cerebral computed tomography in the diagnosis of supratentorial astrocytoma

CEREBRAL COMPUTED TOMOGRAPHY IN THE DIAGNOSIS OF SUPRATENTORIAL ASTROCYTOMA

LEON ARNOLD WEISBERC; Department of Neurology and Psychiatry, Tulane Medical Center, 1415 Tulane Avenue.

New Orleans, LA 70112, and Department of Neurology. Charity Hospital of New Orleans

Abstract The CT features in 146 supratentorial astrocytomas are presented. Those features whtch permit differentiation from other pathological processes are reviewed and those CT tindings which are seen III different stages of malignancy are defined.

Supratentorial astrocytoma multiformae

Low-grade astrocytoma Anaplastic astrocytoma Glioblastoma

INTRODUCTION

Because of the exquisite sensitivity of computed tomography (CT) the diagnosis of intracranial neoplasms has been established at an earlier stage than was previously possible with conventional neurodiagnostic procedures. Frequently, when the tumor is detected it is small, causes little mass effect, and minimal infiltration into contiguous normal brain parenchyma; therefore, these patients are frequently less neurologically impaired. The changing spectrum of neurological diagnosis in the CI scan era is reflected in one study which demonstrated an incidence of 30”,, for low-grade astrocytomas compared with 57% in the pre-CT scan era [l].

The purpose of this present study is to analyze the CT findings in patients with histologically proven supratentorial astrocytoma. Special emphasis will be directed towards an analysis of two specific problems; 1, the identification of those CT patterns which are relatively specific for astrocytoma and permit differentiation from other neoplasms and non-neoplastic conditions and 2, those non-contrast and post-contrast CT characteristics which correlated with the histological grading of malignancy of the astrocytoma.

MATERIAL AND METHODS

One hundred and forty-six patients with supratentorial astrocytoma, which was subsequently proven by histological analysis (operative or necropsy findings), were evaluated by CT scan at Tulane Medical Center. In addition, the CT scans of 50 other patients were also retrospectively reviewed in whom astrocytoma had been the primary diagnosis. In these cases repeat CT scan, subsequent clinical course, angiographic or pathological findings were more consistent with an alternative diagnosis.

Almost all CT scans were performed with an EMI Mark I head scanner utilizing a 160 x 160 matrix system and 13 mm collimation. Four non-contrast scan sections, extending from the base of the skull to the vertex region, were initially performed. The entire scan sequence was repeated after the rapid (5 min) intravenous infusion of 300 ml of iothalamate meglumine (Conray-30).

The clinical symptomatology and neurological findings are listed in Table 1. In all cases, the neurological findings were confirmed by two physicians with training in neurodiagnosis. The results of other neurodiagnostic studies are outlined in Table 2. Supratentorial astrocytomas were histologically graded according to the classification established by Kernohan [2,3]: 1, low grade astrocytoma, which corresponds to Grade I; 2, anaplastic astrocytoma, including both Grade II and Grade III tumors and 3; glioblastoma multiformae, which corresponds to Grade IV astrocytomas.

The non-contrast CT scan was evaluated for the following parameters; (1) mass effect, (2) density patterns, (3) edema, (4) hydrocephalus, (5) cyst formation and (6) enhancement. The density characteristics were analyzed visually as either increased, decreased or isodense relative to surrounding structures. In select cases the actual attenuation coefficients of specific subregions of the neoplasm

87

LEON ARNOLD WEISHEKG

Table 1. Clinical symptomatology and findings in 146 patients with supratentorial astrocytoma

Symptoms

Headache Vomiting Seizure

generalized focal

Behavioral change Progressive deficit

motor sensory

Rapid deterioration

Low-grade Anaplastic Glioblastoma glioma glioma multiformae

(Grade I) (Grade 11 and III) (Grade IV) (12 cases) (60 cases) (74 cases)

4 21 39 0 5 26 6 23 42 4 IX 26 2 5 16 3 6 13 2 20 41 2 17 37 1 3 4 0 8 17

Neurological findings No abnormality Hemiparesis Hemisensory deficit Visual field deficit Papilledema Abducens nerve paresis Oculomotor paresis Altered sensorium Organic brain syndrome Memory impairment

6 13 16 4 40 50 1 24 37 1 I1 18 0 8 26 0 7 14 0 3 9 0 4 17 0 5 5 2 6 I2

Table 2. Results of neuro-diagnostic studies in 146 cases of supratentorial astrocytoma in which the diagnosis was established by computed tomography

Procedure Low-grade (Grade I)

Anaplastic (Grade II and III)

Glioblastoma (Grade IV)

EEG Normal Diffuse abnormal Focal-slow

Radionuclide scan Normal Abnormal Not performed

Skull radiogram Normal Abnormal Not performed

Echoencephalogram Normal Midline shift Not performed

CSF Examination Normal Abnormal Not performed

Angiogram Normal Abnormal

avascular mass stain pattern

Not performed

Air study Normal Abnormal Not performed

5 11 6 2 12 14 5 34 52

12 0

12 0

12 0

9 3

0 2

10

25 33 4 18

31 23

33 34 6 10

21 30

22 12 10 15 28 44

5 10 45

4 4 35 50 35 50

8 13 21 20

-

60

10 14 50

14

Cerebral computed tomography in the diagnosis of supratentorial astrocytoma 89

were determined. The post-contrast scan was evaluated for the presence of enhancement and the enhancement pattern was classified as to contour, thickness, and shape.

