What three types of holoprosencephaly are recognised (list them in order of increasing severity)?
Lobar, semilobar and alobar (most severe).
What are the main differentials, and what features enable you to make the distinction between these entities?
1. Semilobar holoprosencephaly: partial separation into hemispheres; rudimentary occipital and temporal horns. 2. Hydranencephaly: thalami are often visible and are not fused; not associated with midline facial abnormalities; no cortex present, or sometimes small islands of tissue; falx usually present. 3. Severe hydrocephalus: falx usually present; bilateral choroid plexus present; thalami not fused; not associated with midline facial abnormalities.
What configurations can the cortex present in alobar holoprosencephaly take?
1. Pancake: cerebral tissue is confined to the anterior basicranium. 2. Cup: cerebral tissue lines variable amounts of the anterior cranium with a dorsal cyst present posteriorly (this case). 3. Ball: a complete rim of tissue surrounds the monoventricle without dorsal cyst.
Non-contrast CT demonstrates a thin rim of cerebral tissue anteriorly, without midline cleft. There is a large CSF-density space posteriorly. There is no evidence of a falx cerebri. The cerebellum is malformed with abnormal appearance of the fourth ventricle. Brainstem is visualised.
In addition there are a number of other midline abnormalities:
- bony defect in the occipital bone with an occipital meningiocoele
- cleft lip and palate
- under-developed nose and hypotelorism