Neuroradiologv
Neuroradiology 17, 21-23 (1978)
© by Springer-Verlag1978
The Differential Diagnosis of Pontine Angle Meningioma and Acoustic Neuroma with Computed Tomography A. M611er, A. Hatam and H. Olivecrona Department of Neuroradiology,KarolinskaSjukhuset,Stockholm,Sweden
Summary. Seven pontine angle rneningiomas were examined with computed tomography (CT). The result was compared with that of a study of 61 acoustic neuromas. These two tumor types differ in manner of growth, volume, shape, attenuation, attachment to bone, cisternal deformation, frequency of calcification, peripheral edema, and bone changes. Key words: Computed tomography - Pontine angle meningioma - Acoustic neuroma -- Differential diagnosis.
An analysis of the CT appearance of pontine angle meningioma compared with that of acoustic neuroma has not yet been treated in the literature on CT, although cases of pontine angle meningiomas have appeared in works on pontine angle tumors [1, 2, 4, 7]. Pontine angle meningiomas are rare compared to acoustic neuromas, consequently the meningioma material is small. It nevertheless contains sufficient information to allow at least some generalized conclusions as to the differential diagnosis between these two tumor forms.
Material and Methods Seven patients, all females, aged between 39 and 64 years, with pontine angle meningioma have been examined with CT and the results will be compared with those of an analysis of 61 acoustic neuromas [3, 6]. All seven tumors were classified as meningiomas at operation, and six had histological verification, whereas in one case microscopic diagnosis was uncertain. At operation also this latter tumor was classified
as meningioma by an experienced neurosurgeon, the tumor was inoperable and the small specimen taken was inadequate for histological diagnosis. This patient had no hearing loss or trigeminal affection. Carotid and vertebral angiography did not demonstrate contrast staining in this case but there was local deformation of vessels in the pontine angle. All the patients had pathological carotid and vertebral angiograms as well as negative skull examinations as to widening of the internal acoustic meatus. The point of origin was the petrosal bone in five of the patients, medial to the porus in three cases, at the porus in one case, and lateral to it at the junction between the transverse and sigmoid sinuses in the fifth case. The rim of the middle part of the tentorial notch was the origin of one tumor which previously had been partially removed. This tumor had an infratentorial extension at the level of the pontine angle as well as a supratentorial portion. The point of origin was not possible to estimate at operation in one incompletely removed tumor growing anteriorly in the pontine angle. Hearing defects occurred in three of the patients. Intravenous injection of contrast medium was made in six patients. A bolus of i ml of Isopaque cerebral (280 mg I/ml) was injected per kg body weight. The CT technic used in the present investigation, as well as the planning and the technic for analyzing the data obtained were the same as for the material of acoustic neuromas [6].
Results The attenuation was higher (Fig. 1 a) than that of normal brain in six tumors and was markedly increased in four of these because of calcification. The calcification occupied the whole tumor in three 0028-3940/78/0017/0021/$01.00
22
A. M611er et al.: The Differential Diagnosis of Pontine Angle Meningioma and Acoustic Neuroma Table 1. Comparison of different CT findings with acoustic neuroma and pontine angle meningioma
Fig. l a and b. Pontine angle meningioma a with moderately increased attenuation, and b with marked contrast enhancement. The tumor reaches anteriorly to level of dorsum. Broad attachment to petrous bone
Fig. 2. Calcified pontine angle meningioma Fig. 3a-c. Pontine angle meningioma, a Center of tumor located anterior to porus. The tumor reaches anteriorly to clivus, h The tumor is also invading the supraseilar cistern and e causes lateral displacement of posterior part of third ventricle
of these four cases, resulting in an almost bony appearance (Fig. 2) of the tumor. The calcification was located at the periphery and shell-shaped in one of the tumors. One isoattenuating tumor contained a cyst; the remaining six were solid. Contrast enhancement (Fig. 1 b) occurred in six tumors, though it was
Tumor changes
Acoustic neuroma
Meningioma
Increased attenuation Volume > 35 cm 3 Volume < 13 cm 3 Marked calcification Oval shape Round shape Apparently broad attachment to bone Tumor reaches dorsum sellae anteriorly Center of tumor anterior to porus Tumor reaches > 2 cm above dorsum Peripheral edema Widening of porus or other bone changes
