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Information

Nervous System Disorders

= mesodermal defect of calvarial suture + dura with extracranial extension (= herniation) of intracranial structures and persistent connection to subarachnoid space

Cranial meningocele: = herniation of meninges + CSF only

Encephalocele = herniation of meninges

(Meningoencephalocele) + CSF + neural tissue

Nomenclature: based on origin of their roof + floor

eg, frontonasal: frontal bone = roof, nasal bone = floor

Prevalence:

1–4÷10,000 live births; 5–6–20% of all craniospinal malformations; predominant neural axis anomaly in fetuses spontaneously aborted <20 weeks GA; 3% of fetal anomalies detected with MS-AFP screening; 6% of all detected neural tube defects in fetuses

Cause:

failure of surface ectoderm to separate from neuroectoderm early in embryonic development (3rd week GA)

In 60% associated with:

  1. Spina bifida (7–30%)
  2. Corpus callosum dys- / agenesis
  3. Chiari malformation
  4. Dandy-Walker malformation
  5. Cerebellar hypoplasia
  6. Amniotic band syndrome: multiple irregular asymmetric off-midline encephaloceles
  7. Migrational abnormalities
  8. Chromosomal anomalies in 44% (trisomy 18)

Prognosis: dependent on associated malformations + size and content of lesion; 21% liveborn; 50% survival of liveborns, 74% retarded

Risk of recurrence: 3% (25% with Meckel syndrome)

DDx: teratoma, cystic hygroma, iniencephaly, scalp edema, hemangioma, branchial cleft cyst, cloverleaf skull

Occipital Encephalocele (75%)!!navigator!!

Most common encephalocele in Western Hemisphere

Associated with:

  1. Meckel-Gruber syndrome
    = occipital encephalocele + microcephaly + cystic dysplastic kidneys + polydactyly
  2. Dandy-Walker malformation
  3. Chiari malformation
  4. Callosal + migrational anomalies
  • external occipital mass

Location: supra- and infratentorial structures involved with equal frequency

  • skull defect (visualized in 80%)
  • flattening of basiocciput
  • ventriculomegaly
  • “lemon” sign = inward depression of frontal bones (33%)
  • cyst-within-a-cyst (ventriculocele = herniation of 4th ventricle into cephalocele)
  • acute angle between mass + skin line of neck and occiput

DDx: cystic hygroma

Sincipital Encephalocele (13–15%)!!navigator!!

= FRONTOETHMOIDAL ENCEPHALOCELE

Most common variety in Southeast Asian population

Location: midface about dorsum of nose, orbits, and forehead

Cause: failure of anterior neuropore located near optic recess to close normally at 4th week GA

Types:

  1. Nasofrontal (40–60%)
    = herniation of dura mater through foramen cecum + fonticulus frontalis
    Site: along nasal bridge between nasofrontal sutures into glabella
  2. Nasoethmoidal (30%)
    = persistent herniation of dural diverticulum through foramen cecum into prenasal space
    Site: between nasal bone + nasal cartilage (beneath nasal bone + above nasal septum)
  3. Naso-orbital
    Site: between maxilla + lacrimal bone (= along medial orbit at level of frontal process of maxilla and ethmoid-lacrimal bone junction)

Common root: foramen cecum (= small ostium anterior to crista galli formed by closure of frontal + ethmoid bones)

Associated with: midline craniofacial dysraphism (dysgenesis of corpus callosum, interhemispheric lipoma, anomalies of neural migration, facial cleft, schizencephaly)

  • obvious nonprogressive pulsatile mass
  • broad nasal root, hypertelorism, nasal stuffiness, rhinorrhea
  • change in size during crying / Valsalva maneuver
  • positive Fürstenberg test = change in size during jugular compression
  • soft-tissue mass extending to glabella / nasal cavity
  • pedunculated intranasal mass extending from superomedial nasal cavity downward
  • enlarged foramen cecum

OB-US:

  • widened interorbital distance

CT:

  • bifid / absent crista galli
  • absent cribriform plate / frontal bone

MR:

  • isointense relative to gray matter
  • may be hyperintense on T2WI (due to gliosis)

N.B.: biopsy is CONTRAINDICATED (→ potential for CSF leaks, seizures, meningitis)

Risk of recurrence: 6% of congenital CNS abnormalities for younger siblings

Rx: complete surgical resection with repair of dura mater (NO neurologic deficit due to abnormal function of herniated brain)

DDx:

  1. Dacryocystocele / nasolacrimal mucocele
  2. Nasal glioma (no subarachnoid connection on cisternography)

Sphenoidal Encephalocele (10%)!!navigator!!

= BASAL ENCEPHALOCELE

Age: present at end of 1st decade of life

  • clinically occult ← internal protrusion
  • mass in nasal cavity, nasopharynx, mouth, posterior portion of orbit increasing with Valsalva
  • mouth breathing due to nasopharyngeal obstruction
  • diminished visual acuity with hypoplasia of optic disks
  • hypothalamic-pituitary dysfunction

Associated with: agenesis of corpus callosum (80%)

Types:

  1. transethmoidal = through midline cribriform plate
  2. sphenoethmoidal = through sphenoid + ethmoid
  3. trans-sphenoidal = through floor of sella may be associated with: cleft palate
    • displacement of cavernous sinus (laterally), pituitary gland, hypothalamus, optic nerves, chiasm
  4. frontosphenoidal
  5. sphenopharyngeal = through sphenoid body
  6. sphenoorbital = through superior orbital fissure
  7. sphenomaxillary = through maxillary sinus

Parietal Encephalocele (10–12%)!!navigator!!

Associated with: dysgenesis of corpus callosum, large interhemispheric cyst

  • hole in sphenoid bone (seen on submentovertex film)
  • cranium bifidum = cranioschisis = “split cranium” (= skull defect) = smooth opening with well-defined sclerotic rim of cortical bone
  • hydrocephalus in 15–80% (from associated aqueductal stenosis, Arnold-Chiari malformation, Dandy-Walker cyst)
  • nonenhancing expansile homogeneous paracranial mass
  • mantle of cerebral tissue often difficult to image in encephalocele (except with MR)
  • intracranial communication often not visualized
  • metrizamide / radionuclide ventriculography DIAGNOSTIC
  • microcephaly (20%)
  • polyhydramnios

DDx:

  1. sonographic refraction artifact at skull edge
  2. clover leaf skull (± temporal bone partially absent)

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