====== Cerebellopontine angle arachnoid cyst ======

===== Epidemiology =====

[[Middle cranial fossa]] is the most common site of [[intracranial arachnoid cyst]]s, followed by the [[cerebellopontine angle]] (CPA) and [[suprasellar area]]. 

===== Etiology =====

Gardner et al., in [[1960]] attributed a embryonal [[atresia]] of the [[fourth ventricle]] as the cause of "[[arachnoid cyst]]" of the [[cerebellopontine angle]]
((GARDNER WJ, McCORMACK LJ, DOHN DF. Embryonal atresia of the fourth ventricle. 
The cause of "arachnoid cyst" of the cerebellopontine angle. J Neurosurg. 1960
Mar;17:226-37. PubMed PMID: 13826545.
)).

===== Clinical features =====
They usually remain asymptomatic so they are often diagnosed incidentally during radiological evaluation for other reason
((Gönül E, Izci Y, Onguru O. Arachnoid cyst of the cerebellopontine angle
associated with gliosis of the eighth cranial nerve. J Clin Neurosci. 2007
Jul;14(7):700-2. PubMed PMID: 17475499.
)).

As these cysts enlarge, they may compress surrounding structures and cause neurological symptoms. Patients may present with vague, nonspecific symptoms such as [[headache]] and [[ataxia]].
((Jallo GI, Woo HH, Meshki C, Epstein FJ, Wisoff JH. Arachnoid cysts of the
cerebellopontine angle: diagnosis and surgery. Neurosurgery. 1997 Jan;40(1):31-7;
discussion 37-8. Review. PubMed PMID: 8971821.
)).

These cysts also can cause dysfunction of specific cranial nerves, including III, IV, VI (to cause [[diplopia]]), V (to induce [[trigeminal neuralgia]]), VII (to cause congenital or acquired [[facial nerve paralysis]]), VIII (to cause [[hearing loss]], [[tinnitus]], [[vertigo]]), X (to result in [[hoarseness]] and [[dysphagia]])
((Hayden MG, Tornabene SV, Nguyen A, Thekdi A, Alksne JF. Cerebellopontine angle cyst compressing the vagus nerve: Case report. Neurosurgery. 2007;60:E1150.))
((Babu R, Murali R. Arachnoid cyst of the cerebellopontine angle manifesting as contralateral trigeminal neuralgia: Case report. Neurosurgery. 1991;28:886–7.))
((Messerer M, Nouri M, Diabira S, Morandi X, Hamlat A. Hearing loss attributable to a cerebellopontine-angle arachnoid cyst in a child. Pediatr Neurosurg. 2009;45:214–9.)).


Gurkas et al. report a patient with cranial nerve palsies and mirror movements found in upper extremities. They postulated that CPA arachnoid cyst compressing the brain stem and the pyramidal decussation may lead to mirror movements
((Gurkas E, Altan BY, Gücüyener K, Kolsal E. Cerebellopontine angle arachnoid
cyst associated with mirror movements. J Pediatr Neurosci. 2015
Oct-Dec;10(4):371-3. doi: 10.4103/1817-1745.174440. PubMed PMID: 26962347; PubMed
Central PMCID: PMC4770653.
)).

===== Diagnosis =====

[[Cerebellopontine angle arachnoid cyst diagnosis]]

===== Differential diagnosis =====
A cerebellopontine angle lesion could be a vestibular schwannoma, meningioma, epidermoid cyst, or less likely, arachnoid cyst, metastasis, lower cranial nerves schwannoma, lipoma, hemangioma, paraganglioma, or vertebra-basilar dolichoectasia. Primary meningeal melanocytoma is a rare neoplasm, especially when it occurs at the cerebellopontine angle
((Elbadry R, Elazim AA, Mohamed K, Issa M, Ayyad A. Primary meningeal
melanocytoma of the cerebellopontine angle associated with ipsilateral nevus of
Ota: A case report. Surg Neurol Int. 2018 Dec 4;9:245. doi:
10.4103/sni.sni_235_18. eCollection 2018. PubMed PMID: 30613434; PubMed Central
PMCID: PMC6293867.
)).

MRI is helpful in differentiating arachnoid cysts from those cystic lesions. If a pathologic cause of a retrocochlear disorder is suspected in a patient with a unilateral sensorineural hearing loss and tinnitus, MRI should be performed to evaluate the cerebellopontine angle. 