11% 4% 76% 0% 8% 92%
6/7 4/7 0/7 4/7 5/7 2/7
28%
5/6 (83%)
0%
5/7 (71%)
0%
3/7 (43%)
3% 44%
5/7 (71%) 0/6
77%
0/7
(86%) (57%) (57%) (71%) (28%)
less marked in the three extensively calcified cases. Contrast medium was not administered in one case. The volume of each of the seven tumors was 13, 19, 19, 35, 39, 48, and 70 cm 3, respectively. The center of the tumor was located anterior to the level of the internal auditory meatus in three cases (Fig. 3 a), considerably posterior to that level in two cases, and at the same level as that of the porus in two cases (Fig. 1 b). The three tumors which had their centers anterior to the porus and one of the tumors at the porus were oval (Fig. 3), the remaining tumors were round. Five tumors had a broad attachment to the petrous bone (Fig. 1). Six tumors extended in a direction perpendicular to the supraorbitomeatal plane 1-5 cm above the level of the dorsum sellae. Anteriorly, five of the tumors reached the upper part of the clivus and the dorsum sellae (Fig. 3 a). Three of these invaded the suprasellar cistern ipsilaterally (Fig. 3b). The posterior part of the third ventricle was displaced laterally in one of these cases (Fig. 3 c). Two tumors reached the middle fossa over the petrous bone and one of these displaced the temporal horn. None of the tumors was surrounded by edema. Bone changes were not observed in any case. The fourth ventricle was displaced contralaterally in six cases, and in one case this was not possible to evaluate. Except for one patient with a shunt the remaining six patients had a moderate degree of hydrocephalus. The cisternal changes varied. The pontocerebellar cistern was either compressed or obliterated (Fig. 1 and 3) by the tumor in five instances. This cistern was deformed and widened in an uncharac-
A. M6Uer et al.: The Differential Diagnosis of Pontine Angle Meningioma and Acoustic Neuroma
teristic way in one case. The pontocerebeUar cistern could not be evaluated in another case. The supratentorial part of the ambient cistern was partly or completely compressed in four cases. It was widened ipsilaterally in two cases, in one of these part of the tumor had grown into the cistern.
Differential Diagnosis The results of the present investigation will be compared with those obtained from the material of acoustic neuromas [6]. Acoustic neuromas have a well-defined point of origin and 'therefore produce rather uniform changes. In contrast to this, pontine angle meningiomas have various points of origin and hence produce a greater variety of changes. The various findings and their frequency with these two tumor groups are shown in Table 1. Unlike acoustic neuromas, pontine angle meningiomas are often calcified; this may give them a markedly increased attenuation (Fig. 2). The attenuation of non-calcified pontine angle meningiomas may be slightly increased (Fig. 1 a), a finding met with in about 10% of acoustic neuromas. Both tumor types may be large but acoustic neuromas rarely exceed 35cm 3. Pontine angle meningiomas are probably seldom less than 13 cm 3, whereas this is a common occurrence with acoustic neuromas. The center of the tumor of acoustic neuromas is rarely located anterior to the level of the porus and the tumor rarely reaches anteriorly as far as to the level of the dorsum. This may occur with pontine angle meningiomas (Figs. 1 and 3 a). Acoustic neuromas expand mainly in a posterior and medial direction. They may, however, reach rather high up in the middle part of the tentorial notch although they rarely reach the extreme heights of pontine angle meningiomas, which may grow up so high supratentorially as to cause lateral displacement of the temporal horn and the third ventricle (Fig. 3 c). This rarely happens with acoustic tumors [6]. Pontine angle meningiomas may have a broad attachment to the bone [5] (Fig. 1), but acoustic neuromas may also not infrequently be located so close to the petrous bone as to appear broadly attached to it. Pontine angle meningiomas may often be oval [5] (Figs. 1 and 3), which is a shape that does not frequently occur with acoustic tumors. Brain edema around the tumor seems to occur more frequently with acoustic neuromas than with pontine angle
23
meningiomas. Porus changes are probably rare with pontine angle meningiomas, whereas this is a frequent CT finding with acoustic neuromas [3]. We did not observe any meningioma causing bone changes on CT. Meningiomas in the pontine angle may protrude into the suprasellar cistern (Fig. 3 b), whereas this is rarely seen with acoustic tumors. Acoustic neuromas produce more uniform cisternal changes [5, 6], which pontine angle meningiomas do not because of the more individual manner of growth.
