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859
MR Imaging Features Medulloblastomas
of
.
..,
r
Steven P. Meyers1 Susan S. Kemp1 Robert W. Tarr
‘
.
‘t’
.
,i-”:
.
‘‘t’,
The preoperative MR studies of 25 patients with surgically proved medulloblastomas were retrospectively reviewed in order to characterize these neoplasms with regard to their MR signal intensity, size, location, and appearance after contrast enhancement. Gadopentetate dimeglumine-enhanced MR images were available in I 1 patients. On short TR/short TE images, medulloblastomas generally had low to intermediate signal, and were predominantly slightly hyperintense relative to muscle and hypointense relative to white matter. On long TR/long TE images, medulloblastomas generally had Intermediate to moderately high signal, predominantly hyperintense relative to muscle and white matter. Tumor signal relative to gray matter varied considerably on both short TR and long TR images. Signal heterogeneity on long TR/long TE images was observed In 91% of the lesions and resulted from intratumoral cystic zones, small blood vessels, and/or calcifications. In the patients who received gadopentetate dimeglumine, the fraction of tumor volume showing enhancement was found to be less than one third in two cases, between one third and two thirds in four cases, and greater than two thirds in five cases. The mean tumor size was 3.6 x 4.0 x 3.5 cm. The most frequent location of medulloblastoma was the mid and inferior vermis. We conclude that the unenhanced and enhanced MR characteristics of medulloblastomas are somewhat variable. Medulloblastomas should be included in the differential diagnosis when the MR findings described are present in the appropriate patient population.
AJR 158:859-865,
April
1992
Medulloblastomas are a group of primitive neuroectodermal tumors that occur in the posterior cranial fossa [1 -3]. These tumors account for 33% of posterior fossa neoplasms in children, and up to 25% of all intracranial neoplasms in infants and children [3, 4]. Medulloblastomas have relatively rapid growth rates and can invade
adjacent
neural
tissue
and metastasize
along
nostic imaging of these neoplasms is important tumor bulk and extension. Although the CT features of medulloblastomas MR features
are not. To our knowledge,
only a few cases Received September 18, 1991 ; accepted revision November 25, 1991.
after
Department of Radiology, University of PiUsSchool of Medicine, Pittsburgh NMR Institute, 3260 Fifth Ave., Pittsburgh, PA 15213. Address reprint requests to S. P. Meyers. 2 Department of Radiology, Case Western ReI
as part of a larger
CSF
pathways
for preoperative
are well characterized
the MR features
series
[i -3].
have
of intracranial
Diag-
assessment [5-8],
been
reported
neoplasms
of the in
[9]. We
retrospectively reviewed the preoperative MR studies of 25 patients with medulloblastomas in order to characterize these tumors with regard to size, position, and extension; signal intensity; and enhancement with gadopentetate dimeglumine.
burgh
serve University, 44106.
2074
Abington
Rd., Cleveland, OH
0361 -803X/92/1 584-0859 C American Roentgen Ray SOCiety
Materials
and
Methods
We reviewed the tumor registry files and surgical and pathologic reports from two university centers (1 985-1991) and found records of 35 patients who had initial surgical resection of medulloblastomas. For 25 of these patients, preoperative MR examinations were medical
available
for
retrospective
analysis.
This
group
had
1 5 males
and
1 0 females
1 -42
years
old
MEYERS
860
AJR:158,
April 1992
(mean, 10 years; median, 8 years). Fourteen patients were less than 10 years old, eight were 10-20 years old, and three were more than
view and relative to gray and white matter. The fraction of the tumor
20 years old. Twenty-one
as
(less than one third), intermediate (one third to two thirds), or large (more than two thirds). Tumor signal was categorized as homoge-
with desmoplasia. MR imaging was performed at 1 .5 T for 18 patients and at 1 .0 T for seven patients. Multisection spin-echo pulse sequences were used in all MR studies and included short TR/TE (450-800/i 5-20) for 25 patients and long TA/first-echo TE, second-echo TE (20003200/1 5-30,75-1 00) sequences for 23 patients. Short TA images were obtained in the axial plane for all patients and in the sagittal plane for most patients. Long TA images were acquired in the axial plane for 22 patients and in the coronal plane for one patient. MR
neous, slightly heterogeneous, or markedly heterogeneous for both enhanced images and unenhanced long TA/long TE images. The
classical
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ET AL.
imaging
tumors
medulloblastomas
was
performed
gadopentetate the patients;
and
the
immediately
dimeglumine short
were
TRITE
histologically
other
after
four
the
(0.1 mmol/kg
subclassified
as medulloblastomas
manual
IV injection
MA
images
tamed in sagittal and axial planes. Flow compensation five
enhanced
examinations.
For
the
other
tions, signal misregistration
within
ing direction
contrast-enhanced
resulting
from
six
the tumors
were
ob-
was used for
enhanced
examina-
along the phase-encodblood
in the
sigmoid
and transverse sinuses was not encountered and gradient-moment nulling techniques were not applied. MA images were 5 mm thick with interimage 256x 128to256
gaps of 1 mm. The acquisition x256.
matrix
ranged
from
For all images, the signal intensity of each tumor was assessed as hype., iso-, or hyperintense relative to muscle tissue in the field of
A
contrast
enhancement
was qualitatively
categorized
as small
size, center point, and extension of each tumor were determined. MA examinations were evaluated for the presence of associated hydrocephalus. Preoperative unenhanced CT scans were available for review in 18 of 25 cases. CT scans were obtained on thirdgeneration
scanners
and were
evaluated
for the presence
of intratu-
moral calcifications.
of
of body weight) for 1 1 of
(500-800/20-30)
showing
Results
Tumor
Size and Configuration
Medulloblastomas ranged in size from i .0 x 2.5 x 2.0 cm to 6.0 x 5.0 x 5.2 cm (mean, 3.6 x 4.0 x 3.5 cm) in craniocaudal, spectively.
transverse,
Tumor
and anteroposterior
margins
were
dimensions,
mostly
convex
and
re-
well
defined on unenhanced spin-echo images in 23 of 25 cases (Figs. 1-4). The two exceptions were lesions involving the vermis,
alteration
which were seen as poorly defined zones on the long TR images only (Fig. 5).
of signal
B
Fig.
