also known as neurilemomas are neuroectodermal
derived lesions. The cell of origin is Schwann
cell, which is responsible for maintaining the
myelin coating of neurons.1 Schwann
cells are glial cells that provide insulation for
both the motor and the sensory neural signal in
the peripheral nervous system. They have
predilection for sensory nerves with the eighth
nerve being most frequently affected.2
usually isolated, solitary, slow-growing and well
encapsulated lesions. In some cases, they are
associated with neurofibromatosis syndrome and
patients develop multiple Schwannomas, known as
Aims of the present
study are to analyse the spectrum of demographic
and clinical presentations of Schwannoma with
special emphasis on occurrence at unusual sites,
to discuss the histopathological features of this
lesion at these unusual locations and analyse with
the available literature.
Materials and Methods
retrospective cross-sectional observational study
was done on 18 diagnosed cases of Schwannoma
located at unusual sites after procuring
Institutional Ethical Committee Clearance
(IEC:15/23). The clinical, radiological and
pathological details were retrieved from the
hospital records and the pathology database.
Parameters described in Table 1 were analysed.
Table 1: Proforma
9. Frozen diagnosis if any
10. Gross features
3. Clinical presentation
11. Histopathological diagnosis
4. Size of the lesion
5. Site of the lesion
13.Immunohistochemistry, if done
14. Follow up
7. Preoperative radiology
8. Clinical diagnosis
Of the 18 cases
studied, the age ranged from 20- 82 years with a
mean age being 45.5 years. Sex ratio was equal.
Head and neck
region, and the lower limb were the most common
sites, consisting for 28% cases each, followed by
22% cases in abdomen/retroperitoneum region, 16 %
cases in thorax, and 6% of cases in the upper limb
1: Topographical distribution of the
Majority of cases
(38 %) presented with painless swelling. Other
symptoms included backache (11%), abdominal pain
(11%), limb pain (5%). Symptoms like blurring of
vision (5%) and reduced hearing (5%) were noted in
patients who presented with retro maxillary
lesion. The duration of symptoms ranged from 5
days to 6 years.
Imaging was done in
10 cases. Majority of cases underwent magnetic
resonance imaging (MRI) (50%) followed by computed
tomography (30%), ultrasonography (10%) and
radiography (X-ray) (10%). The radiology in all 10
cases were suggestive of benign lesion (Figure 2).
2: Axial view of CT showing ill-defined
heterogenous soft tissue density lesion in
right infratemporal fossa (arrow)
diagnosed clinically in 7/18 cases. Other
suggested clinical diagnosis were paraganglioma,
sebaceous cyst and retro-maxillary tumour in one
case each. No clinical diagnosis was mentioned in
8 cases. The clinico-histopathological correlation
underwent complete surgical excision through
Frozen was done in 2
cases and were reported as spindle cell neoplasm.
Grossly, the lesions ranged 0.5- 15 cm in greatest
dimension. Mean size was 4 cm (Figure 3).
3: Gross - well encapsulated lesion with
examination of all cases revealed the classic
findings of Schwannoma with 33% cases associated
with secondary changes like microcytic change,
hemosiderin-laden macrophages, foam cells, myxoid
change, edema, bizarre nuclei and verocay body
formation. In 5/18 cases confirmatory
immunohistochemistry S100 was done and found to be
positive (Figure 4).
