Dysembryoplastic neuroepithelial tumor
Dysembryoplastic neuroepithelial tumors are rare, indolent, low-grade tumors found in children and young adults. Most commonly affecting the temporal
Mar. 22, 2021
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The authors review the etiology, presentation, investigation, and treatment of arachnoid cysts in the brain and spine. Arachnoid cysts are common incidental findings (1.4% of adults and 2.5% of children having an MRI scan). Arachnoid cysts are usually intracranial and supratentorial in location, but spinal, and even intraneural, cysts may be identified and possibly cause symptoms. Asymptomatic cysts do not require active management. However, some are associated with seizures, local pressure effects, or hydrocephalus and may require treatment. Urine should be checked for glutaric acid in cases of bitemporal arachnoid cysts as glutaric aciduria type 1 is present in 25% of cases. Symptomatic cysts will require intervention in the presence of hydrocephalus or spinal cord compression. Surgical intervention to treat seizures or headache is successful in only 33% to 50% of cases. Electroencephalographic seizure focus coinciding with temporal arachnoid cyst and SPECT imaging demonstrating impaired cerebral perfusion may be helpful when considering intervention. Minimally invasive neuroendoscopic techniques are being more widely practiced where there is hydrocephalus or suprasellar cysts, but resection and marsupialization for large Sylvian fissure and cortical arachnoid cysts has superior success rates to neuroendoscopic procedures. Endoscopic fenestration, although less effective at reducing cyst size, has a lower complication rate. The complication rate of fenestration of arachnoid cysts in pediatric cases is over 35%. About 10% of arachnoid cysts recur after fenestration, and subdural hygromas requiring re-operation occur in 6% of all cases of large Sylvian fissure arachnoid cysts.
• Be certain that the cyst is responsible for symptoms before considering intervention. In over 40% of patients, some other underlying condition on the differential diagnosis, and not the arachnoid cyst, was revealed to be the cause of the symptoms.
• Arachnoid cysts in children are as likely to decrease in size as they are to increase.
• Two thirds of cases are temporal fossa arachnoid cysts.
• There may be rupture of bridging veins or vessels in the wall of the cyst, which can result in subdural hematoma or bleeding into the cyst.
• Endoscopic procedures for temporobasal arachnoid cysts have the lowest success rate (81%), highest recurrence (19%), and highest complication rate (24%).
• A systematic review of published case reports for individuals with arachnoid cysts who suffered a structural brain injury during a sport or recreational activity did not find evidence to support recommending against participation in sports for patients with arachnoid cysts.
Arachnoid cysts are classified as developmental cysts; they were first described in 1831 (10). These cysts lie between 2 membranes of normal arachnoid matter and are more properly described as intra-arachnoid cysts (101). Congenital or developmental arachnoid cysts differ from secondary or acquired arachnoid cysts, as the latter are loculations of CSF surrounded by arachnoid scarring. A classification of midline cysts based on neuroembryologic analysis and imaging, suggests 2 categories:
Category 1: Expansion of the roof plate of the brain vesicle (eg, Dandy Walker cyst, Blake pouch cyst, communicating interhemispheric cysts with callosal agenesis, or dorsal cyst with holoprosencephaly).
Category 2: Cysts consisting of extra-axial structures, eg, arachnoid membrane or migrating ependymal cells (arachnoid cyst, arachnoid pouch, mega cisterna magna) (113).
Suprasellar arachnoid cysts have been classified as noncommunicating intra-arachnoid cysts of the diencephalic membrane of Liliequist as well as communicating cystic dilations of the interpeduncular cistern, based on MRI, CT cisternograms, and neuroendoscopy (60). One of the first successful surgical interventions for an arachnoid cyst was a partial removal by Placzek and Krause in 1907, resulting in clinical improvement (78). The traditional surgical approach to arachnoid cyst, namely removal of as much of the cyst wall as was possible (56), was often complicated by damage to the surrounding brain and cyst recurrence. Although shunting recurrent cysts was often successful, shunt insertion as primary treatment was only first advocated in 1981 (103).