FINDINGS

Twelve patients had low-grade astrocytoma (Grade I). In 5 of these 12 cases, skull radiogram, electroencephalogram (EEG), isotope scan and CSF examination were all normal. Angiography showed no evidence of mass effect in 6 of 12 cases. Air study was performed in only 2 cases and the pneumographic detail did not supplement the CT findings. Five patients presented with only non- focal seizures or headache. Since the neurological examination and preliminary neurodiagnostic studies had been negative (skull radiogram, EEG and isotope scan), it is probable that air study and angiography would not have been performed if the CT scan had not visualized abnormal density patterns. In 6 of these 12 patients, neurological examination was entirely normal.

In 11 cases non-contrast CT showed a low-density, homogeneous lesion which had a speckled (salt and pepper) pattern; whereas in one case the low density lesion was heterogeneous with an interspersed high-density portion (Table 3). Based on the measured attention value, this subregion appeared to contain calcium; this was confirmed pathologically. In 5 of the 12 cases, the low-density lesion was sharply-marginated with a clear delineation from the surrounding brain parenchyma. The CT findings of a sharply-marginated round or ovoid homogeneous low-density lesion (5 cases) sug- gested a cystic component, but no macroscopic cyst was found in 3 cases (Fig. 1). In 7 cases the low- density lesion had irregular margination (Fig. 2) and none of these had a cystic component (Fig. 2).

Mass effect which was manifested by distortion, effacement or displacement of the ventricles and subarachnoid spaces was seen in 6 cases (50%). In the low-grade astrocytomas, this consisted of ventricular distortion without any evidence of displacement, although several of the lesions were quite large in their dimensions. Edema fluid was manifested by frond-like projections into the subcortical gray and white matter region and this was seen in only one case. In no case was hydrocephalus or evidence of transtentorial herniation visualized. Following contrast infusion abnormal enhancement was seen in 6 cases. This enhancement was diffuse, patchy and faint in appearance (Fig. 2).

Based on the plain and post-contrast CT features, the diagnosis of a low-grade astrocytoma was considered the most likely pathological process in these 12 cases. It was not possible to exclude an angioma without angiography and it was not always possible to exclude a solitary metastasis or a non-neoplastic cyst prior to surgery. However, the CT scan characteristics of a low-grade astrocytoma were quite different from those seen in cerebral infarction, multiple sclerosis, focal cerebritis and contusional injury. Accurate pre-operative diagnosis of a low-grade astrocytoma was possible in all cases when the CT scan findings were considered in conjunction with the clinical data and the angiographic findings.

Anaplastic astrocytomas (Grade II and III) showed a more variable CT pattern (Table 4). The non-contrast scan showed these neoplasms either as a low-density or a mixed-density lesion (Fig. 3). Of the mixed-density appearing anaplastic astrocytomas, the high-density component had attenuation coefficient values which were consistent with calcification in 7 cases (Fig. 4). The calcified areas appeared as punctate or linear high-density areas (Fig. 5); the dense, globular calcification observed in oligodendroglioma and meningioma was not seen in the anaplastic astrocytomas. In no case did the CT scan fail to identify macroscopic calcification which was identified by surgical or necropsy findings. In 22 other cases, the high-density component appeared to be non-calcified and heterogeneous in appearance; pathological analysis revealed neither hemorrhage or calcification (Fig. 3). The anaplastic astrocytomas which were of mixed-density had an irregular contour and poorly marginated borders.

In 31 cases the plain scan showed a low-density homogeneous lesion. In 16 of these cases ‘there was an ovoid or round sharply-marginated lesion: the presence of a cystic component was paqholo- gically confirmed in 11 of these cases. The density characteristics of these cystic lesions speared variable as either a homogeneous speckled (Fig. 6) or uniformly low-density pattern (Fig. 7). An analysis of the fluid content of these neoplastic cysts was not performed. Fifteen low-density lesions had an irregular contour and jagged-edged margination; none of these were cystic. In onIy one case of an anaplastic astrocytoma did the non-contrast scan show a questionable area of low-density

