====== Spinal intradural arachnoid cyst ======


Spinal [[arachnoid diverticula]] are [[intradural cyst]]s of the [[arachnoid]] membrane which communicates with the [[subarachnoid space]]. Characterized by a narrow rostral ostium, the diverticula may collect [[cerebrospinal fluid]], empty incompletely with positional changes, and produce signs of [[spinal cord compression]].

Intradural [[spinal arachnoid cyst]] is a rare lesion, occurring within the spinal subarachnoid space. 

===== Etiology =====

Intradural arachnoid cysts may be congenital or may follow infection or trauma.

After epiduroscopic neural decompression
((Cho EJ, Jeon K, Kim YH, Moon DE. Occurrence of a spinal intradural arachnoid cyst after epiduroscopic neural decompression. Korean J Anesthesiol. 2013 Sep;65(3):270-2. doi: 10.4097/kjae.2013.65.3.270. PubMed PMID: 24101965; PubMed Central PMCID: PMC3790042.)).

There are a few case reports of intradural arachnoid cysts associated with syringomyelia, but recent evidence suggests that its occurrence is more common than previously thought. A combination of these two diseases is thought to be caused by blockage of cerebrospinal fluid (CSF) flow, which is also thought to cause adhesive [[arachnoiditis]]. For this reason, resection of the arachnoid cyst could improve the CSF flow and contribute to the shrinkage of syringomyelia
((Ishi Y, Aoyama T, Kurisu K, Hida K, Houkin K. [Intradural arachnoid cyst associated with syringomyelia: a case report]. No Shinkei Geka. 2014 May;42(5):467-72. Japanese. PubMed PMID: 24807552.)).

Especially, idiopathic lesions, in which other possible etiological factors have been ruled out, seem to be rare.

see [[Idiopathic spinal intradural arachnoid cysts in children]]


====Differential diagnosis====
Cysticercosis
((Yoo M, Lee CH, Kim KJ, Kim HJ. A case of intradural-extramedullary form of primary spinal cysticercosis misdiagnosed as an arachnoid cyst. J Korean Neurosurg Soc. 2014 Apr;55(4):226-9. doi: 10.3340/jkns.2014.55.4.226. Epub 2014 Apr 30. PubMed PMID: 25024830; PubMed Central PMCID: PMC4094751.)).

It may be reasonable to include serum ELISA in the differential diagnosis of spinal intradural cystic lesions, particularly in cysticercosis endemic regions such as Korea
((Hawk MW, Shahlaie K, Kim KD, Theis JH. Neurocysticercosis : a review. Surg Neurol. 2005;63:123–132. discussion 132.)).

The detection of an intradural cystic lesion through MRI leads primarily to a differential diagnosis of arachnoid cyst versus spinal cysticercosis, based on incidence. Moreover, other lesions, such as dermoid cysts, hydatid cysts, tuberculosis, sarcoidosis, and forms of subarachnoid neoplasia, have to be taken into consideration in the differential diagnosis of the disease
((Paterakis KN, Kapsalaki E, Hadjigeorgiou GM, Barbanis S, Fezoulidis I, Kourtopoulos H. Primary spinal intradural extramedullary cysticercosis. Surg Neurol. 2007;68:309–311. discussion 312.)).

MRI is a sensitive diagnostic tool for the identification of cystic lesions in the spine; however, it is difficult to distinguish cysticercosis from a noninfectious cyst, such as an arachnoid cyst, without using gadolinium enhancement. Contrast-enhanced MRI is mandatory for evaluating spinal cysticercosis
((Rahalkar MD, Shetty DD, Kelkar AB, Kelkar AA, Kinare AS, Ambardekar ST. The many faces of cysticercosis. Clin Radiol. 2000;55:668–674.))

