Fully Endoscopic Supraorbital Resection of Congenital Middle Cranial Fossa Arachnoid Cysts: A Report of 2 Cases
By Mohamed S. Kabil, M.D. and Hrayr K. Shahinian, M.D.
Access to arachnoid cysts of the middle cranial fossa and the sylvian region has traditionally required a transcranial approach to fenestrate; partially or completely excise the cyst. This could be performed via either traditional open microsurgical techniques or endoscopically, in both cases requiring brain retraction which is inevitably injurious to the normal brain tissue. Nevertheless, unless only fenestration of the cyst is planned, wide exposure of the surgical field via potentially disfiguring skin incisions is required for traditional microsurgery, thus, subjecting the patient to undesirable neurological and cosmetic morbidity.
Endoscopic, Supraorbital, Eyebrow, Minimally invasive, Skullbase, Arachnoid cyst, Middle fossa
We report the use of a fully endoscopic supraorbital approach through the eyebrow for excision of congenital middle cranial fossa arachnoid cysts. The approach was performed on two patients, a 9-month-old infant and a 12-year-old female patient. In both cases, the arachnoid cysts were resected in their entirety utilizing a 1cm "keyhole" craniotomy without the need for a corticotomy and with virtually no brain retraction. The outcomes were favorable and both patients were discharged from the hospital within 48-hours of surgery. There were no perioperative complications and cosmetic outcomes were excellent.
Arachnoid cysts, also known as intra-arachnoid cysts, meningeal cysts, leptomeningeal cysts, and arachnoid diverticula, are benign intra-arachnoid fluid collections with a wall that is composed of arachnoidal cells encompassing a cavity containing a fluid similar to cerebrospinal fluid (CSF); this cavity frequently communicates with the subarachnoid space. Emryologically, congenital arachnoid cysts most probably arise by way of anomalous splitting and duplication of the endomeninx . The cyst has an incessant tendency to grow or recur but the growing mechanism is still a mystery and the mechanism by which they expand is yet not known. Fluid may be secreted directly into the cyst by arachnoidal cells making up its wall or by ectopic choroid-like structures. Arterial pulsations via a "one-way slit-valve mechanism" at the point of communication may be another possible mechanism of cyst growth; the latter has been confirmed during endoscopic procedures by several authors [2,3,4].
Arachnoid cysts are reported to account for about 1% of all intracranial space-occupying lesions. However, intracranial arachnoid cysts have become more frequent findings as a result of modern imaging techniques. Computed tomography (CT) scan and magnetic resonance imaging (MRI) are diagnostic in the majority of cases. Arachnoid cysts are often discovered incidentally on MRIs performed for a variety of reasons. Primary or congenital arachnoid cysts are maldevelopmental anomalies and should be differentiated from secondary arachnoid cysts that have resulted from a variety of such etiologies as trauma and infection .
The most frequent localization of congenital intracranial arachnoid cysts is in the middle cranial fossa constituting more than half of the cases reported in the literature. Less commonly, they occur in the sellar and parasellar regions and around the foramen magnum[6,7]. The origin of middle fossa arachnoid cysts is related to two theories: primary arachnoidal maldevelopmental abnormality  or secondary evolvement due to partial agenesis / hypogenesis of the temporal lobe .
Attributable to their benign nature and slow expansion, congenital intracranial arachnoid cysts may remain asymptomatic, produce only subtle symptoms and signs or result in mild neurological impairment relative to their large size. If symptomatic, they mostly present with unspecific symptoms of elevated intracranial pressure (ICP); less commonly they may present with focal signs suggestive of their location, epileptic seizures, craniomegaly, or delayed developmental milestones [10-13].
With this wide variation in the natural course of congenital arachnoid cysts and its concomitant clinical manifestations, there has also been a considerable controversy regarding the indications, choice and timing of surgical intervention. The goals of surgical treatment are to drain the cyst and to prevent the recollection of fluid, allowing for re-expansion of the compressed neighboring neural tissue. However, the optimum surgical modality to achieve these goals has been a subject of debate, mostly due to the inherent risks associated with each surgical modality. Cystoperitoneal shunting and craniotomy with transcortical cyst excision/fenestration or marsupialization into the subarachnoid space (whether microsurgically or endoscopically) are recognized as standard procedures. However, numerous other operative procedures have been recommended including stereotactic aspiration, cysto-cisternostomy and ventriculocystostomy. These wide modalities of surgery are in their self indicative of lack of optimum module and it remains controversial which is most advisable.
