Arachnoid cysts (ACs) are congenital developmental malformations. They account for 1% of all intracranial space-occupying lesions.[2,3] Usually, asymptomatic and diagnosed incidentally when imaging is done for other causes, they can become symptomatic when they enlarge and compress neighboring neural structures or if there is intracystic bleeding. Increase in size of AC may be due to the secretion of fluid by the lining membrane or accumulation of cerebrospinal fluid (CSF) driven inwards either by brain pulsation through a one way valve in the wall or inflow following an osmotic gradient.
The posterior fossa is the second most common site for AC and these are usually found in the cerebellopontine angle. In the midline of posterior fossa (accounting for 10% of all AC), supravermian location is the most common followed by the retrocerebellar variant. Enlargement of supracerebellar posterior fossa AC can cause cerebellar and brain stem compression as well as tonsillar descent and their presentation and management strategies are well described while those that are retrocerebellar essentially have been treated such as Chiari malformations with foramen magnum decompression, C1 laminectomy, and duraplasty alongwith with fenestration of the AC after treating any supratentorial hydrocephalus that may be present.
Reports of symptomatic AC straddling the craniovertebral junction (CVJ) are very rare.[2,7] In a PubMed search using the terms “Craniovertebral” and “AC,” we obtained only 17 results while a search using the terms “Craniospinal” and “AC” gave 22 results. The relevant case reports with presentations and surgeries performed after discounting the ventrally located cysts, intramedullary cysts, postoperative cysts, and those that were purely in the posterior fossa or spine are summarized in Table 1.
A 38-year-old female presented with intermittent episodes of headache and neck pain that increased on coughing and straining for 2 years with gait ataxia for the past 6 months. On examination, she had no findings except positive Romberg’s sign. Magnetic resonance imaging (MRI) of the brain showed a large posterior fossa AC extending up to C1 arch effacing the 4th ventricle, lifting the cerebellar hemispheres and compressing the cervicomedullary junction. The CSF column in the front of the medulla was not visible [Figure 1a and b and Figure 2a]. She underwent C1 laminectomy and drainage of the AC by wide fenestration of the inferior wall of the cyst into the spinal subarachnoid space. Postoperative MRI done 6 months later showed regression of the AC, opening up of the 4th ventricle, absence of brain stem compression [Figure 1c and Figure 2b], and she was asymptomatic.
Dorsally placed AC of the CVJ produce symptoms either by compression of the lower medulla or upper cervical cord and may present with spastic quadriparesis, ataxia and lower cranial nerve dysfunction[2,3,7–16] or alternatively by causing alterations in CSF flow with resultant features of obstructive papilledema[2,11,12] hydrocephalus or syringomyelia. Our patient presented with ataxia alone. Headache and neck pain have also been frequently described in these patients[2,11–13,15] and was present in our case too.
Most of the cases described in literature had presented with a long history of symptoms-sometimes of several years[7,8,15,16]-with the exception of one case reported by Fukushima etal. where papilledema, headache, and vomiting occasioned by raised intracranial pressure resulted in an early diagnosis (within 1 month). Our case was symptomatic for 2 years and had undergone computed tomography (CT) scan of the brain previously and this was reported as normal. Dorsally placed AC at the CVJ is often confused on CT scan with an enlarged cisterna magna or dismissed as “incidental findings.” A plain CT scan of brain showing just CSF spaces in the lowermost cuts may miss the diagnosis and is an inadequate diagnostic tool. The extent of medullary and cord compression, the lower limit of the cyst, delineation of additional pathologies such as signal changes and syrinx and differentiation from epidermoid mandate that MRI be the investigation of choice.
Some cases described in literature like ours had a large posterior fossa component of the cyst,[2,10,11] while in others, the posterior fossa component was small. However, what is striking is the lack of reports of cerebellar symptoms in the literature. The vertical extent of the lesion in the cervical spinal canal has also varied between C1 and C5. Numerous procedures have been described in literature including partial or complete excision, fenestration,[3,8–11,13,16] and cystoperitoneal shunting with suboccipital craniotomy and cervical laminectomy of varying extents.
