Keywords
accumulation of CSF - anterior cervical arachnoid cyst - arachnoid cysts - intradural arachnoid cyst - spinal arachnoid cysts
Introduction
Arachnoid cysts are fluid-filled sacs occurring in the brain and spine. They are mostly congenital (primary) and contain fluid identical to the cerebrospinal fluid (CSF).[1] Rarely they may also be caused by trauma or infection (secondary). While common in the brain, spinal arachnoid cysts (SACs) are uncommon. SACs may be intradural or extradural, with the latter being more common.[2]
[3]
[4]
It is not yet clear what leads to this cyst. Nonetheless, congenital conditions with arachnoid membrane herniation are the most likely causes. Other cases may arise from spinal punctures, infections, trauma, postoperative complications, or inflammations. According to some authors, the development of cysts is caused by an accumulation of CSF as a result of an arachnoid mater defect.[3]
[5]
[6] Being mostly congenital, arachnoid cysts often occur at a young age. Some cases have also been reported in older patients and small children.[7]
Clinical symptoms appear once there is cyst expansion. Compression of the spinal cord leads to features of myelopathy or myeloradiculopathy. The presentation ranges from mild radicular pain, sensory changes, incontinence of urine to paraparesis or quadriparesis depending upon the site of lesion.[8] This cyst most commonly affects the dorsal spine (65%), but some reports of its occurrence have also been made in the lumbar and lumbosacral region (13%), thoracolumbar region (12%), and sacral region (7%). It is extremely rare to occur in the cervical region.[9]
Magnetic resonance imaging (MRI) has proven to be quite effective as the modality of choice in diagnosing an arachnoid cyst. MRI can also determine the anatomical relationship of the cyst with its surrounding structure.[10] Asymptomatic patients can be conservatively managed and observed. In patients who have developed neurological deficit, surgery is the most effective course of treatment.[8]
[11]
Arachnoid cysts are most commonly found in the posterior aspect; anterior locations are extremely uncommon. In light of the pathology's rarity in this particular location, we present here an uncommon case of an anteriorly located cervical arachnoid cyst.
Case Report
A 14-year-old adolescent boy presented to the emergency department complaining of weakness in both upper and lower extremities for the past 3 days. Weakness started in the left lower limb and quickly covered both upper and lower limbs within 10 days. The patient also complained of radiating pain associated with numbness in both upper extremities. There was no history of trauma or significant weight loss.
On physical examination, the patient was conscious and alert. All his vital parameters were normal including respiratory rate. Motor examination showed obvious weakness in all four limbs with power in right upper limb being grade 4/5 in all groups, with 50% grip, and that in the left upper limb being grade 3/5, with 0% grip. The right lower limb showed a strength of 4/5 and the left lower limb showed a strength of 2/5. No sensory deficit was seen. The bladder and the bowel were intact.
The radiological examination was done with contrast-enhanced MRI, which showed a T1-hypointense lesion with T2-hyperintense and nonrestricted diffusion-weighted imaging (DWI), nonblooming susceptibility-weighted imaging (SWI) resembling CSF intensity at the C4–C5 and C5–C6 levels, which was markedly compressing the cord ([Fig. 1]). A provision diagnosis of intradural arachnoid cyst was made.
Fig. 1 T2-weighted (A) sagittal and (B) axial MR images show a hyperintense lesion at C4–C6, with similar intensity to CSF.
The patient underwent surgery in the prone position with a cervical midline incision at the appropriate level. The C4–C6 lamina flap was excised en bloc. The dura was tense and seemed to be under considerable pressure. The dura was opened in the midline, which revealed a splayed spinal cord with pressure from the anteriorly located arachnoid cyst. After sectioning the dentate ligament from the right side and mild retraction of the cord, a cystic mass with transparent wall is visible ([Fig. 2A, B]). A small incision in the cyst wall was made, which showed clear fluid similar to CSF. Subsequently the cyst wall was fenestrated with partial removal of the cyst wall. The C4–C6 lamina flap was repositioned with titanium miniplates and screws to preserve the anatomy of the posterior spinal elements ([Fig. 2C]).
Fig. 2 (A) Image showing positioning of the patient on horseshoe. (B) Intra-op image showing arachnoid cyst after retraction of the cord. (C) Intra-op image showing lamina fixation with miniplates and screws.
The postoperative period was uneventful, and the patient made full recovery. Postoperative MRI showed complete resolution of the cyst ([Fig. 3]). The patient remained in follow-up and returned to his previous activities within 6 months.
Fig. 3 T2-weighted (A) sagittal and (B) axial images of post-op MRI showing complete resolution.
