12.1 Introduction

Trauma leading to fracture of the anterior skull base is a frequent cause of transethmoidal encephaloceles in the pediatric age group. Larger series in literature, however, report congenital encephaloceles as the most common variety. ¹ A congenital encephalocele is defined as an extension of intracranial structures through a cranial defect resulting from an embryological malformation in a patient, with a medical history negative for secondary causes. ² Encephaloceles can be meningoceles if they only contain meninges or meningoencephaloceles if they contain brain matter and meninges. ³

Basal encephaloceles, especially the transsphenoidal type, are difficult to diagnose and to treat. ² They have been traditionally treated by an open transcranial approach. The advent of extended endoscopic cranial base surgery has allowed for a new endonasal approach for the treatment of basal encephaloceles, thereby minimizing patient morbidity.

In this chapter, we review the endoscopic endonasal management of anterior basal encephaloceles and present our experience regarding the effectiveness of endoscopic management in the pediatric population.

12.2 Classification

Suwanwela and Suwanwela ⁴ proposed an origin-based classification for encephaloceles including congenital, spontaneous, or traumatic. Encephaloceles can also be classified according to their localization as anterior (frontoethmoidal or sincipital and basal) and posterior (infra- and supratorcular). Posterior or occipital types are the most common and compose 75% of the encephaloceles. Frontoethmoidal and basal encephaloceles have also been defined as nasal encephaloceles. Frontoethmoidal types originate between the frontal and ethmoid bones, commonly at or anterior to the foramen cecum, and typically present as a facial mass over the nose and/or as an intranasal mass. Basal encephaloceles herniate posterior to the cribriform plate and present in the nasal cavity as opposed to external masses. Depending on the site of herniation, they are classified into five anatomic types ⁵ : sphenoethmoidal, transsphenoidal, spheno-orbital, transethmoidal, and sphenomaxillary (Table 12‑1). Sphenoidal encephaloceles can be subdivided into transsphenoidal encephaloceles (▶ Fig. 12.1), which traverse the floor of the sinus and protrude into the nasal cavity or nasopharynx, and intrasphenoidal encephaloceles, which extend into the sphenoidal sinus. In the case of intrasphenoidal encephaloceles, most defects occur in the lateral wall of the sphenoidal sinus (▶ Fig. 12.2), the so-called temporosphenoidal encephaloceles.

12.3 Epidemiology, Embryology, and Pathogenesis

Encephaloceles occur in approximately 1 in 3,000 to 5,000 and the basal encephaloceles with an estimated incidence of 1 in every 35,000 live births. Nasal encephaloceles have a higher incidence in Southeast Asia than in Western countries and the Middle East. ⁶

Basal encephaloceles, and the often-associated anomalies of midline structures of the brain and face, are considered to be sporadic abnormalities developed as a consequence of a neurulation disorder, or as a consequence of a mistake occurring in the complex process of ossification of the sphenoid bone. ² Neural tissue overgrowth, viral infection, radiation, hyperthermia, hypervitaminosis, salicylates, trypan blue, hypoxia, and numerous other agents have been suggested as causes of persistent openings in the neural tube. ⁷

12.4 Clinical Presentation

Unlike frontoethmoidal encephaloceles that mostly present at birth as skin-covered masses or visible protrusions on the face, over the nose, glabella, or forehead, basal encephaloceles are not externally visible, so the age of clinical diagnoses is determined by the large size of the encephalocele causing respiratory difficulties. The most frequent symptoms of anterior basal encephaloceles in neonates and infants (i.e., runny nose, nasal obstruction, mouth breathing, or snoring) are often overlooked. Cerebrospinal fluid (CSF) rhinorrhea may be mistaken for runny nose and may finally be identified by recurrent episodes of meningitis. Concomitant congenital malformations of the face, eyes, and brain are the most important clues for the diagnosis of basal encephalocele in the neonatal or infantile period. ^{2 ,​ 6}

The majority of transsphenoidal meningoencephaloceles are usually diagnosed in very young pediatric patient due to manifestations such as respiratory distress caused by epipharyngeal obstruction, feeding difficulties, cranial midline defects with cleft lip or cleft palate, hypertelorism, optic malformations with anophthalmia, retinal abnormalities, optic nerve hypoplasia, unexplained bouts of recurrent meningitis, or endocrine abnormalities. They are commonly associated with pituitary dysfunction and visual problems attributable to the distension of the pituitary gland, hypothalamus, and optic pathways within the herniated sac. No mental retardation was seen in these patients. ^{2 ,​ 3 ,​ 7}

12.5 Diagnosis

MR imaging and CT scans are crucial preoperatively to assess associated brain abnormalities and to identify vital structures in the herniated sac. CT scans allow evaluation of bony anatomy and the associated craniofacial skeleton defects. The anterior skull base in infants is incompletely ossified or unossified. No consensus exists as to which imaging modality is considered to be most advantageous. Both CT and MRI are considered to be essential. ⁸ Biopsy is contraindicated for the diagnosis of nasal encephaloceles due to persisting intracranial communications. ³ Histologically, encephaloceles have shown to contain glial cells, cerebral tissue, nonfunctional neural tissue, choroid plexus, and ependymal cells. ⁶

In the diagnosis of basal encephalocele, a complete hormone screening is necessary; diabetes insipidus is the most common finding of pituitary deficiency and is usually indicated by a variable thyroid hormone and cortisol response. Hormone profiles need to be monitored postoperatively and deficiencies may manifest many years after initial diagnosis. ⁹ Visual assessment is also recommended.