In 2002, our group adopted the use of the fully endoscopic supraorbital approach through the eyebrow for resection of tumors of the anterior cranial base and have published our results . While routinely using this approach to access tumors of the anterior cranial base, we found that the adaptation of rigid endoscopy to the supraorbital approach broadens the available surgical exposure, thus providing extended access to the middle and not only the anterior cranial fossa without additional dissection or retraction. Utilizing the fully endoscopic supraorbital approach to access the middle cranial fossa, we cognized that the endoscope enhanced our ability to appreciate the anatomy of this area due to its superior visibility, and to undergo a more complete excision of middle cranial base tumors. Additionally, we found the technique to be useful when applied to surgery of middle cranial fossa arachnoid cysts in children, carrying the advantage of being minimally invasive and also avoiding an injurious corticotomy for a lesion that is basically extra axial, benign and respectful to the anatomy of the brain in its natural pattern of growth. In this report we describe the use of the fully endoscopic supraorbital approach for excision of two relatively large congenital middle fossa arachnoid cysts.
The operation starts with the patient placed on the operating room table in the supine position, the head of the bed is slightly raised to improve venous drainage. Following the induction of general anesthesia, the patient's neck is extended approximately 15°-30°. Thus positioned, the frontal and also the temporal lobes will retract with gravity away from the orbital roof and the floor of the anterior and middle skull base once CSF is drained; opening up a direct route for the endoscope to access the middle cranial fossa from an anterior approach. Thus positioned, the head is fixed in place using a Mayfield with three pediatric pins. The frontal and para-nasal areas are cleansed with an aqueous antiseptic solution and then draped.
The base of a pneumatically powered endoscope holding arm (Mitaka Kohki Co., Tokyo) is fastened to the operating room table opposite the surgeon; the arm extends to hold the endoscope firmly. A 2.7 mm 0° rigid endoscope (Karl Storz of America, Culver City, CA, USA) is attached to the holding arm.
A standard skin incision is placed within the hair of the eyebrow 2-3 mms above the orbital rim. The incision is bounded medially by the supraorbital notch and laterally by the lateral end of the eyebrow just anterior to the frontozygomatic suture. Subsequent to skin and soft tissue incision, a 1 cm "keyhole" supraorbital craniotomy is performed with its lower end flush with the skull base. The dura is incised and CSF is slowly drained. A combination of mild hyperventilation, positioning and CSF drainage opens a space as the frontal lobe "relaxes" away from the anterior cranial base. The endoscope is introduced through the "keyhole" and advanced between the frontal lobe and the floor of the anterior cranial base, closely sliding over the orbital roof and the lesser wing of the sphenoid bone all the way to the middle cranial fossa. At this point a panoramic view of the arachnoid cyst is displayed on the screen and an endoscopic survey of the area is conducted for anatomical orientation.
Utilizing ultra-thin endoscopic instrumentation, Penfields, suction/irrigation, and bipolar electrocoagulation, fenestration of the cyst's wall followed by gradual circumferential dissection and resection of the cyst is carried out. Once it is certain that the cyst is completely removed the zero-degree endoscope is withdrawn and a thirty-degree endoscope is introduced and rotated in a clockwise and anticlockwise direction to conduct a survey of the middle cranial fossa and look for any residual cyst wall out of the forward view of the zero-degree endoscope. Any residual cyst wall is identified and resected to minimize the chance of cyst recurrence or reaccumulation.
Although, the sphenoid ridge and/or the superior orbital roof could both be drilled away from this approach to either give a wider basal view or an expanded access to the middle cranial base, this is not usually required. If the frontal sinus is accidentally opened during the bony work, the mucosa should be stripped, the nasofrontal duct obliterated and the sinus is cranialized. Patients are then monitored in the intensive care unit overnight and are typically discharged to their home within 24-48 hours.
Finally, the dura is reapproximated, the bone flap reconstructed using absorbable microplates and screws, the subcutaneous tissue is reapproximated and the skin incision is closed with a subcuticular stitch with careful attention to the aesthetic repair.
