Arachnoid duration and paraesthesias in both lower limbs

Arachnoid
cysts of spinal cord are a rare entity, and often encounter as an asymptomatic
incidental finding during examination performed for other causes. Most of the
arachnoid cysts are extradural in location, though it can be intradural and
further sub classified as either extra medullary or intramedeullary. On the basis of findings of
surgical examinations, radiological features and histopathological review of 22
cases, first attempt to classify the arachnoid cysts in the spine have been done
by Nabors et al. in 1986 1 as: Type 1-extradural cysts without spinal nerve
roots; Type 2-extradural cysts with spinal nerve root fibers; Type 3-intradural
cysts.

Herniation through dural defect is considered the
etiopathogensis of extradural arachnoid cyst, while the intradural cysts are
thought to arise from proliferation of arachnoid trabeculae. The mechanisms
behind the pathological development  of  these intramedullary cysts is still unclear
with various hypothesis of congenital, traumatic and inflammatory causes.2,3,4,5 . 

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Most of the literature concerning with intra
medullary arachnoid cyst are in the form of case reports from the peadiatric
population. Here we are reporting clinico pathological characteristics along with
review of relevant literature of two cases of intramedullary arachnoid cyst in
adult age group.

CASE REPORT:-

CASE 1

This 45 year old female presented with
dull mid-backache for 6 month duration and paraesthesias in both lower limbs
for duration of 2 months. She completely deny any complaints related to bowel
and bladder disturbances. Examination revealed normal bilateral upper limbs
with spastic weakness (MAS-1+) of both lower limbs with power of 4-/5 in all
major groups of muscles, and she was able to walk with minimal support.  Lower limb deep tendon reflexes were brisk
with bilaterally extensor planter. Sensory examination showed decreased
sensations to pin prick, touch and temperature below D12 with spared sacral
sensations.

 MRI of the spine showed an intra axial lesion,
hypointense on T1 and hyperintense on T2 weighted sequences respectively. Lesion
was seems to be expanding the cord and extending from D9-D11 region with no
contrast enhancement .There was no evidence of any communication with the
central canal.

The patient underwent D8 to D12
laminectomy. Following durotomy, the cord was found to be protruding. Midline
myelotomy performed and cyst was tapped. There was clear fluid like CSF. Fluid
sent for routine biochemistry, a thin membrane was found and was biopsied and
sent for histochemical analysis. There was no communication of the cyst to the
central canal. A watertight dural closure was performed.  Histopathological examination revealed a cystic
lining resting on fibrocartilaginous tissue with irregularly shaped cells, and
a thin cystic lining possibility of arachnoid cyst suggested by our pathologist
and for further confirmation marker study performed. Immunohistochemistry
carried out on formalin fixed paraffin embedded section, tumor cells were negative
for S100,P 53 ,CEA and Glial fibrillary acidic protein (GFAP). Cells were strongly
positive for epithelial membrane antigen (EMA) the antibody and their clones
used for detection were belongs to Biogenix and biocare SIGMA USA. Immunomarkers
study confirmed the diagnosis arachnoid cyst.

CASE
2-

Another case , a 40 Year
old male presented with 2 year history of low back ache that had worsen since
last 3 month and at the time of admission he also complaints of numbness in
bilateral lower limb. Examination showed  mild weakness in distal grtoup of muscles with
increased spaticity .Sensory examination revelead decresed sensation below D11
level.

For this reason, the
patient had undergone a spinal MRI revealing the presence of an intramedullary,
non-enhancing Cerebrospinal Fluid (CSF) intensity cystic lesion at the conus
medullaris. He underwent D9-D11 laminectomy, dorsomedian Myelotomy, and cyst
decompression. The cyst contained clear fluid. Safe,gaurded and incomplete
removal of cyst wall done,because it was adherent to the neural tissue.
Histopathological examination revealed arachnoid cyst. Follow up done for three
month , Now days,he is  neurologically
intact, and  suffers occasionally back
ache.

REVIEW OF
LITERATURE:

 Spinal intramedullary arachnoid cyst is one of the extremely rare lesions
and has been sparsely reported in the English literature. They are usually
asymptomatic, but become symptomatic once the cyst starts compressing the cord
or nerve roots. The most common presenting symptom is back ache and slowly
progressive weakness in the limbs because of gradual and continuous enlargement
of the cyst.

The origin, etiopathogenesis and course of spinal
intramedullary arachnoid cyst is still debatable and not clear. Misplaced
cellular remnants during embryogenesis as a possible cause of intramedullary
arachnoid was postulated by Hyndman and Gerber (6). Fortuna and Mercuri 7
postulated the hypothesis that trapped arachnoid granulation at various locations
including intramedullary is a causative factor in CSF production and accumulation,
hence cyst formation. This view was also supported by Goyal et
al.8

An  abnormal anatomical communication between
subarachnoid space  and cyst acting as a
one way  valve-like mechanism for
expansion of the cyst is also postulated.(9) 

In  the
support  of congenital cause Voss(10) and
Rabb(11) had described arachnoid cysts in relation with dysraphic anomalies of
spinal cord. Currently no evidence available for the genetic
predisposition of arachnoid cyst, However report of familial spinal
intradural arachnoid cysts 12 raises a concern and may merit further study.

The
available literature suggests a benign course and excellent recovery in spite
of partial excision. There is no report of recurrence even with inadequate excision.
Which suggest that a free communication between cyst and subarachnoid space is
sufficient only. However long terms follow up and MRI surveillance is not
available.

 

 

 

 

The first case of intramedullary arachnoid cyst
was reported by Aithala et al. (13) in a child, who went to
dorsomedian Myelotomy and got rapid and complete recovery within first week.
Since then, to the best of author’s knowledge 8 cases has been reported in
peadiatric population and upper dorsal is the most common site reported for
arachnoid cyst in same population. The
probable embryonic malformations can be speculated as an etiological factor, no
sex predilection found and all patients under goes for Myelotomy and drainage
of cyst with or without fenestration. Final outcome in all patients were satisfactory,
promising and almost complete recovery. Follow up done from 5 days to 24 month
and we are fortunate that, no cyst recurrence/treatment failure reported till
date worldwide..

 

 

 

 

 

The first
case of intramedullary arachnoid cyst  in
adult was reported by Goyal et al.(8) in 2002.To the best of our knowledge, so far  7 cases has been reported. As seen from the
published data, it is evident that the intramedullary variant of arachnoids
cysts are exclusively reported in dorsal cord in adult age group .As opposed to
peadiatric population there is female sex predisposition. The surgical
treatment of the symptomatic intramedullary arachnoid cyst in majority of cases
includes dorsomedian Myelotomy, with drainage of cyst and removal of the cyst
wall as much as possible with avoiding of neurological deficit, where’s Gezici
et al (14) preferred dorsal root
entry zone Myelotomy. In majority of cases the cyst wall is found to be densely
adhere to nearby glial tissue and most of the time it is very difficult to
excise it completely, but fortunately no recurrence is till the date.  Fenestration of the cyst with or without
shunting to the subarachnoid space is another available treatment modality.

 

We report
here two cases of intramedullary cyst and discuss imaging,histopathology and
immunohistochemistry characterstic of this lesion.Although these are very rare
entity,We thought spinal intramedullary arachnoid cyst should be considered and
kept  as a differential diagnosis of
intramedullary pathology even in adult patients. More importantly these lesion
should undergo for surgical treatment as they afford very good clinical results,
excellent prognosis and almost no recurrence.

 

 

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