Arachnoid cysts can occur throughout the neuraxis, but are most commonly found intracranially. In large retrospective prevalence studies based on MRI, approximately 1.4% of cranial MRI scans demonstrated an arachnoid cyst (02). Most are asymptomatic and incidental. Intracranial arachnoid cysts occur most frequently in the middle cranial fossa (66%) and convexity (14%), but they can occur anywhere, as shown in Table 1 (31). In the middle cranial fossa, they are usually unilateral, but bilateral cysts are found in up to 10% of cases of middle cranial fossa arachnoid cysts (30; 71). The clinical manifestations are nonspecific and depend on the age at presentation and the location of the cyst. Generally, midline cysts present earlier in life and present with signs and symptoms of hydrocephalus. A preoperative case-control study found that patients with arachnoid cysts had more neurocognitive deficits on tests of verbal fluency and the Tower test than a control group admitted for spinal surgery, and, postoperatively, improvements were only seen in the group with arachnoid cysts (07). Bilateral temporal arachnoid cysts occur in association with glutaric aciduria type 1 in up to 25% of cases. Urine should be checked for glutaric acid in cases of bitemporal arachnoid cysts, as even simple operations may be risky (51).
• Middle fossa (Sylvian)
Arachnoid cysts can be identified prenatally (16) or in the elderly (123); however, it has been estimated that up to 80% are diagnosed before the age of 16 years (82). Symptomatic infants and children commonly present with raised intracranial pressure or cyst expansion causing macrocephaly (71.5%), and cranial asymmetry (75). Some children may also have developmental delay or epilepsy (18%). A particularly intriguing presentation in children is "bobble-head doll syndrome." This occurs in about 10% of cases with suprasellar arachnoid cysts and consists of a head-bobbing motion due to neck tremor (77). Suprasellar arachnoid cysts have been associated with isosexual precocious puberty (102).
Most symptomatic adults present with epilepsy. It is contentious whether arachnoid cysts actually cause seizures or are simply a "flag" that there is some coexisting process in the underlying brain (eg, hypoplasia). Nevertheless, the presence of an abnormal co-localizing electroencephalogram will often influence neurosurgeons to treat surgically (107). Symptomatic interhemispheric arachnoid cysts in the elderly are usually not associated with agenesis of the corpus callosum (125). Approximately 18% of middle cranial fossa cysts present with progressive symptoms, whereas 44% present with nonprogressive symptoms and 37% present with symptoms not associated with the arachnoid cyst (76). Subtle cognitive deficits may be identified in patients with left temporal arachnoid cysts (119). Psychosis is also a common association. Arachnoid cysts have been identified in 2% of psychiatric admissions with psychosis, but it is uncertain how often the cyst is the cause of psychosis and how often it is an incidental finding (27). Posture-related psychosis has been described in one case with an intraventricular arachnoid cyst, with resolution of psychosis following operation (121).
In the posterior fossa, arachnoid cysts usually present with facial pain, isolated cranial nerve palsies, cerebellar signs, or raised intracranial pressure from obstructive hydrocephalus. Suprasellar cysts may present with progressive hydrocephalus, spasticity, gait disturbance, and visual impairment, and up to 60% have hypothalamic-pituitary signs (77).
Spinal arachnoid cysts may be intradural or extradural. The symptoms from spinal arachnoid cysts are progressive lower limb weakness, spasticity, radicular pain, scoliosis, and recurrent urinary tract infection. Cases with acute presentations or intermittent symptoms and signs are well described (120). Spinal intradural arachnoid cysts are generally anteriorly situated in the cervical spine (87%) and posteriorly situated in the thoracic spine (85%). In general, children with spinal arachnoid cysts present with motor deficit (76%) although 25% had back pain only (21).
Intraneural arachnoid cysts are an extremely rare cause of isolated cranial nerve palsies and are potentially reversible if the cysts are properly identified and treated with surgical intervention (09).
