Malignant Peripheral Nerve Sheath Tumor of Scalp: A case report with
review of literature.
Abstract
Malignant Peripheral nerve sheath tumors(MPNST) account for approximately 5-10% of soft
tissue sarcomas and occur most often in limbs and paraspinal region. This entity is an
extremely rare occurrence in the scalp with sporadic case reports appearing in English
literature since 2003.Here we describe a case of 38 year old male with MPNST of the scalp
over the right temporo-mastoid region, its course of management and the difficulties
encountered. The case represents not only a rare tumor occurring in a rarer location but also
the difficulties in obtaining clear margins of resection for sarcoma in scalp with bone erosion
as dura does not seem to present any significant barrier for local invasion.
Introduction
Malignant peripheral nerve sheath tumor ( MPNST) are defined as malignant tumors either
arising from a peripheral nerve sheath ( except epineurium and vasa nervorum ) or showing a
nerve sheath differentiation (1). MPNST usually arise from large peripheral nerves and are
more common in limbs. Head and neck region in general and scalp in particular are extremely
uncommon locations for their occurrence . One of the largest single institution series of
MPNST had only nine cases in head and neck region of a total of 200 cases (2). Here we
describe the presentation and management of a rare case of a MPNST of scalp with calvarial
erosion.
Case Report
A 38 year old male presented with a large slowly growing swelling over right temporomastoid region of head over a period of 2 years. The patient had noticed an increased rate
of growth over the previous 8 months and it had become painful since about 3 weeks before
admission. The swelling was uniformly firm in consistency, with well defined margins, globular
in shape, non- transilluminant , and was immobile over the underlying structures. The skin over
the lesion was not pinchable and showed an area of ulceration over its posterior extent . He
had been employed as a driver in a middle eastern country and had undergone an incisional
biopsy from the lesion there and the incision site had not apparently healed and had
persisted as an ulcer. The margins of this ulceration were everted and the floor was covered
with slough. A thin serous discharge was also observed from the ulcer.( Fig 2) There was no
lymphadenopathy. There were no stigmata of NF1. CT scan had revealed a soft tissue mass
with evidence of strong enhancement with bone window revealing erosion of skull( Fig 1). The
patient was taken up for wide excision of the mass by neurosurgery service . Intraoperatively ,
the lesion seemed to have vague capsule around it but had areas where it was infiltrating
the temporalis muscle . There was no clear plane of the lesion from the scalp . The lesion was
pinkish in coloured and was relatively avascular. An area of erosion of skull was seen. Wide
excision of the of the lesion was done . The final histopathology report was suggestive of
MPNST .(Fig 3)Immunohistochemistry for S-100 antigen was done revealing 60% positivity. A
diagnosis of malignant peripheral nerve sheath tumor was made.
The patient was planned for re-excision as only 1cm margin had been obtained in the first
instance. This needed excision of the ipsilateral pinna for which the patient was not ready. He
was started on chemotherapy with Adriamycin( 100mg) every 3 weeks for six cycles. After
about 2 months of completion of chemotherapy, a recurrence was observed at the posterior
margin of the resection( occipital region). This time, he underwent radiotherapy( 50 Gy in 25
fractions).This was unable to control the growth and he underwent chemotherapy with
Gemcitabine(900 mg/sq m on day 1 and 8) and Docetaxel(35 mg/sq m on day 1 and 8) every
3 weeks for six cycles. The external growth was controlled with chemotherapy. However, he
had an episode of seizure and the imaging revealed massive dural invasion and involvement
of transverse and sigmoid sinuses with involvement of underlying brain. The extent of
involvement precluded a safe resection. After discussion about the available options, the
patient decided to take up therapy with Pasopanib( 800mg daily for two months).
At the time of reporting, the patient has been under treatment for almost two years since
his first surgery. Presently, the patient is symptomatically relieved while off Pasopanib for
one month.
Discussion:
MPNSTs are uncommon malignancies accounting for 5 to 10% of all soft tissue sarcomas
with an incidence of 0.1/100,000 per year in the general population (2). These lesions are
commonly located in thighs, buttocks, and brachial plexus. Scalp in particular and head and
neck in general are extremely uncommon locations for their occurrence and very few case
reports have been appearing in English literature since 2003 (3,4,5,6,7,8,9).However, the
diagnosis should be strongly considered in any patient with rapidly enlarging swelling of the
scalp. The only prognostic indicators for recurrence and metastasis have been negative tumor
margins after excision and radiotherapy. Tumor location has not been found to directly affect
the same. However, the inability to provide tumor free margins in certain locations like headneck, retro peritoneum and thoracic cavity may render these locations unfavourable.
Approximately two- thirds of MPNSTs arise by malignant degeneration of pre-existing
neurofibromas with or without neurofibromatosis 1. Others arise de-novo. A higher incidence
of MPNST has also been noted after radiation exposure(1). Our case seems to have been a
malignant lesion from the beginning.
Imaging features of MPNST in other locations like pelvis have been well summarised by
some authors (10) and include diffuse or ring enhancement of MPNST as against central
enhancement of their benign counterparts.
Microscopically, MPNST is a densely cellular tumor that shows fascicular areas with alternate
myxoid areas in a swirling pattern classically called merbellisation (1). Cells may be spindle
shaped with irregular contours. Malignancy as in other tissues is suggested by invasion of
surrounding tissues, Invasion of vascular structures, nuclear pleomorphism, necrosis and
mitotic activity. S-100 immunoreactivity has been widely used in diagnosing PNSTs. Though it
shows focal positivity in almost 70 to 90% MPNSTs, a more diffuse positivity suggests BPNSTs
including degenerating schwannomas (11). Ki-67 immunoreactivity of more than 5% has been
suggested as an additional supporting criterion.
The present consensus about management of MPNSTs is carry out a wide surgical excision
and follow it up with adjuvant radiotherapy. Chemotherapy has a role in case of advanced
local disease and metastatic disease. The local recurrence rate for MPNSTs has historically been
reported to range from 40-65% and the distant recurrence rate has similarly been reported to
range from 40-68% (12).
In conclusion, MPNSTs though extremely rare in head and neck region, should be strongly
considered in differential diagnosis of rapidly enlarging solid lesion of scalp. These are
aggressive lesions and demand an early diagnosis and multimodality treatment.
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