1-5-year-old
girl with classical
medul-
loblastoma. A, Short
TR (650/20)
axial
MR image
shows
midline mass in vermis (arrows). Tumor margins are well defined. B, Enhanced short TR (650/20) axial MR image shows minimal tumor enhancement in a markedly heterogeneous pattern. C, Long TR/short TE (2500/15)
axial
MR Im-
age shows mass is predominantly isointense relative to gray matter. 0, Long TR/Iong TE (2500/90)axial MR image shows mass has slightly hyperintense signal relative to gray and white matter. Note mild signal heterogeneity within mass and crescent-shaped peripheral
C
D
zone
of high signal
(arrow).
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861
MR OF MEDULLOBLASTOMA
AJR:158, April 1992
Fig. 2.-25-year-old woman with classical medulloblastoma in right cerebellar hemisphere extending into vermis. Short TR (760/20) axIal MR image shows mass with relatively well-defined margins (whIte arrows) that dIsplaces fourth ventricle to left (black arrow). B, Enhanced short TR (760/20) axial MR image shows moderate contrast enhancement with tumor in markedly heterogeneous pattern. C, Long TR/long TE (2500/90) axial MR image shows mass Is predominantly isointense compared with gray matter. Note small foci of very high signal wIthin mass, surrounding high-signal white matter “edema” (solW arrows), and thin peripheral zone of high signal (open arrows) adjacent to tumor. A,
Fig. 3-8-year-old boy with classical medulloblastoma. A, Short TR (780/20)sagfttal MR image shows well-marginated mass involving mid and inferior portions of vermls (arrows). Mass Is hypointense relative to brain parenchyma and extends anteriorly, compressing fourth ventricle and resulting In a mild degree of hydrocephalus. Note mild caudal dIsplacement of cerebellar tonsils (arrowhead). B, Enhanced short TR (760/20) axIal MR Image shows marked tumor enhancement (arrows) In a mildly heterogeneous pattern.
Fig. 4.-1V2-year-old boy with classical meShort lB (500/20) sagfttal MR Image shows mass (arrows) involving superior portion of vermis. Mass extends anteriorly, cornpressing cerebral aqueduct and resulting In
dulloblastoma.
moderate hydrocephalus.
FIg. 5.-23-year-old dulloblastorna. Long
classical meaxIal MR Image shows paddy marginated mass (arrows) within vermis that was seen on long TR Images lB
man with (2500/75)
and not on short TR Images. hanced Images were available.
No contrast-en-
4
5
862
Tumor
MEYERS
Location
Twenty
patients
(ages 1 .5-23
years) had primary
tumors
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that were midline lesions involving the anterior portion of the vermis. Nineteen of these neoplasms were located in the mid
and inferior zones of the vermis (Fig. 3), and one was in the superior
zone
(Fig.
4). Eighteen
of these
tumors vermis were classical medulloblastomas and two moplastic medulloblastomas. Two other patients
within
the
were des(ages
17
and 42 years) had desmoplastic medulloblastomas located laterally within a cerebellar hemisphere (Fig. 6). The remaining three patients (ages 1 5, and 25 years) had classical medulloblastomas that involved both the vermis and hemisphere ,
(Fig. 2). Twenty-four cephalus. The one within
a cerebellar
of the 25 lesions had associated exception was a lesion located
hemisphere.
Hemiation
resulting from the medulloblastomas cases (Figs. 3 and 7).
of cerebellar was
observed
hydrolaterally
tonsils in 13
ET AL.
Characteristics
of Medulloblastomas
Short TA/short TE images.-On short TA/short TE images, medulloblastomas generally had low to intermediate signal intensity. In comparison with muscle, medulloblastomas were
April 1992
intensity. In comparison with muscle, medulloblastomas were predominantly slightly hyperintense in 20 cases (80%), isointense in two (8%), and mixed in three (1 2%). In relation to
gray matter, medulloblastomas were predominantly hypointense in 12 cases (48%), isointense in eight (32%), and mixed in five (20%). The tumors were hypointense relative to white matter in 24 cases (96%) and isointense in one (4%). None
of the medulloblastomas had foci of very high signal on the short TA images that would suggest the presence of methemoglobin.
One patient
signal comparable
had several
well-defined
to that of CSF involving
zones
of low
most of the tumor
(Fig. 8). Nine other patients had small foci of decreased signal within the tumors. Long TR/short TE images.-Medulloblastomas were predominantly hyperintense relative to muscle in 23 of 23 cases. In comparison with gray matter, these tumors were predominantly hyperintense in 1 1 cases (48%), isointense in eight
(35%), tense
Signal
AJR:158,
and mixed relative
in four (1 7%). The tumors
to white
matter
in 22 cases
were hyperin-
(96%)
and hypoin-
tense in one (4%). Long TA/long medulloblastomas
TE images.-On long TA/long TE images, generally had intermediate to moderately
high signal intensity. Medulloblastomas hyperintense compared with muscle
were predominantly in 23 of 23 cases. In
Fig. 6.-42-year-old man with desmoplastic medulloblastoma. A, Long TR/long TE (2500/90) coronal MR image shows primary tumor (straight arrow) In right cerebellar hemisphere. Mass Is predominanfly hyperintense relative to adjacent gray and white matter. Hyperintense signal (curved arrow) in white matter adjacent to lesion represents
“edema.” B, Enhanced
short
TR (800/20)
coronal
MR
Image shows metastatic
lesion (arrow) with no in left lateral ventricle. Pri-
definite enhancement mary tumor had only a few small foci of enhancement (not shown).