Conclusion Several different indirect and direct tumor changes occurring with pontine angle meningiomas do not at all or rarely occur with acoustic neuromas and vice versa. This makes the differential diagnosis between pontine angle meningioma and acoustic neuroma possible in many instances with CT.
References 1. Davis, K.R., Parker, S.W., New, P.F.J., Robersen, G.H., Taveras, J.M., Ojemann, R.J., Weiss, A.D.: Computed tomography of acoustic neuroma. Radiology 124, 81-86 (1977) 2. Gyldensted, C., Lester, J., Thomsen, J.: Computer tomography in the diagnosis of cerebellopontine angle tumours. Neuroradiology 11, 191-197 (1976) 3. Hatam, A., M611er, A., Olivecrona, H.: Computed tomography in evaluation of the internal auditory meatus with acoustic neuromas. To be published 4. King, T.T., Ambrose, J. A. E.: C.A.T. scanning in tumours of the cerebellopontine angle. In: The First European Seminar on Computerised Axial Tomography in Clinical Practice (eds. G.H. du Boulay and I.F. Moseley), pp. 134-138. Berlin, Heidelberg, New York: Springer 1977 5. Liliequist, B.: Pontine angle tumor-encephalographic appearanees. Acta Radiol. [Suppl.] (Stockh.) 186, (1959) 6. M611er, A., Hatam, A., Olivecrona, H.: Diagnosis of acoustic neuromas with computed tomography. Neuroradiology 17, 25-30 (1979) 7. Naidich, T.P., Lin, J. P., Leeds, N. E., Kricheff, I. I., George, A.E., Chase, N.E., Pudlowski, R.M., Passalaqua, A.: Computed tomography in the diagnosis of extra-axial posterior fossa masses. Radiology 120, 333-339 (1976) Received: July 26, 1978
Dr. Anders M611er Department of Neuroradiology Karolinska Sjukhuset S-10401 Stockholm Sweden
Neuroradiology 17, 21-23 (1978)
© by Springer-Verlag1978
The Differential Diagnosis of Pontine Angle Meningioma and Acoustic Neuroma with Computed Tomography A. M611er, A. Hatam and H. Olivecrona Department of Neuroradiology,KarolinskaSjukhuset,Stockholm,Sweden
Summary. Seven pontine angle rneningiomas were examined with computed tomography (CT). The result was compared with that of a study of 61 acoustic neuromas. These two tumor types differ in manner of growth, volume, shape, attenuation, attachment to bone, cisternal deformation, frequency of calcification, peripheral edema, and bone changes. Key words: Computed tomography - Pontine angle meningioma - Acoustic neuroma -- Differential diagnosis.
An analysis of the CT appearance of pontine angle meningioma compared with that of acoustic neuroma has not yet been treated in the literature on CT, although cases of pontine angle meningiomas have appeared in works on pontine angle tumors [1, 2, 4, 7]. Pontine angle meningiomas are rare compared to acoustic neuromas, consequently the meningioma material is small. It nevertheless contains sufficient information to allow at least some generalized conclusions as to the differential diagnosis between these two tumor forms.
Material and Methods Seven patients, all females, aged between 39 and 64 years, with pontine angle meningioma have been examined with CT and the results will be compared with those of an analysis of 61 acoustic neuromas [3, 6]. All seven tumors were classified as meningiomas at operation, and six had histological verification, whereas in one case microscopic diagnosis was uncertain. At operation also this latter tumor was classified
as meningioma by an experienced neurosurgeon, the tumor was inoperable and the small specimen taken was inadequate for histological diagnosis. This patient had no hearing loss or trigeminal affection. Carotid and vertebral angiography did not demonstrate contrast staining in this case but there was local deformation of vessels in the pontine angle. All the patients had pathological carotid and vertebral angiograms as well as negative skull examinations as to widening of the internal acoustic meatus. The point of origin was the petrosal bone in five of the patients, medial to the porus in three cases, at the porus in one case, and lateral to it at the junction between the transverse and sigmoid sinuses in the fifth case. The rim of the middle part of the tentorial notch was the origin of one tumor which previously had been partially removed. This tumor had an infratentorial extension at the level of the pontine angle as well as a supratentorial portion. The point of origin was not possible to estimate at operation in one incompletely removed tumor growing anteriorly in the pontine angle. Hearing defects occurred in three of the patients. Intravenous injection of contrast medium was made in six patients. A bolus of i ml of Isopaque cerebral (280 mg I/ml) was injected per kg body weight. The CT technic used in the present investigation, as well as the planning and the technic for analyzing the data obtained were the same as for the material of acoustic neuromas [6].
