CSF was abnormal only for an elevated pressure with normal protein content. Initial CT scan without contrast infusion was normal (a) and the diagnosis of “pseudotumor cerebri” was made, but angiogram was not performed. Symptoms and papilledema resolved but recurred one year later. Repeat CT was performed; plain scan showed low-density area in right frontal region (b). Post-contrast study showed dense bifrontal, sharply-marginated, homogeneous enhancement with surrounding rim of low-density (c) consistent with meningioma, and this was surgically confirmed.
DISCUSSION In this series, CT was the most sensitive neuro-diagnostic procedure to detect meningioma. Isotope scan was positive in 73% of the cases but was less sensitive in detecting juxtasellar, tentorial and posterior fossa lesions (44%). Plain skull radiogram showed an abnormality in only 33%; this is lower than that previously reported and this was believed due to earlier diagnosis with CT [3]. Angiography was positive in 90% of meningioma but failed to detect juxtasellar and posterior fossa lesions in five cases [4]. The exquisite sensitivity of CT is demonstrated by the fact that this remarkable technique visualized an intracranial meningioma in 4 patients who had no abnormal neurological findings, negative skull radiogram and isotope scan. Based upon the
CT in the diagnosis
of intracranial
meningloma
Fig. 6. Plain scan shows vague semilunar low-density area in the right frontal parietal region (a). Following contrast infusion there is dense, consolidated, homogeneous lenticular-shaped enhancement (b). This appears contiguous with bone and bulges medially inward: these findings are consistent with parietal convexity meningioma.
of abnormal findings in these four cases, it is unlikely that angiography would have been paucity performed if the diagnosis had not been suggested by the CT findings. In addition, CT was calpable of sensitively detecting the presence of multiple meningiomas more reliably than isotope scan and angiography in two cases. The CT pattern and density characteristics of meningiomas usually reflected their patholc jgical features. On the plain scan, 33% were of homogeneous speckled, high-densities with regular contours (round, ovoid, wedge-shaped) and were sharply marginated from the surrounding parenct lyma. The actual densities were 22-32 EM1 units; this was less than the values seen in calcified le:;ions. Pathological findings confirmed the presence of prominent and widespread psammoma hod! I’formation in these neoplasms. It is postulated that the failure to measure attenuation coeffic:ients
Fig. 7. Plain
scan shows
thickening of the left petrous ridge with calcified angle consistent with petrous ridge meningioma.
mass
in the cerebellopontine
L. A. WEISBERG
Fig. 8. Plain scan shows low-density lesion in right frontal region without significant mass effect (a). Following contrast infusion there is dense right frontal homogeneous enhancement extending across the midline anteriorly. The falx appeared to be bowed. displaced to the left. and appears slightly thickened (b).
in the range of calcium in these cases represented the effect of partial volume tissue averaging with surrounding lower-density tissue in the 13-mm section. In 6 cases (1 lx), there was evidence of calcification within the meningioma. The actual densities ranged from 45-350 EMI units. This calcification was seen in several patterns, and it appeared as small punctate areas, circular rim, or as dense, globular, ovoid, sharply-marginated, calcified masses. Two meningiomas which were densely calcified on plain scan showed no evidence of contrast enhancement. Since angiographic analysis showed an abnormal vascularity in these men-
Fig. 9. Patient had cerebellar tumor removed 2 yr previously, and was then re-evaluated because of persistent neck pain. but the patient had no new neurological deficit, CT findings: plain scan showed calcified mass contiguous with bone with surrounding low-density region (a). Post-contrast scan shows dense, homogeneous, infratentorial enhancement. The fourth ventricle is not seen with lateral and third ventricle being dilated (b). Surgical findings confirmed the diagnosis of posterior fossa meningioma with no supratentorial extension.