Fig. 7.-Il-year-old
girl with classical
medul-
loblastoma. A, Sagfttal short TA (600/20) MR image shows a mass (arrowhead) in mid and inferior vermis
that compresses fourth ventricle, resulting in moderate hydrocephalus. Mass causes caudal displacement of cerebellar tonsils (arrow). B, Enhanced short TR (600/20) sagittal MR image shows prominent enhancement (arrowhead) within tumor. Abnormal enhancement (arrows) in posterior aspect of brainstem represents tumor invasion.
AJR:158,
relation
to gray
matter,
these
tumors
were
OF
MEDULLOBLASTOMA
predominantly
nine
863
of the tumors.
Six tumors
contained
small irregular
zones
hyperintense in 1 3 cases (56%), isointense in two (9%), and mixed in eight (35%). In comparison with white matter, these
of decreased signal on long TA images that correlated with CT findings of clumplike calcifications (Fig. 1 0). Two other
tumors
patients
were predominantly
and mixed
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MA
April 1992
in three
hyperintense
in 20 cases (87%)
(13%). No difference in signal characterbetween desmoplastic and classical me-
istics was observed dulloblastomas on long TA/long TE images as well as on long TR/short TE and short TA/short TE images. Tumor signal on long TA/long TE images was homogeneous in two cases
markedly with
(9%), mildly
heterogeneous
a very high signal
heterogeneous
in 1 2 (52%),
in nine (39%). Small well-defined similar
to that of CSF were
present
had CT scans that showed several tiny intratumoral that were not apparent on the MR images. Of the seven patients for whom CT scans were not available for calcifications
comparison,
none had histologic
Findings
consistent
were evident
and foci
fined
to the
in
three
classical
nine tumors (Fig. 9). Another patient had a tumor consisting mostly of large cystic components. Small tubular structures with signal void representing blood vessels were detected in
evidence
of intratumoral
calcifications.
with
peritumoral
for both desmoplastic
white
matter
edema
medulloblastomas con(Fig. 6) and for one of
cerebellar hemispheres medulloblastomas involving both vermis and hemisphere (Fig. 2). Thin crescent-shaped zones with signal characteristics similar to CSF were present at the periphery of 1 1 tumors (Figs. 1 and 2).
Fig. 8.-i-year-old boy with classical medulloblastoma. A and B, Short TR (500/17) sagittal (A) and coronal (B) MR images show mass (arrows) involvlng vermls and a cerebellar hemisphere. Mass contains multiple areas with signal char-
acteristics
sImIlar to those of CSF. Mass comof fourth ventricle, resulting in moderate hydrocephalus. presses
outlet
A Fig. 9-7-year-old
girl with classical
medullo-
blastoma. Long TA/long TE (2600/80) axial MR image shows small foci of high signal (arrows) within tumor, representing sites of cystic or necrotic degeneration, and large cystic component (arrowhead) at periphery of tumor.
B
Fig. 10.-13-year-old boy with classical medulloblastoma. A and B, Long TR/long TE (2400/80) axial MR image (A) shows small areas of decreased signal (arrow) within tumor that are similar in location to sites of clumplike calcification (arrow) on unenhanced T scan (B).
864
MEYERS
Findings
on Contrast-Enhanced
MR Images
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fraction oftumor volume showing enhancement was less than one third in two cases (1 8%) (Fig. 1), between one third and two thirds in four (36%) (Fig. 2), and greater than two thirds in five (46%) (Figs. 3 and 7). The enhancement pattern was
markedly heterogeneous in nine cases (82%) (Figs. 1 and 2) and mildly heterogeneous in two (1 8%) (Fig. 3). Because of the heterogeneous enhancement pattern, tumor margins were often less well delineated on the enhanced scans than scans.
However,
abnormal enhancement at on unenhanced scans were and could have represented included the pons in one peduncle
in three
cases,
enhanced
scans
showed
sites where signal abnormalities not definite for tumor infiltration peritumoral edema. These sites case (Fig. 7), middle cerebellar
and foramina
of Luschka
and Ma-
gendie in one case. Only one patient had metastatic disease at presentation. A single unenhancing metastatic lesion was observed within a lateral ventricle of a 42-year-old patient who had a primary tumor with only a few small foci of enhancement (Fig. 6).
of two large series of medulloblastomas evaluated by CT in which unenhancing areas of low attenuation representing cystic or necrotic degeneration were present in 47% and 59% of the primary tumors [5, 8]. In our series, intratumoral cystic foci were small in almost all cases (Fig. 9). The one exception was a tumor consisting predominantly of cystic components (Fig. 8). Signal heterogeneity in other medulloblastomas correlated to histopathologic findings of small intratumoral
blood
necrotic
changes.
to occur
in 21 % of medulloblastomas
grees
Primitive neuroectodermal tumors are histologically similar malignant neoplasms that occur in both intracranial and peripheral regions of the nervous system [1 2, 10]. Medullo,
blastoma, which originates within the cerebellum, is the most common primitive neuroectodermal tumor of the CNS [3]. On gross pathologic examination, medulloblastomas appear as moderately well demarcated gray pink masses that may contam areas
of necrosis
or cystic
foci [1
type of medulloblastoma
,
3]. Histologically,
is composed
the
of sheets
of
small cells with scant cytoplasm and relatively large hyperchromatic round or angular nuclei [1 3J. Medulloblastomas containing bands of connective tissue interspersed among the small malignant cells have been classified as desmoplastic ,
medulloblastomas. Compared with classical mas, the desmoplastic type is less common, patients,
and is more
often
lateral
medulloblastotends to occur in position
[3, 8,
10]. Tumor location and the age and sex distribution of patients with medulloblastomas in our study were similar to those reported in larger series of these neoplasms evaluated by CT [5, 8]. On MR images
obtained
with
short
TA/short
TE, medullo-
blastomas generally had low to intermediate signal, and were predominantly hyperintense relative to muscle and hypointense relative to white matter. On long TA/short TE and long TA/long TE images, the tumors generally had intermediate to moderately high signal that was predominantly hyperintense
relative to muscle and white matter. Tumor signal relative to gray matter varied considerably on both short TA and long TA images.
