ALOBAR HOLOPROSENCEPHALY 

This is the most severe form in which the prosencephalon fails to divide.
 

ULTRASOUND
  • Interhemispheric fissure absent.
  • Falx cerebri absent.
  • Single primitive ventricle (holoventricle) with a large dorsal cyst.
  • "Horseshoe" or "boomerang" configuration of the brain (peripheral rim of cerebral cortex displaced rostrally in a coronal plane).
    • Pancake configuration - cortex covers monoventricle to edge of dorsal cyst.
    • Cup configuration = more cortex present posteriorly.
    • Ball configuration = complete covering of monoventricle with dorsal cyst.
  • Thalami are fused in the midline (thalami and basal ganglia protrude into the monoventricle).
  • Midbrain, brainstem and cerebellum are structurally normal.
  • Absent third ventricle, neurohypophysis, olfactory bulbs and tracts.
  • Absent septum pellucidum, falx cerebri and corpus callosum.

 

 

 

ORBITAL AND FACIAL ANOMALIES

 (5 categories described) (1).

A normal face is present in 17% of cases.

  1. Cyclopia.  
    • 1 eye or partially divided eyes in a single orbit.
    • Arhinia (absent nose with a proboscis that implants above the orbit).

 

 

 

 

Video clip of Cyclopia

 

 

 

  1. Ethmocephaly.
    • Marked hypotelorism, arhinia, absent nose with a proboscis above the orbit or between narrowly placed orbits.

 

 

  1. Cebocephaly.
    • Marked hypotelorism, proboscis like nose (normally placed but having a single nostril).

 

 

  1. Face with median cleft lip.
    • Hypotelorism with a flattened or absent nose.
  2. Face with median philtrum-premaxilla a large and flat nose.
    • Bilateral cleft lip/palate, hypotelorism and flat nose.

 

 

1+2
3+4
5

- Alobar holoprosencephaly
- Alobar or Semilobar holoprosencephaly
- Semilobar or Lobar holoprosencephaly

Other less common facial anomalies include micrognathia, trigonocephaly, microphthalmia and microcephaly.
 

EXTRAFACIAL ANOMALIES ASSOCIATED WITH HOLOPROSENCEPHALY

Extrafacial anomalies have been reported in approximately 52% of cases (2)

  • Myelomeningocele.
  • Renal dysplasia.
  • Omphalocele.
  • Esophageal atresia.
  • Cardiac defects.

 

 

REFERENCES
  1. DeMyer W, Zeman W. Alobar holoprosencephaly (arhinencephaly) with median cleft lip and palate: Clinical electroencephalographic and nosologic considerations. Confin Neurol 1963;23:1.
  2. McGahan JP, Nyberg DA, Mack LA. Sonography of facial features of alobar and semilobar holoprosencephaly. Am J Roentgenol 1990;154:143-148.