90 LEON ARNOLD WEISHERG

Fig. 1. Thirty-two-year-old man presented with a right focal motor seizure. Air study and angiogram were consistent with an intra-axial temporal lobe neoplasm. The patient was irradiated without prior surgical biopsy. Six months later the seizures increased in frequency. CT findings: Large, ovoid, homogeneous, low-density non-enhancing lesion in the left hemisphere with marked evidence of mass effect (top left). Surgical biopsy showed a low-grade astrocytoma (Grade I). Eight months later the patient became aphasic and developed a right hemiparesis. CT findings: Irregularly marginated, mixed-density lesion (top right) which shows a thick, irregularly shaped ring enhancing pattern (bottom). This was surgically confirmed to

be a ghoblastoma multiformae (Grade IV).

whereas post-contrast scan showed nodular enhancement. No interval treatment (surgery, irradia- tion or chemotherapy) was performed; repeat scan 6 months later showed that the lesion was now a more extensive oval shaped low-density lesion with larger nodular enhancement pattern (Fig. 8).

There was evidence of mass effect in 93% of the anaplastic astrocytomas. This included evidence of ipsilateral ventricular effacement and displacement to the contralateral side., In 6 cases the scan showed evidence of transtentorial herniation manifested by distortion of the shape of the suprasellar cistern or a low-density lesion in the occipital region due to posterior cerebral artery infarction.


Fig. 2. Twenty-one-year-old man had a generalized major motor seizure. Neurological examination, skull radiogram, EE-G and isotope scan were normal. CT findings: Plain scan shows an irregularly shaped, poorly marginated, homogeneous low-density lesion and no evidence of mass effect (left): post-contrast scan shows only faint, patchy enhancement (right). Surgical biopsy demonstrated a low-grade astrocytoma (Grade I).

Edema was present in 19 cases; these neoplasms showed more marked mass effect than those which showed no evidence of edema. No mass effect was seen in four anaplastic astrocytomas (Fig. 9).

Abnormal contrast enhancement was seen in 47 cases (78%). The enhancement was homogeneous (diffuse or nodular) in 19, and heterogeneous in 28 (Table 6). The finding of eccentric nodular enhancement within a sharply-marginated low-density lesion was quite characteristic of anaplastic astrocytoma, although this pattern was occasionally seen in metastasis, meningioma, and abscess. Peripheral ring enhancement was the next most frequent enhancement pattern detected in anaplastic astrocytomas (Fig. 10). The shape and thickness of the ring was quite variable. In 2 anaplastic astrocytomas, the ring was thin, faint in density and regular in shape; in these cases differentiation from a ring-enhancing hematoma or brain abscess was not possible based on a single scan without angiography or surgical biopsy. In 12 cases the enhancing ring appeared irregular in shape and thickness; it was always denser and thicker on its deeper subcortical surface than on its peripheral cortical portion (Fig. 10).

Table 3. CT findings in 12 cases of low-grade (Grade I) supratentorial astrocytoma

Characteristic

Density Decreased Mixed

Increased--calcified Isodense

Incidence (%)

l I (92%)

I@%) 0

Mass effect None visualized Ventricular distortion Ventricular effacement Ventricular displacemtnt

Cyst formation Edema Hydrocephalus Enhancement

6 (50%) 6 (50%) 0 0 2 (16%) I@%) 0 6 (50%)

Table 4. CT findings in 60 cases of anaplastic (Grades II and III) supratentorial astrocytoma

Characteristics Incidence (%)

Density Decreased 31 (527,) Mixed 29

Increased--calcified 7 (127”) Increased-non-calcified 22 (36Y;J

Isodense 0

Mass effect None visualized Ventricular distortion only Ventricular effacement Ventricular displacement

Cyst formation Edema Hydrocephalus Enhancement

4 (7”,,) 14 (23%) 26 (43%) 16 (27%) ll(18”;) 19 (32”“) 16 (27%) 47 (784<;)

92 LEON ARNOLD WEISBEKG

Fig. 3. Plain scan shows a faintly visible, high-density rii ng in the anterior portion of the corpus callosum with extensive surrounding irregularly shaped low-density ’ portion (left). Post-contrast scan shows an irregularly shaped ring enhancing pattern which appears thi, cker on the deep subcortical ventricular surface

(right). Surgical biopsy demonstrated an s maplastic astrocytoma (Grade III).

In all cases the diagnosis of an astrocytoma was in eluded in the initial differential diagnosis. In 33 of 60 cases it was possible to establish the diagnosis of an anaplastic astrocytoma based on the CT findings prior to angiography or surgical biopsy. In 52 of 60 cases, the interpreter made the diagnosis of an astrocytoma (not specifically of th e anaplastic type) based on the CT findings, although in 8 cases the diagnosis of metastasis, me ningioma, ring-enhancing hematoma or brain abscess was considered more probable prior to angic lgraphy or surgical biopsy.

Fig. 4. Plain scan shows a mixed-density irregularly sh; aped lesion with a calcified portion (4248 EM1 units) in the left temporal parietal region (left). Post-con trast scan shows enhancement which is nodular, heterogeneous, dense and poorly marginated (right). Biol rsy showed an anaplastic astrocytoma (Grade II).