Signal
heterogeneity
of medulloblastomas
on long
TA/long TE images was observed in 91 %, and in 48% of these cases was the result of cystic or necrotic foci that were also seen histopathologically. These observations are similar
clumplike
Clumplike
medulloblastomas
than half the tumors
Discussion
in older
vessels,
areas of calcification, and has been reported [5]. Findings of peritu-
calcification
moral white matter “edema” were present in three patients. Eleven patients had small crescent-shaped peripheral fluid collections adjacent to the tumors that may represent peripheral zones of necrosis, edema, or entrapped CSF. No difference in signal characteristics was observed between classical and desmoplastic medulloblastomas. All but two of the medulloblastomas were generally welldefined masses with convex margins. The two exceptions were identified as poorly defined zones of abnormal signal relative to brain parenchyma and muscle on long TA/long TE images. Neither of the patients with these lesions had contrast-enhanced MR imaging. The degree of gadopentetate dimeglumine enhancement within
classical
AJR:158, April 1992
to those
MR images were obtained before and after IV administration of gadopentetate dimeglumine in 1 1 of 25 patients. All of the medulloblastomas showed contrast enhancement. The
on the unenhanced
ET AL.
of enhancement.
varied
showed
considerably.
Slightly
more depattern
only small or intermediate
In addition,
the
enhancement
within tumors was heterogeneous in all 1 1 cases. All enhanced images in our series were acquired immediately after the manual IV injection of gadopentetate dimeglumine. Therefore, it is unknown what the effect of delaying the time between contrast administration and imaging might have on the degree and pattern of tumor enhancement. To our knowledge, the only previous report describing gadopentetate dimeglumine enhancement of medulloblastomas before surgery was a case series that included only two medulloblastomas, both of which showed intense enhancement [9]. The variable MA enhancement
findings
of medulloblastomas
in our study
are analogous to those seen with contrast-enhanced CT [5]. Enhanced MA images were useful in showing sites of tumor invasion of adjacent neural tissue. These sites of tumor invasion
demonstrated
on the MR examinations
were
con-
firmed at surgery. The occurrence of intracranial metastatic disease at presentation in our study is similar to that reported by Nelson et al. [5], who found
imaging
evidence
of metastatic
disease
in
5% of 233 patients with medulloblastomas evaluated by CT. Only one of 25 patients in our series had intracranial metastatic disease at the time of MR imaging. This patient had a primary desmoplastic medulloblastoma that showed only a few small foci of enhancement. The single metastatic lesion was located in a lateral ventricle and showed no evidence of contrast enhancement. This observation suggests that metastatic disease could be underestimated by reliance on only the enhancement features of these tumors. Similar limitations can also apply for recurrent medulloblastomas. Rollins et al. [1 1] reported that three of nine recurrent medulloblastomas showed no enhancement on either MR imaging or CT scans of the head after
the administration
of contrast
material.
MR OF MEDULLOBLASTOMA
AJR:158, April 1992
The differential trocytoma,
diagnosis
ependymoma,
of medulloblastoma metastases,
and
includes choroid
as-
plexus
Downloaded from www.ajronline.org by 179.109.201.123 on 11/03/15 from IP address 179.109.201.123. Copyright ARRS. For personal use only; all rights reserved
papilloma. The results of this study show that the unenhanced and enhanced MR characteristics of medulloblastomas are somewhat variable. Medulloblastomas should be included in
the differential diagnosis when the MR findings described are present. MR, with its high contrast resolution and multiplanar imaging capability, has an important role in defining tion, size, and intracranial extent of medulloblastomas. Effective
treatment
of medulloblastomas
requires
the locasurgical
resection of as much tumor as possible followed by high-dose radiotherapy (>5000 cGy) to the posterior fossa [3, 12]. Because medulloblastomas can invade the leptomeninges
and metastasize tive
radiotherapy spine has been
along CSF pathways, (3500-4000 cGy) reported to improve
additional
postopera-
to the whole
brain
and
survival rates [3, 12]. In our institutions, MR imaging of the spine is routinely performed for the evaluation of intradural metastatic disease after tumor resection. The value of gadopentetate dimeglumine for detecting intradural metastases in patients with medulloblastomas is unknown and awaits future study. ACKNOWLEDGMENT We thank Kathryn tion
of this
manuscript.
Frazier for technical
assistance
in the prepara-
865
REFERENCES 1 . Becker nervous
LE, Hinton D. Primitive neuroectodermal tumors of the central system. Hum Pathol 1983;14:538-550 2. Rorke LB. The cerebellar medulloblastoma and its relationship to primitive neuroectodermal tumors. J Neuropathol Exp Neurol 1983;42: 1-15 3. Russell DS, Rubenstein U. Medulloblastomas. In: Pathology of tumors of the nervous system, 5th ed. Baltimore: Williams & Wilkins, 1989:251 -279
4. Arseni C, Ciurea AV. Statistical survey of 276 cases of medulloblastoma (1935-1978). Acta Neurochir 1981;57: 159-166 5. Nelson M, Diebler C, Forbes WStC. Paediatric medulloblastoma: atypical CT features at presentation in the SlOP II trial. Neuroradiology 1991;33: 140-1 42 6. zimmerman RA, Bilaniuk LT, Pahlajani H. Spectrum of medulloblastomas demonstrated by computed tomography. Radiology 1978;126: 137-1 41 7. zee CS, Segall HO, Miller C, et at. Less common CT features of medulloblastoma. Radiology 1982;144:97-102 8. Sandhu A, Kendall B. Computed tomography in management of medulloblastomas. Neuroradiology 1987:29:444-452 9. Powers TA, Partain CL, Kessler AM, et al. Central nervous system lesions in pediatric patients: Gd-OTPA-enhanced MR imaging. Radiology
1988;i69:723-726 10. Gusnard
DA.