Discussion
SACs account for only 1% of primary spinal cord tumours.[12] They may be extradural or intradural. Intradural arachnoid cysts are usually uncommon, and the most common location is the thoracic spine followed by the lumbar and cervical regions. SACs usually arise posterior to the cord, but the intradural anteriorly placed arachnoid cysts in the cervical region are very rare.[3] In the study by Kendall et al, eight out of nine cases on intradural arachnoid cyst were posteriorly located in the thoracic region.[13] Furthermore, all 17 of the intradural arachnoid cyst cases—including 8 cases in the cervical region—reported by Alvisi et al were posteriorly located.[14]
Pathogenesis
The pathogenesis of SACs is not fully understood. According to a number of theories, the arachnoid cyst is a congenital dura mater defect that is always connected to the subarachnoid space by minor dura defects and arachnoid herniation.[1]
[9] Trauma, infections, inflammations, postsurgical complications, and lumbar punctures may all be the cause of acquired arachnoid cyst in several cases.[3]
According to Rabb et al, these cysts had neural tube abnormalities, suggesting that they were congenital.[15] Based on two cases in two generations with a Mendelian dominant variant, Arabi et al hypothesized that the cysts are caused by septum posticum widening.[16] However, this theory will only support some cases of dorsally placed arachnoid cysts. According to Agnoli et al, these may be caused by the pathological distribution of arachnoid trabeculae that lead to diverticula, resulting in cyst formation due to degeneration of trabecular cells, which build up pressure within the cyst transudation of fluid within.[17]
The most commonly accepted mechanism of cyst expansion is by the one-way valve effect in cysts that communicated with CSF space through the fistula orifice. Another mechanism is based on hyperosmotic or secretory theory–based fluid production in the cyst wall in a noncommunicating arachnoid cyst.[8]
An acquired arachnoid cyst occurs secondary to trauma, infection, subarachnoid hemorrhage, or spine surgery. Trauma may contribute to the formation of an arachnoid cyst by rupturing the arachnoid or by turning a silent cyst into a symptomatic one. Chen and Chen reported an arachnoid cyst developed in a 9-year-old due to fibrous thickening of the arachnoid membrane.[18] Two cases of Chiari II malformations after foramen magnum decompression were reported by Jean et al.[19] They believed that significant craniocervical decompression might change the dynamics of CSF pressure in a way that could cause the anterior subarachnoid space, which had previously been compressed, to dilate and form cysts. This could be the result of perimedullary arachnoiditis.[19] This hypothesis is also supported by Kazan et al.[20]
As compared to the CSF, an arachnoid cyst is filled with clear fluid of low protein, and the increase in cyst volume could be due to secretion by the cystic wall, unidirectional valve, and liquid movement secondary to the pulsation of the veins.[21]
Clinical Feature
An SAC is mostly asymptomatic. The level and size of an SAC and severity of cord compression determine the clinical picture. Sometimes a congenital asymptomatic cyst may become symptomatic after trauma.[20]
The most common presentation is spinal pain or radicular pain or tingling and numbness. Neurological signs include monoparesis, paraparesis or quadriparesis, sensory changes, gait changes, and bowel and bladder disturbances.[20]
[22] If the cyst is located in the high cervical region, then the patient may present with respiratory failure.[21]
Imaging
In the pre-MRI era, myelography and computed tomography (CT) myelography were the methods used to diagnose these lesions.[13]
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[23] Displacement and compression of the spinal cord were visible in a conventional myelogram, but for this, supine delayed myelogram was required because the cyst could have filled only in the supine delayed myelogram When it comes to CT, intrathecal metrizamide is nearly always required to confirm and clarify the details, even though CSF attenuation may be visible on plain CT scans using a rapid high-resolution machine.[20]
[23]
MRI is the investigation of choice to diagnose anterior cervical arachnoid cyst and will give the details regarding size, extent, and nature of the cyst as well as mass effect on spinal cord and signs of arachnoiditis. Arachnoid cysts appear as round or oval lesions filled with fluid with CSF intensity. These days, more intradural arachnoid cysts are reported in earlier stages of cord compression and with greater frequency due to increased use of MRI.
Treatment
Surgery is the treatment of choice in cases of symptomatic SACs. The most common surgical procedure is laminectomy or laminoplasty with excision of the cyst. Although the complete surgical excision is desirable in all cases, it is usually not possible due to adherence to the cord or roots and scarring. Wide fenestration with partial removal of the cyst and making communication with the CSF space are successfully done in the majority of cases. In the current case also fenestration with partial excision of the cyst was done. Recurrence is usually expected in case of insufficient fenestration or when only aspiration is used as the treatment modality.[19]
[24]
The cyst may be approached anteriorly or posteriorly. The posterior approach is preferred by most, being simple and effective in addressing the cyst with minimal anatomical disruption. The anterior approach gives direct access to the cyst with excision or fenestration to the subarachnoid space. Other treatment options reported in the literature are resection of the cyst, aspiration of the cyst, aspiration and reservoir placement, cystoperitoneal, pleural, or atrial shunts, and MRI-guided cyst aspiration.[25]
Outcome
Excellent results and a full recovery are anticipated, particularly if the arachnoid cysts are diagnosed early. In our case also, the patient made full recovery and returned to previous activities within 6 months.
Conclusion
An anterior cervical arachnid cyst is a very rare lesion and should be considered in children and young adults who presented with neck pain or radiculopathy, especially if they are followed with motor weakness. They can be easily diagnosed with MRI, and prompt treatment yields excellent results.
