Download Alireza Mansouri, HBsc (1T1), Faculty of Medicine, University of

Alireza Mansouri, HBsc (1T1), Faculty of Medicine, University of Toronto
Travis Tierney, M.D, Division of Neurosurgery, Toronto Western Hospital
C.R. was a 51 year old, right hand dominant lady who presented to clinic with a 2 week history
of mid back pain and spasms that started when she initiated mild intensity back exercises. Within
a week, she developed bilateral leg pain as well (ranging from 7-8/10 in intensity, left more than
right). Two days prior to presentation, she developed progressive leg weakness, left more than
right, to the point that she was unable to ambulate independently. She had been afebrile and
denied weight loss, chills or rigors.
She did not report any history of congenital abnormalities or past surgeries. C.R. has been
generally healthy with the exception of two episodes of seizures for which she is currently taking
trileptal. She takes no other medications. There was no family history of cancers or neurological
issues.
On examination, she had significant difficulty ambulating secondary to back spasms and
shooting pain in the left leg. As a result, it was not possible to assess her gait. Straight leg raise
(SLR) on the left reproduced her leg pain at about 10º; SLR was negative on the right side.
Motor examination revealed a significantly diminished left-sided strength (1/5) in the L4-5 nerve
root distribution and a mild decrease in the L1-2 (4/5) and L5-S1 (3/5) nerve root distributions.
Strength on the right side was normal (5/5). Pin-prick sensation was diminished in the L5
dermatome on the left side but otherwise intact. Light touch and proprioception were also intact.
There was no saddle anaesthesia and rectal tone was normal. Babinski was down-going
bilaterally. Reflexes were 2+ bilaterally and symmetrical.
MR imaging of her spine (Figure 1) revealed a diagnostically-challenging lesion. A saggital view
of the T1-weighted MRI without Gadolinium enhancement (Fig. 1a) revealed an obvious L1-L2
disc herniation. However, in addition to the herniated disc, a hypo-intense lesion extending from
T12-L2 was also evident on the posterior portion of the spinal canal. The lesion did not enhance
post-gadolinium infusion (Fig. 1b). On T2-weighted imaging the lesion appeared to be isointense to the cerebrospinal fluid (Fig. 1c). In the axial view of the T2-weighted image (Fig. 1d)
the nerve roots were eccentric secondary to the compression caused by the lesion. Within this
view, the lesion appears to be divided (arrow). This was believed to be either the dural sac, with
the lesion surrounding it, or a septum which had developed within the lesion. Based on the
radiographic images, it was difficult to ascertain whether the lesion was intra or extra dural;
hence the challenge in diagnosis. The patient was taken to the operating room for L1-L2
laminectomy (for decompression of the spinal cord). Final diagnosis of the unknown lesions was
only possible intra-operatively…
(A)
(C)
(B)
(D)
Figure 1. MR imaging of C.R.’s spine. (A) Saggital view, T1-weighted image, no Gadolinium (B) T1weighted image, post Gadolinium (C) T2-weighted image (d) Axial T2-weighted image, arrow points to
septation
What is the diagnosis?
Septated AC with arachnoiditis
Definition and epidemiology
The extension of an arachnoid-lined diverticular membrane, from the subarachnoid space, and
the subsequent creation of a pouch-like entity that communicates with the rest of the CSF space
results in the creation of Arachnoid cysts (AC)1. It has been estimated that approximately 4% of
the population has an AC2. However, due to the slow growing nature of these cysts, many are
often asymptomatic. Symptoms such as back pain, spasms, and radicular pain due to
compression of the spinal cord or nerve roots3 are often difficult to distinguish from other neural
compressive disorders. ACs can occur either intra-cranially or less frequently within the spine.
Data in the literature indicate that spinal cysts extend an average length of 4.6 vertebral bodies
with the ventral ones spanning almost double that of dorsal ones (6.2 vs 3.6). Post- traumatic
cysts are often significantly larger than non-traumatic ones. In terms of location within the spine,
the thoracic spine is the most common area to be affected followed by the cervical region;
lumbosacral cysts are the least common. While symptoms can arise at any age they are
frequently observed in individuals in the 30-50 age range4.
Classification
ACs can be classified into three groups based mainly on their relationship to the dural sac and
nerve roots5. Type I cysts are those that are extra-dural and do not involve the nerve root fibers
whereas type II cysts do; the latter are also known as perineural or Tarlov’s cysts and are
commonly found in the sacral region. Intra-dural cysts are classified as type III. In the case
described here, definitive diagnosis and classification of the lesion was only possible intraoperatively. Based on our findings, it appeared that the lesion was most consistent with a type III
AC.