The wall of the arachnoid cyst does not appear enhanced, whereas that of the cysticerci are well enhanced in gadolinium enhanced MR images
((Nash TE, Neva FA. Recent advances in the diagnosis and treatment of cerebral cysticercosis. N Engl J Med. 1984;311:1492–1496.)). 

The cyst walls were enhanced in all reported PSC cases. Moreover, the MRI sequence can distinguish between the CSF like fluid of the arachnoid cyst and the protein-rich fluid of an infectious cyst
((Bustos JA, Pretell EJ, Llanos-Zavalaga F, Gilman RH, Del Brutto OH, Garcia HH, et al. Efficacy of a 3-day course of albendazole treatment in patients with a single neurocysticercosis cyst. Clin Neurol Neurosurg. 2006;108:193–194.)).

Because arachnoid cysts have a low concentration of metabolites, similar to the CSF, the signal intensity is not increased relative to that of the CSF. On T2-weighted MR images, the signal intensity of neurocysticercosis is increased because of its higher protein content. 

The experience with a case and the review of the published literature suggest that contrast-enhanced MRI may provide useful information in the differential diagnosis of spinal cystic lesions, especially in patients with an unusual clinical course
((Yoo M, Lee CH, Kim KJ, Kim HJ. A case of intradural-extramedullary form of primary spinal cysticercosis misdiagnosed as an arachnoid cyst. J Korean Neurosurg Soc. 2014 Apr;55(4):226-9. doi: 10.3340/jkns.2014.55.4.226. Epub 2014 Apr 30. PubMed PMID: 25024830; PubMed Central PMCID: PMC4094751.)).

Although MRI is the method of choice for the diagnosis of neurocysticercosis, particularly in the presence of calcification, computed tomography (CT) has an advantage compared with MRI
((Paterakis KN, Kapsalaki E, Hadjigeorgiou GM, Barbanis S, Fezoulidis I, Kourtopoulos H. Primary spinal intradural extramedullary cysticercosis. Surg Neurol. 2007;68:309–311. discussion 312.)).

The initial stage of cysticercosis is characterized by less tissue response. At this stage, CT shows areas of decreased density surrounding the lesion and does not have an advantage compared with MRI as a diagnostic method. At the final stage of the disease, the dead larvae have calcified, and CT shows multiple calcified nodules, which are best identified on CT compared with MRI
((Hawk MW, Shahlaie K, Kim KD, Theis JH. Neurocysticercosis : a review. Surg Neurol. 2005;63:123–132. discussion 132.)).

====Treatment====
Early treatment may correlate with improvement in radiological findings and neurological symptoms.

====Case report====
===2015===
A 69-year-old man with a spinal arachnoid cyst of the thoracic spine presented with gait disturbance. Magnetic resonance images showed a mild anterior displacement and flattening of the spinal cord at T4-T5. They performed ultrasonography before incision of the dura during the operation and observed the movement of the cyst consisting of not only pulsation in accordance with the cardiac cycle but also rhythmic expansion and contraction in accordance with the respiratory cycle. In the inspiratory phase, the cyst gradually expanded and pulsated in accordance with the cardiac cycle. In the expiratory phase, the cyst gradually contracted with the same pulsation. After resection of the cyst, the patient's neurological improvements were excellent. This is the first report of animated respiratory movement of a spinal arachnoid cyst visualized by intraoperative ultrasonography. Although cine magnetic resonance imaging can detect spinal intradural arachnoid cysts preoperatively, intraoperative ultrasonography is useful for close analysis of their movement and pathology. Considering the dynamic compression mechanism revealed in this study, the authors think that an early operation should be performed for such cysts
((Miyashita T, Ataka H, Tanno T. Animated respiratory movement of a spinal
intradural arachnoid cyst visualized by intraoperative ultrasonography. Neurosurg
Rev. 2015 Apr;38(2):391-3. doi: 10.1007/s10143-014-0598-7. Epub 2014 Dec 23.
PubMed PMID: 25530355.)).
===2014===
Atypical intradural arachnoid cysts can be related to perineural injections and can cause symptoms of spinal stenosis. Its spontaneous vanishing is a very rare event, up to now reported by Mailleux et al.
((Mailleux P, Milbouw G, Koerts G, Verbeek P, Willems X. Appearance and
vanishing of a spinal intradural arachnoid cyst after multiple epidural
corticosteroid injections. A spontaneously resolving cause of symptomatic lumbar 
stenosis. JBR-BTR. 2014 Jul-Aug;97(4):251-3. PubMed PMID: 25603637.)).

