Fig. 16.1
(a) Arachnoid cyst of the middle fossa. Note the inner layer bulging medially behind the carotid artery. (b) Same patient as shown in (a), coronal view, where a large area of possible fenestration is easily identified. (c) Endoscopic view, where nerves and arteries are easily identified through the translucent layer of the cyst and delimitate areas of fenestration. (d) A safe, posterior window of fenestration is identified between the free edge of the tentorium and the third cranial nerve. (e, f) Postoperative MRI showing good flow artifact behind the carotid artery on axial T2 turbo spin echo sequences (e) and reduction of the cyst volume on coronal T1 (f)
Shunting, as the first surgical procedure, should be avoided in middle fossa cysts, because of the well-known risk common to all shunts (infection, mechanical dysfunction) and the higher probability of overdrainage, with slit cyst syndrome and secondary Chiari malformation that can be challenging to treat.
16.1.3 Authors’ Preferred Surgical Technique
We use a surgical technique similar to those described by Di Rocco et al. [13] and Spacca et al. [12]. The aim of the procedure is to establish communication between the cyst and interpeduncular or carotid cistern (cyst-cisternostomy). The site of fenestration is between the optic nerve and the carotid artery, between the carotid artery and the oculomotor nerve, and between the third nerve and the free edge of tentorium. Electromagnetic neuronavigation is a very useful tool in order to choose the optimal entry point and to plan the best trajectory. It also provides real-time control of the endoscope position. The patient is positioned supine with the head tilted contralaterally. A small incision is performed over the temporal muscle behind the hairline. A burr hole is drilled directly above the cyst, avoiding residual cerebral mantle. The dura mater is opened with a knife to favor dural closure at the end of the procedure. A 30° free-hand rigid scope (Storz ®, Tuttlinger, Germany) is inserted within the cyst. The landmarks for the orientation are the free edge of the tentorium, the sylvian fissure with the arterial trunks, and the cranial nerves. The site of fenestration is decided on the basis of the aspect of the deep membrane (thickness and transparency). Usually the safest site is between the tentorial edge and the third cranial nerve. It allows to reach the interpeduncular cistern with good visualization of the basilar artery. Whenever possible, several holes within the deep membranes are performed. Based on the experience of Karabagli, multiple perforations are associated with decreased risk of cyst regrowth [19]. The best way to fenestrate the membranes is using Tulium LASER coagulation and forceps. Scissors should be used with great caution, because of the risk of arterial bleeding from small vessels. The stoma is also enlarged using the double-balloon catheter (neuro-balloon catheter from Integra Neurosciences®, Antipolis, France). Care is taken to open all layers. The cyst-cistern communication is considered satisfactory when it is possible to directly view the basilar artery and cerebrospinal fluid (CSF) pulsation through the fenestration. At the end of the procedure, the endoscope is removed. The dura mater is closed. The muscular fascia and the superficial layers are sutured in a standard fashion.
16.1.4 Follow-Up
CT scan or MRI is obtained until 24 h following operation to exclude major complication, in particular subdural effusion. MRI is planned in the first few weeks to confirm the presence of a flow artifact through the fenestration.
After hospital discharge, the patients are regularly controlled (clinical examination and brain MRI) 3 and 6 months and 1, 2, and 3 years after surgery.
Postoperative radiological appearance is very variable: in most successful cases, the cysts remain unchanged, or with minimal reduction of mass effect on surrounding tissue. The flow of CSF through the cyst- cisternostomies is confirmed by signal voids around ICA or tentorial edge on postoperative T2-weighted coronal MR imaging studies (flow artifact). There is no concordance between clinical and radiological outcome: patients who show radiological improvement not always demonstrate a corresponding improvement of clinical symptoms, especially if the reason for surgery was not clearly related to the cyst. Conversely, the patients who show clinical improvement, not always have radiological improvement [15].
Disappearance of the cyst following fenestration is very rare. In Choi’s series [15], the cyst disappeared in 4/39 cases (10 %) and significantly decreased in 16/39. Sometimes the decrease of the cyst may be associated with the increase in size of the ventricles (especially at the level of the temporal horn) and presence of subdural fluid collection.
16.1.5 Complications
The main complication of the endoscopic series is subdural hygroma, with an incidence as high as 40 % of cases [4, 13, 15, 17]. This complication also occurs in microsurgical series and often requires surgical treatment with subduro-peritoneal shunt.
Leakage of CSF is another important complication, which has been reported to occur in 3.9–6 % of patients both in endoscopic and microsurgical series [16, 18]. Often, patients with CSF leaks are younger than 1 year of age and need a CSF diversion procedure.
Other surgical-related complications are subcutaneous collection, CSF infection, and third cranial nerve palsy.