Fig. 5. Sixteen-year-old girl had a generalized non-focal seizure. Neurological examination showed bilateral papilledema. EEG was diffusely slow and isotope scan was negative. CT findings: An irregularly-shaped. poorly-marginated mixed-density heterogeneous lesion seen in the bifrontal region with evidence of calcification (left). There is marked evidence of mass effect and the post-contrast scan shows a faint, irregular strand of enhancement (right). Surgical biopsy showed evidence of a calcified anaplastic astrocytoma

(Grade II).

The non-contrast findings in 74 patients with glioblastoma multiformae Grade IV reflected their polymorphic pathological characteristics (Table 5). A low-density homogeneous lesion with irregular margination was seen in 41 cases; whereas in 33 cases the neoplasm appeared as a mixed-density heterogeneous lesion (Fig. 11). Of the mixed-density lesions, attenuation coefficient measurements identified a hemorrhagic component (5 cases) or a calcified component (3 cases) and this was

Fig. 6. There is a speckled, low-density, round, sharply-marginated and non-enhancing lesion located in the left frontal region. There is slight mass effect with distortion of the anterior frontal lateral ventricle. Surgical

biopsy showed a cystic anaplastic astrocytoma (Grade II).

94 LEON ARNOLD WEISBERG

Fig. 7. Plain scan shows a sharply-margmated, ovoid, low-density lesion with marked mass effect in the left hemisphere (top left). There is slight enhancement in the medial portion of this lesion (top right). Following subtotal resection of a cystic anaplastic astrocytoma (Grade II) repeat CT scan showed residual low-density cyst which is much smaller than the previous scan with several areas of diffuse enhancement. This enhance-

ment may represent residual tumor or post-surgical non-neoplastic enhancement (bottom).

confirmed by pathological analysis. In no case was a macroscopic area of hemorrhage or calcification not visualized by the CT pattern. In one case the hemorrhagic component had a fluid level; this represented recent bleeding within the neoplasm.,All patients who showed hemorrhage within the neoplasm presented with rapid neurological deterioration. In 12 other patients with glioblastoma multiformae who presented with an apoplectic onset, CT showed a mixed-density non-calcified lesion which was not hemorrhagic. None of the glioblastoma multiformae appeared isodense on the non-contrast scan. In 44 neoplasms the low-density glioblastoma multiformae contained prominent

Cerebral computed tomography in the diagnosis of supratentorial astrocytoma 9s

Fig. 8. Twenty-two-year-old girl with Von Recklinghausen’s disease developed a right focal motor seizure. EEG, isotope scan and angiogram were negative. CT findings: Plain scan shows a vague low-density lesion in the left parietal region (top left) with homogeneous nodular enhancement (top right). The patient remained asymptomatic on anticonvulsant therapy and had repeat scan 7 months later. CT findings: Sharply-marginated low-density lesion is seen on the non-contrast scan (bottom left) with dense nodular enhancement (bottom right). This lesion was surgically confirmed to be an anaplastic astrocytoma

(Grade III).

irregular frond-like projections which represented edema. In 8 cases the low-density area was sharply-marginated and cyst formation was identified within the neoplasm. Mass effect was uniformly present and 14 showed evidence of descending transtentorial herniation. Hydrocephalus was present in 27 cases.

Post-contrast study showed evidence of abnormal enhancement in all cases (Table 6). This enhancement included the following patterns; (1) ring, (2) garland, (3) nodular, (4) diffuse and (5)

96 LEON ARNOLD WEISBERC;

Fig. 9. Plain scan shows a mixed-density, non-calcified lesion in the left temporal parietal region with no mass effect (left). Post-contrast scan shows an irregularly shaped thick enhancing rim with a central nodular densely enhancing region (right). This was surgically confirmed to be an anaplastic astrocytoma (Grade II).

Table 5. CT findings in 74 cases of glioblastoma multiformae (Grade IV)

Characteristic Incidence (%)

Density Decreased Mixed

Increased hemorrhage Increased calcified Increased non-calcified

Isodense

Mass effect 74 (100%) Ventricular distortion 12 (16%) Ventricular effacement 23 (32%) Ventricular displacement 39 (52%)

Cyst formation 8 (13%) Edema 44 (73%) Hydrocephalus 27 (45%) Enhancement 74 (100%)

28 (38%) 40 (62%)

5 (7%) 3 (4%)

38 (51%) 0

Table 6. Enhancement pattern in 146 astrocytomas following intravenous contrast material

Pattern

Low-grade Anaplastic Glioblastoma glioma glioma multiformae

(Grade I) (Grade II and III) (Grade IV)