On MRI, arachnoid cysts appear as smooth-surfaced lesions that in all magnetic resonance sequences exhibit a signal characteristic of CSF. In contrast, epidermoid cysts show mixed signals on FLAIR images and high signals on diffusion weighted images. Neurenteric cysts present high signals on T1-weighted images and cystic schwannomas show some foci of contrast enhancement on T1-weighted postcontrast images
((Brackmann DE, Arriaga MA: Extra-axial neoplasms
of the posterior fossa. In: Cummings CW, Fredrickson
JM, Harker LA, Krause CJ, Richardson MA, Schuller
DE (eds) Otolaryngology Head and Neck Surgery. 3rd
ed. St. Louis, MO: Mosby-Year Book: 1998: 3294-3314.))
((Bonneville F, Sarrazin JL, Marsot-Dupuch K,
Iffenecker C, Cordoliani YS, Doyon D, Bonneville JF:
Unusual lesions of the cerebellopontine angle: a
segmental approach. Radiographics 2001; 21: 419-43.)).
----
The rising of a neuroglial cyst from the nerve sheath is a finding that brings other possible origins of neuroglial cysts into consideration
((Samadian M, Omidbeigi M, Bakhtevari MH, Asaadi S, Jafari A, Rezaei O.
Nerve-Sheath-Risen Neuroglial Cyst: A Case Report and Review of the Literature.
World Neurosurg. 2019 Jan 17. pii: S1878-8750(19)30082-8. doi:
10.1016/j.wneu.2018.12.203. [Epub ahead of print] PubMed PMID: 30660890.
)).

===== Treatment =====
The optimal surgical management of arachnoid cysts remains controversial. 

Although surgery for these entities is controversial, arachnoid cysts can be treated surgically with open craniotomy for cyst removal, fenestration into adjacent arachnoid spaces, shunting of cyst contents, or endoscopic fenestration. 

Alaani et al. support a conservative management approach to the majority of these cysts
((Alaani A, Hogg R, Siddiq MA, Chavda SV, Irving RM. Cerebellopontine angle
arachnoid cysts in adult patients: what is the appropriate management? J Laryngol
Otol. 2005 May;119(5):337-41. PubMed PMID: 15949094.
)).

The definitive treatment for these arachnoid cysts is a retrosigmoid suboccipital craniotomy and microsurgical resection and fenestration of the cyst walls
((Jallo GI, Woo HH, Meshki C, Epstein FJ, Wisoff JH. Arachnoid cysts of the
cerebellopontine angle: diagnosis and surgery. Neurosurgery. 1997 Jan;40(1):31-7;
discussion 37-8. Review. PubMed PMID: 8971821.
)).

===== Outcome =====
The risks of surgery are few, but complications (meningitis, hemiparesis, oculomotor palsy, subdural hematoma, grand mal epilepsy, and death) have been reported
((Alaani A, Hogg R, Siddiq MA, Chavda SV, Irving RM. Cerebellopontine angle
arachnoid cysts in adult patients: what is the appropriate management? J Laryngol
Otol. 2005 May;119(5):337-41. PubMed PMID: 15949094.
)).
((Ucar T, Akyuz M, Kazan S, Tuncer R: Bilateral
cerebellopontine angle arachnoid cysts: case report.
Neurosurgery 2000; 47: 966-968.))
((Eslick GD, Chalasani V, Seex K: Diplopia and
headaches associated with cerebellopontine angle
arachnoid cyst. ANZ J Surg 2002; 72: 915-917.)).

Olaya et al. report the first case of complete recovery from sensorineural hearing loss and facial weakness following endoscopic fenestration
((Olaya JE, Ghostine M, Rowe M, Zouros A. Endoscopic fenestration of a
cerebellopontine angle arachnoid cyst resulting in complete recovery from
sensorineural hearing loss and facial nerve palsy. J Neurosurg Pediatr. 2011
Feb;7(2):157-60. doi: 10.3171/2010.11.PEDS10281. PubMed PMID: 21284461.
)).




===== Case series =====
[[Cerebellopontine angle arachnoid cyst case series]]

===== Case reports =====

[[Cerebellopontine angle arachnoid cyst case reports]].

===== Cerebellopontine angle arachnoid cyst cases from the General University Hospital of Alicante =====

Both [[vestibulocochlear nerve]]s (VIII) with normal and symmetrical caliber and morphology are identified, with no evidence of areas of focal thickening that suggest the existence of intra or extracanalicular [[vestibular schwannoma]]. The round image up to 21mm in the right [[cerebellopontine angle]] follows the [[fluid]] [[signal]] in all the sequences and displaces the origin of the 
the [[facial nerve]]s (VII), and the [[vestibulocochlear nerve]]s (VIII), anteriorly.
Findings are suggestive of a right [[cerebellopontine angle arachnoid cyst]].

{{::cerebellopontine_angle_arachnoid_cyst_cases_from_the_general_university_hospital_of_alicante.jpg?200|}}


===== References =====