Patients and Methods: History-Patient 1
A 10-month-old, caucasian baby-boy with a congenital left middle cranial fossa arachnoid cyst. The patient suffered from neonatal autoimmune thrombocytopenia/petechia; the cyst was discovered incidentally when MRI of the brain was performed shortly after birth to rule out hematoma. The patient subsequently had a small temporal craniotomy at another institution with fenestration of the cyst but it eventually recurred. Additionally, the patient developed a partial complex seizure disorder shortly after the first operation in which episodes involved right arm jerking and eye tearing. Each episode lasted three to five minutes, with a frequency of 3-5 episodes per day. Medication (Diastat per rectum and trileptal (2.5 mg p.o. b.i.d.)) has been partially effective in controlling the intensity and frequency of the seizures but they still occurred. Family history was negative for neurological problems, bleeding dyscrasia or other relevant diseases.
A normocephalic baby-boy, with no fontanellar bulge but with an appararent bulge in the left temporoparietal region in relation to a previous craniotomy. The baby appeared to be alert, with no focal neurological deficits, cranial nerves 2-12 intact and pupils equal, round, and reactive to light. Vital signs were within normal range, the rest of his examination was unremarkable.
A CT scan of the brain was performed from the base of the skull to the vertex revealing a large left sided lesion of CSF signal occupying the left temporal fossa and largely replacing the temporal lobe in keeping with the diagnosis of congenital (recurrent) arachnoid cyst. The lesion measured 4.5 x 8.5 cm and was associated with evident temporal lobe hypogenesis. In addition, there were evident post-surgical changes in relation to a previous craniotomy and focal thinning of the overlying temporopariental bone, a small amount of intracranial air was observed but no hemorrhage was noted. The cyst was noticed to have significantly enlarged since the first procedure but the ventricles were of normal size and configuration and there was no mass effect or midline shift.
Under general anesthesia, after positioning, prepping, draping, skin incision and initial exposure in the previously described manner. A zero-degree endoscope was introduced into the anterior cranial fossa and gradually advanced all the way to the middle cranial fossa. Immediately, a yellowish arachnoid cyst, occupying most of the left middle cranial fossa was visualized. Using a hook, a puncture was made in the anterior wall of the cyst and a copious amount of CSF was drained. The opening in the anterior wall of the arachnoid cyst was enlarged from the optic canal, medially, all the way laterally to the skull. After a large fenestration was performed, the endoscope was further advanced into the left middle fossa and the entire wall of the arachnoid cyst was visualized. Utilizing microdissection techniques and microinstruments, including micro hooks and Penfields, the wall of the arachnoid cyst was gradually resected and circumferentially peeled off the adjacent brain. A piece of the cyst's wall was sent for permanent histopathology. Once it was certain that a complete resection of the cyst was achieved, the zero-degree endoscope was withdrawn and a thirty-degree endoscope was introduced for surveying the area confirming that there was no "out of view" cyst remenats. Finally, the temporal lobe was visualized and was noted to be flattened, possibly from the pressure of the arachnoid cyst. The area was copiously irrigated and no major bleeders were identified, the entire area was then flooded with sterile saline. The endoscope was withdrawn from the surgical field, and closure was carried on in the previously described fashion.
The patient tolerated the procedure well and on extubation he was moving all four extremities and was taken to the pediatric intensive care unit (PICU) in a stable condition.
A 12-year-old female patient with a history of nausea and chronic intractable headaches for which she had undergone an extensive workup including electroencephalography (EEG) and numerous other investigations that failed to explain the etiology of her headaches. The patient was seen in surgical consultation else where, and was informed along with the parents that the only way to fenestrate the cyst is by a formal craniotomy but the parents desired a minimally invasive alternative. The patient was presented to our practice and was informed along with her parents that she would be a candidate for right sided endoscopic supraorbital craniotomy, with fenestration or possible complete resection of the arachnoid cyst.
On examination the patient's vital signs were within the normal range. The patient was awake and well oriented, with no focal neurological deficits; the rest of her examination was unremarkable.
MRI revealed a right middle cranial fossa, well-defined, cystic mass which was non-enhancing and isointense to CSF consistent with an arachnoid cyst and measuring 3.5 x 2.2 cm with displacement of the temporal pole but without associated temporal pole signal abnormality. The posterior extent of the cyst was adjacent to the right semilunar ganglion. The ventricles appeared to be of normal size and configuration.