Homogeneous Nodular Diffuse

0 16 7 6 3 3

Heterogeneous Multiple nodular Ring-shaped Garland-shaped Mixed

Total

- 7 5 14 28

1 13 6 18

6 47 74


Fig. 10. (A) Plain scan shows homogeneous ovoid low-density lesion with marked mass effect in the left hemisphere (top left). Following contrast infusion, there is an irregularly shaped enhancing ring which is thicker on its medial than on its lateral surface (top right). This was surgically confirmed to be an anaplastic astrocytoma. (B) Post-contrast scan shows a round, incompletely formed peripherally enhancing ring which is irregular in thickness such that the deeper ventricular surface is thicker than the more peripheral cortical

surface. This was surgically confirmed to be an anaplastic astrocytoma (Grade III) (bottom).

mixed. The finding of an irregularly-shaped enhancing ring of variable thickness was seen in 24 cases. This pattern was quite characteristic of glioblastoma multiformae (Fig. 12). An enhancing ring which had a regular (round or ovoid) shape but was of variable thickness was seen in 4 cases. This pattern was less specific as it was also seen in metastatic neoplasms. In no case did the glioblastoma multiformae show a regularly-shaped, thin-walled enhancing ring. Garland-shaped enhancement was seen in 13 cases and this pattern was highly specific for glioblastoma. Multiple contiguous


Fig. 11. Elderly man developed a rapidly progressive left hemiparesis and hemisensory deficit. EEG showed a right temporal delta slow wave pattern and isotope scan showed an abnormal uptake in the right temporal region. CT findings: Plain scan shows a mixed-density lesion in the right temporal region with marked mass effect (left). Following contrast infusion there is a dense irregularly-shaped enhancing lesion (right). This was surgically confirmed to be a glioblastoma multiformae (Grade IV) (Right is on the readers

left side).

nodular areas of enhancement were seen in 5 cases. Mixed (nodular and ring) enhancement was seen in 18 cases; this was pathognomonic of glioblastoma multiformae (Fig. 13). In 10 cases, diffuse or homogeneous nodular enhancement was demonstrated and this was more consistent with a low- grade or anaplastic astrocytoma.

In all 74 cases the CT scan pattern was consistent with the diagnosis of an astrocytoma. In 64 of 74 cases an astrocytoma was the primary diagnosis whereas in 10 cases the diagnosis of a metastasis, brain abscess, or meningioma was the primary diagnosis. In 55 cases, the diagnosis of glioblastoma was the primary diagnosis. In 5 cases the presence of multiple, nodular contiguous enhancing lesions made metastasis the primary diagnosis prior to pathological analysis. In 10 cases, glioblastoma

Table 7. Final diagnosis in 50 cases in which the diagnosis of supratentorial astrocytoma was initially considered

Condition Number of

cases

Neoplastic Solitary metastasis Reticulum cell sarcoma Meningioma

12 1 3

Non-neoplastic Ring enhancing hematoma Non-hemorrhagic infarction

without enhancement with enhancement

Arteriovenous malformation Aneurysm Contusional injury Demyelinated areas (multiple sclerosis) Abscess Subarachnoid cyst Cerebritis Gliosis

2

3 5 3 1 3 2 6 3 3 3


Fig. 12. Plain scan shows an irregularly-shaped low-density lesion (top) which shows dense, thick, irregularly-shaped ring enhancing pattern (bottom). This was histologically proved to be a glioblastoma

multiformae (Grade IV).

multiformae showed diffuse nodular enhancement, and the diagnosis of a low-grade or anaplastic astrocytoma was considered a more likely diagnosis.

For our retrospective analysis of 50 other cases in which the diagnosis of astrocytoma was initially considered the most likely diagnosis based on the CT findings, we have defined several diagnostic problems (Table 7). These diagnostic errors can be classified into two types; (1) lack of experience with certain atypical CT features of non-hemorrhagic cerebral infarction, ring-enhancing hematoma, traumatic hemorrhagic contusion, demyelinated areas (Fig. 14), abscess, focal cerebritis and (2) conditions which may have identical CT features to glioma including metastases, men-

100 LEON ARNOLU WEISBEKC;

Fig. 13. Plain scan shows a large mixed-density lesion. The low-density component has irregularly-shaped frond-like projections in the left frontal region and a non-calcified high-density ring component in the anterior portion of the corpus callosum (left). Following contrast infusion, there is dense irregularly-shaped enhancement which is thickest in the region of the corpus callosum and has a mixed ring and nodular

pattern (right). This was surgically confirmed to be a glioblastoma multiformae (Grade IV).

ingioma, reticulum cell sarcoma, angioma, non-neoplastic cyst, gliosis (Fig. 15), and in which accurate pathological diagnosis was dependent upon angiographic and surgical findings.

