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|Year : 1999 | Volume
| Issue : 1 | Page : 61-4
Sacral nerve root cysts : A review on pathophysiology.
ArunKumar MJ, Selvapandian S, Chandy MJ
Department of Neurological Sciences, Christian Medical College and Hospital, Vellore, Andhra Pradesh, India.
Department of Neurological Sciences, Christian Medical College and Hospital, Vellore, Andhra Pradesh, India.
Nerve root cysts of the sacral region are generally asymptomatic but are known to cause neurogenic claudication. In this paper we present an elderly lady who presented with claudication, whose MR imaging showed a sacral cyst. She underwent lumbo-sacral laminectomy, partial excision of the cyst wall with plication. A review of the possible pathophysiology of such a lesion is discussed.
|How to cite this article:|
ArunKumar M J, Selvapandian S, Chandy M J. Sacral nerve root cysts : A review on pathophysiology. Neurol India 1999;47:61
Sacral nerve root cysts are intriguing lesions. Since their description there has been controversy regarding their origin, clinical significance, pathophysiology and management. These were first described by Tarlov in 1938 as incidental autopsy finding. Since then, there have been infrequent reports discussing their clinical features and treatment.,, Various terminologies have been used to define the lesion depending on the authors' perceptions regarding the origin. We describe a case of a symptomatic sacral nerve root cyst and discuss the likely pathophysiology based on the observations recorded.
A 55 year old known hypertensive and diabetic lady, presented to us with a history of intermittent low back ache for the last 5 years. During the last 3 months, the pain had become intense and was associated with neurogenic claudication involving the posterior aspect of the thighs and gluteal regions bilaterally, the left more than the right. There was no history suggestive of any motor weakness or sensory impairment. On examination, she had multiple subcutaneous nodules. There was minimal wasting of the extensor digitorum brevis on the left side with normal power in all groups of muscles. There was no sensory impairment and the deep tendon reflexes were normal. Gait was normal and examination of the spine did not reveal any focal tenderness or skeletal deformities.
X-ray of the lumbo sacral spine showed mild canal stenosis at the level of L 4,5 with early degenerative changes in the form of osteophytes. MR imaging of the lumbo sacral spine showed a cystic mass lesion of the size 3.2 x 3.2 cm. at S 1- S 2 level. This mass appeared hypointense on T1 and hyperintense on T2 weighted images. The lesion was isointense with CSF and more on to the left side. There was scalloping of the S 1 and S 2 vertebral bodies [Figure 1a] [Figure 1b].
L4 to S 2 laminectomy was done. At L 4-5 level there was moderate canal stenosis due to thickened ligaments. The S 1 and S 2 laminae were thinned out. There was a large thin walled cyst within the sacrum stretching the sacral roots [Figure 2a] [Figure 2b] [Figure 2c]On opening the normal dural tube at the lumbar region just above the cyst, there was no reduction in the size of the cyst. The cyst wall was opened using a separate incision and clear CSF flowed out. Fascicles of a nerve root could be seen coursing through the wall of the cyst ventrally. The inner wall of the cyst appeared smooth. There was a narrow, short pedicle connecting the cyst to one of the nerve root fascicles coursing through the pedicle and the cyst wall, the neck could not be ligated. The arachnoid at the opening in the pedicle was divided to widen the communication so as to prevent a `valve-like' action. A portion of the cyst wall was excised and the rest plicated and sutured to reduce its size. Free fat graft was placed around the cyst. Following surgery, the claudication pain resolved with no motor or sensory deficits. At follow up after 18 months, the patient was totally free of the claudication pain.
Histopathological examination of the wall of cyst showed bands of fibrocollagenous connective tissue lined by flattened cells. There was a scattered infiltrate of chronic inflammatory cells. These findings were consistent with arachnoid cyst.
