I. Overview
Intracranial arachnoid cysts are non-neoplastic, cystic lesions formed by the intracranial arachnoid membrane and containing cerebrospinal fluid.
Etiology
1. Congenital (primary) increase in cerebrospinal fluid accumulation during the embryonic period, combined with various causes of abnormal development of the subarachnoid space during the embryonic period, resulting in the formation of a poorly drained localized cystic bag that gradually expands under the action of mechanisms such as osmotic pressure gradient, unidirectional valve obstruction, cystic wall secretion and vascular pulsation.
2. Acquired birth injury or postnatal intracranial hemorrhage, intracranial infection, etc. produce viscous secretions, or craniotomy injury, etc. cause local adhesions of the arachnoid membrane, resulting in significant obstruction of the local subarachnoid space and brain pool, which, together with the pushing effect of the one-way valve and CSF pulsation, cause CSF to accumulate and form cysts.
III. Incidence
Arachnoid cysts account for about 1%~3% of intracranial occupying lesions, mostly congenital, male:female=4:1, and left temporal:right temporal=2:1 in males.
IV. Clinical manifestations
1. 60%~80% of patients can have clinical symptoms, mainly headache and vomiting caused by increased intracranial pressure, seizure is the common first symptom, and also cranial enlargement, local cranial augmentation (temporal and occipital), hemiplegia, mental retardation, cerebellar ataxia, vision loss, bilateral temporal hemianopia, sensory loss and hearing loss.
2. Obstructive hydrocephalus and intracranial hypertension often appear earlier in the posterior cranial fossa, deep brain and midline areas.
Cysts located in the convex surface of the cerebral hemispheres and the anterior part of the middle cranial fossa often present first with progressive worsening of symptomatic epilepsy.
4. Intracranial arachnoid cysts should be considered in children who develop clinical symptoms that are not easily explained after minor head trauma.
V. Diagnosis
1. Head CT shows isointense relative to cerebrospinal fluid (hypointense relative to brain parenchyma) occupying lesion, no enhancement of cyst wall, no surrounding edema band, local brain tissue compression deformation or displacement, and obstructive hydrocephalus if located in the midline.
2. cranial MRI low T1, high T2 signal, lesions with the same signal as CSF, differentiated from cysts and inflammatory granulomas secondary to intracranial infection.
3.CT brain pool imaging immediately shows the arachnoid cyst without drug filling, and delayed imaging 1.5~4.5 hours shows the contrast gradually entering the cyst and evenly distributed, which can understand the extent of the cyst and its patency with the subarachnoid space.
4. SPECT radionuclide brain pool imaging (scintigraphy) can understand the location, morphology, size, traffic, traffic site and circulation rate of the cysts, which are classified into closed type (cysts are not visualized), open type with good traffic (visualized within 2 hours, peak time <3 hours, peak uptake rate 60%, 24-hour retention rate <30%) and open type with poor traffic according to the visualization and semi-quantitative index.
VI. Treatment
1. Treatment principles: asymptomatic patients do not need surgery, but must be followed up and dynamic intracranial pressure monitoring is feasible for 48-72 hours, and surgery is advocated if the intracranial pressure increases or abnormal waveforms appear; children should be operated early once detected, especially temporal lobe cysts.
2. Indications for surgery
① those with increased intracranial pressure, brain compression, midline shift and ventricular system obstruction.
② those with intracranial (intracapsular or subdural) hemorrhage.
③those with significant limited neurological deficits.
(iv) Those with intractable epilepsy with spiking discharges around the cyst.
⑤ those with mild neuropsychiatric symptoms, memory loss, thought inattention, and cognitive decline (left temporal fossa cyst) on neuropsychological test.
3. Surgical strategy
①Cyst wall resection so that the cyst has extensive communication with the surrounding subarachnoid space, brain pool and ventricle is the key to successful surgery; slowly release the cyst fluid during surgery, and remove as much of the cyst wall as possible without damaging the brain tissue; pay attention to protecting the pontine veins in the lateral wall of the cyst, especially the lateral fissure vein; intraoperative EEG monitoring should be performed in those with intractable epilepsy, and resection of epileptogenic foci around the submural cyst, submural arch in the functional brain area, and transection of the corpus callosum. The patient should undergo intraoperative electroencephalographic monitoring and perform subperitoneal cyst excision, subperitoneal archotomy, and corpus callosotomy.
(2) Cystic cavity placement with a tipped myocardial flap Temporal or occipital myocardial flap placement is used for cystic cavity placement in the temporal or occipital region, far from the brain pool or where there are important structures in the cyst site and the cyst wall is tightly adhered and not easily separated.
③Cyst-abdominal shunt is used for those who are old, frail and sickly and have huge cysts, or those who have recurrence after cyst wall resection.
④Stereotactic surgery and neuroendoscopic surgery are suitable for small cysts in the deep brain and skull base such as intracerebroventricular, intradistal, and saddle areas.
⑤Ommaya bursa can be used for elderly people with complications.
4. Complications after craniotomy
①Severe headache, high fever or even convulsions and coma in a short period of time
②Intraoperative cavity hemorrhage or subdural hematoma
③Acute brain swelling.
5. Postoperative recurrence causes
①Incomplete development of brain lobes, poorly repositioned brain tissue expansion
② skull base deformity, surgery failed to establish effective extensive traffic
③Heavy surgical trauma and residual hematogenous CSF
④Rehemorrhage
⑤Arachnoiditis
VII. Prognosis
The best result is achieved by the large part of cyst wall resection with the traffic of ventricle and brain pool; the application of stereotactic, locking hole and neuroendoscopic techniques is the current development direction, especially unique for deep brain cysts.