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NQ-050 Answer: (B) Alobar holoprosencephaly

Diagnosis: (B) Alobar holoprosencephaly

Pathology of the cases:

Frontal view: On the frontal view, the two cerebral hemispheres appear to be fused in the midline although there is a falx like structure at the midline. In contrast, the cerebellum and the medulla seems to have split well into the right and left half.
Occipital View: The cerebral hemispheres shows that the occipital portion is reduced to a thin translucent seam (white arrow). This is best illustrated in the image with the specimen submerged under water. The occipital portion of the parietal and occipital pallium is entirely converted into a thin membrane. The thalamus and the basal ganglia appear to have split into the left and right half. There is a single, dilated ventricle with no septum pellucidum.
Occipital Glial-ependymal Seam: As only the frontal half of the telencephalon exists, it would appear as like a shield on lateral view and this type of holoprosencephaly is also called the shield type holoprosencephaly [click here to see an MRI online].
Continuation of gray matter across midline: On a coronal cut, the gray matter cross over the midline and no corpus callosum is present and, again, no septum pellucidum is found. Continuation of gray matter across the midline and a lack of septum pellucidum are two hall mark features that can aid in easily recognizing lobar or semilobar holoprosencephaly.

De Morsier Syndrome (Septo-optic dysplasia) is characterized by optic nerve hypoplasia, aplasia or defects of the septum pellucidum (an inconstant finding), and pituitary-hypothalamic dysfunction (hypopituitarism). Two of the three features must be present to fulfill the diagnostic criteria and only a minor portion of cases have all three features. The floor of third ventricle, a structure embryonically related to the development of the optic placodes, is abnormal in some cases. Olfactory aplasia is frequent. Other features include elevation of the tentorium cerebelli and lateral and transverse sinuses and torcula, lack of patency of the foramina of Magendie and Luschka, and hydrocephalus. Not all these features are present in every case. Although the septum pellucidum can be missing to suggest holoprosencephaly but their similarities stop there, the brain clearly splits normally into the left and right hemisphere.

	Click on this icon to see the frontal view.
	Click on this icon to see the occipital view. The seam is highlighted by the arrow.
	Click on this icon to see the submerged occipital view. The glial ependymal seam is highlighted by the arrow.
	Click on this icon to see the occipital view with a coronal cut. Note the continuation of gray matter across the midline and the lack of a septum pellucidum.