Presentation
Acute-onset syncope associated with headache and vomiting.
Patient Data
Axial T2 MRI shows parallel orientation and separation of frontal horns with separation and enlargement of occipital horns of the lateral ventricles (colpocephaly).
Sagittal T2 MRI shows a small distorted genu with a prominent anterior commissure. The body, rostrum, and splenium of the corpus callosum are not visualized (partial agenesis of the corpus callosum).
"Racing car sign” noted on axial imaging: frontal horns, body, and occipital horns of the lateral ventricles bear resemblance to a racing car. Seen with colpocephaly and partial or complete agenesis of the corpus callosum.
"Moose head appearance" or "Viking helmet sign" noted on coronal T2 MRI: near-parallel orientation of the frontal horns and eversion of cingulate gyri into the frontal horns bilaterally. Seen due to partial agenesis of the corpus callosum.
Case Discussion
Colpocephaly is a congenital brain malformation that is typically diagnosed during childhood due to severe symptoms such as seizures and developmental abnormalities. It is rare to be diagnosed as an adult and the diagnosis is usually incidental in adults 1-3.
It is most commonly associated with partial or complete agenesis of the corpus callosum. Other associated malformations include microcephaly, schizencephaly, lissencephaly and Chiari malformation 1,3.
Patients usually present with non-specific symptoms such as headaches, dizziness, seizures, vertigo, nausea and gait instability 1-5.
Colpocephaly is characterized by imaging findings such as parallel orientation and separation of frontal horns with separation and enlargement of occipital horns of the lateral ventricles. Apart from that, posterior-to-anterior ratio (P/A ratio) is often used to diagnose colpocephaly. It refers to the ratio of the maximal width of the occipital horn and the maximal width of the anterior horn of the lateral ventricle 6. A P/A ratio greater than or equal to 3 represents disproportionate dilation of the occipital horns, making colpocephaly more likely 5,6. The P/A ratio is known to have low sensitivity and high specificity in diagnosing colpocephaly 3.
The most significant differential diagnosis of colpocephaly is normal pressure hydrocephalus (NPH) 3,5,7. Clinically, NPH is associated with specific symptoms (such as the triad of dementia, gait abnormalities, and urinary incontinence). The P/A ratio has been reported to be highly specific for diagnosing colpocephaly in cases where the main differential was NPH 5. Other than that, the following markers on imaging can be used to diagnose NPH:
Evans index: ratio of maximum width of the frontal horns of the lateral ventricles and the maximum internal diameter of the skull at the same level; a ratio >0.30 indicates ventriculomegaly 5
callosal angle: angle between medial superior borders of the left and right ventricle through the posterior commissure, perpendicular to the anterior-posterior commissure on coronal images; an acute angle can indicate idiopathic NPH 5
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