Basis of diagnosis
MR imaging, often with contrast, is often helpful in diagnosing ACs. However, as described
above, intra-operative assessment may also be necessary in certain cases. ACs can be identified
on MRI as well-demarcated masses that are iso-intense with the CSF on T2-weighted
sequences4. Intra-operatively, the presence of a cystic lesion containing clear fluid of similar
consistency to the CSF would suggest the diagnosis of an AC but pathological analysis may also
be required.
Causes
Genetics play a key role in the pathogenesis of ACs. In fact, most cysts are congenital in
origin6,7. Arachnoiditis subsequent to spinal surgery, epidural injections, or disc disease is
another cause of ACs. Other inflammatory processes affecting the arachnoid matter, such as
subarachnoid bleeding or meningitis, can also result in the creation of these cysts4.
Pathophysiology
The pathophysiological basis of spinal ACs involves the proliferation of fibroblasts that are
recruited for the repair of the arachnoid membrane post insult in a manner that is similar to the
repair of serous membranes. This involves very little in the form of inflammatory cellular
exudates but extensive fibrous exudate. As a result, adhesions are formed between the fibrincoated nerve roots and the meninges of the nerve roots themselves or the thecal sac.
Consequently, CSF flow is obstructed and pockets of CSF are created8. These cysts expand in
size via a valve-like mechanism4. Symptoms arise either when the lesion becomes large enough
to cause compression or when a new lesion is created in the presence of a long-standing cyst.
Based on the extensive boney remodeling of the vertebral bodies adjacent to the cyst in the
present case, it is highly likely that our patient has had a long-standing cyst and would have
experienced symptoms as a result of the latter scenario.
Differential diagnosis
Among intra-dural cystic lesions of the spinal cord, ACs are the most common. However, it is
important to consider other possible diagnoses as part of the differential. Other cystic lesions that
can be found in the thoracic region include neuroepithelial (ependymal), epidermoid or dermoid,
and neurenteric cysts4. Certain tumors, such as schwannomas and astrocytomas, can also present
as cystic lesions. ACs can be differentiated from synovial cysts of the facets based on the fact
that the latter attach to the articular cavity4. The hypointensity of the lesion relative to the
surrounding fatty tissues on T1-weighted imaging and the absence of dysraphism on the outer
skin argue against a lipoma4. Ependymal cysts can be identified based on their low density
appearance on non-enhanced T1 images and their hyperintensity on T2-weighted images9.
Dermoid cysts, rare developmental tumors, also tend to have fatty components associated with
them and are usually midline. Often, other signs such as sacral dimpling or tufts of hair will also
help in the diagnosis of dermoid cysts10. These tend to be heterogenous on MRI but they appear
as homogenous areas of low attenuation on CT; however, calcifications within the cyst can be
identified on the CT. Epidermoid cysts on the other hand can be identified on diffusion studies as
brightly-appearing lesions; these cysts are hyperintense relative to the CSF11. Neurenteric cysts
are another group of developmental anomalies and they tend to be iso/ hyper intense relative to
the CSF, depending on the protein content within the cyst; like other cysts secondary to a
developmental anomaly, other anatomical defects should be noted as part of the clinical exam12.
It is noteworthy to mention that the smoothness of the septation and the dural sac argue against a
surgical, traumatic or inflammatory cause for the cyst6. Furthermore, as mentioned previously,
the contour that can be observed on the adjacent vertebral body suggests that the cyst had been
present for a long time, likely before the herniation of the disc. Put together, these findings
suggest that C.R. had a rare form of a congenital AC, which was discovered accidentally as a
result of a mild disc herniation.
Treatment
Expectant management is a treatment option for asymptomatic patients. However, the presence
of neurologic signs dictates the need for surgical evaluation. Complete neurosurgical resection is
the treatment of choice for ACs. For extensive spinal cysts that require multiple laminectomies,
ventrally located cysts that require significant cord manipulation, and for multiple adhesions it is
possible to partially resect the cyst or fenestrate it4.
Prognosis
Untreated, ACs may cause permanent severe neurological damage due to the progressive
expansion of the cyst(s) or hemorrhage3.
Recurrences of these cysts are probably the result of the cyst sealing after an insufficient primary
resection13. The incidence of recurrence varies, and they have recurred even after aggressive
removal of the cyst wall14. The results of surgery are usually excellent, with weakness,
hyperreflexia and incontinence more likely to improve than neuropathic pain and numbnes15. For
patients with a predominant radicular pain syndrome, lasting relief can be achieved after
surgery13. Neurological recovery is related to the duration and severity of cord compression and
to the associated atrophy or myelomalacia rather than the location of the cyst.
Back to the case …
After surgical removal of the cyst, C.R. remained in the hospital for 2 days for pain control and
to assess wound dehiscence. She was discharged and follow-up with MR imaging of the spine
was arranged for 6 weeks later.
References
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