Meningoencephalocele

The exact cause of meningoencephalocele is not known. Some studies have suggested that environmental factors could play a role in causing the condition. Exposure during pregnancy to aflatoxins, toxins produced by a mold that grows in nuts, seeds, and legumes, has been proposed to be a possible cause in some cases. However, its potential role in causing the condition is unclear. It has also been suggested that folate deficiency during pregnancy might play a role, because the condition is so closely related to spina bifida, which can be caused by folate deficiency. However, there have been no studies regarding the relationship of maternal folate deficiency and meningoencephalocele.^[1] There might additionally be some underlying genetic factors given evidence of familial clustering and cases of meningoencephalocele identified in individuals with an underlying genetic disorder.^[2][3] Further studies are needed to to clarify what may cause the meningoencephalocele.

Meningoencephalocele is not thought to be an inherited condition. Studies have proposed that meningoencephalocele is likely a multifactorial defect. This means that both environmental factors and multiple genes may interact with each other to cause the condition. Studies have suggested that environmental factors probably play an important role. This information is supported by the fact that several studies have not identified the condition among close relatives of affected individuals. To date, there have been no genes identified that are likely to play a strong part in causing the condition.^[1]

The exact number of individuals diagnosed with meningoencephalocele is not known. Although the term "meningoencephalocele" refers specifically to the protrusion of both meninges and brain tissue due to a skull defect, this condition is sometimes more generally referred to as an "encephalocele" which may encompass all conditions characterized by herniation of any intracranial material due to a cranial defect. The worldwide frequency of encephaloceles in general is not exactly known but has been reported to vary between 1/2500 and 1/10,000 individuals.^[4] For unknown reasons, the incidence of frontoethmoidal encephalocele (relating to the ethmoid and frontal bones) is highest in Southeast Asia.^[3]

The prognosis for each individual with meningoencephalocele depends on the size and location of the sac, whether brain tissue is present in the sac, and if other brain abnormalities are also present.^[4] Survival is generally better when brain tissue is not involved in the sac.^[5] Individuals with encephaloceles located in the face (at the frontal and nasal bones) tend to have better survival and development than those located at the back of the head (at the occipital and parietal bones).^[6][5] Several studies have found that approximately two-thirds (66%) of individuals with meningoencephalocele in the back of the head survive; of those survivors, approximately half have normal intelligence. Infections, such as meningitis, may develop and could also affect the outcome.^[5][4]