Alobar holoprosencephaly

![Illustrations depicting the three subtypes of alobar holoprosencephaly, in crescent order of severity from the top to the bottom row. In the “ball” shape (first row), residual brain parenchyma (dotted circle) completely encircles the monoventricle. Note that a dorsal cyst is not present. In the “cup” shape (second row), an intermediate subtype, there is a partial cleavage (arrow) of the posterior convexity, the monoventricle is not entirely encircled, and there is a focal “dorsal cyst” (asterisk) posteriorly. Finally, in the most severe subtype, the “pancake” shape (third row), the remnant brain tissue (arrowhead) is flattened and located in the frontal region, compressed by a large dorsal cyst (star)

Gomez, G.D., Corrêa, D.G., Trapp, B. et al. Holoprosencephaly spectrum: an up-to-date overview of classification, genetics and neuroimaging. Jpn J Radiol 43, 13–31 (2025). https://doi.org/10.1007/s11604-024-01655-8](attachment:4dc298f4-5546-42c4-9ed2-3bf1d92cb234:image.png)

Illustrations depicting the three subtypes of alobar holoprosencephaly, in crescent order of severity from the top to the bottom row. In the “ball” shape (first row), residual brain parenchyma (dotted circle) completely encircles the monoventricle. Note that a dorsal cyst is not present. In the “cup” shape (second row), an intermediate subtype, there is a partial cleavage (arrow) of the posterior convexity, the monoventricle is not entirely encircled, and there is a focal “dorsal cyst” (asterisk) posteriorly. Finally, in the most severe subtype, the “pancake” shape (third row), the remnant brain tissue (arrowhead) is flattened and located in the frontal region, compressed by a large dorsal cyst (star)

![Alobar holoprosencephaly “cup” appearance. Axial CT image shows absence of interhemispheric fissure, cleavage failure of the frontal lobes, which remain fused through the midline (thick black arrows), and large holoventricle (asterisk), partially encircled by the remaining brain tissue, which morphology resembles a cup

Alobar holoprosencephaly “cup” appearance. Axial CT image shows absence of interhemispheric fissure, cleavage failure of the frontal lobes, which remain fused through the midline (thick black arrows), and large holoventricle (asterisk), partially encircled by the remaining brain tissue, which morphology resembles a cup

![Alobar holoprosencephaly “pancake” appearance. Illustration (a) and T1-weighted imaging in the sagittal plane (b) depict a residual flattened and anteriorly dislocated brain parenchyma (arrowheads), associated with a prominent dorsal cyst that continues with the holoventricle (star). Coronal T2-weighted image (c) shows cleavage failure of the most basal and anterior aspect of the remaining frontal lobes that are fused through the midline (thick white arrow). T2-weighted imaging in the coronal plane displays cleavage failure of the basal ganglia and thalami that remain fused through the midline (thin white arrows in d). Illustration (e) and axial T2-weighted images (f–h) show absence of the interhemispheric fissure, cleavage failure of the most anterior aspect of the remaining frontal lobes, that are fused through the midline (arrowhead in e and thick arrows in g and h), associated to a large dorsal cyst that communicates with the holoventricle (stars) and fused basal ganglia and thalami in the midline (thin arrow in f)

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Alobar holoprosencephaly “pancake” appearance. Illustration (a) and T1-weighted imaging in the sagittal plane (b) depict a residual flattened and anteriorly dislocated brain parenchyma (arrowheads), associated with a prominent dorsal cyst that continues with the holoventricle (star). Coronal T2-weighted image (c) shows cleavage failure of the most basal and anterior aspect of the remaining frontal lobes that are fused through the midline (thick white arrow). T2-weighted imaging in the coronal plane displays cleavage failure of the basal ganglia and thalami that remain fused through the midline (thin white arrows in d). Illustration (e) and axial T2-weighted images (f–h) show absence of the interhemispheric fissure, cleavage failure of the most anterior aspect of the remaining frontal lobes, that are fused through the midline (arrowhead in e and thick arrows in g and h), associated to a large dorsal cyst that communicates with the holoventricle (stars) and fused basal ganglia and thalami in the midline (thin arrow in f)