Meningiomas are common neoplasms arising from the central nervous system meninges. On the other hand, primary ectopic meningiomas are extremely rare and usually limited to the head and neck region or to the paravertebral soft tissues. Their occurrence in the mediastinum is even rarer. Until now, only 4 cases of primary mediastinal meningioma have been reported in the literature searched on Medline. Because of its rarity and intriguing pathogenesis, we report here a case of primary mediastinal meningioma that was treated by surgical resection. The clinical features, treatment, pathological findings, and prognosis are analyzed, and the literature on ectopic meningioma is reviewed

A Perry

AJ Wilson

Akira Mogi

D Palimento

D Sandberg

Ei Yamaki

F Chen

Hiroyuki Kuwano

Junko Hirato

K Kodama

LA Langford

LD Thomson

M Drlicek

M Falleni

MH Sanei

PG Robinson

R Mair

RA Erlandson

S Kakizoe

Takayuki Kosaka

U Tomaru

VJ Amatya

English

PubMed

Springer - Publisher Connector

CASE REPORT Open Access
Primary mediastinal atypical meningioma: Report
of a case and literature review
Akira Mogi1*, Junko Hirato2, Takayuki Kosaka1, Ei Yamaki1 and Hiroyuki Kuwano1
Abstract
Meningiomas are common neoplasms arising from the central nervous system meninges. On the other hand,
primary ectopic meningiomas are extremely rare and usually limited to the head and neck region or to the
paravertebral soft tissues. Their occurrence in the mediastinum is even rarer. Until now, only 4 cases of primary
mediastinal meningioma have been reported in the literature searched on Medline. Because of its rarity and
intriguing pathogenesis, we report here a case of primary mediastinal meningioma that was treated by surgical
resection. The clinical features, treatment, pathological findings, and prognosis are analyzed, and the literature on
ectopic meningioma is reviewed.
Keywords: ectopic meningioma, atypical, mediastinum, surgical treatment
Background
Meningiomas are one of the most common neoplasms of
the central nervous system, and the cell of origin for the
meningioma is called the arachnoid cap cell, found on the
surface coverings of the brain in the pacchionian granula-
tions. Meningiomas are usually benign and slow-proliferat-
ing and account for about 15-20% of all intracranial
tumors. On the other hand, primary ectopic meningiomas
are exceedingly rare, and they are usually found in the
head, neck, or paraspinal soft tissues [1]. Other possible
ectopic sites include the foot, lung, skin, and mediastinum
[2-4]. A Medline search revealed only 4 cases to date of
primary mediastinal meningioma [5-8]. Furthermore, only
one case of meningioma arising from the anterior medias-
tinum has been reported [8].
Here, we report an ectopic atypical meningioma arising
from the anterior mediastinum because of its extreme
rarity.
Case presentation
A 64-year-old male was referred to the Gunma University
Hospital with complaints of a progressive oppressive feel-
ing in the left thoracic region. His past medical history
was unremarkable. At admission, general conditions were
satisfactory, and a physical examination of the thorax was
normal. Routine laboratory tests were within normal
values, but a chest roentgenogram revealed an oval-shaped
anterior mediastinal mass in the left hemithorax. An
enhanced computed tomography (CT) scan of the chest
revealed the presence of an ovoid mass about 9-cm at its
greatest dimension in the left anterior mediastinal region.
Its border, adjacent to the left lung parenchyma, was
poorly demarcated. The mass showed a heterogeneous
densitometric characteristic accompanied with areas of
necrosis after contrast enhancement (Figure 1). From the
graphical specifications and laboratory studies, an invasive
thymoma was strongly suggested, and we decided to per-
form a radical resection of the tumor.
Written informed consent concerning the operation was
obtained from the patient before surgery, and the patient
was admitted to the Gunma University Hospital for surgi-
cal resection of the tumor. The patient underwent tumor
excision and thymectomy through sternotomy with con-