16.1.6 Results
Good clinical outcome with complete recovery or significant improvement has been achieved in more than 90 % of cases in several series [12, 13, 19]. Relief of headache and other neurological deficits was obtained in all series but that of Choi et al. [15], in which headache was not always related to the presence of the cyst. These data are similar to those achieved by Levy et al. [18] following microsurgical fenestration. In the series of Choi et al. [15], the results are not so satisfactory, especially in infants, where the rate of surgical failure (need for additional operations such as a shunt or a second fenestration procedure) was 50 % (3/6). These results were also noted by others, so that some authors consider cyst-peritoneal shunt more effective in the infant group. In our opinion, the advantage of being shunt-free overcomes the risk of second surgery in the infant population, in which also the shunt-related problems (high rate of shunt revision, lifelong shunt dependency, overdrainage, and even brain herniation) are more frequent.
A second line of repeat endoscopy, craniotomy, or shunt may be considered in case of failures. In recurrent middle fossa cysts, we rarely perform repeat endoscopy and we prefer to offer craniotomy and microsurgical fenestration in case of absent flow artifact on neuroimaging (with the aim to achieve larger fenestrations of the deep membranes). If the fenestration appears to be patent on neuroimaging but symptoms are still present, cyst-peritoneal shunt is the preferred option, especially in younger children.
In conclusion, recent reports indicate that increasing number of authors prefer endoscopic approach as the first-line management of middle fossa arachnoid cysts [12, 13, 19–21]. However, larger randomized series are needed to identify the real advantages in managing middle fossa cysts by endoscopy, rather than alternative techniques (Table 16.1).
Table 16.1
Review of case series for pure neuroendoscopic treatment of middle fossa cysts
Authors | Cohort size | Results | Complications |
|---|---|---|---|
Elhammady et al. [20] | 6 | Six successful | Subdural hygroma (n = 3) |
Di Rocco et al. [13] | 17 | Two recurrences | Venous bleeding (n = 1) |
Spacca et al. [12] | 40 | Satisfactory outcome reported in 92.5 % cases; cyst reduction in 72.5 % of cases; 10 % requiring second procedure | Subdural hygroma (n = 4) |
El-Ghandour [22] | 32 | Clinical improvement reported in 87.5 % cases; reduction in cyst size in 71.9 % cases; three cases of recurrence | Subdural hygroma (n = 2), CN III palsy (n = 1) |
Karabagli and Etus [19] | 20 | Eighteen successful cases (in three endoscopy was repeated); two failures (CP shunt) | Asymptomatic subdural hygroma (n = 1) |
16.2 Suprasellar Cysts
Endoscopic surgery has radically changed the management of deep-seated arachnoid cyst. Patients with arachnoid cysts in the suprasellar region, especially if associated with hydrocephalus, are ideal candidates to endoscopic surgery, which allows wide fenestration of the cyst, both in the ventricular system and in the cisternal spaces [8], avoiding major surgical procedures, such as craniotomy and transcallosal approach. For this kind of cysts, endoscopic surgery is the treatment of choice, considering repeat endoscopy in case of failures and reserving shunting only to refractory cases. Typically, the suprasellar cysts elevate the floor of the third ventricle, often appearing just under the body of the lateral ventricle. Hydrocephalus due to obstruction of the CSF pathways either at the foramen of Monro or at the level of the cerebral aqueduct is often associated. Miyajima et al. [23] identified two different types of suprasellar arachnoid cyst, according to the position of the basilar artery. In the first type, the basilar artery is inside the cyst. They speculated that these cysts arise from invagination of the membrane of Liliequist. In the second type, the basilar artery is pushed posteriorly by the cyst. Their interpretation was that these cysts arise from cystic dilatation of the interpeduncular cistern.
16.2.1 Indication for Surgery
Suprasellar cysts are rare. They represent 8–15 % of all intracranial cysts. Treatment is indicated in case of symptomatic cysts or in case of coexisting hydrocephalus. The majority of cysts become symptomatic in early childhood, usually presenting with hydrocephalus and symptoms and signs of increased intracranial hypertension. Other frequent symptoms are visual field defects/impaired visual acuity (about 30 % of cases) and endocrinological disorders (about 60 % of cases) secondary to compression of the chiasm and hypothalamic-pituitary axis. Head bobbing in children is a rare feature, but quite typical of suprasellar cyst. Recurrent seizures are also indication for surgery.
Incidentally discovered cysts are usually not candidates for surgery, even if demonstration of cyst growth or the presence of neural compression, especially in children, should be an indication for consideration of surgical treatment to allow the potentially normal development and function of the adjacent brain [11].
16.2.2 Selection of Candidates to Endoscopic Procedure Versus Alternative Treatments
The location of the suprasellar may favor a different surgical treatment compared with cysts in other locations. The cysts are always in close relationship with the third ventricle; so, in case of sufficient ventricular dilatation, endoscopic treatment is the treatment of choice [24]. Usually, the cyst can be approached from the ventricles through a standard precoronal burr hole. Shunt placement is no longer suggested because of the need for foreign body implantation and the concomitant risk of shunt infection, failure, or lifelong shunt dependence. It should be reserved only to refractory cases.
Open surgical approaches are associated with a relatively higher surgical morbidity compared with endoscopic procedures and have success rate that does not exceed 70 % [11]. Microsurgery, through a subfrontal or pterional approach, should be reserved to those few cases not associated with ventricular dilatation. In the very rare cases in which the cyst expands from the suprasellar region to reach laterally the temporal fossa, the cyst can be approached with endoscope from a temporal burr hole, even if hydrocephalus is absent.