----
Ishi et al. present the even-more rare case of an intradural arachnoid cyst associated with syringomyelia at the same spinal level.

The patient was a 66-year-old man who presented with bilateral leg numbness and gait disturbance. Magnetic resonance imaging (MRI) revealed an intradural arachnoid cyst located dorsal to, and compressing, the thoracic spinal cord at the level of the 7th thoracic vertebra (Th 7). In addition, syringomyelia existed at the level of Th 8, slightly caudal to the intradural arachnoid cyst. We dissected the cyst but did not perform any surgical procedures for the syringomyelia. Post-operative MRI showed that the cyst had disappeared and the syringomyelia had spontaneously shrunk. The patient was discharged with improvement in his numbness and gait disturbance. 
((Ishi Y, Aoyama T, Kurisu K, Hida K, Houkin K. [Intradural arachnoid cyst associated with syringomyelia: a case report]. No Shinkei Geka. 2014 May;42(5):467-72. Japanese. PubMed PMID: 24807552.)).

===2013===
Occurrence of a spinal intradural arachnoid
cyst after epiduroscopic neural decompression
((Cho EJ, Jeon K, Kim YH, Moon DE. Occurrence of a spinal intradural arachnoid cyst after epiduroscopic neural decompression. Korean J Anesthesiol. 2013 Sep;65(3):270-2. doi: 10.4097/kjae.2013.65.3.270. PubMed PMID: 24101965; PubMed Central PMCID: PMC3790042.)).

===2012===
Symptomatic spinal cord compression from an
intradural arachnoid cyst with associated syrinx in a child
((Su DK, Ebenezer S, Avellino AM. Symptomatic spinal cord compression from an
intradural arachnoid cyst with associated syrinx in a child: case report. Pediatr
Neurosurg. 2012;48(4):236-9. doi: 10.1159/000348885. Epub 2013 Apr 18. PubMed
PMID: 23615079.)).

===== Animals =====

Fifty-seven [[dog]]s were included in the study. The most common type of surgery was [[durectomy]] (28 dogs) followed by [[marsupialization]] (11 dogs), durotomy alone (seven dogs), [[shunt]] [[placement]] (six dogs), and [[stabilization]] (five dogs). A higher proportion of intra-arachnoid shunt dogs became unable to walk in the immediate postoperative period (24 hours postsurgery) (4/6, 66%) compared to all dogs five of 57, 9% (2/7 durotomy alone, 3/28 durectomy alone). Of the nine dogs with immediate postoperative deterioration, seven had improved, walking without assistance, by 3 to 5 weeks postoperatively.

Clinical significance: This study does not identify an influence of surgical technique on short-term outcomes. Dogs with a thoracolumbar intra-arachnoid diverticulum that undergo a shunt placement are likely to deteriorate neurologically in the immediate 24-hour postoperative period but appear to improve by 3 to 5 weeks after surgery. Further work is required to evaluate whether one surgical technique is superior for preventing or reducing long-term relapse
((Jones B, Behr S, Shaw T, Cappello R, Jeffery N, Liebel FX, Harcourt-Brown T. Surgical techniques used in the management of intra-arachnoid diverticula in dogs across four referral centres and their immediate outcome. J Small Anim Pract. 2022 Feb 9. doi: 10.1111/jsap.13486. Epub ahead of print. PMID: 35137433.))