tinuous anterior thoracotomy of the third intercostal
space. During the operation, the tumor, as seen on the CT
scan, was 9-cm wide, elastic, and off-white in color. It was
found to have infiltrated the upper lobe of the left lung.
Based on this surgical finding, partial resection of the lung
together with the tumor was performed with a sufficient
surgical margin. On the basis of its morphologic and
immunohistochemical features, the tumor was diagnosed
as a mediastinal atypical meningioma. The patient had an
* Correspondence: akmogi@showa.gunma-u.ac.jp
1Department of General Surgical Science, Gunma University Graduate School
of Medicine, 3-39-22, Showa-machi, Maebashi, Gunma 371-8511, Japan
Full list of author information is available at the end of the article
Mogi et al. World Journal of Surgical Oncology 2012, 10:17
http://www.wjso.com/content/10/1/17 WORLD JOURNAL OF 
SURGICAL ONCOLOGY 
© 2012 Mogi et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
uneventful recovery and was discharged on postoperative
day 6. An ectopic pulmonary site of origin, such as the
mediastinum in this case, should be accepted only after
the possibility of spread or metastasis from primary intra-
cranial or intraspinal origin has been excluded. One
month after operation, the patient had an enhanced mag-
netic resonance imaging (MRI) of the head and spine, and
no abnormal findings were observed, which eliminated the
possibility of an intracranial or intraspinal origin. He has
been monitored for 12 months as an outpatient without
any symptoms of recurrence or metastasis.
The surgical specimens were routinely fixed with 10%
formaldehyde and embedded in paraffin. Tissue sections
(6-μm thick) were stained with hematoxylin and eosin (H-
E), and periodic acid-Schiff (PAS) with and without dia-
stase digestion. For immunohistochemical studies, tissue
sections were incubated using the standard avidin-biotin
peroxidase complex (ABC) method with the following
antibodies: epithelial membrane antigen (EMA), vimentin,
S-100, MIB-1, CD34, D2-40, aSMA, desmin, synaptophy-
sin, and neurofilament. Macroscopically, the resected
tumor measured 9-cm in its greatest dimension and
adhered to a parenchyma of the left lung. The oval-shaped
tumor had a smooth surface, and its cut surface was
homogenously solid and yellow-white in color (Figure 2).
Microscopically, the tumor was partially encapsulated
and composed of bundles of spindle-shaped cells with
elongated nuclei and syncytial nets of tumor cells with oval
nuclei. A few tumor cells had an intracellular cytoplasmic
inclusion. In some areas, many typical whorl formations
for fibrous meningioma were observed (Figure 3A). There
were several foci of small cells with a high nuclear/cyto-
plasmic ratio (Figure 3B). Spontaneous and zonal necroses
were occasionally seen (Figure 3C). In addition, the tumor
involved adjacent pulmonary parenchyma (Figure 3D). The
mitotic index was four per 10 high-power fields (hpf) at
the areas where the mitotic figures were most frequently
observed, and the Ki-67/MIB-1 labeling index was approxi-
mately 7% in relatively higher positive-rate fields (Figure
3E). Immunohistochemical examinations showed positivity
to EMA (Figure 3F) and vimentin, focal positivity to S-100,
CD34, and D2-40, and negativity to aSMA and desmin.
Some oval tumor cells containing large cell bodies were
stained for synaptophysin and neurofilament.
Discussion
Meningiomas usually arise in the cranial cavity or spinal
canal. On the other hand, because meningiomas arise
from arachnoid cells present in the meninges, they can
occur in any location where meninges or ectopic meninges
exist. Primary ectopic meningiomas are extremely rare
pathological entities and have been reported sporadically.
They usually occur in cephalic and paravertebral soft tis-
sues and skin and, more rarely, in the ear [9], temporal
bone [9], mandible, foot [2], lung [10], and mediastinum
[5-8]. The histopathogenesis of ectopic meningiomas is
still unclear. However, three hypotheses are that they arise
from an extension of the arachnoid cells along cranial
nerve sheaths during development, from the arachnoidal