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ingiomas, it is believed that the lack of visualized enhancement may be spurious in that the neoplasm was initially of such high-density, that actual contrast enhancement did not alter the observed attenuation values sufficiently to be observed [S]. Oligodendrogliomas and low-grade astrocytomas also showed dense globular calcification to simulate the appearance of meningioma, but the latter neoplasms usually had irregular edges. Intracerebral hematoma also show dense consolidated, highdensity mass but the location, irregular edges, actual density measurements, more prominent mass effect and accompanying edema usually permitted differentiation from meningioma; and the clinical presentation was also most dissimilar. The finding of a peripheral rim of calcification was also seen in aneurysm, angioma and neoplasms including craniopharyngioma; whereas punctate areas of calcification was seen in many varied neoplastic (including low-grade astrocytoma, ependymoma, medulloblastoma, pinealoma, pituitary adenoma) and certain non-neoplastic disorders. In those meningiomas with peripheral rim of calcification, dense enhancement of the peripheral rim and central region was always seen following contrast infusion. In 30% of meningiomas, plain scan showed homogeneous, non-speckled, sharply-marginated, ovoid or wedge-shaped, low-density lesion. In none of these meningiomas did pathological examination demonstrate prominent psammoma body formation, although the pathological findings were otherwise quite typical of meningioma. The homogeneous appearance was quite characteristic of meningiomas although this was seen in certain low-grade gliomas, angioma or infarction. When the meningioma appeared as a wedge-shaped, low-density lesion, this may suggest these alternative diagnoses; differentiation was then established by the post-contrast enhancement pattern. In three cases, the low-densities measure 338 EM1 units and were sharply-marginated and round in shape; this suggested cystic component but this finding was not confirmed by pathological findings. In 17% of cases, plain scan showed a mixed-density pattern; this lesion was visualized by CT to contain calcification in 33% of them. This pattern was also seen in astrocytomas and angiomas. In 13% of cases, plain scan showed no abnormal density pattern, and the diagnosis was established only on post-contrast study. In two meningiomas which appeared as isodense lesions, the failure to perform post-contrast study led to diagnostic failures of CT. The previously-described characteristic surrounding rim of low-density which is believed to represent widened subarachnoid space or edema [6] was seen in 24% of the cases. This wellcircumscribed, thin, low-density rim was more commonly seen in smaller meningiomas, whereas the larger meningiomas usually were associated with frond-like low-density regions which projected into surrounding parenchyma (41%). Since the circumscribed halo was also seen in acoustic neurinomas, pituitary adenomas, in craniopharyngiomas and in aneurysms, it was considered a non-specific finding. Bone change (hyperostosis) was specific for meningioma and was seen in 7% of cases. Following contrast infusion, enhancement was seen in 96% of cases. Meningiomas showed homogeneous pattern which was either speckled or consolidated in appearance. Ring enhancement was seen in only three cases; two were angioblastic meningioma and one was seen in an unusual intracerebral meningioma. In the latter case, the enhancement pattern was that of an irregular, complex ring which was more consistent with malignant infiltrative neoplasm than with meningioma. In those cases with ring or no evidence of enhancement, the specific diagnosis of meningioma was not possible by CT analysis alone. In the other cases, the homogeneous, speckled or dense, consolidated enhancement with sharply marginated borders was quite characteristic of meningioma. In 28 of 35 meningiomas (80%) which were located in the convexity, parasagittal, subfrontal, sphenoid ridge or middle fossa, plain and post-contrast CT scan findings were sufficiently characteristic to establish the diagnosis of meningioma, and this was confirmed by pathological findings. There were 3 cases of meningioma in which ring enhancement suggested an alternative diagnosis of glioma or metastases and diagnosis was not established by CT. In addition, there were 3 cases in which the CT pattern was believed to be characteristic of meningioma but this was not confirmed by operative findings: (i) one parasagittal glioma showed dense, homogeneous, sharply-marginated enhancement; (ii) two metastases appeared as dense, consolidated, sharply-marginated, round masses with surrounding low-density, frond-like projections. In another case, the diagnosis of angioma was made because the contiguous enhancing choroid plexus was incorrectly interpreted as a draining vein. Two false negative cases were reported. In one case, the diagnosis of juxtasellar
