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Neuropathology 2012; 32, 267–271

C a se Repor t

neup_1249

doi:10.1111/j.1440-1789.2011.01249.x

267..271

Abnormal tau deposition in neurons, but not in
glial cells in the cerebral tissue surrounding
arteriovenous malformation
Tomoya Kon,1,2 Fumiaki Mori,1 Kunikazu Tanji,1 Yasuo Miki,1,2 Masahiko Tomiyama,2
Masayuki Baba,2 Yutaka Umehara,3 Hidekachi Kurotaki4 and Koichi Wakabayashi1
1

Department of Neuropathology, Hirosaki University Graduate School of Medicine, Hirosaki, and Departments of
2
Neurology, 3Surgery and 4Pathology, Aomori Prefectural Central Hospital, Aomori, Japan

We report an autopsy case of arteriovenous malformation
(AVM) of the right frontal lobe in a 50-year-old man,
in whom post mortem examination revealed massive tau
deposition in the affected cerebral cortex. The patient was
diagnosed as having AVM at the age of 21 years, and died
of unknown cause at the age of 50 years. Immunostaining
with anti-phosphorylated tau antibody (AT8) revealed
many NFTs and neuropil threads, but not glial tau accumulation, in the right frontal cortex surrounding the AVM.
The NFTs and neuropil threads contained both 3-repeat
and 4-repeat tau. Ultrastructurally, the NFTs consisted of
paired helical filaments. In the other brain areas, a few
NFTs were found in the parahippocampal gyrus. There was
no amyloid deposition in the brain. A variety of disease
conditions, including brain tumor, viral encephalitis,
angioma and cervical spondylotic myelopathy, have been
reported to show Alzheimer-type NFTs. The present findings indicate that abnormal tau deposition can occur in
neurons, but not in glial cells, of the affected cerebral
cortex surrounding AVM.
Key words: arteriovenous malformation, neurofibrillary
tangle, neuropil thread, phosphorylated tau, tauopathy.

INTRODUCTION
Tauopathies are defined as neurodegenerative diseases
with prominent tau pathology in neurons and glial cells in

Correspondence: Tomoya Kon, MD, Department of Neuropathology,
Institute of Brain Science, Hirosaki University Graduate School of
Medicine, 5 Zaifu-cho, Hirosaki 036-8562, Japan. Email: tomoya_kon@
med.pref.aomori.jp
Received 5 July 2011; revised 12 July 2011 and accepted 14 July
2011; published online 17 August 2011.

© 2011 Japanese Society of Neuropathology

the CNS. Moreover, the occurrence of NFTs has been
reported in a variety of disease conditions, including brain
tumor (meningioangiomatosis,1 ganglion cell tumors,2,3
hamartoma4), viral infection (subacute sclerosing panencephalitis (SSPE),5–7 post-encephalitic parkinsonism8), vascular malformation (arteriovenous malformation (AVM),9
sclerosing angioma10), traumatic diseases (boxer’s brain,11
repeated mild head injury,12 cervical spondylotic myelopathy13), toxins (aluminium,14 lead,15 manganese16), metabolic
disease (Niemann-Pick disease type C17), developmental
abnormalities (verrucose dysplasia,18 congenital hydrocephalus19), muscle disease (myotonic dystrophy20) and
genetic disorders (tuberous sclerosis21). However, most
of these cases have been described before immunohistochemical demonstration of tau-positive glial fibrillary
tangles or identification of tau isoforms.
Previously, the clinico-pathological profile in cases of
AVM with occurrence of NFTs has not been described in
detail, since it was only reported as an abstract.9 Recently,
we encountered an autopsy case of AVM of the right
frontal lobe in a 50-year-old man and carried out histological, immunohistochemical and ultrastructural analyses in
this patient. Here, we report that abnormal tau consisted of
three- and four-repeat isoforms can occur in neurons, but
not in glial cells, of the cerebral cortex surrounding the
AVM.

CLINICAL SUMMARY
A Japanese man developed epileptic seizure at the age of
21 years. He consulted a physician and was diagnosed as
having AVM in the right frontal lobe. Thereafter he
received an anti-convulsant therapy, which was beneficial.
At the age of 45 years, he suffered from subarachnoid
hemorrhage in the basal cistern and was treated with coil

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T Kon et al.