cells trapped in extracranial locations when the skull bone
fuses, or from differentiation of Schwann cells into menin-
gocytes [1,11,12].
To make a definite diagnosis of an ectopic meningioma
is difficult, and such a diagnosis can only be made on the
basis of microscopic morphological and immunohisto-
chemical findings. In this case, and despite the unusual
location of the tumor, the morphological and immuno-
histochemical findings closely resembled a meningioma
in the central nervous system. Furthermore, as there was
Figure 1 Enhanced chest computed tomography shows a
heterogeneous 9.0 × 7.5 cm mass arising in the anterior
mediastinum.
Figure 2 The oval-shaped tumor had a smooth surface, and its
cut surface was homogenously solid with a yellowish-white
color. The tumor was partially involved in the lung parenchyma
(arrowhead).
Mogi et al. World Journal of Surgical Oncology 2012, 10:17
http://www.wjso.com/content/10/1/17
Page 2 of 5
no clinical or radiological evidence of any intracranial or
intraspinal lesion, we concluded that the meningioma in
this case was of complete mediastinal origin.
In view of the rarity of extracranial meningiomas, cau-
tion must be used in ruling out possibilities in the dif-
ferential diagnosis. Regarding the histological differential
Figure 3 Numerous typical whorl formations (A) and small cells with a high nuclear/cytoplasmic ratio (B) were observed in the tumor.
Spontaneous necrosis was occasionally seen (C). The tumor was partially involved in the adjacent pulmonary parenchyma (D). There were some
mitotic figures, and the Ki-67/MIB-1 labeling index was approximately 7% in relatively higher positive-rate fields (E). Marked immunoreactivity for
epithelial membrane antigen (EMA) was seen (F).
Mogi et al. World Journal of Surgical Oncology 2012, 10:17
http://www.wjso.com/content/10/1/17
Page 3 of 5
diagnosis of epithelial thymomas, they are composed of
cells with large numbers of desmosomes often contain-
ing numerous cytoplasmic cytokeratin filaments in the
desmosomes per se and lying free in the cytoplasm [13].
Cytokeratin filaments are absent in meningiomas.
Because of its morphological findings, as typical whorl
formation for fibrous meningiomas, solitary fibrous
tumors, schwannomas, and hemangiopericytomas could
be diagnosed by exclusion. Additionally, hemangioperi-
cytomas could be excluded by positivity of EMA in
immunohistochemical results, because EMA stains show
typically positive in meningiomas and negative in
hemangiopericytomas. Positivity of EMA was compatible
with the diagnosis of this tumor as a meningioma.
Furthermore, leiomyomas could be excluded by negativ-
ity of aSMA in immunohistochemical results.
Histological grading of meningiomas is based on the
2007 WHO classification [14]. Atypical meningioma
(WHO grade II) shows increased mitotic activity or three
or more of the following histological features: increased
cellularity, small cells with a high nuclear/cytoplasmic
ratio, prominent nucleoli, uninterrupted patternless or
sheet-like growth, and foci of spontaneous or geographic
necroses. Increased mitotic activity is defined as four or
more mitoses per 10 hpf. In addition, brain invasion was
included in an otherwise grade I tumor as an additional
criterion for a WHO grade II lesion [14]. In our case, the
presence of small cells, spontaneous and zonal necroses,
invasion into the pulmonary parenchyma, and mitotic
activity of the tumor (four mitotic cells per 10 hpf) corre-
spond histologically to an atypical meningioma. Expres-
sion of proliferation markers, such as MIB-1 and Ki-67,
has generally shown progressive increases in the labeling
index with a WHO grade from 1.00-1.35% for grade I to
1.90-9.30% for grade II or atypical meningiomas and 5.60-
19.5% for grade III or anaplastic meningiomas [15,16]. In
addition, the median MIB-1 proliferation indices are 3.4%
in ordinary meningiomas, 6.6% in atypical meningiomas,
and 11.8% in malignant meningiomas [17]. These data
further support the classification of the meningioma in
this case into an atypical category.
