AJR 2001; 177:1475-1478
© American Roentgen Ray Society
MR Appearance of Lipomatous Ependymoma in a 5-Year-Old Boy
Wesley En-Tse Chang1,2 and
Laura S. Finn3
1
Department of Radiology, University of Washington, P. O. Box 357115, Seattle,
WA 98195.
2
Present address: Consultants in Radiology, P. A., 1101 Sixth Ave., Fort Worth,
TX 76104.
3
Department of Pathology, Children's Hospital and Regional Medical Center, 4800
Sand Point Way N.E., P. O. Box 5371, Seattle, WA 98105.
Received February 6, 2001;
accepted after revision May 8, 2001.
Address correspondence to W. E. Chang.
Introduction
Fat within several types of brain tumors has been previously recognized,
but lipomatous differentiation within ependymomas is a recent discovery,
described twice in the pathology literature
[1,
2]. The MR imaging findings of
a lipomatous ependymoma are reported here for the first time, to our
knowledge, in the radiology literature.
Case Report
A 5-year-old boy presented to his pediatrician with a 1-month history of a
slight hand tremor. In the week before his presentation, the tremor had
progressed to right-sided weakness and clumsiness. The patient was referred to
a tertiary hospital for neurosurgical evaluation. At examination, his gait was
slightly ataxic with a loss of balance on heel and tandem walk. A right
homonymous hemianopsia was present. The patient's medical history revealed
macrocephaly from birth. Laboratory findings were normal.
MR imaging ordered by the patient's pediatrician showed a left-sided
parietooccipital mass measuring 11 x 7.5 x 8 cm. The mass was
predominantly cystic with signal characteristics approaching those of water,
but at its posterolateral wall, the mass contained a 4.5 x 3.5 x 4
cm nodule extending into the parietal cortex. The nodule showed scattered
punctate areas of T1 shortening and T2 prolongation (Figs.
1A and
1B), which on a fat-saturation
T2-weighted sequence were retrospectively noted to show signal loss compatible
with fat (Fig. 1C). Most of the
nodule, along with the rim of the cystic portion of the tumor
(Fig. 1D), enhanced vigorously
after gadolinium administration.
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Fig. 1A. —5-year-old boy with lipomatous ependymoma. Axial T1- and
T2-weighted MR images show predominantly cystic parietal tumor with mass
effect on adjacent structures and midline shift. Posterolateral nodule
contains foci of hyperintensity suggesting fat (long arrow,
A). Adjacent edema is also seen on T2-weighted image (arrows,
B).
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Fig. 1B. —5-year-old boy with lipomatous ependymoma. Axial T1- and
T2-weighted MR images show predominantly cystic parietal tumor with mass
effect on adjacent structures and midline shift. Posterolateral nodule
contains foci of hyperintensity suggesting fat (long arrow,
A). Adjacent edema is also seen on T2-weighted image (arrows,
B).
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Fig. 1C. —5-year-old boy with lipomatous ependymoma. Solid areas
corresponding to foci of increased T1 shortening and T2 prolongation show loss
of signal on sagittal fat-saturated T2-weighted MR image (arrows),
confirming presence of intratumoral fat.
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Fig. 1D. —5-year-old boy with lipomatous ependymoma. Sagittal
gadolinium-enhanced T1-weighted MR image reveals that nodule enhances
heterogeneously with peripheral enhancement of cystic portion.
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Mass effect on the left basal ganglia, mid-brain, and cerebellum was
present with dilatation of the right lateral ventricle, indicating obstructive
hydrocephalus. Midline shift measured approximately 2 cm, and vasogenic edema
extended into the left temporal, parietal, and occipital white matter. A CT
scan was not obtained. Preoperative differential possibilities included cystic
astrocytoma or ependymoma.
At craniotomy, a thinned bone flap with scalloping along the inner surface
of the bone, suggesting chronic increased intracranial pressure, was removed.
An extremely vascular tumor was seen on the brain's surface. Before the dura
was opened, cone needle aspiration of one of the large cysts produced
approximately 50 mL of xanthochromic viscous yellow fluid. The vascular tumor
was removed, and prolific feeding vessels identified from the dura and pia
were sacrificed along with several large draining veins. Three separate cystic
portions were seen, one of which occupied approximately one quarter of the
brain. After the tumor was removed, it was cut in half, showing necrotic and
firm areas as well as vascular portions.
Pathology showed findings of ependymoma
(Fig. 1E), but pleomorphic
giant cells and multiple foci of lipomatous differentiation were seen. The
fat-containing tumor cells composed approximately 50% of the resected specimen
and were scattered through the cellular regions, but in several areas the
tumor cells were more densely clustered, resembling mature adipose tissue
interspersed with clusters of small tumor cells
(Fig. 1F). Positive
immunostaining for glial fibrillary acidic protein and S-100 protein also
supported the diagnosis of ependymoma. Patchy calcification was present. The
tumor was graded as anaplastic, associated with focal areas of mitotic
activity, extensive necrosis, and endothelial proliferation.