Under general anesthesia, exposure of the surgical field was carried out in the previously described manner. The zero-degree endoscope was advanced to the middle cranial fossa and immediately a large arachnoid cyst was identified; however, along its anterior wall were several vessels, both venous and arterial, that could not be sacrificed. Therefore, dissection was carried down inferior and superior to those bridging vessels, and a large opening "fenestration" on both sides of the anterior wall of the cyst was performed. This was followed by "CSF-like" fluid egression from within the cyst which was noted to be under mild to moderate pressure and complete drainage of the cyst was pursued. Following that, endoscopic micro-scissors were used to create large openings within the cyst wall, and more of the cyst's wall, anteriorly, laterally, and medially was similarly excised. Then, using Penfields, the remainder of the wall was circumferentially peeled off the brain and resected until complete resection of the cyst was felt to be accomplished. The zero-degree endoscope was withdrawn and a thirty-degree endoscope introduced to survey for any remenats of the cyst wall out of the direct view of the zero-degree endoscope. Small remenants of the the cyst's wall were identified and were gently teased and peeled off the brain tissue. At this stage it was certain that an adequate cyst removal was achieved, and the endoscope was removed. The dura was re-approximated and the craniotomy was reconstructed in the previously described fashion.
On extubation, the patient seemed to have tolerated the surgery well without complications and her examination was negative for any visual or other neurological deficits. Therefore, she was transferred to the PICU in a stable condition; on the second postoperative she was subsequently transferred to the floor in a favorable condition before being discharged to home.
The substantial controversy with regards to the indication and optimum surgical management for congenital intracranial arachnoid cysts, unmasks a polemic difference in opinion. While some authors such as Galassi et al.  and Sato et al.  concluded from their experiences that all arachnoid cysts should receive surgical treatment because of their frequent complications, including acute cyst enlargement, subdural effusion following rupture of the cyst and subdural or intracystic bleeding; others such as Ciricillo et al.  and Lawton et al. do not stand in favor of this concept. However, in spite of the abundance of different opinions in the literature regarding the optimum therapy for this condition, it is widely agreed that large space-occupying cysts that exert a mass effect or those causing neurological impairment require surgical intervention as the potential for hindering normal development and function of the adjacent brain in this group outweighs the risk of operative treatment. In addition, there is a common consensus that small cysts with minimal symptoms should be treated conservatively with regular clinical and radiological follow-up.
Apart from the controversy on the indication of surgery, there is another controversy regarding the type of surgery to be performed. The two main surgical modalities by which middle cranial fossa arachnoid cysts have been most commonly treated are formal craniotomy with excision/marsupialization of the cyst or cysto-peritoneal shunting. These approaches, however, involve access and surgical dissection that often comes at the expense of a significant degree of unnecessary brain retraction, which in turn may result in undesirable perioperative morbidity and inability to completely excise the cyst due to a limited exposure.
While open craniotomy for removal or fenestration of the cyst is considered too aggressive, when surgery is performed endoscopically usually only fenestration or marsupilization of the cyst is obtainable and it is difficult to completely excise the cyst, which in turn affects the rate of recurrence. On the other hand, although cysto-peritoneal shunting is safer than open surgery, it is not free of risk and well known shunt complications such as obstruction, infection, unexpected hemorrhage and life-long shunt dependence can not be dismissed.
As arachnoid cysts are primarily benign and extra-axial in their pattern of growth they could be readily removed from an equally "anatomical" extra-axial approach (rather than transcortically or the need for excessive brain retraction and suboptimal exposure that leads to an inability to respect the natural anatomy of these benign lesions resulting in a suboptimal surgery). We believe that the endoscopic supraorbital approach offers the opportunity to appreciate the natural pathotphysiology of congenital arachnoid cysts thus providing a more "complete" operation with the advantage of avoiding potential complications of craniotomy and transcortical approaches and also the known complications of shunt devices. In addition, it provides an effective alternative for surgery of small symptomatic arachnoid cysts occurring at the temporal pole as in these cases it is difficult to fenestrate the basal cisterns by transcortical endoscopic techniques and at the same time traditional microsurgical techniques would be too aggressive whereas the endoscopic supraorbital approach will provide the most direct and the least injurious route to access the cyst.
