Key-words:
Meningioma - metaplastic - xanthomatous
Introduction
Meningioma is a group of slow growing neoplasms derived from the meningothelial cells
of the arachnoid layer. Metaplastic meningioma is one of the variants of benign meningioma
with focal or widespread mesenchymal components. Xanthomatous meningioma is a rare
subtype of metaplastic meningioma. Imaging features may point towards the diagnosis
of xanthomatous meningioma, however definitive diagnosis requires histopathological
examination. The prognosis in patients with this type of meningioma appears to be
excellent. Here we report the case of a 44 year old man, who presented with left hemiparesis
secondary to an extra axial space occupying lesion, which was diagnosed as a case
of xanthomatous meningioma.
Case Report
A 44-year-old male presented with progressive weakness of left upper and lower limbs
for 1 month. There was no history of headache, vomiting, or seizures. He did not have
any other comorbid illnesses, addictions, allergies, or significant family history.
On examination, his vital signs were stable. He was fully conscious and his cranial
nerve examination was normal. He had Grade 4/5 power in the left upper limb. The power
in the left hip and knee was 3/5 while ankle flexion and extension were 3/5 and 4/5,
respectively. Both right upper and lower limbs had 5/5 power. The deep tendon reflexes
were brisk on the left upper and lower limbs, and Babinski sign was positive on the
left side. Examination of rest of the neurological system and that of other systems
were normal.
His blood investigations were normal. Magnetic resonance imaging (MRI) of the brain
with gadolinium contrast showed a 4.0 cm × 5.0 cm × 6.5 cm extra-axial mass lesion
in the right mid-third of the parasagittal region [[Figure 1]]a and [[Figure 1]]b. The lesion was abutting the superior sagittal sinus and extending down along
the falx and had multiple hypodense areas within the lesion. It showed weak heterogeneous
enhancement with contrast [[Figure 1]]c and [[Figure 1]]d. There was mild mass effect on the adjacent brain parenchyma.
Figure 1: Preoperative axial T1.weighted (a), fluid.attenuated inversion recovery (b), post
contrast axial T1.weighted (c) and sagittal T1.weighted (d) magnetic resonance imaging
of the brain demonstrated the extra.axial mass lesion in the right mid.third parasagittal
region abutting the superior sagittal sinus and extending down along the falx and
showed weak contrast enhancement. Postoperative T1.weighted axial (e) and T1.weighted
coronal (f) images after IV contrast showed no residual tumor
He underwent a right mid-third parasagittal craniotomy and tumor excision. The specimen
was sent for histopathological examination. Following the surgery, his left sided
weakness gradually resolved and wound healed. Postoperative contrast-enhanced MRI
scan did not show any residual tumor [[Figure 1]]e and [[Figure 1]]f.
The specimen was composed of multiple gray-white pieces together measuring 5 cm ×
5 cm × 4 cm. Cut section of the larger pieces showed gray-white and yellowish areas.
Light microscopy showed a tumor composed of meningothelial cells arranged in sheets
and vague whorled pattern. There were multiple aggregates of foamy cells amid the
meningothelial cells [[Figure 2]]a and [[Figure 2]]b. Occasional mitotic figures were noted. There was no pleomorphism, increased cellularity,
necrosis, or brain invasion. Immunohistochemistry for epithelial membrane antigen
(EMA) showed positivity in the meningothelial and xanthomatous areas [[Figure 2]]c, but CD68 was positive only in the xanthomatous areas [[Figure 2]]d. Considering these features, a diagnosis of xanthomatous meningioma of the World
Health Organization (WHO) Grade I was made.
Figure 2: Photomicrograph showing sheets of xanthomatous cells (H and E, ͯ20) (a), photomicrograph
showing meningothelial cells in sheets admixed with xanthomatous cells H and E, ͯ20
(b), immunohistochemistry stain for EMA showing positivity in the meningothelial and
xanthomatous areas. (c) CD68 immunostain showing positivity in the xanthomatous areas
(d)
Discussion
Meningioma is a morphologically heterogeneous tumour. The WHO has classified meningioma
based on histology into 15 different types.[[1]] Based on biological behavior, they are subclassified into three Grades – I, II,
and III. The grade of the tumor has essential bearing on the prognosis of the patient.
“Xanthomatous meningioma” was a term coined by Kepes in 1994 and refers to a subclass
of metaplastic meningioma.[[2]] Metaplastic meningioma is characterized by focal or widespread mesenchymal differentiation
in the form of bone, cartilage, fat, or xanthomatous cells. Only a few cases of xanthomatous
meningioma have been reported in the literature.