As for the clinical course, the surgical excision was as
curative as a complete resection with a sufficient surgical
margin. Although this was an atypical meningioma with
invasion into lung tissue, no adjuvant therapies, such as
radiotherapy, were performed. This decision was based
on the fact that Mair et al. retrospectively reviewed the
records of 114 consecutive patients with diagnosed
WHO grade II meningiomas and reported that radiother-
apy for WHO grade II atypical meningiomas was not
appropriate after a first-time resection of those lesions in
which a gross-total resection has been achieved [18]. In
addition, we consulted with the neurosurgeons of Gunma
University Hospital, who were experienced in the treat-
ment of cerebral meningioma.
According to our review of the literature, this is the
first reported case of primary mediastinal atypical menin-
gioma [Table 1]. Of all the reported cases of mediastinal
meningiomas, only one was malignant. All but one was
surgically treated alone. The exception was treated with
consecutive radiation after surgical resection. Regarding
the clinical course of these cases, including this case,
every case was disease-free for at least 9 months after
surgery except for two cases for which the clinical course
was not discussed. Although a longer follow-up is neces-
sary, the findings strongly suggest that surgical resection
is an acceptable and adequate treatment for ectopic med-
iastinal meningiomas.
Conclusions
Here, we report an ectopic atypical meningioma arising
from the anterior mediastinum because of its extreme
Table 1 Clinical features of reported primary mediastinal meningiomas.
authors published year
sex
site site (origin) symptoms greatest
diameter
subtypes treatment follow
up
Wilson AJ
et al. [5]
1979 63
M
right sympathetic chain
(Stellate ganglion)
Horner’s syndrome 4.0 cm ND surgery ND
Falleni M
et al. [6]
2001 45
F
right mediastinal
paravertebral
lesion
none 4.5 cm transitional surgery 11 years
disease
free
Palimento D et
al. [7]
2006 45
F
left posterior
paravertebral
lesion
spontaneous
hemothorax
12 cm angioblastic surgery ND
Chen F et al. [8] 2009 41
M
right anterior
mediastinum
chest distress
cough
12 cm malignant surgery +
radiation
9 months
disease
free
Present case 64
M
left anterior
mediastinum
oppressing feeling 9 cm atypical surgery 12
months
disease
free
ND: Not described
Mogi et al. World Journal of Surgical Oncology 2012, 10:17
http://www.wjso.com/content/10/1/17
Page 4 of 5
rarity. Surgery is a feasible and effective treatment strat-
egy for ectopic meningioma of the mediastinum.
Consent
Written informed consent was obtained from the patient
for publication of this case report and the accompanying
images. A copy of the written consent is available for
review by the Editor-in -Chief of this medical journal.
List of abbreviations
CT: computed tomography; MRI: magnetic resonance imaging; H-E:
hematoxylin and eosin; PAS: periodic acid-Schiff; ABC: avidin-biotin
peroxidase complex; EMA: epithelial membrane antigen; αSMA: α smooth-
muscle actin; hpf: high-power fields.
Author details
1Department of General Surgical Science, Gunma University Graduate School
of Medicine, 3-39-22, Showa-machi, Maebashi, Gunma 371-8511, Japan.
2Department of Human Pathology, Gunma University Graduate School of
Medicine, 3-39-22, Showa-machi, Maebashi, Gunma 371-8511, Japan.
Authors’ contributions
AM drafted and co-wrote the manuscript with JH and HK. AM, TK, and EY
were involved in the clinical care of the patient. JH reported pathological
findings and prepared slides for manuscript inclusion. All authors have read
and approved the final version of the manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 25 July 2011 Accepted: 21 January 2012
Published: 21 January 2012
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doi:10.1186/1477-7819-10-17
Cite this article as: Mogi et al.: Primary mediastinal atypical
meningioma: Report of a case and literature review. World Journal of
Surgical Oncology 2012 10:17.
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Primary mediastinal atypical meningioma: Report of a case and literature review

