Kinking of the brainstem is a rare finding in fetal or pediatric neuroimaging, invariably seen in association with other cerebral abnormalities. It generally heralds a poor neurological outcome.
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Clinical presentation
A kinked brainstem may be seen on fetal MRI, commonly after referral from ultrasound with ventriculomegaly +/- other intracranial abnormalities.
Alternatively, it may be detected on MRI of a neonate presenting with a poor neurologic state, hypotonia, seizures, abnormal visual examination or abnormality of head size (micro or macrocephaly).
Etiology
A kinked brainstem has been reported in association with:
a-dystroglycanopathies (including Walker-Warburg syndrome, muscle-eye-brain disease)
tubulinopathy (TUBA1A mutation)
X-linked hydrocephalus (L1CAM mutation)
Radiographic Features
Kinking of the brainstem refers to an exaggerated flexure at the pontomesencephalic junction.
There is a wide range of associated findings. Cerebellar hypogenesis is almost always seen. Other findings include:
- ventriculomegaly
- dysgenesis of the corpus callosum
- delayed cortical development
- disorders of neuronal migration (e.g. lissencephaly)
- Dandy-Walker malformation
- vertex encephalocele
- abnormality of the globes
- abnormality of head size (microcephaly or macrocephaly)
Practical Points
When a kinked brainstem is detected with ventriculomegaly on prenatal MRI, an attempt should be made to distinguish between the three possible causes, to direct genetic testing and counseling.
- L1CAM mutation suggested with
- male fetus
- non-visualization of cerebral acqueduct high T2 signal (though this should be interpreted cautiously, as small fetal size and motion may produce a false positive finding)
- spasticity and adduction of thumbs (best seen on ultrasound dynamically)
- NO abnormality of globes or ganglionic eminences
- dystroglycanopathy
- cobblestone lissencephaly suggests Walker-Warburg syndrome (often difficult to detect in the fetus due to stretching of brain parenchyma by ventriculomegaly)
- enlarged ganglionic eminences
- encephalocele not diagnostic but suggestive
- ocular abnormalities (persistent hyperplastic primary vitreous (PHPV), microphthalmia, buphthalmos, retinal detachment) strongly suggestive, though may not be visible prenatally
- tubulinopathy
- enlarged ganglionic eminences