Keywords brachial plexus - giant - plexiform schwannoma
Background
Plexiform Schwannoma is a rare variant of Schwannoma that accounts for only 5% of
all Schwannomas, which typically shows a plexiform or multinodular growth pattern
mimics plexiform neurofibroma. It was first described by Harkin and Reed in 1978 [[1 ]]. Plexiform Schwannoma usually develops in the dermis or subcutaneous tissue, and
it is uncommon for the Schwannoma to develop in deep-seated nerves. Its histological
features include Antoni A and B areas, diffuse and strong positivity with immunohistochemical
markers like S-100, laminin and collagen type IV.
On the other hand, plexiform neurofibroma lacks Antoni A and B areas of schwannoma
and shows weak S-100 positivity. Plexiform schwannoma shows up to 5% association with
neurofibromatosis-2 and schwannomatosis, but has no association with neurofibromatosis-1
like plexiform neurofibroma [[2 ],[3 ]]. This report describes the rare case of a giant plexiform Schwannoma in the brachial
plexus.
Case presentation
The patient was a 64-year-old male. More than 30 years earlier, he had experienced
numbness in his left upper extremity. By his own account, he had undergone surgery
and was diagnosed with a brachial plexus tumor. He stopped visiting the hospital after
the surgery, no records of the surgery remain and the details thereof are unknown.
The patient was diagnosed with diabetes mellitus 2 years earlier. He had no family
history of a similar tumor. The patient noticed muscle weakness in his left arm 5
years earlier, but never visited a medical facility. Thereafter, the muscle weakness
worsened, and he finally visited a local doctor 2 years earlier. His upper extremity
was far from functional, and so he was referred to our hospital for further examination
and treatment.
On examination a biloculate mass was observed in the left supraclavicular area, and
Tinel’s sign caused paraesthesia in his left arm. There was no evidence of the other
tumor anywhere on his body. We found no café-au-lait spots or other signs of Recklinghausen
disease neither.
Manual muscle testing of his left upper extremity revealed the following results:
deltoid [[1 ]], biceps [[1 ]], brachioradialis [0], triceps [[4 ]], extensor digitorum [[2 ]], extensor digiti minimi [[2 ]], extensor pollicis brevis [[2 ]], extensor pollicis longus [[2 ]], extensor indicis [[2 ]], extensor carpi radialis [[4 ]], extensor carpi ulnaris [[4 ]], flexor carpi radialis [0], flexor carpi ulnaris [[5 ]], pronator teres [0], pronator quadratus [0], flexor digitorum superficiali [I-IV][0],
flexor digitorum profindus (index finger) [0] and II-IV [[5 ]], flexor pollicis longus [0], flexor pollicis brevis [0], and flexor digiti minimi
[0]. There was sensory loss in his axillary nerve, lateral brachial cutaneous nerve,
and median nerve. The ulnar nerve was intact. Therefore, impairment of the lateral,
posterior, and part of the median cord of the brachial plexus was suspected.
There were no abnormal findings in his cervical radiography. Magnetic resonance imaging
showed a continuous, multinodular, plexiform tumor from the left C5 to C7 nerve root
along the course of the brachial plexus to the left brachia. The tumor showed the
same intensity as the muscle on T1-weighted images and slightly higher intensity on
T2-weighted images. Gadolinium-enhanced images showed no enhancement of the tumor.
There was no sign of the tumor inside the vertebral canal ([Figure 1 ]).
Figure 1 . Magnetic resonance imaging images. Magnetic resonance imaging showed a continuous,
multinodular, plexiform tumor from the left C5 to C7 nerve root along the course of
the brachial plexus to the left brachia. The tumor showed the same intensity as the
muscle on T1-weighted images (T1WI), and slightly higher intensity on T2-weighted
images (T2WI). Gadolinium-enhanced images (T1WI+C) showed no enhancement of the tumor.
There was no sign of the tumor inside the vertebral canal.
Tumor excision was attempted via exploration from the axilla to the cubital fossa.
There was no abnormality in the ulnar nerve, but the median and musculocutaneous nerves
were extremely enlarged by the tumor. Judging from the MRI and operative findings,
the length of the tumor was approximately 40 cm in length ([Figure 2 ]). We haven’t done electrophysiological examinations prior to the operation, so we
performed electric stimulation during the operation. The tumor showed no response
to it. Therefore, we terminated tumor enucleation, excised part of the musculocutaneous
nerve (about 5 cm) for pathological examination, and performed latissimus dorsi muscle
transposition in order to repair elbow flexion function. The latissimus dorsi muscle
is innervated by C6-C8 nerve roots, mainly C7 nerve root. According to the patient’s
physical findings, C7 nerve root was possibly involved by the tumor. We have considered
the transposition of the sternum part of the pectoralis major muscle which is innervated
by C8-Th1 nerve roots, but since latissimus dorsi muscle maintained as strong muscle
contraction as the pectoralis major, and we were confident of the latissimus dorsi
muscle transposition from the past experiences, we have decided to perform the latissimus
dorsi muscle transposition.