There are several published cases of spontaneous resolution of even large arachnoid cysts, although this is more common with smaller cysts (89). Most arachnoid cysts remain the same size or increase in size only slightly in adulthood, and others fluctuate over time (57). Care should be taken when attributing the patient's symptoms to the presence of the cyst. Neurologic symptoms and disability are common, but death is rare. There may be rupture of bridging veins or vessels in the wall of the cyst, which can result in subdural hematoma or bleeding into the cyst (88; 93). Chronic hematomas are found in approximately 5% of patients with an arachnoid cyst (118). It has been estimated that arachnoid cysts are present in 2.5% of patients with chronic subdural hematomas (74). Extradural hematomas have also been described. A case control study found larger cyst size (greater than 5 cm) and head injury to be significant risk factors for cyst rupture/hemorrhage, although these hematomas may occur spontaneously as well (13). In these instances of arachnoid cysts associated with extra-axial hematoma presence, it may be sufficient to surgically address the hematoma, without resecting the arachnoid cyst, if there are no symptoms specifically associated with the cyst itself (126).
Subdural hygromas requiring re-operation occur in 6% of all cases of Sylvian fissure arachnoid cyst operated on to decompress the cyst. Hygromas are more likely to occur in Galassi type III cysts than in type II or type I arachnoid cysts (106). The acute or subacute symptoms related to subdural hygroma may develop up to 1 month after operation (mean 14 days). From a series of 60 cases of middle cranial fossa arachnoid cysts treated by various measures, it appears that small effusions can be treated conservatively, and in cases in which surgical intervention is considered necessary, burr hole and subdural drainage is effective in most cases (99).
A 61-year-old obese male presented with a 2-month history of episodic lightheadedness and mild headache. Lightheaded episodes lasted 5 to 10 minutes and could occur up to 3 to 4 times per day. There were no neurologic signs on examination, except for a moderately elevated blood pressure of 180/100 and grade 2 hypertensive changes on fundoscopy.
Investigations. A CT scan showed a 3 to 4 cm left middle cranial fossa arachnoid cyst without mass effect. Urea and electrolytes, liver function, thyroid function, full blood count, and erythrocyte sedimentation rate were normal. The ECG met voltage criteria for hypertension. An EEG was normal, and a 24-hour EEG was normal, despite one symptomatic episode. Lumbar puncture found normal pressure and constituents. Repeated blood pressure measurements showed diastolic recordings of up to 120 mm/Hg. A chest x-ray was normal. Further investigation of hypertension did not reveal any cause.
Outcome. The patient began hypertension treatment with a beta-blocker, and he had resolution of his headaches and lightheadedness within 24 hours. No symptoms were present at the follow-up 3 months later. No intervention was performed to address the arachnoid as the patient’s symptoms responded to medical management of his hypertension.
Most arachnoid cysts are developmental and their etiology is unknown, but they can also be acquired after trauma or infection through CSF entrapment within arachnoid adhesions. There is debate whether arachnoid cysts are primary malformations of the arachnoid (101), or secondary to hypoplasia or agenesis of underlying brain (87). Spinal extradural arachnoid cysts (SEDAC) may rarely be familial, associated with lymphedema-distichiasis syndrome (LDS), and associated with FOXC2 mutations; furthermore, arachnoid cysts in the brain are more common in patients with tuberous sclerosis 2 (5.5% vs. 0.5% general population) (68; 08). One case of acquired arachnoid cyst development following temporal lobectomy has been reported (116). Secondary arachnoid cysts can occur after epidural anesthesia, overdrainage of CSF via ventriculoperitoneal shunts, spinal injury or surgery (39), head trauma or radiosurgery (64), craniotomy (53), following phenol injection (85) or following oil-based contrast media (95). Of the 17 neonatal cases of anterior cervical arachnoid cysts reported in the literature, 65% have had either prior myelomeningocele repair or a history of spinal trauma (37). There have been cases of cervicothoracic arachnoid cysts being associated with obstetric brachial plexus palsy (58). Epidural spinal arachnoid cysts occur through small dural defects, in much the same manner as secondary arachnoid cysts.