DISCUSSION

Supratentorial astrocytomas are diffuse, infiltrating, malignant neoplasms which have a predilec- tion for the temporal lobe but may be found in any region [4]. They have poorly-defined irregular borders, jagged edges with finger-like projections which may extend deeply into the thalamus, basal ganglion, corpus callosum, and to the ventricular surface. Cerebral hemispheric astrocytomas may be quite heterogeneous in their gross and microscopic appearances; their characteristics are dependent upon cellular morphology (degree of anaplasia), cellular density, neovascularity, calcification, presence of degenerative change (cyst, hemorrhage, necrosis).

The low-grade astrocytomas consists of astrocytes which show minimal cellular evidence of anaplasia and there is no abnormal vascularity or degenerative change. However, the astrocytoma may show marked variation in the degree of cellular density and calcification. In certain low-grade astrocytomas, the cellular density may be difficult to differentiate from that of normal tissue parenchyma or that of a region of gliosis; whereas other astrocytomas are highly cellular despite a low degree of cellular anaplasia. The malignant astrocytoma has a more polymorphic macroscopic pathological appearance with more cellular anaplasia. The most anaplastic form of astrocytoma is the glioblastoma multiformae; this has a variegated and polymorphic mascoscopic appearance due to prominent degenerative change and a markedly anaplastic cellular morphology.

Despite attempts at classification of the astrocytomas, serious problems have occurred because of the heterogeneous appearance of different portions of an individual neoplasm and the finding of increasing anaplasia with time. Because of these variables, a grading system which is based on a single biopsy specimen may fail to indicate the true heterogeneity and anaplasia of the neoplasm. In addition, serial biopsies obtained from the same portion of the astrocytoma may define different grades of anaplasia. Due to the limitations of pathological classification based on a single surgical biopsy specimen, it was hoped that CT would be an important diagnostic procedure to define spatially and temporally the pathological features of the supratentorial astrocytomas. This could be


Fig. 14. Thirty-five-year-old woman developed a left hemiparesis and diplopia on horizontal and vertical gaze. EEG and isotope scan were negative. CT findings: There is an irregularly-shaped poorly-marginated low lesion in the left parietal region without mass effect (top left). There is evidence of enhancement (top right). Angiography was negative. The patient then developed a right hemiparesis as the left hemiparesis resolved. Repeat CT scan showed no change (not shown). CSF examination showed a normal protein content with a markedly elevated gamma globulin; this was consistent with the diagnosis of multiple sclerosis. The patients’ neurological deficit cleared and the repeat CT scan showed only a vague periventricular low-density lesion without any evidence of enhancement in the left periventricular region (bottom).

achieved in a non-invasive manner which could be repeated serially without risk or discomfort to the patient.

The CT findings of the supratentorial astrocytomas has reflected their heterogeneous, malignant and infiltrative pathological features [S-S]. The astrocytomas were found to have an irregular shape with jagged borders; frequently they show frond-like projections extending into contiguous normal


Fig. 15. Forty-five-year-old hypertensive man presented WI a right temporal delta slow wave pattern; isotope scan a after the onset of neurological deficit. CT findings: no ev contrast scan (top left); post-contrast scan shows an enhar Six weeks later the patient was clinically improved but the temporal parietal region. CT findings: Non-contrast scan right parietal region (bottom left) and there is evidence right). Angiography showed an avascular mass in the parir

gliosis without any evidel

parenchyma. There was no evidence of bone involl vel nent and the shape (round or ovoid) and contour of these lesions was consistent with their intr ‘ac erebral location. In most cases, the astrocytomas extended deeply into the white matter and gr, ay matter masses; however, in 5% the astrocytoma was superficially located to simulate an extra. -a7 tial meningioma.

ith a rapid onset of left hemiparesis. EEG showed ‘as negative. CT scan was performed two weeks ,idc mce of abnormal density is seen on the non- nci. ng ring in the right parietal region (top right). isc ,tope scan showed positive uptake in the right St lows a high-density non-calcified lesion in the

of dense, round, nodular enhancement (bottom :tal region. Surgical specimen showed evidence of nce : of anaplasia.


The density pattern of plain and post-contrast scan correlated with the degree of anaplasia. The low-grade astrocytomas had a homogeneous low-density pattern and only one was calcified. The CT density characteristics did not correlate with the cellular density; the spectrum of 101~ attenua- tiOn COefficients of 3 neoplasms with high cellular density and 9 others with a low cellular density was quite similar. In 5 cases the low-density lesion was regular (round or ovoid) in shape but only 2 of these had macroscopic cyst formation. Only one low-grade astrocytoma (8%) showed evidence of calcification. This is a much lower incidence than was reported in pre-CT scan studies and may reflect earlier diagnosis prior to the development of calcification [9]. Mass effect and enhancement were seen in SO%, consistent with that reported in other series [S-S].