Cerebellar
1990;25:263-278 1 1 . Rollins N, Mendelsohn frequency of tumor 1990:11:583-587 1 2. Hughes EN, Shillito J, Medulloblastoma at the and 1984. The influence survival. Cancer 1988;61
neoplasms
in
children.
Semin
Roentgenol
0, Mulne A, et al. Recurrent medulloblastoma: enhancement Gd-OTPA MR imaging. A/NA Sallan SE, Loeffler JS, Cassady JR. Tarbell NJ. Joint Center for Radiation Therapy between 1968 of radiation dose on the pattems of failure and :1992-1998
859
MR Imaging Features Medulloblastomas
of
.
..,
r
Steven P. Meyers1 Susan S. Kemp1 Robert W. Tarr
‘
.
‘t’
.
,i-”:
.
‘‘t’,
The preoperative MR studies of 25 patients with surgically proved medulloblastomas were retrospectively reviewed in order to characterize these neoplasms with regard to their MR signal intensity, size, location, and appearance after contrast enhancement. Gadopentetate dimeglumine-enhanced MR images were available in I 1 patients. On short TR/short TE images, medulloblastomas generally had low to intermediate signal, and were predominantly slightly hyperintense relative to muscle and hypointense relative to white matter. On long TR/long TE images, medulloblastomas generally had Intermediate to moderately high signal, predominantly hyperintense relative to muscle and white matter. Tumor signal relative to gray matter varied considerably on both short TR and long TR images. Signal heterogeneity on long TR/long TE images was observed In 91% of the lesions and resulted from intratumoral cystic zones, small blood vessels, and/or calcifications. In the patients who received gadopentetate dimeglumine, the fraction of tumor volume showing enhancement was found to be less than one third in two cases, between one third and two thirds in four cases, and greater than two thirds in five cases. The mean tumor size was 3.6 x 4.0 x 3.5 cm. The most frequent location of medulloblastoma was the mid and inferior vermis. We conclude that the unenhanced and enhanced MR characteristics of medulloblastomas are somewhat variable. Medulloblastomas should be included in the differential diagnosis when the MR findings described are present in the appropriate patient population.
AJR 158:859-865,
April
1992
Medulloblastomas are a group of primitive neuroectodermal tumors that occur in the posterior cranial fossa [1 -3]. These tumors account for 33% of posterior fossa neoplasms in children, and up to 25% of all intracranial neoplasms in infants and children [3, 4]. Medulloblastomas have relatively rapid growth rates and can invade
adjacent
neural
tissue
and metastasize
along
nostic imaging of these neoplasms is important tumor bulk and extension. Although the CT features of medulloblastomas MR features
are not. To our knowledge,
only a few cases Received September 18, 1991 ; accepted revision November 25, 1991.
after
Department of Radiology, University of PiUsSchool of Medicine, Pittsburgh NMR Institute, 3260 Fifth Ave., Pittsburgh, PA 15213. Address reprint requests to S. P. Meyers. 2 Department of Radiology, Case Western ReI
as part of a larger
CSF
pathways
for preoperative
are well characterized
the MR features
series
[i -3].
have
of intracranial
Diag-
assessment [5-8],
been
reported
neoplasms
of the in
[9]. We
retrospectively reviewed the preoperative MR studies of 25 patients with medulloblastomas in order to characterize these tumors with regard to size, position, and extension; signal intensity; and enhancement with gadopentetate dimeglumine.
burgh
serve University, 44106.
2074
Abington
Rd., Cleveland, OH
0361 -803X/92/1 584-0859 C American Roentgen Ray SOCiety
Materials
and
Methods
We reviewed the tumor registry files and surgical and pathologic reports from two university centers (1 985-1991) and found records of 35 patients who had initial surgical resection of medulloblastomas. For 25 of these patients, preoperative MR examinations were medical
available
for
retrospective
analysis.
This
group
had
1 5 males
and
1 0 females
1 -42
years
old
MEYERS
860
AJR:158,
April 1992
(mean, 10 years; median, 8 years). Fourteen patients were less than 10 years old, eight were 10-20 years old, and three were more than
view and relative to gray and white matter. The fraction of the tumor
20 years old. Twenty-one
as
(less than one third), intermediate (one third to two thirds), or large (more than two thirds). Tumor signal was categorized as homoge-
with desmoplasia. MR imaging was performed at 1 .5 T for 18 patients and at 1 .0 T for seven patients. Multisection spin-echo pulse sequences were used in all MR studies and included short TR/TE (450-800/i 5-20) for 25 patients and long TA/first-echo TE, second-echo TE (20003200/1 5-30,75-1 00) sequences for 23 patients. Short TA images were obtained in the axial plane for all patients and in the sagittal plane for most patients. Long TA images were acquired in the axial plane for 22 patients and in the coronal plane for one patient. MR
neous, slightly heterogeneous, or markedly heterogeneous for both enhanced images and unenhanced long TA/long TE images. The
classical
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ET AL.
imaging
tumors
medulloblastomas
was
performed
gadopentetate the patients;
and
the
immediately
dimeglumine short
were
TRITE
histologically
other
after
four
the
(0.1 mmol/kg
subclassified
as medulloblastomas
manual
IV injection
MA
images
tamed in sagittal and axial planes. Flow compensation five
enhanced
examinations.