The pathogenesis of arachnoid cysts is controversial. There is MRI evidence of hypoplasia in the temporal lobe in all cases with middle cranial fossa arachnoid cysts (86) and a high incidence of ipsilateral pneumosinus dilatans of the paranasal sinuses (25), suggesting that hypoplasia may be a primary phenomenon rather than secondary to pressure from an expanded arachnoid cyst. Nevertheless, cases followed from infancy have shown no hypoplasia at birth, but the development of hypoplasia and expansion of the cyst with the passage of time (69). Some electron microscopy studies demonstrate that the inner sheath is composed of several layers of arachnoid cells, with underlying connective tissue that is rich in desmosomes and tight junctions as well as intermixed collagen fibers and myofibrils (59). However, an electron microscopic study of 24 symptomatic arachnoid cysts from different sites showed that the cyst wall varied in structure, with some composed of normal arachnoid (50%), others composed of a core of dense fibrous material with simple epithelial lining, and others with nonarachnoid luminal epithelial with microvilli, cilia, and nervous tissue, suggesting formation at early embryonal development as a teratological phenomenon (81).
The role of supratentorial arachnoid cysts in epilepsy is not established, as a cyst may reflect dysplasia of the underlying cortex rather than be a primary agent of cortical damage (05). Nevertheless, operative reduction of cyst size was associated with improved seizure control in a series of 76 patients (45).
Intraspinal arachnoid cysts are commonly associated with other congenital abnormalities. Intradural and extradural locations are found in approximately equal frequency, most commonly in the lower thoracic region. They are usually situated posterior to the cord, but some are anterior (79). Arachnoid cysts contain CSF and can enlarge, through cyst filling via a "slit valve" system where CSF enters the cyst and then cannot escape (35).
The incidence of arachnoid cysts is unknown. An arachnoid cyst is identified in 1.4% of adult patients undergoing an MRI scan and in 2.6% of children undergoing MRI scan (63; 02). It has been estimated that arachnoid cysts account for 1% of intracranial masses (75). In children, arachnoid cysts occur more commonly in boys (p< 0.000001) (64% vs. 36%) (66; 03) but apparently are equally distributed in the elderly (123). Temporal lobe cysts are more commonly found on the left side (2.5:1), and there seems to be a significant male preponderance of temporal arachnoid cysts (p< 0.004). For all other sites, there does not appear to be any sex predilection, apart from the cerebellar pontine angle, which may be more common in women (31).
It has also been reported that arachnoid cysts can occur after gamma knife radiosurgery. These arachnoid cysts are extratumoral and can arise following treatment. They are histologically different from intratumoral cysts that form secondary to hemorrhagic change within the tumor (64).
Arachnoid cysts cannot be prevented.
The differential diagnosis of intracranial arachnoid cysts includes other causes of increased intracranial pressure, epilepsy, psychiatric disorders, or cranial nerve palsy. In the spinal canal, the differential includes any cause of cord or root compression, such as a tumor, hematoma, infection, or disc herniation. Imaging of the site of clinical involvement using CT or MRI usually leads to the correct diagnosis. There can be difficulty in distinguishing between arachnoid cysts of the suprasellar region and other benign cysts commonly found in that region (eg, Rathke cyst, third ventricular dilatation, craniopharyngioma, or epidermoid tumors) (112). Variable-bandwidth steady-state free-precession MRI, diffusion weighted MRI, and MRI spectroscopy may help distinguish arachnoid cysts from epidermoid tumors or other cysts (111; 73; 97). Where these techniques are not available, cisternography with water-soluble intrathecal contrast will help identify the well-defined borders of an arachnoid cyst from the irregular surface of an epidermoid. In the posterior fossa, it can be difficult to distinguish arachnoid cysts from the dilated fourth ventricle of Dandy-Walker syndrome. The hypoplastic vermis that accompanies Dandy-Walker syndrome is usually evident on neuroimaging studies and can aid in making the diagnosis. Spinal intradural arachnoid cysts are seen most commonly in the thoracic region and are situated posteriorly in the canal. In the sacral region the differential diagnosis includes meningoceles or secretory cysts of the nerve root pockets (eg, Tarlov cysts).