4: Microscopy - Hypocellular and
hypercellular areas H and E (X200), Inset
known as neurinomas of Verocay, are slow growing
peripheral nerve sheath tumours composed almost
entirely of Schwann cells. Other tumours
classified as peripheral nerve sheath tumours
include neurofibroma, perineuroma, traumatic
neuroma and malignant peripheral nerve sheath
tumour.1,3–7Neurinomas were first
described in 1910, as a group of neurogenic
tumours. Later on in 1935, these neurogenic
tumours were renamed as 'Neurilemmomas' as it was
proposed that they arise from nerve sheath
elements.3 Lusk et al stated that
highly differentiated perineural cells, the
Schwann cell, gives rise to Schwannomas while
perineural fibrocytes give rise to more invasive
neurofibroma.8 Eventually it was found
that the Schwann cell is the common precursor for
most nerve sheath tumours, hence named as
commonly occur in patients between age group of 20
- 50 years and only about 12% are seen in the
paediatric or adolescent population.9
In our study also, most of the cases were between
3rd – 5th decade. This was
also noted in studies done by Gupta et al and
Adani et al. 9,10
In present study,
equal male to female ratio was found, similar to
studies done by Chikkannaiah et al, Akyildiz et
al, Majumder et al and Hao et al.11–14
However Gilmer et al and Torossian et al found a
female preponderance in their respective case
The symptoms are
mostly related to the tumour location, especially
on the sites of weight bearing and pertaining to
nerve compression. The usual presenting symptoms
ranged from painless swelling to nerve compression
symptoms such as tingling, burning sensation,
weakness, paraesthesia.13,14 Painless
swelling was predominantly the major symptoms in
majority of the studies.4,13,14,17
Occurrence of pain and neurological deficit are
ominous signs suggestive of malignancy. The
unusual symptoms such as nasal obstruction,
hoarseness, epiphora, hearing loss, Horner’s
syndrome, dysphagia, paraesthesia, pain and
respiratory symptoms were noted by few authors
based on the site of lesion.18,19The
most common clinical presentation in our study was
The spectrum of
clinical diagnosis considered by the clinicians
other than Schwannoma include ganglion cyst,
lipoma, Dupuytren’s contracture, fibroma, hydatid
cyst, haemangioma and epidermal inclusion cyst. 14
In present study the other clinical
diagnosis suggested by clinicians were epidermal
inclusion cyst, retromaxillary tumour and
Schwannomas are benign and can occur at a variety
of anatomical location. They mostly arise at
intracranial site from sensory nerve roots. The
most common affected nerve is vestibular branch of
the eighth nerve followed by trigeminal nerve.
Other lower cranial nerves may be involved in the
setting of neurofibromatosis.20 The
unusual sites of occurrence documented are
parotid, nasopharyngeal region, posterior pharynx,
skull base, chest wall, thorax, posterior
mediastinum, abdomen, retroperitoneum, pelvis and
penis.12,14,19,21–26 In our study the
unusual sites reported were retro maxillary
region, paraaortic region of the thorax,
mediastinum, stomach, retroperitoneum and thigh.
The head and neck
region account for 25–45% cases of Schwannomas and
usually affect patients in their fifth decade.27
The uncommon site of extracranial Schwannomas in
the head and neck include parapharyngeal region,
submandibular area, parotid, intraoral and
paranasal sinus.27 Arshad et al, in
their study diagnosed 9/42 cases Schwannoma at
head and neck region. There was no sex
predilection and mean age of 30.7 years.18
Leu and Chang et al reviewed a series of 52 cases
originating in head and neck region over a period
of 8 years where 25 cases occurred in scalp, face,
external ear, 9 cases were located in oral
cavity/nasal cavity and 18 cases in neck. 17
Head and neck was the most common site in
our study as well and constituted 5/18 cases with
a mean age of 54.6 years.
In the lower
extremity, the usual sites of Schwannoma include
posterior tibial nerve and achilles tendon,
however this site is affected in <10% of all
cases.1,5,28–30 Foot and ankle region
are extremely infrequent sites. Kim et al reviewed
397 peripheral nerve sheath tumours, only 8%
Schwannomas were located in the lower extremity.31In
our study, 5/18 cases were reported in lower
extremities at thigh, gluteal lesion and popliteal
fossa with a mean age of 48.6 years.
location is also extremely uncommon with reported
incidence ranging from 0.7 to 2.7%.25
Surendrababu et al reported a rare case of
retroperitoneal Schwannoma mimicking ovarian cyst.
