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Frontonasal Cephalocele

22 wk EGA with “possible proboscis and ACC” by U/S.

Slides 2-3:  In addition to the exophytic lesion extending anteriorly between the orbits, there was a prominent csf space posterior to the fully formed cerebellum and ventriculomegaly within the supratentorial compartment.

Slides 4-5:  The corpus callosum was present, the globes were small and there was hypertelorism.

Dx: frontonasal cephalocele (info below is from StatDx)

Congenital herniation of meninges, CSF ± brain tissue through mesodermal defect in anterior skull/skull base
Heterogeneous, mixed density mass (variable amounts CSF & parenchyma) extending intracranially through bony defect
     Midline frontal: Frontonasal type (FNCeph)
     Intranasal: Nasoethmoidal type (NECeph)
     Inferomedial orbital: Nasoorbital type (NOCeph)

The ventriculomegaly is most likely due to aqueductal stenosis and there is an arachnoid cyst of the posterior fossa.

General Features – Frontoethmoidal cephaloceles
     Prior to 8th week of gestation, 2 potential spaces present
          Fonticulus frontalis: Between frontal, nasal bones
          Prenasal space: Between nasal bones, developing cartilaginous nasal septum
               Anterior neuropore runs in prenasal space, communicating with anterior cranial fossa via foramen cecum
     Dural diverticulum protruding through defects may fail to regress
          FNCeph: Protrudes through unobliterated fonticulus frontalis
          NECeph: Protrudes through foramen cecum into prenasal space
          NOCeph: Protrudes into inferomedial orbit through defect in lacrimal/frontal process of maxillary bones

Additional info on Frontoethmoidal cephaloceles

     Sporadic occurrence
     Not linked to neural tube defects like occipital cephaloceles
     Siblings have 6% incidence of congenital CNS abnormalities
Associated abnormalities
     Intracranial abnormalities (~ 80%)
          Callosal hypogenesis & interhemispheric lipomas
          Neuronal migration anomalies
          Aqueductal stenosis & hydrocephalus
          Colloid or arachnoid cysts
     Midline craniofacial dysraphisms & hypertelorism