CT and MRI are the essential noninvasive studies for diagnosis of intracranial arachnoid cyst, although the cysts can also be demonstrated by ultrasonographically before birth or in infants. CT with contrast or gadolinium-enhanced MRI will demonstrate a cyst with signal similar to CSF and no enhancement. Middle cranial fossa cysts have been categorized based on cyst size (23). Galassi type 1 cysts, which are limited to the anterior part of the temporal fossa and do not cause appreciable mass effect, account for 20% of middle fossa arachnoid cysts. Approximately 50% of middle fossa arachnoid cysts are type 2 cysts, where the cyst occupies the anterior and middle temporal fossa and there may be moderate mass effect. The remaining 30% are type 3 cysts, where the cyst occupies the temporal fossa almost completely, the temporal pole is severely atrophic, and there is compression of the frontal and parietal lobes and striking mass effect.
Bilateral temporal arachnoid cysts occur in association with glutaric aciduria type 1 in up to 25% of cases. Urine should be checked for glutaric acid in cases of bitemporal arachnoid cysts, as even simple operations may be risky (51). Neuropsychological testing can occasionally reveal cognitive deficits, and these can correspond to the temporal lobe being less metabolically active and having reduced cerebral blood flow on PET scanning (94; 127). The PET scan abnormalities recover postoperatively, and in some cases rather vague preoperative symptoms can improve (94). Tc99m-HMPAO SPECT has been shown to demonstrate zones of decreased regional blood flow in up to 70% of cases that corresponded to symptoms. Patients with normal rCBF were asymptomatic or became asymptomatic with conservative management (55).
Intrathecal gadolinium-enhanced MR may also assist in selection of cases of intracranial arachnoid cyst for surgery (105).
Suprasellar arachnoid cysts are often seen on axial neuroimaging studies as rounded areas of cerebrospinal fluid imaging characteristics just behind the frontal horns of the lateral ventricles. The 3 structures resemble the head of a rabbit or "Mickey Mouse," depending on the degree of hydrocephalus. Suprasellar arachnoid cysts cause vertical displacement of the optic chiasm/tracts, upward deflection of the rostral mesencephalon and mammillary bodies and effacement of the ventral pons (115). However, small or multiloculated cysts may be difficult to diagnose with MRI because the CSF signal from the cyst may be virtually indistinguishable from surrounding CSF, save for the lack of flow within the cyst (18). Cine-balanced steady-state free precession MRI (bSSFP) can demonstrate communication between arachnoid cysts and the subarachnoid space correctly in 92% compared with operative findings (50). In cases of parasellar arachnoid cysts, preoperative evaluation should include assessment of hypothalamic-pituitary axis. There may be deficiencies in growth hormone and thyrotropin or stimulation of the hypothalamic-pituitary axis with giantism and obesity (01).
Intraspinal arachnoid cysts are usually readily identified by MRI (84). Delayed CT myelography will also usually demonstrate spinal arachnoid cysts and this information is important when planning dura cleft repair (70).
When a watch-and-wait policy was adopted in 111 children under the age of 18 years, cysts in 11 (10%) of the children increased in size within a median of 3.5 years, 13 (12%) decreased in size, and 87 (78%) remained stable. Young children were significantly more likely to have enlargement and require surgery, and no patient older than 4 years of age at the time of initial diagnosis became symptomatic or had cyst enlargement (03).
A tertiary referral center for management of headache found arachnoid cysts in 4.4% of MRI scans (19). Only 2 of the 11 cases identified were considered symptomatic and underwent surgery. Parenchymal fiberoptic transducers have been used for prolonged intracranial pressure monitoring and have a relatively low complication rate, so intracranial pressure monitoring has been used to try and aid the decision whether to intervene, even in asymptomatic patients (108). Additionally, patients may be symptomatic without imaging signs of focal mass effect from the arachnoid cyst, demonstrating the challenge in relying on imaging as the sole guide in surgical selection. One study used a trial of oral acetazolamide, which reduces CSF production, to reduce the amount of fluid in the cyst as a mimic for surgical decompression in an attempt to identify symptomatic patients who would benefit from surgical management (43). The authors found encouraging results, with 94% of patients who responded to the acetazolamide challenge benefiting from surgery.
A follow-up study of 110 children with intracranial arachnoid cysts treated surgically demonstrated clinical improvement in 87% of patients and radiological improvement in 93% after endoscopic surgery, even higher frequencies of improvement after open microsurgery, and 89% after shunt operations (47). An observational study and literature review found that choroidal fissure arachnoid cysts are very infrequently symptomatic and do not usually require intervention (15).
