The so-called “brain stem is small, but the nuclei are complete”, brain stem injury can present a variety of clinical symptoms and signs. Brainstem dysplasia is a rare disorder characterized by the absence or abnormal development of brainstem structures. They can be difficult to diagnose on MRI. Learn about syndromes caused by missing or dysplastic brainstem structures today.
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Möbius/Möbius Syndrome
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➤Causes:A rare congenital disorder characterized by the absence or hypoplasia of the abducens and facial nuclei . The brainstem is hypoplastic, with a flattened base of the fourth ventricle due to the absence of the facial colliculus (Figure 1).
➤Clinical manifestations: unilateral or bilateral Paralyzed on the side, the face is expressionless, and the mouth or eyes cannot be closed.
Fig.1 Möbius Syndrome) and sagittal (a, sagittal T2-weighted images show absence of abducens and facial nerves at the level of Merkel’s cavity.
Axonal Guidance Disorders
➤Cause: abnormal white matter Fiber bundles, usually not passing through the midline, or ectopic fiber bundles present. It is easier to identify in diffusion tensor imaging (DTI) and tractography. (Figure 2)
➤Clinical manifestations: Horizontal gaze palsy and progressive scoliosis, Joubert syndrome, and pontine tegmental dysplasia.
Figure 2 Horizontal gaze palsy and scoliosis. (a) DTI shows absence of chiasm in the upper cerebellum and absence of chiasm of somatosensory and corticospinal tracts. (be) Axial T2-weighted (b, d), axial inversion-recovery (c), and sagittal T1-weighted (e) images show a reduced pons with facial colliculus and medulla oblongata with midline cleft missing. (f) Radiograph showing lumbar scoliosis.
Multiple System Atrophy (MSA)
➤Causes:Multiple System Atrophy (MSA) is A sporadic neurodegenerative disorder with cerebellar symptoms predominant with olivopontocerebellar atrophy in MSA-C type. MRI showed T2 hyperintensity in the pontocerebellar tract, resulting in a “hot cross bun” sign in the pons and excessive atrophy of the cerebellum and brainstem (Figure 3).
➤Clinical manifestations: with varying degrees of cerebellar ataxia, autonomic Dysfunction, Parkinson’s disease, and corticospinal dysfunction.
Figure 3 MSA-C. (a) Sagittal T-weighted image of cerebellum. (b) Axial T2-weighted image shows cruciform hyperintensity in the pons (hot cross sign), representing selective degeneration of the pontocerebellar tract.
Wernicke Encephalopathy span>
➤Causes:thiamine (vitamin B1 ) deficiency, usually seen in cases of alcoholism. MRI showed symmetrically enhanced areas of T2/FLAIR signal intensity, including the mammillary body, dorsomedial thalamus, tectum, periaqueductal area, and peri-third ventricle (Figure 4).
➤Clinical manifestations:Altered consciousness, ataxia, and ocular dysfunction.
Fig.4 Axial FLAIR images showing the dorsal medial thalamus (axial FLAIR image) Signal enhancement in the periaqueductal area (b) and tectum (c), typical of Wernicke’s encephalopathy.
Osmotic demyelination syndrome Demyelination Syndrome)
➤Causes:This is an acute demyelination caused by altered permeability, usually following rapid correction of hyponatremia.
➤Imaging features: MRI showing pons , basal ganglia, midbrain, subcortical white matter showed symmetrical abnormal signal intensity, T1-weighted image showed low signal, T2-weighted/FLAIR image showed high signal. Diffusion restriction is usually the earliest symptom, presenting in the lower pons within 24 hours of the onset of quadriplegia. Enhancement with gadolinium contrast is usually absent.
Progressive Supranuclear Palsy Palsy)
➤Clinical manifestations:This This neurodegenerative disease usually appears after age 60 and progresses to death within 10-20 years. It is characterized by Parkinsonism, supranuclear vertical gaze palsy, cognitive and language decline, instability and falls.
➤Imaging features: Atrophy of the midbrain, resulting in loss of brainstem convexity , the hummingbird sign appeared in the sagittal plane. Decreased midbrain interlobar diameter at the level of the superior colliculus may give a “Mickey Mouse” appearance (Mickey Mouse sign) in the axial plane. T2 lesions can be seen in the pontine tegmentum, midbrain tectum, and inferior olivary nucleus.
Yimaitong compiled from: Sciacca S, Lynch J, Davagnanam I, Barker R. Midbrain, Pons, and Medulla: Anatomy and Syndromes. Radiographics. 2019 Jul-Aug;39(4):1110-1125. doi: 10.1148/rg.2019180126. PMID: 31283463.