Arachnoid cysts are congenital benign cavities that are filled with cerebrospinal fluid and present a duplication of the arachnoid membrane (arachnoid mater, innermost covering of the brain, pia mater). They can occur anywhere in the brain, most often in the region of the lateral sulcus (approx. 50% of all arachnoid cysts), suprasellar (10%), in the pineal recess (10%), in the cerebellopontine angle (10%), over the cerebellar vermis (10%), interhemispheric (5%) or rarely also in other regions.
Arachnoid cysts are often an incidental finding during head examinations by use of CT or MRI. In about 10-20% of cases they present clinical symptoms that are the result of the pressure of the cyst on the surrounding brain tissue. The most common symptom in cases of arachnoid cysts are headaches. More rarely there are signs of cerebral compression, seizures, hormonal disturbances or symptoms resulting from a local space-consuming lesion.
Children can in rare cases exhibit skull deformations. If the cysts are located in the third ventricle (suprasellar), hydrocephalus can result accompanied by hormonal disturbances, restrictions of vision or visual field, and occasionally involuntary nodding (bobble-head doll syndrome).
Magnetic resonance tomography is the diagnostic method of choice. It permits imaging of cysts on three levels and assessment of the position regarding the important anatomical structures (visual nerve, main artery: carotid artery) as well as the relation of the cyst to the ventricles and the basal cerebrospinal fluid cisterns. This has particular importance for therapy planning.
Only symptomatic arachnoid cysts are an indication for surgical treatment. Asymptomatic, incidentally discovered arachnoid cysts do not require any therapy in normal cases, as the circumstances require that they should be monitored by use of imaging procedures. Only in the case of very large cysts in children do we recommend removal of the cyst in order to provide the brain with space for normal development.
For the surgical treatment of an arachnoid cyst various procedures are available that all aim at establishing communication between the cyst and natural cerebrospinal fluid circulation. The aim of the treatment is to drain the cyst contents in the ventricles or basal cisterns that also conduct and drain the cerebrospinal fluid. The creation of a permanent connection from the arachnoid cyst to the normal cerebrospinal fluid cavities in the brain is necessary for that. This connection is, if possible, created endoscopically. If the endoscopic method does not succeed for anatomical reasons, the operation is continued microsurgically (under the visual control of an operating microscope).
A 1-year-old female patient presented too rapid head growth and vomiting. The MRI showed a large suprasellar arachnoid cyst with compression of the aqueduct (connection between the 3rd and 4th ventricle). Because of that the drainage of the cerebrospinal fluid was impeded and the pressure in the ventricles increased. As a result hydrocephalus with pressure symptoms developed. The cyst was fenestrated to the lateral ventricle and the basal cerebrospinal fluid pathways via an 8 mm borehole (see video). The reddish upper part of the pituitary gland and reddish pituitary stalk, the third cerebral nerve (responsible for ocular movement) on both sides, as well as the brainstem with posterior main artery (basilar artery) and its branches in the front of it were recognizable. The aqueduct was inspected after removal of the cyst and was found to be wide open. Because of the endoscopic fenestration the hydrocephalus resolved. It was possible to avoid artificial drainage (shunt system) with its risks of infection.
A-C: The MRI examination shows the large suprasellar arachnoid cyst (arrows) that displaces the aqueduct (short arrow) and the wide lateral ventricles.
B: The video shows the fenestration of the arachnoid cyst and the inspection of the aqueduct.
C: The postoperative MRI examination shows the considerable reduction in size of the cyst as well as the strong flow of the cerebrospinal fluid through the aqueduct (short arrow).
The 3-year-old boy presented with headaches. The MRI showed a large arachnoid cyst that compressed the normal cerebral tissue. The cyst was fenestrated to the normal cerebrospinal fluid pathways via an 8 mm borehole (see video). One can recognize on the left the optic nerve, on the right the third cerebral nerve (responsible for ocular movement), as well as in the middle the main artery (carotid artery) (arrows). Due to endoscopic fenestration the cyst resolved. It was possible to avoid an open microsurgical operation. Eight years after the surgery the patient is free of complaints. The cyst has not reformed.
A: The MRI examination shows the large arachnoid cyst on the right (arrows)
B: The video shows the fenestration of the arachnoid cyst.
C: The postoperative MRI examination shows complete remission of the cyst 8 years after the surgery.