Different techniques have been advocated for endoscopic fenestration of suprasellar cysts. Some have advocated fenestration only of the apical membrane, usually at the level of the Monro foramen, between the ventricle and the cyst (ventriculocystostomy). Others suggested to also perform concurrent basilar fenestration toward prepontine cistern (cyst-cisternostomy), realizing a ventriculocystocisternostomy (VCC). Decq et al. demonstrated by MR-imaged CSF flow dynamics the importance of fenestrating suprasellar cysts both in the ventricles and in the basal cisterns, to prevent secondary closure of the opening and recurrence of symptoms [8]. The passage of CSF pulse waves in the cyst’s cavity through sufficiently large windows in a “bipolar” fashion lowers the risk of re-formation of the cyst’s membrane [8, 11]. Multiple fenestrations into all arachnoid cisterns that are accessible should lead to a lower rate of recurrence at long-term follow-up than do less aggressive methods, such as single fenestration [11]. Also the more recent paper from Maher and Goumnerova [24], which summarized their experience with 44 published cases, concluded that endoscopic ventriculocystocisternostomy is more effective than ventriculocystostomy.
16.2.3 Authors’ Preferred Surgical Technique
Our surgical technique is similar to that described by Kirollos et al. [11]. Under general anesthesia, a frontal burr hole is drilled 3–4 cm from the midline (usually on the right side, or on the larger side, in case of asymmetrical ventricular dilatation) and on the coronal suture. The ideal position of the entry point and the best trajectory is selected on the basis of preoperative MR imaging. Neuronavigation is useful but usually not mandatory in standard cases, unless the ventricular system is small. The lateral ventricle is tapped, and the endoscope is directed toward the foramen of Monro, where the dome of the cyst is usually protruding into the third ventricle and comes into view. A fenestration is made between the cyst and the ventricle with various techniques, and we prefer to use Tulium LASER coagulation and scissors. Wide fenestration, at least 10 mm in diameter, is achieved, with coagulation of the apical portion of the cyst and removal of the cyst wall if possible. The cyst is then entered with the endoscope to visualize the basal wall of the third ventricle and the position of the basilar artery (inside the cyst, or outside the cyst, pushed toward the brain stem). It is usually possible to observe all the anatomical structures around the interpeduncular cistern through the thin inner layer of the arachnoid cyst, such as the basilar artery, internal carotid artery, posterior communicating arteries, pituitary stalk, optic chiasm, and third cranial nerves. Several openings into the basal prepontine cistern should be created, usually between basilar artery and third cranial nerves from both sides. The openings can be done using a probe without the application of any current and enlarged with balloon catheters. The endoscope is then advanced through the fenestration to visualize the neurovascular structures in the basal cisterns and to ensure the creation of adequate communication between the cyst and the subarachnoid space.
In the rare cases in which suprasellar cyst expand laterally toward the temporal fossa, the cyst can be approached directly through a temporal burr hole, like middle fossa cyst. Once inside the cyst with the endoscope, a cyst-cisternostomy can be performed in standard fashion, trying to make multiple perforations, on both sides of the basilar artery (Figs. 16.2a, b and 16.3a–j).
Fig. 16.2
(a) Type 1 suprasellar cyst, bulging into the third ventricle and occluding both foramina of Monro and the inlet of the aqueduct. (b) Surgical trajectory (arrows) for ventriculocystostomy and cyst-cisternostomy through a coronal burr hole
Fig. 16.3
Type 2 suprasellar cyst with lateral extension as seen on T2 sagittal (a), T2 coronal (b), and T2 axial (c) magnetic resonance. Endoscopic view of the skull base area chosen for fenestration (d). Following fenestrations, the stretching of the cranial nerves has decreased (e). Endoscopic views of the posterior fossa cisterns (f, g) through the fenestrations. Postoperative MRI showing significant decrease of the cyst size on sagittal (h), coronal (arrow indicate flow artifact through the stomy) (i), and axial (j) T2-weighted images
16.2.4 Follow-Up
The follow-up is similar to middle fossa cyst: a neuroradiological investigation (preferably MRI) is obtained until 24 h following operation. The presence of flow artifact through the fenestration at MRI should be addressed before discharge from the hospital. After hospital discharge, the patients are regularly controlled 3 and 6 months and 1, 2, and 3 years after surgery.
The reduction in arachnoid cyst size following endoscopy, also for cysts in this location, is variable. The indications for further intervention depend on the persistence of the patient’s symptoms and not upon the appearance of the cyst on postoperative imaging [11].
Endocrinological disorders usually persist following treatment despite the satisfactory decrease in volume of the cyst [11].
16.2.5 Complications and Results
Reported complication rate is very low in this kind of surgery [10], with few addressed cases of ventriculitis and subdural hygromas. The success rate is high. Maher and Goumnerova [24] in their review calculated a success rate (no need for subsequent surgical procedures) of 86 % when only ventriculocystostomy (VC) was performed, and that increased to 92 % when ventriculocystocisternostomy (VCC) was performed as first procedure.
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