For
the
other
tions, signal misregistration
within
ing direction
contrast-enhanced
resulting
from
six
the tumors
were
ob-
was used for
enhanced
examina-
along the phase-encodblood
in the
sigmoid
and transverse sinuses was not encountered and gradient-moment nulling techniques were not applied. MA images were 5 mm thick with interimage 256x 128to256
gaps of 1 mm. The acquisition x256.
matrix
ranged
from
For all images, the signal intensity of each tumor was assessed as hype., iso-, or hyperintense relative to muscle tissue in the field of
A
contrast
enhancement
was qualitatively
categorized
as small
size, center point, and extension of each tumor were determined. MA examinations were evaluated for the presence of associated hydrocephalus. Preoperative unenhanced CT scans were available for review in 18 of 25 cases. CT scans were obtained on thirdgeneration
scanners
and were
evaluated
for the presence
of intratu-
moral calcifications.
of
of body weight) for 1 1 of
(500-800/20-30)
showing
Results
Tumor
Size and Configuration
Medulloblastomas ranged in size from i .0 x 2.5 x 2.0 cm to 6.0 x 5.0 x 5.2 cm (mean, 3.6 x 4.0 x 3.5 cm) in craniocaudal, spectively.
transverse,
Tumor
and anteroposterior
margins
were
dimensions,
mostly
convex
and
re-
well
defined on unenhanced spin-echo images in 23 of 25 cases (Figs. 1-4). The two exceptions were lesions involving the vermis,
alteration
which were seen as poorly defined zones on the long TR images only (Fig. 5).
of signal
B
Fig.
1-5-year-old
girl with classical
medul-
loblastoma. A, Short
TR (650/20)
axial
MR image
shows
midline mass in vermis (arrows). Tumor margins are well defined. B, Enhanced short TR (650/20) axial MR image shows minimal tumor enhancement in a markedly heterogeneous pattern. C, Long TR/short TE (2500/15)
axial
MR Im-
age shows mass is predominantly isointense relative to gray matter. 0, Long TR/Iong TE (2500/90)axial MR image shows mass has slightly hyperintense signal relative to gray and white matter. Note mild signal heterogeneity within mass and crescent-shaped peripheral
C
D
zone
of high signal
(arrow).
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861
MR OF MEDULLOBLASTOMA
AJR:158, April 1992
Fig. 2.-25-year-old woman with classical medulloblastoma in right cerebellar hemisphere extending into vermis. Short TR (760/20) axIal MR image shows mass with relatively well-defined margins (whIte arrows) that dIsplaces fourth ventricle to left (black arrow). B, Enhanced short TR (760/20) axial MR image shows moderate contrast enhancement with tumor in markedly heterogeneous pattern. C, Long TR/long TE (2500/90) axial MR image shows mass Is predominantly isointense compared with gray matter. Note small foci of very high signal wIthin mass, surrounding high-signal white matter “edema” (solW arrows), and thin peripheral zone of high signal (open arrows) adjacent to tumor. A,
Fig. 3-8-year-old boy with classical medulloblastoma. A, Short TR (780/20)sagfttal MR image shows well-marginated mass involving mid and inferior portions of vermls (arrows). Mass Is hypointense relative to brain parenchyma and extends anteriorly, compressing fourth ventricle and resulting In a mild degree of hydrocephalus. Note mild caudal dIsplacement of cerebellar tonsils (arrowhead). B, Enhanced short TR (760/20) axIal MR Image shows marked tumor enhancement (arrows) In a mildly heterogeneous pattern.
Fig. 4.-1V2-year-old boy with classical meShort lB (500/20) sagfttal MR Image shows mass (arrows) involving superior portion of vermis. Mass extends anteriorly, cornpressing cerebral aqueduct and resulting In
dulloblastoma.
moderate hydrocephalus.
FIg. 5.-23-year-old dulloblastorna. Long
classical meaxIal MR Image shows paddy marginated mass (arrows) within vermis that was seen on long TR Images lB
man with (2500/75)
and not on short TR Images. hanced Images were available.
No contrast-en-
4
5
862
Tumor
MEYERS
Location
Twenty
patients
(ages 1 .5-23
years) had primary
tumors
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that were midline lesions involving the anterior portion of the vermis. Nineteen of these neoplasms were located in the mid
and inferior zones of the vermis (Fig. 3), and one was in the superior
zone
(Fig.
4). Eighteen
of these
tumors vermis were classical medulloblastomas and two moplastic medulloblastomas. Two other patients
within
the
were des(ages
17
and 42 years) had desmoplastic medulloblastomas located laterally within a cerebellar hemisphere (Fig. 6). The remaining three patients (ages 1 5, and 25 years) had classical medulloblastomas that involved both the vermis and hemisphere ,
(Fig. 2). Twenty-four cephalus. The one within
a cerebellar
of the 25 lesions had associated exception was a lesion located
hemisphere.
Hemiation
resulting from the medulloblastomas cases (Figs. 3 and 7).
of cerebellar was
observed
hydrolaterally
tonsils in 13
ET AL.
Characteristics
of Medulloblastomas
Short TA/short TE images.-On short TA/short TE images, medulloblastomas generally had low to intermediate signal intensity. In comparison with muscle, medulloblastomas were
April 1992
intensity. In comparison with muscle, medulloblastomas were predominantly slightly hyperintense in 20 cases (80%), isointense in two (8%), and mixed in three (1 2%). In relation to
gray matter, medulloblastomas were predominantly hypointense in 12 cases (48%), isointense in eight (32%), and mixed in five (20%). The tumors were hypointense relative to white matter in 24 cases (96%) and isointense in one (4%). None
of the medulloblastomas had foci of very high signal on the short TA images that would suggest the presence of methemoglobin.
