Frontonasal meningoencephalocele

A 15-day-old male neonate with clinical data of facial swelling since birth. The mother was from the countryside, and she had no antenatal follow-up or ultrasound scan during pregnancy. The parents noticed the facial swelling only after birth.

There is anterior herniation of intracranial content through frontonasal bone defect. The hernial sac contains brain tissue, paramedian parts of bilateral anterior frontal lobes and CSF (Figures 1, 2 and 3). The frontal bone is displaced superiorly, while the nasal bone is displaced inferiorly by the herniating brain tissue. The bony defect measures about 2cm in maximum cephalocaudal dimension (Figure 4). The extra-cranial portion of the hernia measures about 3.9cm x 3.7cm. Otherwise, there is no associated other intracranial anomaly appreciated.

Background

Encephaloceles refer to the herniation of intracranial contents through the defect in the dura and calvarium. Meningoencephalocele refers to when the hernial sac contains brain tissue, meninges and cerebrospinal fluid.

Encephaloceles are subdivided into the following categories: occipital (commonest), basal, convexity, and sincipital (anterior). Suwanwela and Suwanwela have subdivided the sincipital group further into frontoethmoidal encephaloceles and interferential encephaloceles [1]. Frontoethmoidal encephaloceles are herniations of the intracranial contents through a defect in the skull at the junction of the frontal and nasal/ethmoid bones. The frontoethmoidal group is subdivided further into nasofrontal, nasoethmoidal, and naso-orbital types. In the frontonasal subtype, the bony defect lies at the junction of frontal and nasal bones [1,2].

Frontoethmoidal encephaloceles represent about 15% of all encephaloceles. The incidence occurs in 1 to 4 in 10,000 births.

Clinical features

Clinical presentation depends on the location, subtype and size of the defect. Most patients present with a lump at the base of the nose. Based on the subtypes of frontoethmoidal encephaloceles, the site of the facial swelling can give diagnostic clues; for example, in the case of frontonasal encephalocele, the swelling is midline, intranasal in the case of nasoethmoidal and medial orbital in naso-orbital encephalocele. An associated gross facial deformity can occur if the defect is large. Patients may present with developmental delay, seizure, vision impairment, microcephaly or signs of increased intracranial pressure.

Radiologic findings

Diagnosis can be made with CT and MRI.

Computed tomographic (CT) scans with appropriate brain windows and three-dimensional reconstruction give the best assessment of the diagnosis and pathological anatomy. A CT scan helps to delineate the bone anatomy with the use of volume rendering techniques to obtain a three-dimensional view of the bone defects. In cases of frontonasal encephalocele, the frontal bone is displaced superiorly and the nasal bone is displaced inferiorly. In cases of nasoethmoidal encephalocele, the nasal bone is bowed or displaced anteriorly with tract of herniating tissue protruding through the anterior ethmoidal area. The disadvantage of CT scan is radiation exposure to the neonate, which should be avoided if possible.

MRI is the best imaging tool and should be used as the first modality. MRI is helpful in better characterising frontoethmoidal encephaloceles and in identifying other associated intracranial malformations. The herniating brain tissue shows similar T1W and T2W signal intensity and enhancement pattern to the rest of the brain parenchyma.

The intracranial anomalies associated with frontoethmoidal encephaloceles are schizencephaly, microcephaly, grey matter heterotopia, callosal hypogenesis, agenesis of septum pellucidum, neuronal migration anomalies, interhemispheric lipoma, cerebellar dysplasia, aqueductal stenosis and hydrocephalus, colloid and arachnoid cysts [2,3,6,8].

CT/MRI myelography should only be used when there are still unanswered questions despite full MRI and bone CT examinations.

Management

Management is multidisciplinary. Surgical management at the earliest is the key factor to avoid infections, worsening hydrocephalus, and distortion. Surgical treatment includes removal of the sac and herniated brain parenchyma and reconstruction of the bony defect. Associated hydrocephalus, if present, can be addressed with shunting before the management of encephalocele [2,4,7].

Generally, the prognosis depends on the location of the hernia sac and its content, size of sac, amount of herniated brain tissue, hydrocephalus, associated malformations and infections. Sincipital (anterior) encephalocele generally has a good prognosis and is usually associated with normal intelligence and motor development.

Written informed consent was obtained from the parents of the neonate for publication.