We felt extensive bony decompression with arachnoid dissection might cause arachnoidal scarring and alter the anatomy of the foramen magnum hampering the normal flow of CSF with respect to both direction and velocity. Higher velocities of craniocaudal flow of CSF would be maintained if there was no increase in effective foramen magnum diameter and this, along with the help of gravity in the erect position, would aid in keeping the residual cyst wall collapsed [Figures 3 and 4]. Hence, in our case, following C1 laminectomy, partial inferior cyst wall excision and fenestration of the cyst liberally into the spinal subarachnoid space was done. No attempt was made to separate the wall anteriorly from the lower medulla and upper cervical cord for fear of iatrogenic neural damage.
CSF collections in the posterior fossa seen on CT scans in lower cuts must not be dismissed as enlarged cisterna magna or “benign” ACs as they may enlarge in the future and may cause neural compression. Even large cysts seldom cause cerebellar symptoms and rather may mimic CVJ pathology. If there is clinical suspicion, further investigation with an MRI study that incorporates the upper cervical spine must be done and lower extent of the cyst delineated. Finally, if surgery is indicated, fenestration of the lowermost part of the cyst into the spinal subarachnoid space may suffice compared to more extensive procedures.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
1. Krishnan P, Kartikueyan R. Arachnoid cyst with ipsilateral subdural hematoma in an adolescent –Causative or coincidental:Case report and review of literature. J Pediatr Neurosci 2013;8:177–9.
2. Panigrahi S, Mishra SS, Das S, Patra SK, Satpathy PC. Large intradural craniospinal arachnoid cyst:A case report and review of literature. J Craniovertebr Junction Spine 2012;3:16–8.
3. Gulsen S. Symptomatic fourth ventricle arachnoid cyst extending to the upper border of the dens of the axis:A case report and review of the literature. Maced J Med Sci 2014;2:299–302 Available from:https://oamjms.eu/index.php/mjms/article/view/oamjms.2014.050
[Last accesssed on 2022 Oct 03].
4. Aggouri M, Boujraf SA, Benzagmout M, Chaoui ME. Arachnoid cyst of the posterior fossa. Neurosciences (Riyadh) 2010;15:277–9.
5. Jain R, Sawlani V, Phadke R, Kumar R. Retrocerebellar arachnoid cyst with syringomyelia:A case report. Neurol India 2000;48:81–3.
6. Galarza M, López-Guerrero AL, Martínez-Lage JF. Posterior fossa arachnoid cysts and cerebellar tonsillar descent:Short review. Neurosurg Rev 2010;33:305–14.
7. Pego-Reigosa R, Brañas-Fernández F, Martínez-Vázquez F, Cortés-Laiño JA. Craniospinal intradural arachnoid cyst. Arch Neurol 2000;57:128.
8. Kuroiwa T, Takeuchi E, Yamada K, Ohta T, Miyaji Y, Onomura T. An intradural arachnoid cyst of the craniovertebral junction;A case report. No Shinkei Geka 1991;19:1097–9.
9. Bhatia S, Thakur RC, Devi BI, Radotra BD, Kak VK. Craniospinal intradural arachnoid cyst. Postgrad Med J 1992;68:829–30.
10. Takanashi Y, Mochimatsu Y, Shyudo T, Yamamoto I. A case report of an arachnoid cyst in the craniovertebral junction. No To Shinkei 1995;47:68–70.
11. Fukushima Y, Sato M, Taguchi J, Sasaki M, Kanai N, Hayakawa T. Craniospinal arachnoid cyst:Case report. No Shinkei Geka 1996;24:75–9.
12. Price SJ, David KM, O'Donovan DG, Aspoas AR. Arachnoid cyst of the craniocervical junction:Case report. Neurosurgery 2001;49:212–5.
13. Cakirer S. Arachnoid cyst of the craniospinal junction:A case report and review of the literature. Acta Radiol 2004;45:460–3.
14. Kutlay M, Qolak A, Demircan N, Akin O. Craniocervical junction arachnoid cyst causing hydrocephalus:Case report and review of the literature. Mil Med 2007;172:669–72.
15. Pillai LV, Achari G, Desai S, Patil V. Acute respiratory failure as a manifestation of an arachnoid cyst. Indian J Crit Care Med 2008;12:42–5.
16. Huang H, Li Y, Xu K, Li Y, Qu L, Yu J. Foramen magnum arachnoid cyst induces compression of the spinal cord and syringomyelia:Case report and literature review. Int J Med Sci 2011;8:345–50.