1. Background and Importance
Temporal Lobe Epilepsy (TLE) is the most common form of drug-resistant focal epilepsy. Current understanding of TLE supports the hypothesis of impairment of inhibitory action of basket cells following an insult in a critical brain development period, which is rapidly distributed toward other regions via kindling phenomenon [1, 2]. Several pathologies have been associated with TLE including Mesial Temporal Sclerosis (MTS), developmental malformations, vascular malformations, neoplastic lesions and scars caused by infarctions and infective processes [3]. Arachnoid cysts have been reported in as many as 10% of patients with TLE, and their presence is secondary to abnormal development of temporal lobe in most instances [4].
Fenestration of temporal arachnoid cysts have been associated with variable results for seizure control in patients with TLE, according to major differences in cases included. Those with hippocampal sclerosis had suboptimal improvement with standalone arachnoid cyst fenestration and will have to undergo selective amygdalohippocampectomy for optimal seizure control.

Herein, we are reporting a 26-year-old man with a 13-year history of TLE. His seizures were successfully controlled with endoscopic transsphenoidal fenestration of an anteromedial temporal arachnoid cyst that had extended to sphenoid sinus and pterygopalatine fossa. The normal appearance of mesial temporal structures on pre-operative MRI and extension to sphenoid sinus encouraged us to consider this surgical approach in this very patient.
2. Case Presentation
A 26-year-old healthy male was referred by an epileptologist with a 13-year history of seizures which occurred on a monthly basis despite taking several Anti-Epileptic Drugs (AEDs) (LTG, CBZ, LEV, CLB). His ictus consisted of olfactory and visual hallucinations, and de ja vu with loss of consciousness for 2-3 minutes, but without tonic and clonic phases. The diagnosis was confirmed to be TLE. His drug history included lamotrigine 200 mg daily, imipramine 100 mg daily, alprazolam 0.5 mg at bedtime and trifluoperazine 4 mg daily. His family history was unremarkable for seizures or any other neurological disorders. Brain MRI revealed a left medial temporal cystic lesion, hypointense on T1- and hyperintense on T2- weighted images, respectively which had extended inferiorly to pterygopalatine fossa through temporal fossa floor and also medially bulging into sphenoid sinus through its lateral wall (Figure 1).

Surgical procedure
The cystic lesion was approached endoscopically through transsphenoidal route. After visualizing via a bi-nostril exposure of the sphenoid sinus, the bulged area in the lateral wall of sphenoid sinus was seen. During removal of the eroded thin wall by curettes, the thinned cyst wall was ruptured followed by an abrupt flow of Cerebrospinal Fluid (CSF). After suctioning the fluid, a fat plug was inserted within the opening in cyst wall, and the closure was reinforced with fibrin glue sealants and middle turbinate vascularized flap [5]. Nasal pack was performed with tetracycline ointment 3% soaked mesh.
Pathology
The hematoxylin and eosin stained slides confirmed the diagnosis of arachnoid cyst (Figure 2).
Follow-up
During post-operative course, the nasal pack was removed the next day and the patient was discharged on the second post-operative day. The skull base closure was satisfactory and he did not develop CSF leakage. After a 9-month follow-up, the patient’s seizures were controlled with the previous medications, and post-operative MRI confirmed that the cyst had not recurred (Figure 3).
3. Discussion
Arachnoid cysts are CSF-filled cystic lesions which can present as an incidental neurologic finding, or headache, seizure and neurological deficits according to their size and location. Temporal fossa, which is the most common site for arachnoid cysts, is the most common location that presents with seizures. According to hospital-based cohort studies, the odds for harboring arachnoid cysts in patients with focal epilepsy is five times of their healthy counterparts, which is probably due to shared etiological ancestry rather than a causative association.
The source of epilepsy in patients with temporal arachnoid cysts is a matter of debate; whether it is due to intrinsic malformations and hippocampal dysgenesis or mass effect of the adjacent arachnoid cysts. Variable results have been reported regarding control of seizure after fenestration of temporal arachnoid cysts, with better results seen in those whose MRI does not show abnormal signal intensities in mesial temporal structures.
Herein we presented a patient with temporal lobe epilepsy who was found to have an arachnoid cyst at the anteromedial part of his middle cranial fossa. This case is unique regarding two distinctive features; the first one: presentation with TLE. Seizures are reported to accompany temporal arachnoid cyst, probably due to developmental malformation and hypogenesis [6] or compression on adjacent brain tissue. However, his seizure symptoms of TLE (olfactory and visual hallucinations and de ja vu) were not previously reported in the literature.
The second distinguished feature is the surgical approach; endoscopic transnasal transsphenoidal approach can be considered in resection of variable pathologies within the sphenoid sinus [7]. We used this approach for fenestration of the cyst, which controlled TLE attacks during the 9-month follow-up period.
A few instances of temporal lobe arachnoid cysts with extension to sphenoid sinus have been reported in the neurosurgical and otolaryngology literature. In a recently published article titled: “Enlarging Temporal Arachnoid Cyst Extending Inside the Sphenoid Sinus” by Corona-Ruiz JM et al. [8], a 71-year-old lady presented with headache and was diagnosed to have a huge temporal arachnoid cyst. Her cyst had extension toward sphenoid sinus and erosion of temporal fossa floor, so, craniotomy was performed for resection of the arachnoid cyst and reconstruction of skull base.
Previous reports by Couvreur et al. [9] have shown the efficacy of endoscopic technology through fenestration of cysts via transcranial neuroendoscopy. They claimed seizure control in a third of patients with TLE. However, to our knowledge, endoscope has not been used in any reports from a transsphenoidal corridor for fenestration of the temporal arachnoid cysts. We believe this approach should be considered in patients presenting with lesions in anteromedial part of middle fossa extending to sphenoid sinus or eroding its lateral wall.
Theoretically, this approach avoids the cortical damage induced by craniotomy and transcranial neuroendoscopy, which have the potential of inducing seizure activity. Despite the mentioned benefits of transsphenoidal endoscopic fenestration for such selected patients, this approach has some drawbacks; i.e., the risk of post-operative Cerebrospinal Fluid (CSF) leakage, which can be minimized by a teamwork between otolaryngologists and neurosurgeons for reconstruction of skull base.
A report by Bovenzi CD et al. [10] describing the endoscopic transsphenoidal approach for fenestration of a symptomatic petrous apex arachnoid cyst, confirms that this surgical approach can be considered a safe corridor for fenestration of sellar, suprasellar, retrosellar and parasellar arachnoid cysts in selected individuals [10].
4. Conclusion
Transsphenoidal endoscopic fenestration is a safe and feasible surgical approach for treatment of symptomatic arachnoid cysts in anteromedial part of middle fossa, when they erode the lateral wall of sphenoid sinus or have an intrasphenoidal extension. Despite the need for skull base reconstruction to prevent post-operative CSF leakage, this approach has the privilege of avoiding cortical damage accompanied by craniotomy and transcranial endoscopic procedures.
Ethical Considerations
Compliance with ethical guidelines
The Patient and his family gave informed consent about anonymous use of his surgical intervention, clinical data and MR images for purpose of publishing a research article. Written informed consent was signed by the patient and would be available to editorial office upon request.
Funding
No funding source was used in the preparation and publication of this work.
Authors contributions
Patient’s operation: Arash Saffarian; Surgical intervention and initial draft preparation: Nima Derakhshan and Mousa Taghipour; Contributing in final stages of surgery: Mohammad Faramarzi; Confirming the diagnosis of Temporal Lobe Epilepsy and referred the patient to the clinic: Ali Akbar Asadipooya; Confirming the pathologic diagnosis: Amirreza Dehghanian. Writing – review & editing:  Keyvan Eghbal.
Conflict of interest
The authors declared no conflict of interest.

