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Radiology
Case of the Month
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There
was mild effacement of anterior subarachnoid space with intrinsic abnormal
hyperintense signal seen within the cervical cord suggesting cord edema
/ ischaemia.
On the basis of the enhancement characteristics and intervertebral foramen
widening, the possibility of a schwannoma was entertained. However, with
this degree of bone destruction other possibilities such as a giant cell
tumourand aneurysmal bone cyst were considered in the differential diagnosis.
At surgery (posterior approach) a large fleshy tumour, separate from the
meninges and the nerve roots was removed.
Gross pathological examination revealed grey-white glistening tissue. Histopathology
of the resected mass showed areas of nuclear pallisading and dense areas
of tumour cells alternating with loosely textured myxoid tissue. These findings
were consistent with Antoni type A and Antoni type B tissue respectively.
Immunohistochemical testing for S-100 protein was diffusely positive, whereas
glial fibrillary acidic protein (GFAP) was negative confirming the diagnosis
of schwannoma. There was no evidence of any malignant change within the
resected tumour.
DIFFERENTIAL DIAGNOSIS:
A wide variety of benign and malignant neoplasms can involve the spine and
cause expansion of the vertebra. These include giant cell tumour, osteoblastoma,
aneurysmal bone cyst, solitary plasmacytoma and metastases. Certain spinal
tumours involve one or more contiguous vertebral levels or present as an
expansile lesions in a specific region of the spine providing an important
clue to the diagnosis . Giant cell tumors in spine most commonly occur in
sacrum . When GCT occurs in spine above the sacrum it usually affects the
vertebral body. On conventional radiograph, spinal GCTs demonstrate osteolytic
expansile lesions with no evidence of mineralisation. On CT, these tumors
have soft tissue attenuation with well defined margins that may show a thin
rim of sclerosis. On MRI, hypointensity with heterogeneous hyperintense
foci is seen on T1WI and iso to hyperintense signals on T2WI. They commonly
enhance and frequently show presence of blood degradation products. An osteoblastoma
is fairly common in the spine and most frequently involves the posterior
vertebral elements. Extension into the vertebral body is also common. The
most common radiographic pattern is expansile lesion with multiple small
calcifications and a peripheral sclerotic rim. On MRI it shows low to intermediate
signal intensity on T1WI and intermediate to high signal intensity on T2WI
. Aneurysmal bone cysts most commonly affect the thoracic spine .These lesions
typically affect young patients with 80% being less than 20 years of age.
Radiographs generally show marked expansile remodeling of bone centered
in posterior elements, although extension into vertebral body frequently
occurs . CT and MR imaging suggest the cystic nature of lesion and often
show fluid - fluid levels within ABCs. On T1 and T2 -weighted images they
have increased signal intensity. Solitary plasmacytoma occurs most commonly
in thoracic spine . They usually predominate in vertebral body. In one third
of cases,a multicystic soap-bubble appearance may be seen. At MR imaging,
a solitary plasmacytoma of the bone typically exhibits high homogenous signal
intensity on T2W images and homogenous marked enhancement post gadolinium
images . Uncommonly, metastasis in cervical spine, from kidney and thyroid,
can also present in this fashion.
In this case, with neural foramen enlargement with the dumbbell shape of
the extradural tumor and uniform contrast enhancement, a schwannoma was
thought as a possibility which was confirmed by histopathology of the resected
specimen.
DISCUSSION:
Schwannomas and neurofibromas are the most common nerve sheath tumours found
in the spine. These are benign tumours arising from the Schwann cell or
perineural fibroblasts respectively. These tumours usually present as extramedullary
intradural tumours (70-75%), less commonly both intra and extradural (15%),
extradural (15%) and intramedullary (< 1%). The distribution of these is
fairly uniform throughout the spine, with a slight lumbar predominance.
Schwannomas are typically lobulated, encapsulated masses. Nerve fibers do
not course through them. They have a variable clinical presentation which
includes pain along the distribution of nerve and/ or localized mass. Often
they are detected incidentally.
On MR imaging, nerve sheath tumors are isointense to hypointense on T1WI
and hyperintense on T2WI. They show uniform and marked enhancement on contrast
administration. Spinal schwannomas may undergo cystic degeneration. Cystic,
hemorrhagic, or necrotic degeneration is seen as hyperintense and variably
inhomogeneous central signal intensity on T2 WI. They rarely ever show calcifications.
Schwannomas can cause pressure erosion of the pedicle and the vertebral
body resulting in enlarged foramen and scalloping of the vertebra. However
extensive vertebral destruction is unusual for a schwannoma.
Three possible mechanisms have been postulated by which a nerve sheath tumour
can involve bone:
1. An extra-osseous tumor causing secondary erosion of bone,
2. Tumor arising centrally within the bone (intra-osseous neurinomas),
3. Tumour arising in the nutrient canal and growing in a dumbbell- shaped
configuration, resulting in enlargement of the canal
In conclusion extradural schwannoma should be included in the differential
diagnosis of expansile vertebral lesions, especially with characteristic
imaging findings like neural foramina enlargement and uniform enhancement.
MR imaging with its multiplanar capability and excellent soft tissue differentiation
is invaluable in offering the correct diagnosis.