Introduction

Encephalocele is one of the most severe congenital neural tube defect. It occurs as a result of the failure of separation of surface ectoderm from neuroectoderm leading to a bony defect in the skull (Ugras & Kavak, 2016) characterized by a protrusion of brain and meninges through the defect. Prevalence of 0.8 – 5 per 10,000 live births is seen (Liao et al., 2012).

Occipital encephalocele is the most common type of encephalocele with approximately 90% occurring in the midline and most of the cases are diagnosed prenatally.60% of patients are seen associated with other malformations and chromosomal defects (Ugras et al., 2016). Serum alpha-fetoprotein and ultrasound establishes the prenatal diagnosis, and the prognosis depends on the extent of the herniated neural tissues and associated anomalies (Liao et al., 2012). Many times serum alpha-fetoprotein may remain normal because of intact meninges. Here is a report of one such illustrative case of occipital encephalocele.

Case Report

A 20-year-old third gravida was referred for antenatal USG to rule out fetal anomalies at 21 weeks six days. The present conception was confirmed by first trimester dating scan at seven weeks, and the patient was asked to come for follow up scan at 11 weeks for assessing Nuchal translucency and gross fetal anomalies. Due to the prevailing COVID, 19 pandemic patient was unable to come for her 11 -14 wks USG scan and instead came at 21 weeks for fetal anomaly scan. She could perceive fetal movements well. Past obstetric history - She has one living child; her second conception ended in a first-trimester early pregnancy loss. She had a significant medical history of hypothyroidism for six months and was on OralThyroid supplements (50microgram) with an euthyroid state at present.

Investigations

On Ultrasonography, all the fetal biometric parameters were corresponding to her clinical gestational age of 21 weeks five days. Targeted imaging for fetal anomalies revealed a defect of size 1.5 cm in the occipital bone (Figure 1 & Figure 3) with herniation of posterior fossa contents viz. both cerebellar hemispheres with overlying meningeal covering. The herniated cerebellum appeared partially atrophic with mild changes in contour and architecture with trans cerebellar diameter measuring 1.69 cm corresponding to 17 wks 6 days. Associated Bifrontal indentation with frontal bossing (Figure 2) of the fetal skull was also seen. Biparietal Diameter measured to 520 mm corresponding to the estimated fetal age of 21 weeks six days. No other fetal anomaly could be demonstrated. Craniovertebral junction and the fetal spine appeared normal. Fetal movements were noted with good cardiac activity (FHR – 158 bpm). With this a provisional diagnosis of occipital meningoencephalocele, fetal MRI was done to reassure the findings. On MRI, T2W sequence shows a T2 hyperintense cystic lesion in the posterior aspect of fetal skull communicating to the meningeal cavity through a defect in the fetal skull. The T2 hyperintense CSF containing meningeal cystic outpouching shows internal T2 signal intensities of that of brain parenchyma, resembling partial cerebellar architecture along with the circular herophili (Figure 4). Brain stem and medulla appeared to be intact and within the cranial cavity. The craniovertebral junction could be separately identified with no cervical vertebral or spinal dysraphism (Figure 5). Since this is a congenital anomaly with a grim fetal prognosis, the patient was advised to undergo termination of pregnancy by the department of Obstetrics and Gynaecology.

Discussion

Encephalocele is a type of neural tube defect that occurs as a result of the failure of development between 25 and 27 days after conception (Franco, Jo, Mehta, Pandya, & Yang, 2016).

It forms a part of a spectrum of neural tube defects that includes the following :

• Cephalocele is the term used for the protrusion of intracranial contents through a defect in the skull.

• Meningoencephaloceles are the Cephaloceles that contain herniations of brain tissue, meninges and CSF (Osborn, Hedlund, & Salzman, 2012).

• Meningocele refers to herniation of meninges and accompanying CSF without brain tissue. Atretic Cephaloceles refers to a small defect that contains dura, fibrous tissue and degenerated brain tissue (Osborn et al., 2012).

• Gliocele refers to herniation of glia –lined pouch containing only CSF (Osborn et al., 2012).

Encephaloceles can be congenital or acquired and are classified by location and are named accordingly to the bone through which they herniate. They can be open or skin covered, and most of the congenital Encephaloceles have coexisting intracranial abnormalities of varying severity (Osborn et al., 2012).

Four most common forms of encephaloceles are seen: sincipital(frontoethmoidal), parietal, occipital and skull base (Osborn et al., 2012).

Encephaloceles are multifactorial where environmental and genetic factors play a role. Folate deficiency is also associated with the pathogenesis of meningoencephaloceles (Alwahab, Kharsa, Nugud, & Nugud, 2017).

The most common form of congenital encephalocele is occipital encephalocele (Franco et al., 2016).

Occipital encephaloceles can be diagnosed on ultrasound from about nine weeks. After cranial ossification at ten weeks, the skull defect and occipital sac can also be demonstrated, and in 30% 0f cases associated Spina bifida seen (Chougule, Desai, & Aironi, 2006), and almost up to 80% of meningoencephaloceles are detected during 1^st trimester by Ultrasonography and by 2^nd trimester almost all cases are identified (Liao et al., 2012).

Demonstration of a skull defect with varying degrees of brain herniation is the basis for the diagnosis of encephalocele on prenatal Ultrasonography (Ugras et al., 2016).

On MRI T1 and T2 sequences are done, which shows characteristic signals of the brain and CSF (Franco et al., 2016).

Occipital encephaloceles are associated with syndromes such as

• Meckel-Gruber syndrome which is characterized by broad nasal root, hypertelorism, cleft lip, cleft palate, microcephaly, microphthalmia, polydactyly, polycystic kidneys and ambiguous genitalia (Alwahab et al., 2017; Ganapathy, 2014; Liao et al., 2012).

• Goldenhar’s syndrome consists of a combination of facial macrosomia and auricular malformation associated with occipital encephaloceles (Ali, Chugh, & Ranade, 2019).

• Von Voss – Cherstvoy syndrome involves occipital encephalocele, thrombocytopenia, urogenital abnormalities and upper limb phocomelia (Franco et al., 2016).

• Walker Warburg syndrome is congenital muscular dystrophy which is an autosomal recessive condition consisting of occipital encephalocele, myopia, retinal detachments, cataracts and aplasia (Franco et al., 2016).

• It is also seen as a part of Fraser syndrome, Roberts’s syndrome, and Amniotic band syndrome (Mahapatra, 2005).

Common Differential diagnosis Include Chiari III malformation, cystic hygroma, teratoma, branchial cleft cyst, scalp oedema, hemangioma and Meckel – Gruber syndrome.

In our case, a bony occipital defect was noted through which posterior fossa contents were seen herniating. The herniated contents included both the cerebellar hemispheres covered by intact meninges. The craniovertebral junction was normal. No obvious high cervical or other vertebral spinal anomalies were noted obviating the possibility of Chiari III malformation. No other fetal anomaly/ stigmata of syndrome association were demonstrable. Thus a diagnosis of isolated occipital meningoencephalocele was given.

Conclusion

This is a rare case of occipital meningo-encephalocele associated with a low survival rate. Almost 80% of cases are identified in 1^st trimester with almost all cases in 2^nd trimester. 1^st-trimester scanning of fetal anomalies helps to reduce the morbidity to the mother, and it also gives ample time for psychological counselling regarding expedited termination of pregnancy. In our case, the pregnancy was terminated, and the mother was advised to take pre-conceptional folic acid supplements before the next conception to avoid such congenital anomalies.