In epilepsy cases where the cyst appears to be under pressure, surgery should be considered, although it may not result in seizure control (46; 45). A co-localizing electroencephalogram may aid the decision to intervene when dealing with Sylvian fissure arachnoids cysts; craniotomy and arachnoid cyst marsupialization is still the preferred surgical option by two thirds of surgeons (107).
The surgical options largely depend on the presence or absence of hydrocephalus. Aspiration of the cyst produces early improvement but recollection almost always occurs. In the absence of hydrocephalus the preferred operation is to fenestrate the cyst, producing connections between the cyst and the ventricle, or basal cisterns (22; 42). Endoscopic techniques to fenestrate arachnoid cysts, with or without stereotactic guidance, are yielding improving results (90; 40; 96; 17; 24; 91). It is difficult to gauge whether this is due to improvement in surgeons’ learning curve and better training of endoscopic techniques, or if it reflects publication bias. There have been no randomized controlled trials comparing surgical procedures. In the pediatric population with symptomatic Sylvian fissure arachnoid cysts treated by fenestration, reduction in the volume more than 10% was achieved in 83% of cases, and the volume continued to reduce over the subsequent year and was associated with improvement or resolution of headaches in 75% of cases (91). However, in a longer-term follow-up study (median 38 months) of 75 operated pediatric patients with fenestrated arachnoid cysts, the goal of surgery was only achieved in 28% of cases (12).
Thirty-five complications occurred in 28 patients, frequently including subdural fluid collection postoperatively on imaging. The authors considered the risk-benefit ratio to be poor and called for surgery to be strictly limited to patients in whom it was clear there was a symptomatic link between the arachnoid cyst and the primary symptom. Intraoperative neuroimaging can be used to monitor surgical success in establishing communication between the cyst and cerebrospinal fluid pathways (92; 72). In the presence of hydrocephalus and raised intracranial pressure, a ventriculo-cysto-peritoneal shunt is preferable (82; 75).
An analysis of pooled data from 36 case series totaling 1324 cases compared 4 different neurosurgical techniques—open craniotomy for cyst excision, open craniotomy for cyst fenestration, endoscopic fenestration, or cystoperitoneal shunting—and found similar success rates in general, but with individual differences, and supported an individual treatment strategy for cases requiring surgery (04). Internal shunting from the cyst to the subdural space has been performed in some cases, with shrinkage of the cyst and prolonged symptomatic improvement reported in 66% of patients and only temporary symptomatic improvement in the remaining patients, and with 25% of all cases requiring surgical reintervention and 25% developing subdural hematomas or hygromas (117). An update of this technique, by the same authors, showed good immediate technical results in 31 patients, with shrinkage of the cyst in 87% of cases. Other authors have found similar technical success rates (75%) (28). Complication rates of endoscopic cystocisternotomy range from 19% to 24% (67; 28). Twenty-three percent will have a subdural complication, and 13% to 19% of cases will require re-operation for treatment of this complication (117; 67). The authors found no correlation between volume reduction and clinical improvement, but none of the complications resulted in permanent deficit. Twenty-three percent required later re-operation because of treatment failure after a median of 8.2 years (32). Where cyst recurrence is a problem, stent placement has been successfully performed by stereotactic/endoscopic surgery with an 84% to 92% success rate at 2 years (06; 98). About 10% require further surgical treatment at some stage, and approximately 10% may get complications of intracystic bleeding (98). Following microcraniotomy and fenestration of temporal arachnoid cysts, 18% will show continued cyst enlargement on interval imaging, indicating an unsuccessful technical result. In a series, all patients with hemiparesis showed some improvement, but none with ataxia or behavioral problems improved; two-thirds with epilepsy improved, but only 50% with headaches showed improvement, indicating that the particular symptom a patient presents with may be related to the odds he/she will experience improvement following surgery. Seventy-eight percent of patients with a temporal cyst who underwent cyst surgery demonstrated an improvement in ability to perform a "maze test" postoperatively compared to a control group of patients with cervical disease who performed no differently after surgery (36). Likelihood of clinical improvement was less in patients with grade III cysts, and they may be at a higher risk of complications, such as transient CNIII nerve palsy (6%), pseudomeningocele (10%), and CSF leak (6%), which frequently require further surgical intervention (49). In most cases of ventriculo-cysto-peritoneal shunt, hydrocephalus and endocrine symptoms will resolve, but shunt failure with frequent revisions of shunt are common (114). “Slit ventricle syndrome,” in which patients present with a headache and the CT scan shows no morphological change in the cyst dimensions but shows slit ventricles and elevated CSF pressures, and shunt dependency have been described after cyst-peritoneal shunting of a temporal arachnoid cyst (44; 104). Patients respond to shunting or release of shunt ligation. Overdrainage in shunted intracranial arachnoid cysts is well described, leading to an acquired Chiari malformation and posterior fossa overcrowding (54). Complications from shunt related problems (eg, malfunction, infection, or subdural fluid collections) occur commonly (56%), and 12% require further surgeries (47).
