Meningoencephalocele is categorized according to the location of the herniated sac into two main types: occipital and frontoethmoidal meningoencephalocele. The frontoethmoidal type predominates the Southeast Asian countries including Thailand and seen more in females, while the occipital type is more common in the western world with a predilection for males [4].
The cause of meningoencephalocele is believed to be multifactorial where genetic and environmental factors play a role. Given the observation of familial predilection, genetic background may increase the risk of developing this condition. Yet, no genes have been held responsible for causing the condition. Also, due to close relationship between meningoencephalocele and neural tube defects, folate deficiency has been believed to play a role in the pathogenesis of meningoencephalocele [5].
Meningoencephalocele is associated with facial anomalies including broad nasal root, hypertelorism, cleft lip, cleft palate, polydactyly, polycystic kidneys, ambiguous genitalia (features of Meckel-Gruber syndrome) [6], microcephaly, microagnathia and hydrocephalus.
Gregor J. et all, found that MRI could reveal the exact anatomical description of the meningoencephalocele and displaced brain structures, and showed the typical features of Chiari III malformation in some cases. It also revealed the configuration of the brain stem regions. Moreover, postnatal follow-up MRI confirmed the prenatal findings and showed additional morphological information such as vascular anatomy [7]. Furthermore, Magnetic Resonance Angiography is the optimal investigation to visualize the relationship of the sac to the venous sinuses. While CT scans are used to detect the extent of cranial defect [8].
Several surgical techniques are used to preserve normal brain tissue, if present, in the herniated sac. Expansion cranioplasty uses mesh to provide a space for the herniated sac. Another technique is through ventricular volume reduction. It is a two-stage technique; at first, it increases the ventricular pressure and induces hydrocephalus then, through ventriculoperitoneal shunt, the ventricles contract and the herniated tissue repositions intracranially [9]. In addition, for herniated occipital and cerebellar parenchyma, incision is made in the tentorium to create an infratenterial space for the herniated tissue to retract. Currently nasal endoscopy is a valuable procedure in diagnosis and treatment of memnigoencephalocels, it was introduced in early 1980s and emerged as the procedure of choice for meningoencephaloceles [10]. There are some factors that may influence the prognosis of patients with meningoencephalocele, The size of the herniated sac and the amount of brain tissue it contains determine the prognosis of these patients. Frontoethmoidal meningoencephalocele appears to have better prognosis [3]. Zuckerman et al. reported that the reoccurrence of such cases after the initial surgery was approximately 16% with an average of 7 month interval between the first surgery and the reoccurrence [11].
Meningoencephalocele is categorized according to the location of the herniated sac into occipital and frontoethmoidal subtypes. Antenatally, ultrasonography help evaluating the neural configuration and look for any syndromic characteristics that may influence the fetal outcome.