What is the definition of arachnoid cysts?
Arachnoid cysts are extra-axial, benign cystic lesions formed between the inner and outer layers of the arachnoid, filled with cerebral spinal fluid (CSF).
Where is the most common arachnoid cyst location in the adult population?
One-third of arachnoid cysts are in the posterior fossa, and two-thirds of these cysts are in the supratentorial space. The most common location for this entity is the middle cranial fossa, which accounts for 50%-65% of all intracranial arachnoid cysts.
How is the Galassi classification of middle cranial fossa arachnoid cyst?
Galassi classified arachnoid cysts of middle cranial fossa into three types according to their size and effect on neighboring structures. Type I: small, located in the anterior temporal fossa, without mass effect Type II: medium-size, located in the anterior and middle temporal fossa, with the displacement of the temporal lobe Type III: a large cyst that fills the entire temporal fossa, with mass effect on the temporal, frontal, and parietal lobes.
What are the clinical manifestations of an arachnoid cyst?
Most patients with arachnoid cysts are asymptomatic, and the cysts are found incidentally on CT and MRI. Headaches are the most common symptom. Other symptoms and signs include nausea/vomiting, vertigo, seizure, ataxia, dizziness, visual changes, endocrine disorders, hearing loss, speech abnormalities, mental status changes, cervical myelopathy. The local mass effect may contribute to focal neurological deficits. Arachnoid cyst may produce hydrocephalus by compression of the third ventricle and the fourth ventricle.
What are the characteristics of an arachnoid cyst on CT and MRI?
On Ct, arachnoid cysts are a noncalcified homogeneous extra-axial cystic lesion, similar to CSF attenuation. On MRI, they are isointense to CSF at all pulse sequences. They do not enhance, and they do not exhibit diffusion restriction. Arachnoid cysts can promote bone remodeling, may produce macrocrania and cranial asymmetry. These lesions can also rupture, causing intracystic hemorrhage, subdural hygroma, and subdural hematoma.
What are the treatments of arachnoid cyst?
The treatments of the arachnoid cyst are controversial, and the indication is generally for symptomatic cysts. There are three surgical methods: neuroendoscopic fenestration, microsurgical fenestration, and shunting.
Contrast-enhanced MRI demonstrates a large cyst located at the left middle cranial fossa, isointense to CSF at all MRI pulse sequences, homogeneously hypointense on T1 weighted MR, and hyperintense on T2 Weighted MR. There is no restricted diffusion and no enhancement. Features are characteristic of an arachnoid cyst.
The arachnoid cyst produces a mass effect on the left temporal lobe, which is hypoplastic and displaced posteriorly. The cyst promotes bone remodelling and enlarges the left temporal fossa, with bulging of the temporal bone.