Abstract Meningiomas are common neoplasms arising from the central nervous system meninges. On the other hand, primary ectopic meningiomas are extremely rare and usually limited to the head and neck region or to the paravertebral soft tissues. Their occurrence in the mediastinum is even rarer. Until now, only 4 cases of primary mediastinal meningioma have been reported in the literature searched on Medline. Because of its rarity and intriguing pathogenesis, we report here a case of primary mediastinal meningioma that was treated by surgical resection. The clinical features, treatment, pathological findings, and prognosis are analyzed, and the literature on ectopic meningioma is reviewed.</p

Mogi Akira

Hirato Junko

Kosaka Takayuki

Yamaki Ei

Kuwano Hiroyuki

Directory of Open Access Journals

World Journal of Surgical Oncology

Crossref

CASE REPORT Open AccessPrimary mediastinal atypical meningioma: Reportof a case and literature reviewAkira Mogi1*, Junko Hirato2, Takayuki Kosaka1, Ei Yamaki1 and Hiroyuki Kuwano1AbstractMeningiomas are common neoplasms arising from the central nervous system meninges. On the other hand,primary ectopic meningiomas are extremely rare and usually limited to the head and neck region or to theparavertebral soft tissues. Their occurrence in the mediastinum is even rarer. Until now, only 4 cases of primarymediastinal meningioma have been reported in the literature searched on Medline. Because of its rarity andintriguing pathogenesis, we report here a case of primary mediastinal meningioma that was treated by surgicalresection. The clinical features, treatment, pathological findings, and prognosis are analyzed, and the literature onectopic meningioma is reviewed.Keywords: ectopic meningioma, atypical, mediastinum, surgical treatmentBackgroundMeningiomas are one of the most common neoplasms ofthe central nervous system, and the cell of origin for themeningioma is called the arachnoid cap cell, found on thesurface coverings of the brain in the pacchionian granula-tions. Meningiomas are usually benign and slow-proliferat-ing and account for about 15-20% of all intracranialtumors. On the other hand, primary ectopic meningiomasare exceedingly rare, and they are usually found in thehead, neck, or paraspinal soft tissues [1]. Other possibleectopic sites include the foot, lung, skin, and mediastinum[2-4]. A Medline search revealed only 4 cases to date ofprimary mediastinal meningioma [5-8]. Furthermore, onlyone case of meningioma arising from the anterior medias-tinum has been reported [8].Here, we report an ectopic atypical meningioma arisingfrom the anterior mediastinum because of its extremerarity.Case presentationA 64-year-old male was referred to the Gunma UniversityHospital with complaints of a progressive oppressive feel-ing in the left thoracic region. His past medical historywas unremarkable. At admission, general conditions weresatisfactory, and a physical examination of the thorax wasnormal. Routine laboratory tests were within normalvalues, but a chest roentgenogram revealed an oval-shapedanterior mediastinal mass in the left hemithorax. Anenhanced computed tomography (CT) scan of the chestrevealed the presence of an ovoid mass about 9-cm at itsgreatest dimension in the left anterior mediastinal region.Its border, adjacent to the left lung parenchyma, waspoorly demarcated. The mass showed a heterogeneousdensitometric characteristic accompanied with areas ofnecrosis after contrast enhancement (Figure 1). From thegraphical specifications and laboratory studies, an invasivethymoma was strongly suggested, and we decided to per-form a radical resection of the tumor.Written informed consent concerning the operation wasobtained from the patient before surgery, and the patientwas admitted to the Gunma University Hospital for surgi-cal resection of the tumor. The patient underwent tumorexcision and thymectomy through sternotomy with con-tinuous anterior thoracotomy of the third intercostalspace. During the operation, the tumor, as seen on the CTscan, was 9-cm wide, elastic, and off-white in color. It wasfound to have infiltrated the upper lobe of the left lung.Based on this surgical finding, partial resection of the lungtogether with the tumor was performed with a sufficientsurgical margin. On the basis of