Importantly, there is evidence that rapid surgical decompression of Sylvian fissure cysts, either by microsurgical or endoscopic cyst fenestration or by cystoperitoneal shunting, can rarely lead to brain shift and secondary brain hemorrhage (83).
The first prospective study on the outcome for surgical fenestration and decompression for intracranial arachnoid cysts has been completed. The authors found that patients with headaches and dizziness thought to be secondary to intracranial arachnoid cysts experienced quality of life benefits, as measured by the Visual Analogue Scale and Glasgow Benefit Inventory subscale, from surgical fenestration of the arachnoid cyst, and there was a very low risk of experiencing a surgical complication in the study (62). However, although patients who undergo surgery for their arachnoid cysts often report symptom improvement postoperatively and have significantly decreased cyst volume on postoperative imaging, another study found no difference between preoperative and postoperative neuropsychological testing for patients (80). Additionally, whether the cyst was located in the temporal region or the posterior fossa did not influence the patient’s score on neuropsychological or motor tests. Finally, in over 40% of patients, some other underlying condition on the differential diagnosis, and not the arachnoid cyst, was revealed to be the cause of the symptoms. These seemingly contradictory findings highlight the need for careful patient selection and appropriate patient education prior to proceeding with surgical intervention.
Suprasellar cysts are uncommon. A subfrontal approach to suprasellar cysts is dangerous. A review of the literature revealed a mortality of 5% and a success rate of only 16.5%, with the remaining patients having complications (43% neuroendocrine; 40.5% recurrent hydrocephalus) (77). Where suprasellar cysts are associated with hydrocephalus, ventricular drainage alone actually results in an increase in cyst size in 40% of cases. Fenestration into the lateral ventricle and insertion of an antisiphon device or, alternatively, percutaneous ventriculo-cystostomy under ventriculoscopic control appears to be effective (33; 77; 124). Endoscopic fenestration of the wall of the cyst appears to reduce the risk of complications, because fenestration is under direct vision, and it has been suggested that endoscopic surgery by ventriculo-cystocisternotomy using a rigid neuroendoscope is the procedure of choice (20; 14). Where ventriculo-cystostomy or ventriculo-cysto-cisternography is performed following a prior surgical procedure, the success rate is poorer, with 36% and 12% respectively requiring re-operation (52). Recurrence is particularly common when the arachnoid cyst is complex or is associated with multi-compartmental hydrocephalus. Management is particularly challenging in infants. Neuroendoscopy and shunt catheter placement using intraoperative image-guided surgery, where available, seems to be associated with good results (72). For sellar and suprasellar cystic lesions, transsphenoidal removal aided by endoscopic assessment has been recommended to achieve maximal safe cyst removal and does not appear to be associated with risk of side effects (11). Also, endoscopic fenestration of the third ventricle in the reverse direction when treating a parasellar cyst has been reported and advised especially if the parasellar cyst has thick walls as the anterior commissure and foramen of Monro can be clearly seen (65). In summary, endoscopic treatment is considered the first-line procedure for cases of suprasellar arachnoid cysts with hydrocephalus. Furthermore, although it is more difficult to perform this neuroendoscopic procedure in patients without ventriculomegaly given the difficulties associated with ventricular cannulation of smaller ventricles and the narrow foramen of Monro, there is limited evidence to suggest this procedure is also safe in this setting and successfully improves patients’ symptoms (29). Alternatively, stereotactic intracavitary radiation has been used in recurrent sellar and suprasellar arachnoid cysts, but the long-term effects of this are still to be proven (110). Although surgery is effective for treatment of the symptoms related to hydrocephalus, endocrine symptoms requiring medical management persisted after surgery and, surprisingly, over one third of patients developed endocrine abnormalities such as precocious puberty and growth hormone deficiency after initially being stable during postoperative follow-up (48).