Figure 2 . Operative findings. The median and musculocutaneous nerves were extremely enlarged
by the tumor and showed no response to electric stimulation. There was no abnormality
in the ulnar nerve. Triangle; ulnar nerve Wide arrow; enlarged median nerve Narrow
arrow; musculocutaneous nerve.
The excised specimen was formalin-fixed, paraffin-embedded, and sectioned for pathological
evaluation. We performed hematoxylin and eosin staining, Masson trichrome staining,
and immunohistochemistry for S-100 protein and neurofilamment.
Histologically, the tumor consisted of varying hypertrophic peripheral nerve fascicules
showing a plexiform pattern, along with fibrous connective tissues ([Figure 3-A ]). The tumor was mainly composed of Antoni A areas that showed dense fascicular and
interlacing proliferation of spindle-shaped tumor cells without notable nuclear atypia.
A nuclear palisading pattern was focally observed in the tumor ([Figure 3-B ]). Typical Antoni B areas were not observed in the tumor. The fibrous connective
tissues around the tumor were roughly stained with Masson trichrome ([Figure 3-C ]). Immunohistochemistry results showed that the tumor cells were strongly positive
for S-100 protein ([Figure 3-D ]). There were no neurofilamment-positive areas indicative of axons located inside
or outside the tumor ([Figure 4 ]).
Figure 3 . A. Hematoxylin and eosin staining (×40) . Hematoxylin and eosin staining (×40). The tumor consisted of varying hypertrophic
peripheral nerve fascicules showing a plexiform pattern, along with fibrous connective
tissues.B. Hematoxylin and eosin staining (×100) . Hematoxylin and eosin staining (×100). Antoni A areas, which composed main part
of the tumor. A nuclear palisading pattern was focally observed. C. Masson trichrome staining (×100). Masson trichrome staining (×100). The fibrous connective tissues around the tumor
were roughly stained. Immunohistochemistry for S-100 protein (×100). Immunohistochemistry for S-100 protein (×100). The tumor cells were strongly positive
for S-100 protein.
Figure 4 . Immunohistochemistry for neurofilament (×100). There were no neurofilamment positive
areas indicative of axons inside or outside the tumor.
Morphologically, the tumor consisted of typical Antoni A areas, which are generally
found in Schwannomas but not in neurofibromas, and immunohistochemistry results revealed
a Schwann cell origin of the tumor cells. These features made us suspect that the
tumor was a Schwannoma. However, it is well known that Schwannoma-like lesions can
be seen in some neurofibromas [[4 ],[5 ]]. However in our case, there was absolutely no sign of axon differentiation in the
tumor, and we observed no neurofilament-positive areas. Therefore, the final diagnosis
of plexiform Schwannoma was confirmed.
Sixteen months after the operation, no progression in paralysis was observed. By latissimus
dorsi transposition, the patient acquired elbow flexion up to 100 degrees ([Figure 5 ]). Collateral suture of the left flexor digitorum profundus I to flexor digitorum
profundus II-IV, metacarpophalangeal joint arthrodesis of the left thumb, and reconstruction
of the pollicis opponens with the Makin method improved his activities of daily living.
Figure 5 . Sixteen months after the operation. By latissimus dorsi transportation, the patient
acquired elbow flexion up to 100 degrees.
Discussion
There have been few case report of plexiform Schwannomas in deep-seated nerves, as
observed in our patient [[6 ]]. However, none of these reported Schwannomas was as large as that in our patient.
The differential diagnosis of plexiform Schwannoma with plexiform neurofibroma is
very important. Schwannomas are benign encapsulated tumors originating from Schwann
cells in the peripheral nervous system. Neurofibromas are benign, heterogeneous peripheral
nerve sheath tumors arising from the connective tissue of peripheral nerve sheaths,
especially the endoneurium. Neurofibromas are mostly solitary: however, when associated
with neurofibromatosis type I, they can occur as multiple tumors. Optic glioma, Lisch
nodules, and sphenoid dysplasia can also be found in neurofibromatosis type I, but
non of them was found in our case. We must consider the possibility of neurofibromatosis
type II. Definite criteria for neurofibromatosis type II include bilateral vestibular
Schwannoma or first-degree family members of neurofibromatosis type II, and unilateral
vestibular schwannoma diagnosed younger than 30 years or any two of meningioma, glioma,
or schwannoma [[7 ],[8 ]]. Another differential diagnosis is schwannomatosis. Schwannomatosis is generally
a sporadic, nonfamilial condition that presents in older age groups with longer life
expectancy, with two or more pathologically proven schwannomas. Definite criteria
for schwannomatosis include the lack of neurofibromatosis type II mutations [[5 ]]. It is recently reported that trisomy of chromosomes 17 and 18 are present in a
plexiform schwannoma [[6 ]]. We could not obtain approval of DNA analysis from the patient, but since his schwannoma
was solitary, and there were no signs of vestibular schwannoma, glioma or meningioma,
the possibility of neurofibromatosis type II and schwannomatosis were denied.