Clinical presentation : Sacral nerve root cysts are commonly found during the third and fourth decades. There is no typical characteristic clinical presentation. Most of the cases have been described in elderly women having a clinical picture remarkably similar to that of intervertebral disc prolapse or lumbar canal stenosis, which are often found to co-exist with this lesion. In view of this, some authors believe that these are asymptomatic lesions and by virtue of its association they have been implicated as a `cause'.,,,
Pathophysiology : Tarlov described extradural sacral cysts which were often multiple and multiloculated, usually found at the junction of posterior root with the ganglion., He termed it as perineurial cysts as he felt that these cysts emerged from the space between the endoneurium and perineurium as a result of ischaemic degeneration, trauma or repeated haemorrhages beneath the perineurium of the root. The wall of the cyst was found to contain ganglion cells and nerve fibres. Tarlov felt that these cysts had no communication with the subarachnoid space. Rexed and Wennstrom postulated that these cysts might be a result of proliferative process in the arachnoidea around the dorsal nerve roots, with secondary cystic cavitation. They too felt that there was no communication between the cyst and the subarachnoid space.,
In 1964, Holt and Yates in their series of perineurial cysts of the cervical region found that the cystic cavity was lined by a thin layer of epithelium and had a clear and patent canal that communicated with the radicular subarachnoid space. This fact was supported by myelographic findings, and hence they felt that perineurial cysts are definitely a diverticula in communication with the subarachnoid space lined by the same arachnoidea.
Schreiber described another type of cyst. The arachnoid membrane was found to expand through a congenital defect or weakness in the radicular dura mater towards the epidural space. This membrane had a stalk that got inserted into the nerve root sheath more proximal than the Tarlov type cysts. Though they had a predilection for the sacral region, they could also be seen in the cervical or thoracic regions. The ball-valve like mechanism in the neck of this diverticulum allows the development of high intracystic pressures. The wall of these cysts are made of arachnoid membrane and did not contain ganglion or nerve fibers. Since there was no dura mater, the possibility of the expansion of the cysts were quite high than the Tarlov type. They were mostly unilocular and showed free communication with the radicular subarachnoid space.,, The fact that these cysts are commonly found in elderly or in patients with connective tissue disorders or neurofibromatosis, points to some congenital weakness of the dura which allows herniation of the arachnoid. Plewes and Jacobson felt that these cysts and meningeal diverticuli must be grouped together, as all of them were due to the result of hydrostatic pressure of the CSF acting on a weak point in the radicular meningeal coverings.
Some authors support differentiation between perineurial (Tarlov) and extradural cysts (Schreiber) in the sacral region while others do not accept such a differentiation.,, Nabors et al in 1988 proposed a modified classification of spinal meningeal cysts. They divided extradural arachnoid cysts into two types, based on the presence or absence of spinal nerve root fibers on the cyst wall. They felt that both the perineurial cysts and nerve root diverticula are almost the same lesion on the basis of CT myelography. They showed that these cysts communicated with the spinal subarachnoid space and proposed a congenital origin related to spinal arachnoid proliferation for these lesions. Various mechanisms have been postulated to explain the progressive increase in the size of the cyst such as hydrostatic pressure, osmotic pressure and secretory activity of the cyst wall.,
In our patient, the per operative findings seems to conform to the `Type I cyst' described by Nabors or the type described by Schreiber though with some differences. We found a large solitary cyst with a well formed pedicle connecting the nerve root sleeve and the cyst, with nerve fascicles within the cyst wall. Due to the presence of fascicles traversing the neck of the cyst, a simple ligation could not be performed despite a narrow pedicle. It has been well documented in the past that the increased intracystic pressure is contributed by the valve like action of the inner membrane (arachnoid), and hence it was decided to divide this membrane to disrupt the valve. Partial excision and plication of the cyst wall was also done so as to reduce the size of the cyst and to decompress the surrounding nerve roots. It is still possible for the membrane to regrow or the arachnoid to proliferate to resume the valve-like action in our patient. However, she being an elderly lady, it is very unlike for her symptoms to recur in the near future as it had taken many years for this congenital lesion to become symptomatic.
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