its morphologic andimmunohistochemical features, the tumor was diagnosedas a mediastinal atypical meningioma. The patient had an* Correspondence: akmogi@showa.gunma-u.ac.jp1Department of General Surgical Science, Gunma University Graduate Schoolof Medicine, 3-39-22, Showa-machi, Maebashi, Gunma 371-8511, JapanFull list of author information is available at the end of the articleMogi et al. World Journal of Surgical Oncology 2012, 10:17http://www.wjso.com/content/10/1/17 WORLD JOURNAL OF SURGICAL ONCOLOGY © 2012 Mogi et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction inany medium, provided the original work is properly cited.uneventful recovery and was discharged on postoperativeday 6. An ectopic pulmonary site of origin, such as themediastinum in this case, should be accepted only afterthe possibility of spread or metastasis from primary intra-cranial or intraspinal origin has been excluded. Onemonth after operation, the patient had an enhanced mag-netic resonance imaging (MRI) of the head and spine, andno abnormal findings were observed, which eliminated thepossibility of an intracranial or intraspinal origin. He hasbeen monitored for 12 months as an outpatient withoutany symptoms of recurrence or metastasis.The surgical specimens were routinely fixed with 10%formaldehyde and embedded in paraffin. Tissue sections(6-μm thick) were stained with hematoxylin and eosin (H-E), and periodic acid-Schiff (PAS) with and without dia-stase digestion. For immunohistochemical studies, tissuesections were incubated using the standard avidin-biotinperoxidase complex (ABC) method with the followingantibodies: epithelial membrane antigen (EMA), vimentin,S-100, MIB-1, CD34, D2-40, aSMA, desmin, synaptophy-sin, and neurofilament. Macroscopically, the resectedtumor measured 9-cm in its greatest dimension andadhered to a parenchyma of the left lung. The oval-shapedtumor had a smooth surface, and its cut surface washomogenously solid and yellow-white in color (Figure 2).Microscopically, the tumor was partially encapsulatedand composed of bundles of spindle-shaped cells withelongated nuclei and syncytial nets of tumor cells with ovalnuclei. A few tumor cells had an intracellular cytoplasmicinclusion. In some areas, many typical whorl formationsfor fibrous meningioma were observed (Figure 3A). Therewere several foci of small cells with a high nuclear/cyto-plasmic ratio (Figure 3B). Spontaneous and zonal necroseswere occasionally seen (Figure 3C). In addition, the tumorinvolved adjacent pulmonary parenchyma (Figure 3D). Themitotic index was four per 10 high-power fields (hpf) atthe areas where the mitotic figures were most frequentlyobserved, and the Ki-67/MIB-1 labeling index was approxi-mately 7% in relatively higher positive-rate fields (Figure3E). Immunohistochemical examinations showed positivityto EMA (Figure 3F) and vimentin, focal positivity to S-100,CD34, and D2-40, and negativity to aSMA and desmin.Some oval tumor cells containing large cell bodies werestained for synaptophysin and neurofilament.DiscussionMeningiomas usually arise in the cranial cavity or spinalcanal. On the other hand, because meningiomas arisefrom arachnoid cells present in the meninges, they canoccur in any location where meninges or ectopic meningesexist. Primary ectopic meningiomas are extremely rarepathological entities and have been reported sporadically.They usually occur in cephalic and paravertebral soft tis-sues and skin and, more rarely, in the ear [9], temporalbone [9], mandible, foot [2], lung [10], and mediastinum[5-8]. The histopathogenesis of ectopic meningiomas isstill unclear. However, three hypotheses are that they arisefrom an extension of the arachnoid cells along cranialnerve sheaths during development, from the arachnoidalcells trapped in extracranial locations when the skull bonefuses, or from differentiation of Schwann cells into menin-gocytes [1,11,12].To make a definite diagnosis of an ectopic meningiomais difficult, and such a diagnosis can only be made on thebasis of microscopic morphological and immunohisto-chemical findings. In this case, and despite the unusuallocation of the tumor, the morphological and immuno-histochemical findings closely resembled a meningiomain the central nervous system. Furthermore, as there wasFigure 1 Enhanced