The broadly existing different modalities for surgical treatment of congenital intracranial arachnoid cysts, and the wide skepticism regarding the "cost-benefit" of surgical intervention in the first hand, does indeed reflect the lack of an optimum surgical solution for this condition. Congenital intracranial arachnoid cysts are developmental, benign, extra axial "sacs" that do not communicate with the ventricular system and have a distinct membrane. Therefore, approaching them through normal healthy brain tissue i.e. transcortical or via traditional open craniotomies and excessive brain retraction is associated with inevitable loss of the natural anatomical planes in which it grows leading to inferior intraoperative orientation, limited exposure and inevitable injurious brain dissection/retraction, thus resulting in a suboptimal surgical outcome.
We conclude that the reported procedure offers an effective alternative to traditional open craniotomies, transcortical techniques and cysto-peritoneal shunting. The approach being conducted through an anatomical plane (subfrontal) with virtually no brain retraction is ideally suited for the benign pathophysiology and anatomy of these cysts, thus enabling their resection by following the natural anatomical planes in which they grow resulting in a more "complete" operation. The superiority of the reported technique is due to its numerous advantages including better visualization during surgery, less tissue trauma during exposure, shorter hospital stay (24-48 hrs), shorter recovery period, less post operative discomfort, and minimal postoperative facial swelling or bruising. Additionally, symptomatic small cysts in the deep temporal region are good candidates for this technique as other approaches would be too difficult or too aggressive.
- Brackett CE, Rengachary SS: Arachnoid cysts; in Youmans JR (ed) Neurological surgery, 2nd edn. Saunders, Philadelphia, 1982, pp 1436–1446.
- Caemaert J, Abdullah J, Calliauw L, Carton D, Dhooge, Coster R. Endoscopic treatment of suprasellar arachnoid cysts. Acta Neurochir (Wien) 1992;119:68–73.
- Santamarta D, Aguas J, Ferrer E The natural history of arachnoid cysts: endoscopic and cine-mode MRI evidence of a slit-valve mechanism. Minim Invasive Neurosurg. 1995;38(4):133-7. Review.
- Schroeder HW, Gaab MR Endoscopic observation of a slit-valve mechanism in suprasellar prepontine arachnoid cyst: case report. Neurosurgery 1997;40:198–200.
- Choi JU, Kim DS, Huh R. Endoscopic approach to arachnoid cyst. Childs Nerv Syst 1999;15(6-7):285-91.
- Wester K. Peculiarities of intracranial arachnoid cysts: location, sidedness, and sex distribution in 126 consecutive patients. Neurosurgery 1999;45:775-779.
- Catala M, Poirier J. Arachnoid cysts: histologic, embryologic and physiopathologic review. Rev Neurol (Paris) 1998;154:489–501.
- Starkman SP, Brown TC, Linell SA. Cerebral arachnoid cysts. J Neuropathol Exp Neurol 1958;17:484-500.
- Robinson RG. The temporal lobe agenesis syndrome. Brain 1964;88:87-106.
- Menezes AH, Bell WE, Perret GE. Arachnoid cysts in children. Arch Neurol 1980;37:168-72.
- Harsh IV GR, Edwards MSB, Wilson CB. Intracranial arachnoid cysts in children. J Neurosurg 1986;64:835-42.
- Dei-Anang K, Voth D. Cerebral arachnoid cysts: a lesion of the child's brain. Neurosurg Rev 1989;12:59-62.
- Anderson FM, Segall HD, Caton WL. Use of computerized tomography scanning in supratentorial arachnoid cysts. J Neurosurg 1979;50:333-38.
- Kabil MS, Shahinian HK: Application of the Supraorbital Endoscopic Approach to Tumors of the Anterior Cranial Base. Submitted to J Craniofac Surg. 2005,16(4).
- Galassi E, Piazza G, Giast G, Frank F. Arachnoid cysts of the middle fossa: a clinical and radiological study of 25 cases treated surgically. Surg Neurol 1980;14:211-19.
- Sato K, Shimoji T, Yagushi K, Sumie H, Kuru Y, Ishii S. Middle fossa arachnoidy cyst: clinical, neuroradiological, and surgical features. Child's Brain 1983;10:310-16.
- Ciricillo SF, Cogen PH, Harsh GR, Edwards MSB. Intracranial arachnoid cysts in children. A comparison of the effects of fenestration and shunting. J Neurosurg 1991;74:230-35.
- Lawton MT, Golfinos JG, Harrington T, Sonntag VKH, Spetzler RF. Surgical management of intracranial arachnoid cysts. BNI Quarterly 1995;11:14-8.