In our case, the clinical features and the appearance of the tumor was rather like
that of plexiform neurofibroma. The patient did not show any café-au-lait spots, which
precluded the presence of neurofibromatosis type I. The final diagnosis was thus based
on microscopic tumor findings. In our case, the findings were specific to Schwannoma,
namely, Antoni type A areas, anti-S-100 protein staining, minimal fibrous tissues,
and no evidence of axon growth inside the tumor, which is most important. We excised
only a part of the huge tumor; therefore, we cannot completely deny the possibility
of Schwannoma-like lesions in a plexiform neurofibroma. However, since there were
no neurofilament-positive areas inside or outside the tumor, we are confident in our
diagnosis of Schwannoma.
In our case, the patient experienced paralysis for quite a long time, and we could
thus not expect improvements in nerve function. In addition, because the tumor was
too large to excise, we performed only a biopsy. Whether or not we should have instead
resected the whole tumor is controversial. In past case reports of plexiform Schwannomas
occurred in deep-seated peripheral nerves, paralysis was not present or very mild
([Table 1 ]). Furthermore, in all cases, the size of the tumor was much smaller than that observed
in our case. Deep seated plexiform schwannoma can show necrosis and myxoid change
in 12% of the lesions [[6 ]]. In our case, no such histological abnormality was seen in the excised specimen.
However, considering the severe neurological deficit, necrotic change might have occurred
somewhere in the tumor.
Table 1
Past case reports of plexiform Schwannoma in deep-seated peripheral nerves.
Reference
Case
Tumor site
Size
Paresthesia
Treatment
Oota et al
8 yr, M
C5,6 root
4 × 5 × 3 cm
None (postoperative +)
Enucleation
Ikeda et al
6 yr, F
Sciatic n
9 × 4 cm, 7 × 3 cm
None
Enucleation
Ikeda et al
14 yr, F
C4,5,6root
10 × 5 × 4 cm
None(postoperative +)
Enucleation,
Reconstruction
Ikeda et al
14 yr, F
Median n.
1.5 × 2.5 cm
None
Enucleation
Nakamura et al
64 yr, F
L5 root
1.5 × 4 cm, 2 × 1 cm
None
Enucleation
Sakamoto et al
45 yr, M
Median n.
Atrophy of flexor carpi radialis, thenar eminence
Reconstruction
Maehara et al
42 yr, M
Sciatic n.
21 × 5 cm
None
Enucleation
Okuda et al
19 yr, F
Digital n.
None
Enucleation
Kawakami et al
28 yr, M
Median n.
3 × 3 cm
None
Enucleation
Oono et al
67 yr, F
Brachial plexus
3 × 4 × 5 cm
None
Enucleation
Horikiri et al
54 yr, F
Median n.
4 × 5 cm, 10 × 17 cm
Atrophy of thenar prominence
Enucleation
Kawamura et al
59 yr, F
Ulnar n.
35 cm
None
Enucleation, Reconstruction
We must consider the possibility of worsening paralysis and malignancy when contemplating
tumor resection. If the tumor develops another fascicle, the paralysis may become
worse. However, in our patient, considering his history the development of the tumor
must have been very slow. Furthermore, according to the pathological diagnosis, the
tumor was a plexiform Schwannoma, which is associated with a very low possibility
of malignancy. Instead, we have found only one case report describing malignization
of a plexiform Schwannoma [[9 ]].
Conclusions
We have experienced the rare case of a giant plexiform Schwannoma in the brachial
plexus. The affected nerves did not react to electric stimulation during the operation,
and tumor invasion was extremely extensive, we therefore decided only to remove part
of the tumor as biopsy, and changed the purpose of the operation from tumor removal
the to reconstruction of elbow function. The diagnosis of plexiform Schwannoma had
been made based on the pathological study. The condition of the patient remains satisfactory
thus far, but careful observation of the progression of paralysis is necessary.
Consent
Written informed consent was obtained from the patient for publication of this Case
report and any accompanying images. A copy of the written consent is available for
review by the Editor-in-Chief of this journal.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
SK participated in practice and operation, and constructed the manuscript. YH and
YN participated in practice and operation, and helped to construct the manuscript.
TH and TN carried out the operation. SS carried out pathological study. NO also carried
out the operation, and have given final approval of the version to be published. All
authors read and approved the final manuscript.
Cite this article as: Kohyama et al. : A giant plexiform schwannoma of the brachial plexus: case report. Journal of Brachial Plexus and Peripheral Nerve Injury 2011 6 :9.
