Keywords
dorsal - intramedullary - schwanomma
Palavras-chave
dorsal - intramedular - schwanomma
Introduction
Schwanommas account for 30% of primary intraspinal tumors. Intra-spinal schwanommas
are usually located in the intradural extramedullary (IDEM) space, and are rarely
intramedullary. Intramedullary schwanommas (ISs) only account for 0.3% of intraspinal
tumors, and for 1.1% of intraspinal schwanommas.[1] Most ISs are found in the region of the cervical cord, and less than 20 cases of
been reported in dorsal region to date. The cell of origin of the schwanomma is the
Schwann cell, which is not normally found within the parenchyma of the brain and spinal
cord; therefore, it is not surprising that these lesions are rare. Several theories
have been postulated to explain the origin of these tumors, but none has gained universal
acceptance. We report a rare case of solitary dorsal IS in a young patient who presented
with paraplegia.[2]
[3]
Case
A 20-year-old female patient presented with back pain that had been felt for 1 year,
with gradually progressive weakness in both lower limbs in the previous 2 months.
Upon neurological examination, she had paraparesis in both lower limbs with a power
of 3/5 on the myelomeningocele (MMC) scale. She also had bowel and bladder incontinence.
Her sensory examination revelaed loss of sensation below the level of D5. She was
submitted to a magnetic resonance imaging (MRI) scan of the dorsal spine with contrast,
which revealed a well-defined heterogeneously enhancing intramedullary lesion with
expansion of cord and perilesional edema at the level of D5 to D6 ([Figs. 1]
[2]
[3]). The patient operated with the differential diagnoses of intramedullary tuberculoma
or glioma in mind. She underwent dorsal (D4 to D6) laminotomy with complete excision
of the lesion. Intraoperatively, a greyish-white, well-defined, firm, non-suckable
intramedullary lesion was found ([Figs. 4]
[5]
[6]
[7]). Postoperatively, there was minimal improvement in power in both lower limbs. The
patient was discharged with an indication for physiotherapy and regular follow-up.
Fig. 1 Preoperative magnetic resonance imaging (MRI) scan of the dorsal spine with contrast
showing the intramedullary contrast-enhancing lesion.
Fig. 2 Preoperative magnetic resonance imaging (MRI) scan of the dorsal spine with contrast
showing the intramedullary contrast-enhancing lesion.
Fig. 3 Preoperative MRI of the dorsal spine: T2-weighted images showing the intramedullary
lesion and cord expansion with syrinx formation.
Fig. 4 Intraoperative image showing the lesion within the spinal cord.
Fig. 5 Intraoperative image showing paramedian myelotomy.
Fig. 6 Intraoperative image showing gradual piecemeal removal of the intramedullary lesion.
Fig. 7 Intraoperative image after complete removal of the lesion showing the cavity within
the cord.
To our surprise, the histopathology was suggestive of spindle-cell tumor with pallisading
architecture and intratumoral aggregates of pigments in the hemosiderin-laden macrophages
with cystic changes that is, schwanomma ([Fig. 8]).
Fig. 8 Postoperative MRI of the dorsal spine showing complete excision of the lesion.
Discussion
Spinal schwannomas are the most common primary spinal tumors, accounting for ∼ 25%
of primary intradural spinal cord tumors in adults. Males and females are equally
affected, and the age of onset is usually between 25 and 50 years. Hirano et al. reported
an extended series of 678 spinal cord tumors: schwannomas were the most common histological
type, with a slight prevalence of the male sex. The symptoms are related to tumor
location and its proximity to the spinal cord. Most studies report pain as the first
symptom, followed by sensory deficits. Motor deficits and sphincter impairment are
observed relatively late. The gold standard for the preoperative diagnosis of spinal
schwannoma is the MRI. Schwannomas are more commonly observed in the lumbar spine.
In the literature, 70% to 80% of spinal schwannomas are reported to be intradural
in location, followed by dumbbell tumors, with both intradural and extradural components
accounting for another 15%. Surgical resection is considered the gold standard for
the treatment of spinal schwannomas.[4]
[5]
IS was first reported in 1931 by pathologist James Kernohan. However, to date, less
than 70 cases of IS have been reported, most of them cervical, with less than 20 in
the dorsal region. The most common location of ISs in order of frequency are the cervical
spine (63%), and the thoracic (26%) and lumbar (11%) levels. Intramedullary schwanommas
are benign but clinically progressive lesions. Early surgical intervention remains
the gold standard treatment before the neurological deficits develop.[1]
The intramedullary location is rare, since the origin of the schwanomma is the Schwann
cells, which are not normally found within the parenchyma of the brain and spinal
cord. This has raised speculations about its pathogenesis, and has led to several
theories to explain the origin of these tumors, although none has gained acceptance.[1]
[3]
The theories regarding the possible genesis that have been postulated[3] are:
-
central displacement of Schwann cells during embryonic development;
-
Schwann cells ensheathing aberrant intramedullary nerve fibers;
-
Schwann cells extending along the intramedullary perivascular nerve plexus;
-
possible neoplastic growth from dorsal-root Schwann cells located in a “critical area,”
as suggested by Mason and Keigher, in which the posterior roots lose their sheaths
upon entering the pia mater; and
-
transformation of pial cells of neuroectodermal origin into Schwann cells.
Wood et al. made two important observations: first, that schwannomas are usually located
posteriorly/posterolaterally, and second, that the tumoral vascular plexus, if observed
during surgery, always originates from anterior spinal arteries, never from posterior
spinal arteries. A case of dumbbell-shaped neurofibroma with intramedullary and extramedullary
components has been reported by Gorman et al., supporting the hypothesis of a “critical
area.”
The modality of choice for the diagnosis of intraspinal tumors is the MRI. Intramedullary
schwannomas usually present with two patterns: solid lesions without a cystic portion;
and cystic-solid lesions with associated cyst formation. The solid portion is isointense
to hypointense on T1-weighted images; T2-weighted images usually show a hyperintense
signal, with occasional isointense or low-signal areas. Segmental fusiform dilation
of the cord is common, and peritumoral edema, which is usually present in astrocytoma,
is uncommon. Contrast-enhanced T1-weighted images better delineate the lesion and
differentiate the solid from the cystic components and edema. After gadolinium administration,
variable enhancement can be found, and heterogeneous enhancement is the most common,
with a few cases showing homogeneous and circular enhancement. The preoperative diagnosis
of an IS purely on radiological grounds is difficult, as it is also difficult to differentiate
it from intramedullary gliomas. However, in ISs, the classic dumb-bell appearance
is rarely observed.[3]
[6]
Histologically, schwannomas are composed of an Antoni-A cell areas comprising compact
cells in a reticular framework, and Antoni-B cell areas comprising large cells in
a loose collagenous background. Intramedullary schwannomas do not have any specific
histological feature.[6]
As most of these lesions are well-demarcated, gross total excision of the lesion with
minimal damage to the surrounding neural tissue remains the gold standard treatment.
However, subtotal resection can be performed if it is adherent to surrounding neural
tissue. The use of advanced neurosurgical techniques, surgical microscope and a cavitron
ultrasonic suction aspirator (CUSA) have resulted in better removal of intramedullary
tumors by reducing tumor volume, with minimal retraction of the spinal cord, yielding
better results.[3]
Conclusion
Intramedullary schwanommas are histologically benign tumors, and complete functional
recovery can be achieved after early total excision. They are difficult to diagnose
preoperatively, as there are no pathognomonic signs that enable its differentiation
from other intramedullary tumors. Therefore, IS should be considered in the differential
diagnosis of an intramedullary lesion in the thoracic spine.