chest computed tomography shows aheterogeneous 9.0 × 7.5 cm mass arising in the anteriormediastinum.Figure 2 The oval-shaped tumor had a smooth surface, and itscut surface was homogenously solid with a yellowish-whitecolor. The tumor was partially involved in the lung parenchyma(arrowhead).Mogi et al. World Journal of Surgical Oncology 2012, 10:17http://www.wjso.com/content/10/1/17Page 2 of 5no clinical or radiological evidence of any intracranial orintraspinal lesion, we concluded that the meningioma inthis case was of complete mediastinal origin.In view of the rarity of extracranial meningiomas, cau-tion must be used in ruling out possibilities in the dif-ferential diagnosis. Regarding the histological differentialFigure 3 Numerous typical whorl formations (A) and small cells with a high nuclear/cytoplasmic ratio (B) were observed in the tumor.Spontaneous necrosis was occasionally seen (C). The tumor was partially involved in the adjacent pulmonary parenchyma (D). There were somemitotic figures, and the Ki-67/MIB-1 labeling index was approximately 7% in relatively higher positive-rate fields (E). Marked immunoreactivity forepithelial membrane antigen (EMA) was seen (F).Mogi et al. World Journal of Surgical Oncology 2012, 10:17http://www.wjso.com/content/10/1/17Page 3 of 5diagnosis of epithelial thymomas, they are composed ofcells with large numbers of desmosomes often contain-ing numerous cytoplasmic cytokeratin filaments in thedesmosomes per se and lying free in the cytoplasm [13].Cytokeratin filaments are absent in meningiomas.Because of its morphological findings, as typical whorlformation for fibrous meningiomas, solitary fibroustumors, schwannomas, and hemangiopericytomas couldbe diagnosed by exclusion. Additionally, hemangioperi-cytomas could be excluded by positivity of EMA inimmunohistochemical results, because EMA stains showtypically positive in meningiomas and negative inhemangiopericytomas. Positivity of EMA was compatiblewith the diagnosis of this tumor as a meningioma.Furthermore, leiomyomas could be excluded by negativ-ity of aSMA in immunohistochemical results.Histological grading of meningiomas is based on the2007 WHO classification [14]. Atypical meningioma(WHO grade II) shows increased mitotic activity or threeor more of the following histological features: increasedcellularity, small cells with a high nuclear/cytoplasmicratio, prominent nucleoli, uninterrupted patternless orsheet-like growth, and foci of spontaneous or geographicnecroses. Increased mitotic activity is defined as four ormore mitoses per 10 hpf. In addition, brain invasion wasincluded in an otherwise grade I tumor as an additionalcriterion for a WHO grade II lesion [14]. In our case, thepresence of small cells, spontaneous and zonal necroses,invasion into the pulmonary parenchyma, and mitoticactivity of the tumor (four mitotic cells per 10 hpf) corre-spond histologically to an atypical meningioma. Expres-sion of proliferation markers, such as MIB-1 and Ki-67,has generally shown progressive increases in the labelingindex with a WHO grade from 1.00-1.35% for grade I to1.90-9.30% for grade II or atypical meningiomas and 5.60-19.5% for grade III or anaplastic meningiomas [15,16]. Inaddition, the median MIB-1 proliferation indices are 3.4%in ordinary meningiomas, 6.6% in atypical meningiomas,and 11.8% in malignant meningiomas [17]. These datafurther support the classification of the meningioma inthis case into an atypical category.As for the clinical course, the surgical excision was ascurative as a complete resection with a sufficient surgicalmargin. Although this was an atypical meningioma withinvasion into lung tissue, no adjuvant therapies, such asradiotherapy, were performed. This decision was basedon the fact that Mair et al. retrospectively reviewed therecords of 114 consecutive patients with diagnosedWHO grade II meningiomas and reported that radiother-apy for WHO grade II atypical meningiomas was notappropriate after a first-time resection of those lesions inwhich a gross-total resection has been achieved [18]. Inaddition, we consulted with the neurosurgeons of GunmaUniversity Hospital, who were experienced in the treat-ment of cerebral meningioma.According to our review of the literature, this is thefirst reported case of primary mediastinal