Anaplastic astrocytomas showed a more heterogeneous pattern as 48% were heterogeneous mixed-density lesions. The low-density region was either irregular in shape with frond-like projections or appeared as a sharply-marginated lesion which was regular in shape and contour. In 11 cases in which the CT findings were consistent with cyst formation, the presence of cyst was surgically confirmed. The incidence of calcification was highest in the anaplastic astrocytoma (12:‘/,). In one study, CT showed calcification in only two-thirds of those lesions in which calcification was determined by histological examination [lo]. The failure to detect calcification was postulated to be due to partial volume effect. This problem was not encountered in the present series. In the other 36x, the high-density areas were non-calcified. These high-density regions were highlighted by altering the window-width to increase contrast resolution. The high-density lesion always showed prominent enhancement on the post-contrast scan. When these non-calcified, enhancing high- density lesions were studied pathologically there was no evidence of hemorrhage and ‘this region did not show a relatively high-cellular density or more significant degree of anaplasia. Mass effect was seen in 93% and enhancement was seen in 78% of the anaplastic astrocytomas, consistent with the results of other studies [S-S].

The CT findings in the glioblastoma multiformae reflected the polymorphic pathological features: 62% were mixed-density lesions whereas 38% were low-density. Evaluation of the high-density component may be difficult as prior studies have indicated the problem of differentiating calcification from hemorrhage; small areas of calcification may have a density measurement which is more consistent with hemorrhage due to the partial series. Mass effect and enhancement was visualized in all cases and edema was present in 73%. The enhancement pattern defined the extent of the neoplasm and differentiated that portion of the mass due to tumor from that due to edema. Other studies have confirmed the high incidence of enhancement (9874) in glioblastoma [S]. The finding of an irregular shaped ring of variable thickness, garland-shaped enhancement or a mixed (nodular and ring) enhancement was highly characteristic of glioblastoma.

In certain cases it was possible to differentiate the CT features of supratentorial astrocytoma from other pathological conditions. Cerebral infarction usually appeared as a wedge-shaped, homogeneous (speckled), low-density lesion with sharply-marginated borders which was confined to a specific vascular territory. Enhancement was seen in the superficial gyral or deep gray matter region. This enhancement pattern characteristically developed between the end of the first and fourth week after which time it decreased in intensity. The presence of mass effect, irregular margination of the low-density region or ring enhancement were atypical CT features of infarction which caused diagnostic confusion with astrocytoma. Serial CT findings usually permitted by angiogram in all 8 cases. Spontaneous intra-cerebral hematoma appeared initially as an increased density lesion sur- rounded by a lucent rim of edema with marked mass effect and no enhancement. In 20:4, peripheral ring enhancement has been reported [12]. This is thin-walled, round and regular in shape. The shape and contour of the enhancement and lack of associated mass effect in the ring-enhancing hematoma are important differentiating features from an astrocytoma. The diagnosis was confirmed by angiography in both cases in this series.

Abnormal enhancement with evidence of abnormal vessels is the most characteristic CT feature of angiomas. If this finding is not present, the plain and post-contrast characteristics of an angioma may simulate those patterns of a low-grade or anaplastic astrocytoma. In these cases accurate pathological diagnosis must be established by angiographic findings. However, certain angioma may thrombose in which case angiography may show an avascular mass. In these cases non-contrast CT visualized a high-density (calcified or non-calcified) irregularly-shaped mass and post-contrast scan showed evidence of abnormal vessels even if these were not visualized by angiography [ 131. Precise


definition of these thrombosed angioma requires pathological confirmation and it is important that these be differentiated from astrocytoma as these may have represented “radiation cured gliomas” ill which no surgical biopsy had been initially performed. The CT features of aneurysms which simulate astrocytoma include calcification in the wall or mural nodule and the presence of ring enhancement. More characteristically aneurysms cause dense, intraluminal enhancement and the connection with the involved vessel may be seen utilizing thinner sections and high resolution CT but definite diagnosis still requires angiography.

The CT findings in cerebritis are that of an irregularly-shaped, low-density lesion with mass effect and diffuse enhancement. In cerebritis angiography usually shows as a diffuse avascular mass although it may also be negative. Accurate differentiation of cerebritis is usually established on a clinical basis or due to the response of antibiotics and corticosteroids. In three cases in this series, diflerentiation of cerebritis from astrocytoma based upon CT findings was established by serial scans and confirmed by angiography. Cerebritis may resolve completely or evolve to an encapsu- lated abscess. The abscess appears as a low or mixed-density lesion with peripheral ring enhancement. The ring is usually thinner on its ventricular surface than on its thicker peripheral surface. This is due to better vascularization of the gray matter region and accounts for the rupture of the abscess into the ventricles [14].