One patient
signal comparable
had several
well-defined
to that of CSF involving
zones
of low
most of the tumor
(Fig. 8). Nine other patients had small foci of decreased signal within the tumors. Long TR/short TE images.-Medulloblastomas were predominantly hyperintense relative to muscle in 23 of 23 cases. In comparison with gray matter, these tumors were predominantly hyperintense in 1 1 cases (48%), isointense in eight
(35%), tense
Signal
AJR:158,
and mixed relative
in four (1 7%). The tumors
to white
matter
in 22 cases
were hyperin-
(96%)
and hypoin-
tense in one (4%). Long TA/long medulloblastomas
TE images.-On long TA/long TE images, generally had intermediate to moderately
high signal intensity. Medulloblastomas hyperintense compared with muscle
were predominantly in 23 of 23 cases. In
Fig. 6.-42-year-old man with desmoplastic medulloblastoma. A, Long TR/long TE (2500/90) coronal MR image shows primary tumor (straight arrow) In right cerebellar hemisphere. Mass Is predominanfly hyperintense relative to adjacent gray and white matter. Hyperintense signal (curved arrow) in white matter adjacent to lesion represents
“edema.” B, Enhanced
short
TR (800/20)
coronal
MR
Image shows metastatic
lesion (arrow) with no in left lateral ventricle. Pri-
definite enhancement mary tumor had only a few small foci of enhancement (not shown).
Fig. 7.-Il-year-old
girl with classical
medul-
loblastoma. A, Sagfttal short TA (600/20) MR image shows a mass (arrowhead) in mid and inferior vermis
that compresses fourth ventricle, resulting in moderate hydrocephalus. Mass causes caudal displacement of cerebellar tonsils (arrow). B, Enhanced short TR (600/20) sagittal MR image shows prominent enhancement (arrowhead) within tumor. Abnormal enhancement (arrows) in posterior aspect of brainstem represents tumor invasion.
AJR:158,
relation
to gray
matter,
these
tumors
were
OF
MEDULLOBLASTOMA
predominantly
nine
863
of the tumors.
Six tumors
contained
small irregular
zones
hyperintense in 1 3 cases (56%), isointense in two (9%), and mixed in eight (35%). In comparison with white matter, these
of decreased signal on long TA images that correlated with CT findings of clumplike calcifications (Fig. 1 0). Two other
tumors
patients
were predominantly
and mixed
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MA
April 1992
in three
hyperintense
in 20 cases (87%)
(13%). No difference in signal characterbetween desmoplastic and classical me-
istics was observed dulloblastomas on long TA/long TE images as well as on long TR/short TE and short TA/short TE images. Tumor signal on long TA/long TE images was homogeneous in two cases
markedly with
(9%), mildly
heterogeneous
a very high signal
heterogeneous
in 1 2 (52%),
in nine (39%). Small well-defined similar
to that of CSF were
present
had CT scans that showed several tiny intratumoral that were not apparent on the MR images. Of the seven patients for whom CT scans were not available for calcifications
comparison,
none had histologic
Findings
consistent
were evident
and foci
fined
to the
in
three
classical
nine tumors (Fig. 9). Another patient had a tumor consisting mostly of large cystic components. Small tubular structures with signal void representing blood vessels were detected in
evidence
of intratumoral
calcifications.
with
peritumoral
for both desmoplastic
white
matter
edema
medulloblastomas con(Fig. 6) and for one of
cerebellar hemispheres medulloblastomas involving both vermis and hemisphere (Fig. 2). Thin crescent-shaped zones with signal characteristics similar to CSF were present at the periphery of 1 1 tumors (Figs. 1 and 2).
Fig. 8.-i-year-old boy with classical medulloblastoma. A and B, Short TR (500/17) sagittal (A) and coronal (B) MR images show mass (arrows) involvlng vermls and a cerebellar hemisphere. Mass contains multiple areas with signal char-
acteristics
sImIlar to those of CSF. Mass comof fourth ventricle, resulting in moderate hydrocephalus. presses
outlet
A Fig. 9-7-year-old
girl with classical
medullo-
blastoma. Long TA/long TE (2600/80) axial MR image shows small foci of high signal (arrows) within tumor, representing sites of cystic or necrotic degeneration, and large cystic component (arrowhead) at periphery of tumor.
B
Fig. 10.-13-year-old boy with classical medulloblastoma. A and B, Long TR/long TE (2400/80) axial MR image (A) shows small areas of decreased signal (arrow) within tumor that are similar in location to sites of clumplike calcification (arrow) on unenhanced T scan (B).
864
MEYERS
Findings
on Contrast-Enhanced
MR Images
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fraction oftumor volume showing enhancement was less than one third in two cases (1 8%) (Fig. 1), between one third and two thirds in four (36%) (Fig. 2), and greater than two thirds in five (46%) (Figs. 3 and 7). The enhancement pattern was
markedly heterogeneous in nine cases (82%) (Figs. 1 and 2) and mildly heterogeneous in two (1 8%) (Fig. 3). Because of the heterogeneous enhancement pattern, tumor margins were often less well delineated on the enhanced scans than scans.