32 In our study 4/18 cases were
reported in the retroperitoneum region with a mean
age of 36 years.
represent 15-25% of mediastinal tumours, generally
occurring in the posterior paravertebral area.33
Thoracic neurogenic tumours are generally located
in the mediastinum or on the chest wall. Rarely
these lesions originate in the lung. Matsumoto et
al. reported a 2 cm lesion on the pleura in a 19
year old female which was incidentally detected
and was eventually diagnosed as Schwannoma.34
In present study, only 2/18 cases were noted in
the thorax region with a mean age of 32.5 years.
Occurrence in the
upper extremity is not encountered often. Usually,
the ulnar nerve is involved while only 7% of
Schwannomas involve the median nerve. In the upper
limb, they may be mistaken for ganglion cyst or
carpal tunnel syndrome.14 Typically,
they appear as swollen, slow-growing lesions along
the nerve length. In a study by Tang et al, eight
cases of upper-limb Schwannomas were studied with
a mean age of 56 years.35 In our study
we found only one case in the upper limb region.
usually the first imaging modality, and it often
reveals a solid, strongly defined, ovoid,
homogenous mass. To rule out any bone involvement
or anomalies, an X-ray may be taken. Schwannomas
often exhibit isointense or decreased signal
intensity on T1-weighted images compared to
skeletal muscle and heterogeneously elevated
intensity on T2-weighted imaging. The target sign,
spilt fat sign, and fascicular split sign are some
further characteristics of Schwannoma.35
In our study, MRI was performed on majority of
Complete excision is
recommended since incomplete resection may result
in recurrence.36 Grossly, the lesions
are most often spheric or ovoid, firm or rubbery
tumours. They range in size from 0.5-15 cm. In our
study, grossly the size of the lesion size varied
from 1-4 cm. Strauss et al in their study of 28
cases of benign retroperitoneal Schwannoma have
reported size range from 5-23 cm and weight range
between 0.5-2 kg. 37
The histology of
Schwannoma typically shows encapsulated lesion
with areas of dense cellularity of aggregated
spindle shaped cells arranged short fascicles and
bundles termed as Antoni-A regions. Along with
hypocellular areas with myxoid matrix termed as
Antoni-B regions. Immunohistochemistry is positive
for S100 in majority of the cases, vimentin, and
neuron-specific enolase are positive, but negative
for smooth muscle actin and CD117.13,37,38 Other
differentials like solitary fibrous tumour are
S100 negative; CD34, CD99 and STAT-6 positive.
Paraganglioma are S100 diffusely positive only in
sustentacular cells and chromogranin is diffuse
positive.13,39,40 The distinction
between Schwannoma and neurofibroma is important
because the latter shows a small potential for
Neurofibromas are not encapsulated and lack the
biphasic pattern of Schwannomas. They have a
haphazard arrangement of nerve fibres, what is
likened to “Shredded Carrot” appearance as opposed
to the somewhat oriented nuclei seen in Verocay
bodies, a pathognomonic feature of Schwannomas.40
Malignant transformation of Schwannoma account
for 5% of peripheral nerve sheath tumours. 4,29,42
The histopathological diagnosis of malignant
transformation requires the following criteria: 1.
demonstrable areas of benign Schwannoma, 2.
unequivocal malignant foci manifested by increased
cellularity, numerous mitoses, anaplastic cells
and invasiveness, 3. transitional areas between
malignant and benign regions.43
Schwannomas are rare and usually are associated
with Von Recklinghausen’s disease. They act as
high-grade sarcomas with a high likelihood of
producing local recurrence and distant metastasis.23
The histology of malignant component in most of
the lesions is of epithelioid morphology.44
However, in our study malignant transformation was
not seen in any case during the follow up period
of 3 years.
benign lesion with very good prognosis and have
minimal chance of malignant progression. They have
predilection for cranial nerves and spinal nerve
roots but can occur at unusual sites. These sites
and misleading presentations may pose diagnostic
challenge for both clinician and pathologists
alike. Thus, unawareness of this benign entity can
lead to unnecessary treatment. Pathologists must
be aware of the occurrence of Schwannoma at
unusual sites for the proper management.
- Jack CM, Jones G, Edwards MR, Singh SK. A case
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- Joshi R. Learning from eponyms: Jose Verocay
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