Differential diagnosis for a nasal mass should include nasal glioma, nasal polyp, or dermoid cysts. Though not restricted to the midline, a hemangioma is also included in the differential diagnosis of a pediatric nasal mass. Nasal gliomas are encephaloceles that lack a direct intracranial connection and occur as firm, noncompressible masses within the nasal cavity. In order to clinically distinguish these two entities, the Furstenberg test causes an encephalocele to enlarge due to its connection to the subarachnoid space but not a glioma. ¹⁰ Dermoid cysts present as nonpulsatile, noncompressible masses with a dimple containing a hair follicle. ⁴ Nasal polyps are rare in children and are usually associated with cystic fibrosis. The Furstenberg test is usually negative for most cases of nasal polyps and dermoid cysts. ⁶

12.6 Treatment

Consensus management of basal encephaloceles, including the indication, timing, and the optimal mode of treatment, has yet to be established. The surgical treatment of posterior basal encephaloceles, particularly in the pediatric population, remains a challenge because of their close relationship with the opticochiasmatic structures, the hypothalamo–pituitary axis, and the proximity to the anterior and middle fossa vessels. ⁷ Some surgeons do not recommend the correction of encephaloceles, believing that this would result in worsening morbidity and mortality. ¹¹ On the other hand, review of the literature reveals that a conservative approach to basal encephaloceles is associated with a progression of the signs and/or symptoms, and surgical treatment is associated with a better outcome in the long term. ²

Surgery is the only treatment for these entities, but it requires excellent surgical skill. Strong indications for surgery include persistent CSF leak, recurrent meningitis, progression of neurological deficits, and respiratory obstruction. ¹¹

Reported surgical approaches for transsphenoidal encephaloceles include transpalatal, transcranial, endoscopic endonasal, or combined approaches. ¹¹ Conventional anterior skull base surgery in children can potentially cause disruption of the growth centers in the craniofacial skeleton and result in facial asymmetry. ¹² Endoscopic endonasal procedures achieve definitive repair of most anterior and middle cranial fossa CSF leaks. ¹³ In this sense, the lack of impact of pediatric sinus surgery on long-term facial development has been well documented. ¹⁴ Hence, endoscopic treatment allows minimizing surgical injury and consequently facilitates the management of these lesions at an earlier age.

In cases of transsphenoidal encephaloceles with large cleft palate defects, the transpalatal approaches are preferred by most authors. Performing palatal osteotomies and removing the hard palate may be technically challenging and create additional difficulties for the reconstruction of the skull base and closure of the mucosal layer. Furthermore, splitting of the palate can result in delayed palatal wound healing, palatal dehiscence, and prolonged enteral tube feeding due to velopharyngeal insufficiency. ²

The transcranial subfrontal or pterional approach adds additional technical difficulties to a case of posterior basal encephalocele, particularly transsphenoidal type. The position of the sac in a sphenoethmoidal or transsphenoidal encephalocele is quite low and requires that a significant traction force be exerted on the frontal lobe. Therefore, these approaches are associated with high postoperative rates of morbidity, mortality, and hypothalamic dysfunction. Furthermore, infants are more susceptible to retraction injuries with subfrontal or frontotemporal approaches. In contrast to transcranial approaches, these limitations are not encountered with the endoscopic endonasal approach, because the sac is reached through natural cavities of the nostrils. Although the working space available in pediatric patients with an endoscopic approach is restricted, we have used this approach even in children younger than 1 year. ⁷ Thin rigid endoscopes with an external diameter of 2.7 mm may need to be used in patients with small nares. In basal encephaloceles, except for transsphenoidal subtype, the endoscopic endonasal approach is relatively straightforward. Transsphenoidal encephalocele repair is more complicated, and we will discuss our preferred surgical technique in detail below.

12.6.1 Surgical Technique

The endoscopic endonasal approach with neuronavigation is usually used for most patients. Preparation of patients has been described in this book elsewhere. We routinely prepare the patient’s right thigh and/or abdomen so that autologous fat or fascia lata can be harvested for graft reconstruction of the skull base defect, if needed. Depending on the type and location of the lesion, the extent of the approach and technical nuances may differ. Here, we describe the different endonasal approaches based on the type of the encephalocele.

Transethmoidal Encephaloceles

Direct paraseptal approach is performed for the lesion located in the cribriform plate. To gain access in some cases, it is necessary to perform an upper septoplasty and remove high septal bone. Every effort is made to preserve the middle turbinate. Once the lesion is visualized, the mucosal layer overlying the extruded dural sac is dissected from the surrounding structures to fully expose the bony defect at the skull base. Smaller encephaloceles can be shrunk with bipolar cautery, whereas larger encephaloceles presenting with neural tissue may need to be debulked with a suction-rotation microdebrider. In the majority of cases in this area, the encephalocele consists of nonfunctional neural tissue, which can be removed without neurological sequel. Once the encephalocele is minimized down to the level of the bony skull base defect, hemostasis is carefully obtained and the edges of the bony and dural defects are defined with an angled dissector or curette.

The method for closure of pure transethmoidal encephaloceles largely depends on the size of the defect being repaired. Defects of the cribriform plate smaller than 0.5 cm are usually repaired with a small onlay graft of fat, mucosa, or fascia. Defects sized 0.5 to 1 cm are usually repaired in a multilayer fashion with a piece of fat into the defect reinforced by an onlay fascia lata or free mucosal graft. The fat is pushed into the dural defect by using a blunt angled probe or curette followed by gentle pressure exerted using a cottonoid pledget. A second layer of fascia lata or free mucosal graft is subsequently used as an onlay graft. Larger defects with high-flow CSF leaks may require multilayered watertight closure accompanied by a pedicled flap.

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