atypical menin-gioma [Table 1]. Of all the reported cases of mediastinalmeningiomas, only one was malignant. All but one wassurgically treated alone. The exception was treated withconsecutive radiation after surgical resection. Regardingthe clinical course of these cases, including this case,every case was disease-free for at least 9 months aftersurgery except for two cases for which the clinical coursewas not discussed. Although a longer follow-up is neces-sary, the findings strongly suggest that surgical resectionis an acceptable and adequate treatment for ectopic med-iastinal meningiomas.ConclusionsHere, we report an ectopic atypical meningioma arisingfrom the anterior mediastinum because of its extremeTable 1 Clinical features of reported primary mediastinal meningiomas.authors published yearsexsite site (origin) symptoms greatestdiametersubtypes treatment followupWilson AJet al. [5]1979 63Mright sympathetic chain(Stellate ganglion)Horner’s syndrome 4.0 cm ND surgery NDFalleni Met al. [6]2001 45Fright mediastinalparavertebrallesionnone 4.5 cm transitional surgery 11 yearsdiseasefreePalimento D etal. [7]2006 45Fleft posteriorparavertebrallesionspontaneoushemothorax12 cm angioblastic surgery NDChen F et al. [8] 2009 41Mright anteriormediastinumchest distresscough12 cm malignant surgery +radiation9 monthsdiseasefreePresent case 64Mleft anteriormediastinumoppressing feeling 9 cm atypical surgery 12monthsdiseasefreeND: Not describedMogi et al. World Journal of Surgical Oncology 2012, 10:17http://www.wjso.com/content/10/1/17Page 4 of 5rarity. Surgery is a feasible and effective treatment strat-egy for ectopic meningioma of the mediastinum.ConsentWritten informed consent was obtained from the patientfor publication of this case report and the accompanyingimages. A copy of the written consent is available forreview by the Editor-in -Chief of this medical journal.List of abbreviationsCT: computed tomography; MRI: magnetic resonance imaging; H-E:hematoxylin and eosin; PAS: periodic acid-Schiff; ABC: avidin-biotinperoxidase complex; EMA: epithelial membrane antigen; αSMA: α smooth-muscle actin; hpf: high-power fields.Author details1Department of General Surgical Science, Gunma University Graduate Schoolof Medicine, 3-39-22, Showa-machi, Maebashi, Gunma 371-8511, Japan.2Department of Human Pathology, Gunma University Graduate School ofMedicine, 3-39-22, Showa-machi, Maebashi, Gunma 371-8511, Japan.Authors’ contributionsAM drafted and co-wrote the manuscript with JH and HK. AM, TK, and EYwere involved in the clinical care of the patient. JH reported pathologicalfindings and prepared slides for manuscript inclusion. All authors have readand approved the final version of the manuscript.Competing interestsThe authors declare that they have no competing interests.Received: 25 July 2011 Accepted: 21 January 2012Published: 21 January 2012References1. Sanei MH, Berjis N, Mahzouni P, Naimi A: Meningiomas. A case of neckectopic meningioma. Neuropathology 2008, 28:157-159.2. Tomaru U, Hasegawa T, Hasegawa F, Kito M, Hirose T, Shimoda T: Primaryextracranial meningioma of the foot: a case report. Jpn J Clin Oncol 2000,30:313-317.3. Drlicek M, Grisold W, Lorber J, Hackl H, Wuketich S, Jellinger K: Pulmonarymeningioma. Immunohistochemical and ultrastructural features. Am JSurg Pathol 1991, 15:455-459.4. Kakizoe S, Kojiro M, Hikita N: Primary cutaneous meningioma. Report of acase. Acta Pathol Jpn 1987, 37:511-514.5. Wilson AJ, Ratliff JL, Lagios MD, Aguilar MJ: Mediastinal meningioma. Am JSurg Pathol 1979, 3:557-562.6. 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A: Meningiomas. A case of neck ectopic meningioma. Neuropathology

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Pulmonary meningioma. Immunohistochemical and ultrastructural features.

Pulmonary meningioma. Report of a case with electron microscopic and immunohistochemical findings.

Radiotherapy for atypical meningiomas. J Neurosurg 2011, 115:811-819. doi:10.1186/1477-7819-10-17 Cite this article as: Mogi et al.: Primary mediastinal atypical meningioma: Report of a case and literature review.

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Primary mediastinal atypical meningioma: Report of a case and literature review

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