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meningioma was made by air study and angiography; whereas in the other the diagnosis was established by repeat CT. In both cases, contrast infusion study had not been performed: these false negative CT cases emphasize the importance of post-contrast enhancement study in the diagnosis of intracranial meningioma. CT was a highly-sensitive procedure to detect the presence of a juxtasellar meningioma but accurate differentiation from pituitary adenoma, craniopharyngioma or aneurysm was not always possible. Other studies have reported that meningiomas are eccentric and located laterally in the suprasellar cistern, appear as multilobulated, high-density enhancing masses, and contain thin, peripheral, low-density crescents [7]. In the present series, these characteristics were not helpful in accurate, pre-operative diagnosis of meningioma by CT. Meningiomas located in the cerebellopotine-angle may not always be differentiated from acoustic neurinomas as both may appear as round, densely-enhancing masses which cause displacement and distortion of the fourth ventricle and have surrounding low-density rim [S, 91. Meningioma may initially show evidence of calcification or thickening of the petrous bone which is not seen with neurinomas, and they may extend upward through the tentorial region. Based upon plain and post-contrast characteristics, gliomas and metastases involving the tentorial region were quite similar to meningiomas with the exception that only meningiomas caused thickening of the tentorium. This dural thickening was also seen in falx meningiomas. The CT pattern of the intraventricular meningioma was similar to that of other intraventricular tumors and identical to choroid plexus papillomas. The enhancement pattern seen in recurring meningiomas was identical to that seen on the initial CT scan except in one case which pathologically showed sarcomatous degeneration. In that case there was dense, irregular complex ring formation which was quite non-homogeneous. In all cases in which a recurrent meningioma was suspected, but there was no enhancement visualized by CT, there was neither isotope scan nor angiographic evidence of recurrence. REFERENCES 1. L. E. Claveria, D. Sutton and B. M. Tress, The radiological diagnosis of EM1 scanning, Br. J. Radial. 50, 15-22 (1977). 2. J. Ambrose, M. R. Gooding and A. E. Richardson, An assessment of the accuracy of computerized transverse axial scanning (EM1 scanner) in the diagnosis of intracranial tumor, Brain 98, 569582 (1975). meningiomas: a retrospective analysis of the diagnostic 3. L. H. Gold, S. A. Kieffer and H. 0. Peterson, Intracranial value of plain skull films, Neurology 19, 8733880 (1969). 4. M. Banna and A. Appleby, Some observations on the angiography of supratentorial meningiomas, C/in. Radio!. 20, 3755386 (1969). tumors, Semin. Roetg. 12, 97-110 (1977). 5. D. D. Davis, CT in the diagnosis of supratentorial the anatomic basis of the zone of diminished density surrounding 6. R. M. Sigel and A. V. Messina, Computed tomography: meningiomas, Am. J. RoentgenoL 127, 139-141 (1976). of sellar and parasellar masses by CT, Radiology 120, 9991 I1 (1976). 7. T. R. Naidich and R. S. Pinto, Evaluation and A. Passalaqua, 8 T. P. Naidich, J. P. Lin, N. E. Leeds, I. I. Kricheff, A. E. George, N. E. Chase, R. M. Pudlowski CT in the diagnosis of extra-axial posterior fossa masses, Radiology 120, 333~339 (1976). tomography of infratentorial tumors, Semin. RoentgenoL 12, 109-120 9. M. Gado. I. Huete and M. Mikhael, Computerized
(1977). About the Author-LEON ARNOLD WEISBERG received his B.A. from Yale University in 1963 and M.D. from Columbia Medical School in 1968. Dr. Weisberg completed his neurology residency at the Neurological Institute of the Columbia-Presbyterian Medical Center in 1972. He is at present an Associate Professor of Neurology at Tulane Medical Center and Charity Hospital of New Orleans. He is the senior author of the book Crrehral Computed Tomography: A Text-Atlas.