Results The attenuation was higher (Fig. 1 a) than that of normal brain in six tumors and was markedly increased in four of these because of calcification. The calcification occupied the whole tumor in three 0028-3940/78/0017/0021/$01.00
22
A. M611er et al.: The Differential Diagnosis of Pontine Angle Meningioma and Acoustic Neuroma Table 1. Comparison of different CT findings with acoustic neuroma and pontine angle meningioma
Fig. l a and b. Pontine angle meningioma a with moderately increased attenuation, and b with marked contrast enhancement. The tumor reaches anteriorly to level of dorsum. Broad attachment to petrous bone
Fig. 2. Calcified pontine angle meningioma Fig. 3a-c. Pontine angle meningioma, a Center of tumor located anterior to porus. The tumor reaches anteriorly to clivus, h The tumor is also invading the supraseilar cistern and e causes lateral displacement of posterior part of third ventricle
of these four cases, resulting in an almost bony appearance (Fig. 2) of the tumor. The calcification was located at the periphery and shell-shaped in one of the tumors. One isoattenuating tumor contained a cyst; the remaining six were solid. Contrast enhancement (Fig. 1 b) occurred in six tumors, though it was
Tumor changes
Acoustic neuroma
Meningioma
Increased attenuation Volume > 35 cm 3 Volume < 13 cm 3 Marked calcification Oval shape Round shape Apparently broad attachment to bone Tumor reaches dorsum sellae anteriorly Center of tumor anterior to porus Tumor reaches > 2 cm above dorsum Peripheral edema Widening of porus or other bone changes
11% 4% 76% 0% 8% 92%
6/7 4/7 0/7 4/7 5/7 2/7
28%
5/6 (83%)
0%
5/7 (71%)
0%
3/7 (43%)
3% 44%
5/7 (71%) 0/6
77%
0/7
(86%) (57%) (57%) (71%) (28%)
less marked in the three extensively calcified cases. Contrast medium was not administered in one case. The volume of each of the seven tumors was 13, 19, 19, 35, 39, 48, and 70 cm 3, respectively. The center of the tumor was located anterior to the level of the internal auditory meatus in three cases (Fig. 3 a), considerably posterior to that level in two cases, and at the same level as that of the porus in two cases (Fig. 1 b). The three tumors which had their centers anterior to the porus and one of the tumors at the porus were oval (Fig. 3), the remaining tumors were round. Five tumors had a broad attachment to the petrous bone (Fig. 1). Six tumors extended in a direction perpendicular to the supraorbitomeatal plane 1-5 cm above the level of the dorsum sellae. Anteriorly, five of the tumors reached the upper part of the clivus and the dorsum sellae (Fig. 3 a). Three of these invaded the suprasellar cistern ipsilaterally (Fig. 3b). The posterior part of the third ventricle was displaced laterally in one of these cases (Fig. 3 c). Two tumors reached the middle fossa over the petrous bone and one of these displaced the temporal horn. None of the tumors was surrounded by edema. Bone changes were not observed in any case. The fourth ventricle was displaced contralaterally in six cases, and in one case this was not possible to evaluate. Except for one patient with a shunt the remaining six patients had a moderate degree of hydrocephalus. The cisternal changes varied. The pontocerebellar cistern was either compressed or obliterated (Fig. 1 and 3) by the tumor in five instances. This cistern was deformed and widened in an uncharac-
A. M6Uer et al.: The Differential Diagnosis of Pontine Angle Meningioma and Acoustic Neuroma
teristic way in one case. The pontocerebeUar cistern could not be evaluated in another case. The supratentorial part of the ambient cistern was partly or completely compressed in four cases. It was widened ipsilaterally in two cases, in one of these part of the tumor had grown into the cistern.