Fig. 1 T2-weighted cranial MRI at the age of 50 years showing
huge arteriovenous malformation in the right frontal lobe.

retrieval using an autoclave for 10 min in 10 mmol citrate
buffer (pH 6.0), and immunostained using a Vectastain
ABC kit (Vector, Burlingame, CA, USA). For RD3 immunohistochemistry, the sections were additionally pretreated
with 0.25% KMnO4 for 15 min followed by 2% oxalic acid
for 3 min at room temperature.22
Selected sections were also double-immunolabeled
with polyclonal anti-GFAP (1:100) and monoclonal antiphosphorylated tau (1:100).The secondary antibodies were
Alexa Fluor 488 goat anti-rabbit IgG (Invitrogen, Carlsbad, CA, USA; 1:200) and Alexa Fluor 594 goat anti-mouse
IgG (Invitrogen; 1:200). The sections were examined with
an Olympus Provis fluorescence microscope (Olympus,
Tokyo, Japan).
Immunoelectron microscopy was performed by a preembedding method. Vibratome sections of the right frontal
lobe were incubated with AT8 (1:1000) for 2 days at 4°C,
followed by incubation with a biotinylated secondary antibody (1:200) and ABC (1:200). The reaction was developed
with diaminobenzidine (0.1 mg/mL) containing 0.0015%
H2O2. The immunolabeled sections were post-fixed in 1%
glutaraldehyde and 1% osmium tetroxide, dehydrated in
ethanol, embedded in epoxy resin, and then sectioned and
viewed with a JEOL 1230 electron microscope (JEOL,
Tokyo, Japan).

PATHOLOGICAL FINDINGS
embolization for ruptured aneurysm. At the age of 50
years, he was diagnosed as having hepatocellular carcinoma and underwent a partial hepatectomy under general
anesthesia. Three days after the operation, he was found to
be in cardiopulmonary arrest and died without resuscitation effect. Although general autopsy was performed 1.5 h
after death, the cause of death was not confirmed. An MRI,
which was taken 1 month before his death showed huge
AVM in the right frontal lobe (Fig. 1).

METHODS
For routine histological examination, 4-um thick, formalinfixed, paraffin-embedded sections from multiple cortical
and subcortical regions were stained with HE or by the KB
method. Selected sections were stained by the GallyasBraak method or immunostained using the following
primary antibodies: anti-phosphorylated tau (AT8; Innogenetics, Ghent, Belgium; 1:1000), anti-3-repeat tau (3R-tau)
(RD3; Upstate, Lake Placid, NY, USA; 1:3000), anti-4repeat tau (4R-tau) (RD4; Upstate; 1:500), anti-TDP-43
(10782–1-AP; Protein Tec Group, Inc., Chicago, IL, USA;
1:2000), anti-phosphorylated a-synuclein (#64; WAKO,
Osaka, Japan; 1:5000) and anti-GFAP (DAKO, Glostrup,
Denmark; 1:800). The sections were pretreated with heat

At autopsy, the brain weighed 1171 g. In coronal sections,
the anterior portion of the right frontal lobe was entirely
occupied by AVM, approximately 4 cm in diameter
(Fig. 2a). Histologically, the frontal cortex around the
abnormal vessels showed neuronal loss and gliosis with
mild calcification (Fig. 2b). Myelin and axons were severely
decreased in the right frontal white matter with hemosiderin deposition, scattered microglia, and infiltration of
macrophages and lymphocytes (Fig. 2c).
Many NFTs were found in the right frontal cortex
on HE-stained sections (Fig. 2d). Gallyas-Braak method
and AT8 immunohistochemistry revealed numerous NFTs,
pretangles and neuropil threads in the affected cortex
(Fig. 2e,f). The NFTs and neuropil threads were positive
for both 3R- and 4R-tau (Fig. 2g–j). Ultrastructurally, the
NFTs were composed of paired helical filaments (Fig. 3).
The cerebral tissue around the AVM occasionally
showed fibrillary gliosis with Rosenthal fibers. These structures appeared to be negative for phosphorylated tau. To
determine whether astrocytes contain phosphorylated tau
or not, double-labeling immunofluorescence using antiGFAP and AT8 was performed. The double-labeling demonstrated no co-localization of GFAP and phosphorylated
tau (Fig. 2k–m). No oligodendroglial coiled bodies or
thorn-shaped astrocytes were seen.
© 2011 Japanese Society of Neuropathology

Abnormal tau deposition in AVM

269

Fig. 2 Gross and microscopic findings. (a) Coronal section of the cerebrum showing arteriovenous malformation (AVM) in the right
frontal lobe. (b) Severe neuronal loss in the right frontal cortex surrounding the AVM. HE stain. (c) Fibrillary gliosis in the right frontal
white matter. HE stain. (d–f) NFTs (arrowheads) and neuropil threads in HE-stained (d), Gallyas-stained (e) and phosphorylated
tau-immunostained sections (f). (g–j) Immunoreactivity of 3R-tau (g, i) and 4R-tau (h, j) in NFTs (arrowheads) (g, h) and neuropil threads
(i, j). (k–m) Double-labeling immunofluorescence with anti-GFAP (k) and AT8 (l). Merge image (m) showing no colocalization of GFAP
and phosphorylated tau. Bars = 1 cm (a), 50 mm (b,c), 20 mm (d–j), 10 mm (k–m).