Gliotic reaction without evidence of anaplasia as may result following various pathological processes, i.e. infarction, intracerebral hematoma, was best visualized on post-contrast study. Plain scan shows either an isodense or high-density non-calcified lesion, whereas post-contrast scan showed ring or nodular enhancement. Angiography showed evidence of an avascular mass and differentiation from an astrocytoma was not possible without surgical biopsy. In multiple sclerosis, post- contrast scan showed multiple, round, homogeneous periventricular enhancing lesions. The plain scan usually shows periventricular, irregularly-shaped low-density lesions. In two cases of multiple sclerosis, a solitary, periventricular enhancing lesion was visualized by CT but the patients’ subsequent course and CSF examination were more consistent with the diagnosis of multiple sclerosis [15]. In these cases the CT findings corresponding to the de,myelinated lesions could not be reliably differentiated by single CT study, but resolution was seen on serial scan of multiple sclerosis cases. In contusional injury, plain scan showed a low-density lesion with frond-like projections due to edema, and this lesion usually had a hemorrhagic component, and theic was linear or gyral enhancement pattern. Serial CT scan showed evolution of this irregularly-shaped lesion with significant mass effect to a sharply-marginated low-density non-enhancing lesion.

Solitary metastasis has CT characteristics which may simulate all grades of astrocytoma. One of the characteristic patterns of metastasis is the finding of an extensive low-density lesion with a small peripheral homogeneous enhancing nodule, but differentiation of a solitary metastasis from an astrocytoma is frequently not possible without surgical biopsy. CT is of greatest value in defining multiple non-contiguous lesions which are not visualized by other neurodiagnostic techniques. Meningiomas usually show a hemogeneous, sharply-marginated enhancing lesion. Rarely, cystic meningiomas or sarcomatous degeneration in the meningioma may simulate the appearance of an astrocytoma [16]. Based upon the CT pattern, other gliomas (ependymoma, oligodendroglioma) cannot be differentiated from astrocytomas. Non-neoplastic cysts did not enhance, but in three cases differentiation from cystic astrocytoma was possible based on surgical findings.

The CT patterns in 146 astrocytomas are evaluated, and compared for the different stages of pathological classification.

REFERENCES

1. H. L. Baker, Computed tomography and neuroradiology: a fortunate union, Am. J. Roenfg. 127, 101-110 (1976). 2. J. W. Kernohan, R. F. Mabon and H. J. Svien, A simplified classification of the gliomas, Proc. staff Meet. Mayo Clin. 24,

71-75 (1949). 3. H. J. Svien, R. F. Mabon and J. W. Kernohan, Astrocytomas Proc. stqjf’Meet. Mayo C/in. 24, 54-64 (1949). 4. D. S. Russell and L. J. Rubenstein, Patholoyy of Tumors of the Nervous System. pp. 109-160. Arnold, London (1971). 5. M. S. Huckman, CT in relation to diagnosis of gliomas. Recent Results in Cancer Reseurch, J. HEKMATPANAH, Ed., pp.

79-87. Springer, New York (1974). 6. J. L. A. Thompson, CT and the diagnosis of glioma, Clin. Rudiol. 27, 431441 (1976). 7. S. Tchang, G. Scotti and K. Terbrugge, Computerized tomography as a possible aid to histological grading of supratento-

rial gliomas, J. Neurosurg. 46, 735739 (1977).


8. H. Steinhoff, W. Lanksch and E. Kozner, Computed Tomography in the diagnosis and differential diagnosis of glioblas tomas, Neuroradiology 14, 193-200 (1977).

9. C. Kalan and E. H. Burrows, Calcification in intracranial gliomata, Br. J. R&o/. 35, 589-596 (1962). IO. A. D. Gouliamos, J. P. Jimenez and J. A. Gorce, Computed tomography and skull radiography in the diagnosis of

calcified brain tumor, Am. J. Roentg. 130, 761-764 (1978). Il. G. J. Dohrmann, R. B. Geehr and F. Robinson. Small hemorrhages versus small calcifications in brain tumors: difficulty

in differentiation by computed tomography, Surg. Neural. 10, 309-312 (197X). I?. R. D. Zimmerman, N. E. Leeds and T. P. Naidich, Ring blush associated with intracerebral hematoma. Rtrdiolo~/~ 122.

707-712 (1977). 13. R. A. Kramer and S. D. Wing, CT of angiographically occult cerebral vascular malformations, R~t/io/ocl~ 123, 649 655

(1977). 14. P. F. New, K. R. Davis and H. T. Ballantine, Computed tomography in cerebral abscess, Radio/q! 121, 641-646 (1976). IS. J. Aita, D. R. Bennett and R. E. Anderson, Cranial CT in acute multiple sclerosis, Neuroloyy 28, 251-255 (1978). 16. J. Vassilouthis and J. Ambrose, Computerized tomography scanning appearances of intracranial meningiomas. J. ,~c,uro-

.\ur</. 50, 320.-327 (1979).

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 Associate Professor of Neurology at Tulane Medical Center and Charity Hospital of New Orleans. He is the senior author of the book Cerebrul Computed Tomography: a Teut-Atlas.

cerebral computed tomography in the diagnosis of supratentorial astrocytoma

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