Differential Diagnosis The results of the present investigation will be compared with those obtained from the material of acoustic neuromas [6]. Acoustic neuromas have a well-defined point of origin and 'therefore produce rather uniform changes. In contrast to this, pontine angle meningiomas have various points of origin and hence produce a greater variety of changes. The various findings and their frequency with these two tumor groups are shown in Table 1. Unlike acoustic neuromas, pontine angle meningiomas are often calcified; this may give them a markedly increased attenuation (Fig. 2). The attenuation of non-calcified pontine angle meningiomas may be slightly increased (Fig. 1 a), a finding met with in about 10% of acoustic neuromas. Both tumor types may be large but acoustic neuromas rarely exceed 35cm 3. Pontine angle meningiomas are probably seldom less than 13 cm 3, whereas this is a common occurrence with acoustic neuromas. The center of the tumor of acoustic neuromas is rarely located anterior to the level of the porus and the tumor rarely reaches anteriorly as far as to the level of the dorsum. This may occur with pontine angle meningiomas (Figs. 1 and 3 a). Acoustic neuromas expand mainly in a posterior and medial direction. They may, however, reach rather high up in the middle part of the tentorial notch although they rarely reach the extreme heights of pontine angle meningiomas, which may grow up so high supratentorially as to cause lateral displacement of the temporal horn and the third ventricle (Fig. 3 c). This rarely happens with acoustic tumors [6]. Pontine angle meningiomas may have a broad attachment to the bone [5] (Fig. 1), but acoustic neuromas may also not infrequently be located so close to the petrous bone as to appear broadly attached to it. Pontine angle meningiomas may often be oval [5] (Figs. 1 and 3), which is a shape that does not frequently occur with acoustic tumors. Brain edema around the tumor seems to occur more frequently with acoustic neuromas than with pontine angle
23
meningiomas. Porus changes are probably rare with pontine angle meningiomas, whereas this is a frequent CT finding with acoustic neuromas [3]. We did not observe any meningioma causing bone changes on CT. Meningiomas in the pontine angle may protrude into the suprasellar cistern (Fig. 3 b), whereas this is rarely seen with acoustic tumors. Acoustic neuromas produce more uniform cisternal changes [5, 6], which pontine angle meningiomas do not because of the more individual manner of growth.
Conclusion Several different indirect and direct tumor changes occurring with pontine angle meningiomas do not at all or rarely occur with acoustic neuromas and vice versa. This makes the differential diagnosis between pontine angle meningioma and acoustic neuroma possible in many instances with CT.
References 1. Davis, K.R., Parker, S.W., New, P.F.J., Robersen, G.H., Taveras, J.M., Ojemann, R.J., Weiss, A.D.: Computed tomography of acoustic neuroma. Radiology 124, 81-86 (1977) 2. Gyldensted, C., Lester, J., Thomsen, J.: Computer tomography in the diagnosis of cerebellopontine angle tumours. Neuroradiology 11, 191-197 (1976) 3. Hatam, A., M611er, A., Olivecrona, H.: Computed tomography in evaluation of the internal auditory meatus with acoustic neuromas. To be published 4. King, T.T., Ambrose, J. A. E.: C.A.T. scanning in tumours of the cerebellopontine angle. In: The First European Seminar on Computerised Axial Tomography in Clinical Practice (eds. G.H. du Boulay and I.F. Moseley), pp. 134-138. Berlin, Heidelberg, New York: Springer 1977 5. Liliequist, B.: Pontine angle tumor-encephalographic appearanees. Acta Radiol. [Suppl.] (Stockh.) 186, (1959) 6. M611er, A., Hatam, A., Olivecrona, H.: Diagnosis of acoustic neuromas with computed tomography. Neuroradiology 17, 25-30 (1979) 7. Naidich, T.P., Lin, J. P., Leeds, N. E., Kricheff, I. I., George, A.E., Chase, N.E., Pudlowski, R.M., Passalaqua, A.: Computed tomography in the diagnosis of extra-axial posterior fossa masses. Radiology 120, 333-339 (1976) Received: July 26, 1978
Dr. Anders M611er Department of Neuroradiology Karolinska Sjukhuset S-10401 Stockholm Sweden