Intraventricular CSF-filled cysts are best dealt with by endoscopic treatment, as this has a low complication rate; however, the long-term efficacy remains uncertain (122).
Midline posterior fossa cysts causing hydrocephalus should not be treated by ventriculo-peritoneal shunting alone, because of the potential risk of upward herniation. A retrosigmoid suboccipital craniotomy with microsurgical resection and cyst fenestration has been reported to provide long-term effective decompression for cerebellopontine angle arachnoid cysts (38). Simultaneous cyst and ventricular shunting has also been successful (103).
Spinal subarachnoid cysts can often be surgically excised. Total removal of extradural cysts must be followed by repair of the dural defect, or the cysts are likely to recur. Preoperative imaging studies, such as MRI myelography or intraoperative MRI with phase contrast imaging, can often identify the area of dural defect (61). In one instance, the use of intraoperative Doppler ultrasound in a pediatric case of spinal extradural arachnoid cyst identified the area of pulsatile flow through the communication into the cyst, which was not apparent on the intraoperative phase-contrast MRI (41). A small series of patients undergoing surgical management for extradural spinal arachnoid cysts suggests that symptoms such as lower limb weakness and pain can be improved in a majority of patients who undergo cyst excision and closure of any dural defect (26). For intradural cysts, MRI may demonstrate subtle indentation of the spinal cord at the caudal or cephalic end of the syringomyelia secondary to the intradural arachnoid cyst, which may obviate the need for additional imaging. During surgery, meticulous arachnoid dissection and establishment of good CSF flow is often sufficient for resolution of the syrinx (34; 100). Elements of the walls of intradural cysts may be adherent to the spinal cord; fenestration, partial excision, and cyst shunting are often required (79). Endoscopic cyst fenestration has also been successful for intradural cysts (109).
There is no evidence that pregnancy has any influence on the growth potential of arachnoid cysts. Surgery during pregnancy is not usually necessary unless there is evidence of raised intracranial pressure from hydrocephalus or serious mass effect. If there is a need to operate during pregnancy, the risks to the fetus are the same as from any intracranial operation requiring general anesthesia.
The precautions related to anesthesia are the same as for any intracranial surgery.
Unless there is evidence of mass effect, patients with arachnoid cysts do not require neurologic clearance to undergo other, unrelated invasive procedures.
Although some researchers have postulated that individuals with arachnoid cuts may have a higher rate of structural brain injury after trauma, a systematic review of published case reports for individuals with arachnoid cysts who suffered a structural brain injury during a sport or recreational activity did not find evidence to support recommending against participation in sports for patients with arachnoid cysts (128). As such, currently patients with arachnoid cysts have no contraindication against their participation in sports, although parents and children should be counseled appropriately regarding the possibility of brain injury following trauma.
Rimas V Lukas MD
Dr. Lukas of Northwestern University Feinberg School of Medicine received honorariums from Novocure for speaking engagements, honorariums from Novocure for advisory board membership, and research support from BMS.See Profile
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Neurofibromatosis 1 (NF1) is a common autosomal dominant neurocutaneous disorder displaying a typical pattern of dermatologic and systemic findings. NF1 is characterized by 2 of the following 7 criteria: 6 café-au-lait spots, skinfold freckles, 2 neurofibromas or 1 plexiform neurofibroma, 2 Lisch nodules, distinctive osseous lesion, optic pathway glioma, and/or a first-degree relative with neurofibromatosis 1.
Jan. 03, 2021
Dec. 19, 2020
Dec. 18, 2020