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Fig. 1E. —5-year-old boy with lipomatous ependymoma. Photomicrograph of
histopathologic specimen shows epithelial properties of cellular neoplasm with
multiple canals and clefts that are lined by columnar cells (arrows).
This feature distinguishes ependymomas from other gliomas. (H and E,
x100)
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Fig. 1F. —5-year-old boy with lipomatous ependymoma. Photomicrograph of
histopathologic specimen shows lipomatous differentiation in approximately 50%
of tumor. Glial fibrillary acidic protein stains fat and many intervening
tumor cells. (Diaminobenzidine, x400)
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The postoperative hospital course included a scalp wound dehiscence that
required revision of the left scalp incision. The patient was discharged home
after drainage of a sterile serosanguineous subgaleal fluid collection. In the
8 months before the completion of this study, two additional resections were
required for tumor recurrence. The patient is currently receiving radiation
treatment.
Discussion
Ependymomas are glial tumors arising from the cuboidal or columnar cells
lining the ventricles and central canal
[3]. Such tumors comprise
0.3-8% of primary intracranial neoplasms
[3,
4] and 2-4% of glial tumors
[2]. Most of the intracranial
tumors occur in the infratentorial compartment
[5], whereas approximately
30-40% occur supratentorially
[6,
7]. In children, ependymomas
constitute 15% of posterior fossa tumors
[3]. The peak age at
presentation is 1-5 years, with a smaller peak occurring in the fourth decade.
Common presenting symptoms include nausea, vomiting, disequilibrium, and
headaches; common presenting signs include ataxia and nystagmus
[3].
Subtypes of ependymoma include cellular, papillary, and myxopapillary
forms. Typical gross pathology shows a lobulated mass, often with a cystic
component. Histologic findings include perivascular pseudorosettes with
ependymal cells organized around blood vessels. Less commonly, true rosettes
are seen with cells surrounding an ependymal cavity
[3].
Lipomatous differentiation is a newly reported variant in which fat
droplets exist in neoplastic ependymal cells. These droplets form
intracellular vacuoles that push the nucleus to the periphery. This histologic
appearance is distinctly different from xanthomatous change, in which cellular
lipid droplets are associated with a degenerative or metabolic process. Unlike
lipomatous differentiation, xanthomatous change does not mimic the appearance
of an adipocyte [1].
The cause of these microscopic changes is unclear and may be associated
with alterations in cell metabolism, divergent cellular differentiation, or
metaplasia [1,
2]. In this case, the lifelong
macrocephaly and thinned skull suggest a slow-growing tumor, possibly present
at birth. Six of the nine cases found in the literature occurred in patients
less than 18 years old with no patient more than 45 years old
[1,
2], favoring abnormal
differentiation as the cause for the microscopic changes. The formation of
mesodermal tissue from a neuroectodermal tumor is not unexpected because the
neural crest is a pluripotential precursor composed of migrating cells that
give rise to diverse ectomesenchymal tissues under the tight regulation of
growth factors and microenvironmental influences.
To our knowledge, the MR appearance of lipomatous ependymoma has not been
previously described in the radiology literature. This case shows the usual
findings of a supratentorial ependymoma, described by Armington et al.
[4], that include an
intraparenchymal component, a cystic portion, and a size greater than 4 cm.
The signal characteristics are also typical of ependymomas, with the solid
portion hypointense to isointense compared with white matter on T1-weighted
sequences and hyperintense to white matter on T2-weighted sequences. The
cystic components are usually isointense on T1-weighted sequences and
isointense to hyperintense on T2-weighted sequences compared with
cerebrospinal fluid [7].
Enhancement after administration of gadolinium is heterogeneous
[6,
7]. The T1-weighted appearance
can also be heterogeneous, associated with hemorrhage or calcification. In
this case, the tumor's heterogeneous appearance is at least in part related to
the foci of fat, which composed 50% of the submitted pathology specimen. Only
patchy calcifications were described. A CT scan was not obtained. With CT,
presumed foci of fat on the T2-weighted fat-saturation sequence could have
been confirmed with Hounsfield unit measurements. CT might have also clarified
whether areas of low T1 and T2 signals on MR images were calcified.
Possibilities for fat containing intraaxial tumors other than ependymoma
include teratoma, medulloblastoma, cerebellar and central neurocytoma,
cerebellar and spinal astrocytoma, and mixed neuronal-glial tumor of the brain
[2]. Signal characteristics are
of limited value in diagnosing the tissue type of tumors
[8] but can suggest the
possibility of fat and, in combination with location and other characteristics
such as a cystic component, may help in narrowing the differential diagnosis
of a tumor.
Whether this lipomatous variant suggests an improved outcome has yet to be
determined. In the case of medulloblastoma, the presence of fat yields a
better prognosis [1,
2]. From a series of five
cases, Sharma et al. [2] have
suggested that the outcomes for this lipomatous form may be similar to those
of ependymomas of similar grade. The recurrences of this anaplastic tumor
support this idea, but the follow-up of the other eight cases found in the
literature and this current case provide too little data to confirm this
hypothesis.
Acknowledgments
We thank Eugene Tong for reviewing this manuscript.
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Introduction
Case Report
