Congenital meningoencephaloceles of the skull base are commonly classified according to the site of the bone defect^2,3,4 and can also result in epileptic disease. Pollock classifies them as follows: (1) sphenopharyngeal or trans-sphenoidal, when they protrude into the epipharynx and/or sphenoid sinus; (2) spheno-orbital, when the protrusion is through the superior orbital fissure into the superior orbit producing unilateral exophthalmus; (3) sphenoethmoidal, when the cerebral mass extends through the sphenoid and ethmoidal bones into the posterior nasal cavity; (4) transethmoidal, when the encephalocele extends into the anterior nasal cavity; and (5) sphenomaxillary, when the meningoencephalocele passes through the superior orbital fissure into the orbit and through the inferior orbital fissure into the pterygopalatine fossa.²

The trans-sphenoidal meningo(encephalo)celes are congenital caused by incomplete embryogenesis of the Ala sphenoidalis major thus protruding in the pterygopalatine fossa.⁵ They are extremely rare among the meningo(encephalo)celes of the skull base. Their cardinal symptom is temporal lobe epilepsy. The extension of gliosis from the encephalocele in direct continuity to the amygdalohippocampal region, the most active epileptic area, is considered as the pathomechanism of epilepsy.⁵ Occasionally, this lesion can be discovered during evaluation for recurrent meningitis.⁶

Computed tomography (CT) usually demonstrates the bony gap and magnetic resonance imaging (MRI) reveals the extent of soft tissue prolapse and allows differentiation between cerebrospinal fluid (CSF) and tissue. Further, MRI detects cases that cannot be diagnosed by CT, which is obligatory in evaluating epilepsy.⁷

Surgical approach to the middle skull base and pterygopalatine fossa for any kind of benign and malignant processes is a challenge for both neurosurgeons and maxillofacial surgeons and results in sophisticated procedures, such as infratemporal approach, or after anterior subtemporal craniotomy or temporary sagittal mandibulotomy.^{8,9,10,11,12,13}

The patient had an intense lifestyle with alcohol and cigarette abuse and was exposed to professional physical strain as well. He reported that seizures usually occurred during infections of the upper respiratory tract while blowing his nose, or after extreme body fatigue. Antiepileptic treatment for the last 2 years failed to prevent them. There was no history of head injury at birth or later.

The patient's physical examination was normal. Neurological evaluation including electroencephalogram confirmed a left temporal lobe dysfunction. Epileptic activity was recorded from the mesial and anterior neocortical surfaces.

CT of the skull base demonstrated a defect at the left Ala sphenoidalis major and soft tissue protruding into the pterygopalatine fossa as typical trans-sphenoid meningocele (Fig. 1). This location allowed its approach via midfacial degloving.¹⁴ Under general anesthesia, the classical four incisions were performed: (l) bilateral sublabial incision in the oral vestibule; (2) complete transfixion between nasal septum and nasal columella; (3) bilateral circumvestibular incision of the piriform aperture extending to the oral vestibule; and (4) bilateral intercartilaginous incision between alar and lateral nasal cartilage (Fig. 2A).

The periosteum of the canine fossae was elevated, preserving the infraorbital nerves. The skin of the lower third of the nose was cranially dislocated toward the glabella by using a wet gauze (Fig. 2B). The ventral wall of the left maxillary sinus, together with the caudal part of the frontal process of the left maxilla, were osteoplastically removed to open the maxillary sinus (Fig. 2C). Its healthy mucosa was preserved and the mucosa of the dorsal sinus wall was elevated as a flap to expose the open posterior antral wall. This was temporarily removed in toto by osteotomy with a fine chisel to access the pterygopalatine fossa. Under the surgical microscope, the internal maxillary artery was dissected and closed by using vasosurgical clips. Further dissection was necessary to expose the thin dura of the meningocele out of the surrounding fat and follow it toward the bony defect. The whole cele was then amputated, resulting in a CSF leak. This was sealed by using lyophilized dura, collagen fleece with fibrin glue, and abdominal fat. Lumbar drain was not necessary. The posterior antral wall was then repositioned and supported by the mucosal flap and fibrin glue. The ventral antral wall was also repositioned and stabilized with slowly resorbable sutures (Fig. 2D) and all incisions were closed with proper material. Endonasal dressing was not implemented and neither supra- nor infraturbinal antrostomy was necessary, since the healthy antral mucosa was completely preserved (Fig. 3). Histological examination confirmed the diagnosis.

Since these meningo(encephalo)celes protrude in the pterygopalatine fossa, they are not apparent during clinical examination and sometimes even the CT scan fails to reveal them. For that reason, the presence of the meningocele was evident intraoperatively during temporal lobectomy for the treatment of temporal lobe epilepsy.^5,15 Thus, this disease should be seriously considered in the differential diagnosis of late-onset temporal lobe epilepsy. MRI is recommended for definitive exclusion or confirmation.⁷

Because surgical access to the region is very demanding, various approaches have been described. Most of them refer to malignant processes, where functional and esthetic compromises can be tolerated to achieve radical tumor resection.^8,9,10,11 However, extended facial scars as well as high risk of facial nerve or other cranial nerve palsies after temporary sagittal mandibulotomy are obsolete for treatment of benign processes like the trans-sphenoid meningocele. Anterior subtemporal craniotomy, which requires severe retraction of the brain to access the region (with high morbidity), seems to be over-treatment as well. Recent minimally invasive endoscopic techniques for benign processes of the nose and paranasal sinus are indicated only for minor surgery in the pterygopalatine fossa.^12,13