As described above, NFTs and neuropil threads were
widely distributed in the right frontal cortex around the
AVM. Phosphorylated tau-immunoreactive structures
were found in the superior and inferior frontal gyri, anterior cingulate gyrus, rectal gyrus and orbital gyri on the
right side (Fig. 4). In the other brain areas, a few NFTs were
found in the parahippocampal gyrus. There were no
Lewy bodies, Lewy neurites, TDP-43-positive inclusions or
amyloid deposition in the brain.
© 2011 Japanese Society of Neuropathology

DISCUSSION
To the best of our knowledge, our study is the first to address
the ultrastructural profile and tau isoforms of NFTs in cases
of AVM. Tauopathies are now classified as predominant
3R-tau pathology (Pick’s disease type), mixed 3R/4R-tau
pathology (Alzheimer type) and predominant 4R-tau
pathology (progressive supranuclear palsy type). The most
striking finding in the present case is the occurrence of

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T Kon et al.

Fig. 3 (a) Electron micrograph of NFT in the right frontal cortex
showing longitudinal (left) and cross-sectional profiles (right). (b)
Higher magnification view of another area showing paired helical
filaments. Bars = 0.2 mm.

Fig. 4

Distribution of phosphorylated tau in the present case.

Gallyas- and 3R/4R-tau-positive NFTs in the cerebral
cortex surrounding the AVM. They were composed of
paired helical filaments.Thus, NFTs observed in our case are
Alzheimer-type tau deposition. Our results are in accordance with a previous study that demonstrated the presence
of paired helical filaments in cases of sclerosing angiomas.10
We further demonstrated that massive tau deposition
was found in the neuronal cell bodies and processes, but
phosphorylated tau was not accumulated in glial cells in
the lesions.There have been only a few reports with respect
to abnormal tau accumulation in glial cells in disease
conditions other than tauopathies. Shimizu et al. have
described abnormal tau accumulation in neurons and glial
cells in the spinal cord from 11 cases of cervical spondylotic
myelopathy.13 They reported that NFTs contained both 3Rand 4R-tau, whereas tau deposited in astrocytic processes
and thorn-shaped astrocytes were predominantly 4R-tau.
Ikeda et al. reported that oligodendroglial tau-positive
structures (coiled bodies) were found in two cases of SSPE
with NFTs but not in the other two cases of SSPE without
NFTs.7 These findings suggest that the process of abnormal

tau accumulation in glial cells is different between vascular
malformation, traumatic diseases and viral infection.
In our case, AVM was pointed out about 30 years prior
to the patient’s death. Although it is difficult to precisely
determine how long the disease condition was present,
NFT formation is related to the disease duration in SSPE
and ganglion cell tumors. SSPE patients with NFTs are
older than those without NFTs.6,23 Brat et al. studied 72
ganglion cell tumors from patients aged between 7 months
and 72 years.3 They reported that NFTs were present in
four of 26 ganglion cell tumors from patients over 30 years
old (ages 31, 38, 50 and 58 years) and no NFTs were seen in
46 patients under 30 years old. These findings suggest that
NFT formation in disease conditions other than tauopathies may require long disease duration.
One of the possible mechanisms of abnormal tau deposition in AVM is ischemia.24 Previously, tau deposition has
been reported in the area of cerebral infarction.25 Ischemia
induces an increase of calcium and glutamate levels, which
alters the activities of intraneuronal calcium-dependent
kinases or phosphatases and exhibits tau deposition.26
As suggested previously, chronic microenvironmental
factors such as local inflammation,27,28 calcium toxicity,29
and increased blood brain–barrier permeability28 may also
contribute to abnormal tau deposition in cases of AVM.
In conclusion, we demonstrated that abnormal tau
deposition can occur in neurons, but not in glial cells, of the
affected cerebral cortex surrounding AVM. Further accumulation of similar cases will clarify the mechanism of tau
deposition in disease conditions other than tauopathies.

ACKNOWLEDGMENTS
This work was supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture,
Sports, Science, and Technology, Japan (FM, KT and KW)
and a Grant for Hirosaki University Institutional Research
(KW). The authors wish to express their gratitude to M.
Nakata for her technical assistance.

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