It should be noted that the xanthomatous changes seen in a xanthomatous meningioma
are different from the xanthogranulomatous inflammation that may be seen in pyelonephritis
and cholecystitis. Xanthogranulomatous inflammation is characterized by exuberant
clustering of foamy histiocytes of monocytic derivation with associated chronic inflammatory
cell infiltrates.[[3]] However, inflammatory changes are not a feature of xanthomatous meningioma. Another
differential diagnosis is lipomatous meningioma, which is characterized by meningothelial
neoplastic cells with adipocyte-like features. However, these cells which resemble
adipocytes exhibit large round eccentric nuclei displaced by large lipid vacuoles
resembling mature adipocytes. Another tumor that can lead to diagnostic confusion
is microcystic meningioma. This can be differentiated on the basis of numerous cystic
spaces filled with edematous fluid forming a cobweb like background by large stellate-shaped
meningothelial cells with long cytoplasmic processes, which are highly unusual in
xanthomatous meningioma. Finally, glycogen-rich clear cell meningioma, a Grade II
tumor, can also appear similar to xanthomatous meningioma and can be differentiated
by cells with clear glycogen-rich cytoplasm and prominent blocky stromal and perivascular
collagen, which is not a typical feature of the latter.
It is difficult to make a diagnosis of xanthomatous meningioma by radiology. These
tumors may appear hypodense on computed tomography (CT) of the brain.[[4]] Hypodensity may sometimes be focal and limited to the lipid part.[[5]] The tumors can show variable contrast enhancement leading to an erroneous diagnosis
of glioma or metastasis.[[6]] A MRI may provide a useful clue to the diagnosis of xanthomatous meningioma when
a hypodense mass is demonstrated on CT. On MRI, the tumors may be hyperintense on
both T1 and T2-weighted images.[[7]] Like the hypodensity on CT, these findings are due to the large amount of lipid
in the tumor.
The origin of the xanthomatous cells in these tumors has been debated. Some authors
believe that they are meningothelial macrophages that had possibly migrated to the
site of tumor degradation.[[8]] This is supported by the fact that xanthomatous meningioma cells express the macrophage
immunomarker CD68. However, the expression of CD11c, which is a pan-macrophage marker,
has not been documented. It has to be noted that CD68 also stains lysosomes and is
not specific to macrophages alone. This has led certain others to speculate that CD68
positivity is due to degenerating tumor cells, which typically contain a large number
of lysosomes.[[9]] This hypothesis requires further clarification. Another point of view is that the
xanthomatous change is merely a degenerative change within the tumor. This view is
supported by the expression of EMA in both the xanthomatous and nonxanthomatous components
of the tumor.[[10]],[[11]] The persistence of the meningothelial immunohistochemistry profile suggests that
xanthomatous change is not true histiocytic metaplasia but rather a degenerative process
which occurs in the central portion of the tumor, which is poorly nourished.[[12]] Further studies are required to elucidate which of these competing points of view
are correct.
Xanthomatous meningioma is one of the rarest variants of metaplastic meningioma with
only about 18 cases reported in the literature till date, and this case is the nineteenth
one. It was once thought that the meningothelial-derived tumor cells retained their
ability to differentiate, and that is why xanthomatous meningioma is classified under
metaplastic meningioma. However, recent studies have identified lipid-filled xanthomatous
tumor cells, which were of meningothelial origin by ultrastructural criteria. These
cells showed complex plasmalemmal interdigitations bound by well-formed desmosomes
and hemidesmosome-like intercellular specializations.[[2]] These features are not typical of macrophages. Moreover, the designation of this
tumor as metaplastic has been criticized. Because of these findings, there are those
who advocate for a separate class for xanthomatous meningioma, and a new term “lipidized
meningioma” or lipomatous meningioma subtype has been proposed.[[13]]
Since this is a rare entity, the evidence assessing the clinical behavior of xanthomatous
meningioma is weak. However, anecdotal evidence and expert opinion suggest an excellent
prognosis.
In conclusion, xanthomatous meningioma is a sporadic type of metaplastic meningioma.
Hypodensity on CT scan and hyperintensity on both T1- and T2-weighted MRI images may
point toward the diagnosis of xanthomatous meningioma. Definitive diagnosis requires
histopathology, and the prognosis in patients with xanthomatous meningioma appears
to be excellent.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient has given consent for images and other clinical information
to be reported in the journal. The patient understands that his name and initials
will not be published and due efforts will be made to conceal his identity, but anonymity
cannot be guaranteed.
Approval of ethics committee
The study was approved by the institutional ethics committee.