However,
abnormal enhancement at on unenhanced scans were and could have represented included the pons in one peduncle
in three
cases,
enhanced
scans
showed
sites where signal abnormalities not definite for tumor infiltration peritumoral edema. These sites case (Fig. 7), middle cerebellar
and foramina
of Luschka
and Ma-
gendie in one case. Only one patient had metastatic disease at presentation. A single unenhancing metastatic lesion was observed within a lateral ventricle of a 42-year-old patient who had a primary tumor with only a few small foci of enhancement (Fig. 6).
of two large series of medulloblastomas evaluated by CT in which unenhancing areas of low attenuation representing cystic or necrotic degeneration were present in 47% and 59% of the primary tumors [5, 8]. In our series, intratumoral cystic foci were small in almost all cases (Fig. 9). The one exception was a tumor consisting predominantly of cystic components (Fig. 8). Signal heterogeneity in other medulloblastomas correlated to histopathologic findings of small intratumoral
blood
necrotic
changes.
to occur
in 21 % of medulloblastomas
grees
Primitive neuroectodermal tumors are histologically similar malignant neoplasms that occur in both intracranial and peripheral regions of the nervous system [1 2, 10]. Medullo,
blastoma, which originates within the cerebellum, is the most common primitive neuroectodermal tumor of the CNS [3]. On gross pathologic examination, medulloblastomas appear as moderately well demarcated gray pink masses that may contam areas
of necrosis
or cystic
foci [1
type of medulloblastoma
,
3]. Histologically,
is composed
the
of sheets
of
small cells with scant cytoplasm and relatively large hyperchromatic round or angular nuclei [1 3J. Medulloblastomas containing bands of connective tissue interspersed among the small malignant cells have been classified as desmoplastic ,
medulloblastomas. Compared with classical mas, the desmoplastic type is less common, patients,
and is more
often
lateral
medulloblastotends to occur in position
[3, 8,
10]. Tumor location and the age and sex distribution of patients with medulloblastomas in our study were similar to those reported in larger series of these neoplasms evaluated by CT [5, 8]. On MR images
obtained
with
short
TA/short
TE, medullo-
blastomas generally had low to intermediate signal, and were predominantly hyperintense relative to muscle and hypointense relative to white matter. On long TA/short TE and long TA/long TE images, the tumors generally had intermediate to moderately high signal that was predominantly hyperintense
relative to muscle and white matter. Tumor signal relative to gray matter varied considerably on both short TA and long TA images.
Signal
heterogeneity
of medulloblastomas
on long
TA/long TE images was observed in 91 %, and in 48% of these cases was the result of cystic or necrotic foci that were also seen histopathologically. These observations are similar
clumplike
Clumplike
medulloblastomas
than half the tumors
Discussion
in older
vessels,
areas of calcification, and has been reported [5]. Findings of peritu-
calcification
moral white matter “edema” were present in three patients. Eleven patients had small crescent-shaped peripheral fluid collections adjacent to the tumors that may represent peripheral zones of necrosis, edema, or entrapped CSF. No difference in signal characteristics was observed between classical and desmoplastic medulloblastomas. All but two of the medulloblastomas were generally welldefined masses with convex margins. The two exceptions were identified as poorly defined zones of abnormal signal relative to brain parenchyma and muscle on long TA/long TE images. Neither of the patients with these lesions had contrast-enhanced MR imaging. The degree of gadopentetate dimeglumine enhancement within
classical
AJR:158, April 1992
to those
MR images were obtained before and after IV administration of gadopentetate dimeglumine in 1 1 of 25 patients. All of the medulloblastomas showed contrast enhancement. The
on the unenhanced
ET AL.
of enhancement.
varied
showed
considerably.
Slightly
more depattern
only small or intermediate
In addition,
the
enhancement
within tumors was heterogeneous in all 1 1 cases. All enhanced images in our series were acquired immediately after the manual IV injection of gadopentetate dimeglumine. Therefore, it is unknown what the effect of delaying the time between contrast administration and imaging might have on the degree and pattern of tumor enhancement. To our knowledge, the only previous report describing gadopentetate dimeglumine enhancement of medulloblastomas before surgery was a case series that included only two medulloblastomas, both of which showed intense enhancement [9]. The variable MA enhancement
findings
of medulloblastomas
in our study
are analogous to those seen with contrast-enhanced CT [5]. Enhanced MA images were useful in showing sites of tumor invasion of adjacent neural tissue. These sites of tumor invasion
demonstrated
on the MR examinations
were
con-
firmed at surgery. The occurrence of intracranial metastatic disease at presentation in our study is similar to that reported by Nelson et al. [5], who found
imaging
evidence
of metastatic
disease
in
5% of 233 patients with medulloblastomas evaluated by CT. Only one of 25 patients in our series had intracranial metastatic disease at the time of MR imaging. This patient had a primary desmoplastic medulloblastoma that showed only a few small foci of enhancement. The single metastatic lesion was located in a lateral ventricle and showed no evidence of contrast enhancement. This observation suggests that metastatic disease could be underestimated by reliance on only the enhancement features of these tumors. Similar limitations can also apply for recurrent medulloblastomas. Rollins et al. [1 1] reported that three of nine recurrent medulloblastomas showed no enhancement on either MR imaging or CT scans of the head after
the administration
of contrast
material.
MR OF MEDULLOBLASTOMA
AJR:158, April 1992
The differential trocytoma,
diagnosis
ependymoma,
of medulloblastoma metastases,
and
includes choroid
as-
plexus
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papilloma. The results of this study show that the unenhanced and enhanced MR characteristics of medulloblastomas are somewhat variable. Medulloblastomas should be included in
the differential diagnosis when the MR findings described are present. MR, with its high contrast resolution and multiplanar imaging capability, has an important role in defining tion, size, and intracranial extent of medulloblastomas. Effective
treatment
of medulloblastomas
requires
the locasurgical
resection of as much tumor as possible followed by high-dose radiotherapy (>5000 cGy) to the posterior fossa [3, 12]. Because medulloblastomas can invade the leptomeninges
and metastasize tive
radiotherapy spine has been
along CSF pathways, (3500-4000 cGy) reported to improve
additional
postopera-
to the whole
brain
and
survival rates [3, 12]. In our institutions, MR imaging of the spine is routinely performed for the evaluation of intradural metastatic disease after tumor resection. The value of gadopentetate dimeglumine for detecting intradural metastases in patients with medulloblastomas is unknown and awaits future study. ACKNOWLEDGMENT We thank Kathryn tion
of this
manuscript.
Frazier for technical
assistance
in the prepara-
865
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DA.
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