References
Bryson A, Gardner H, Wilson I, Rolfe T, Archer J. Temporal lobe epilepsy following maintenance electroconvulsive therapy-Electrical kindling in the human brain? Epilepsia. 2016; 57(11):e216-e20. [DOI:10.1111/epi.13565] [PMID]
Taghipour M, Ghaffarpasand F. Selective amygdalohippocampectomy for mesial temporal sclerosis: Special considerations in geniuses. World Neurosurgery. 2018; 111:429-30. [DOI:10.1016/j.wneu.2017.11.135] [PMID]
Armstrong DD. The neuropathology of temporal lobe epilepsy. Journal of Neuropathology and Experimental Neurology. 1993; 52(5):433-43. [DOI:10.1097/00005072-199309000-00001] [PMID]
Sztriha L, Gururaj AK, Bener A, Nork M. Temporal lobe epilepsy in children: Etiology in a cohort with new‐onset seizures. Epilepsia. 2002; 43(1):75-80. [DOI:10.1046/j.1528-1157.2002.24201.x] [PMID]
Simal Julián JA, Miranda Lloret P, Cárdenas Ruiz-Valdepeñas E, Barges Coll J, Beltrán Giner A, Botella Asunción C. Middle turbinate vascularized flap for skull base reconstruction after an expanded endonasal approach. Acta Neurochirurgica. 2011; 153(9):1827-32. [DOI:10.1007/s00701-011-1064-8] [PMID]
Wester K. Arachnoid cysts-historical perspectives and controversial aspects. In: Wester K, editor. Arachnoid Cysts Epidemiology, Biology, and Neuroimaging. Cambridge, MA: Academic Press; 2018. [DOI:10.1016/B978-0-12-809932-2.00001-6]
Saffarian A, Derakhshan N, Taghipour M, Eghbal K, Roshanfarzad M, Dehghanian A. Sphenoid aspergilloma with headache and acute vision loss. World Neurosurgery. 2018; 115:159-61. [DOI:10.1016/j.wneu.2018.04.054] [PMID]
Corona-Ruiz JM, De Jesus O. Enlarging temporal arachnoid cyst extending inside the sphenoid sinus. World Neurosurgery. 2018; 115:1-4. [DOI:10.1016/j.wneu.2018.03.119] [PMID]
Couvreur T, Hallaert G, Van Der Heggen T, Baert E, Dewaele F, Kalala Okito JP, et al. Endoscopic treatment of temporal arachnoid cysts in 34 patients. World Neurosurgery. 2015; 84(3):734-40. [DOI:10.1016/j.wneu.2015.04.053] [PMID]
Bovenzi CD, Perez E, Ladner TR, Shrivastava R, Iloreta AM. Petrous apex arachnoid cyst fenestration via an endoscopic transsphenoidal approach: A case report and review of the literature. Journal of Neurological Surgery Part B: Skull Base. 2016; 77(S 01):P124. [DOI:10.1055/s-0036-1580069]