Where is the lesion located in a patient with right upper limb incoordination and bilateral lower limb dyslexia?

Lesion Location in Right Upper Limb Incoordination with Bilateral Lower Limb Dyslexia

The lesion is most likely located in the cerebellum and/or brainstem, specifically in the infratentorial region, based on the combination of upper limb incoordination and bilateral lower limb symptoms.

Neuroanatomical Considerations

Upper Limb Incoordination

• Right upper limb incoordination (dysmetria) suggests a lesion in the cerebellum or its pathways, particularly involving the cerebellar hemispheres or the intermediate zone of the cerebellum 1
• The intermediate zone of the cerebellum is particularly important for multi-joint limb control in both goal-directed movements and locomotion 1
• Lesions affecting the interposed and adjacent dentate nuclei are frequently associated with impaired limb placement and coordination 1

Bilateral Lower Limb Symptoms

• Bilateral lower limb involvement suggests a midline lesion affecting both sides of the cerebellum or brainstem pathways 2
• Infratentorial lesions, particularly those in the brainstem and cerebellar peduncles, can cause bilateral symptoms 2
• Truncal ataxia and bilateral lower limb symptoms often indicate involvement of the midline cerebellum 2

Specific Lesion Locations to Consider

Cerebellar Lesions

• Lesions in the superior cerebellum and brachium conjunctivum typically present with limb dysmetria and overshoot 3
• Lesions involving the inferior cerebellum often cause patients to topple, lean, or veer when attempting to sit, stand, or walk 3
• Cerebellar lesions are typically hyperintense on T2-weighted MRI sequences and may occur along the entire spinal cord, though the cervical portion is more frequently involved 2

Brainstem Lesions

• Pontine lesions often present with ataxia accompanied by weakness and pyramidal tract signs as part of an ataxic hemiparesis syndrome 3
• In the pons, most multiple sclerosis lesions are contiguous with the cisterns or involve the floor of the fourth ventricle, often affecting the medial longitudinal fasciculus 2
• Medullary lesions, particularly those with a uni- or bilateral paramedian location, can cause ataxia 2

Spinal Cord Lesions

• Cervical spinal cord injury can cause upper limb dysmetria, mimicking cerebellar dysfunction 4
• Spinal cord lesions are typically multiple and short in cranio-caudal diameter, hyperintense on T2-weighted sequences 2
• To be considered diagnostic, spinal cord lesions should be focal with clearly demarcated borders, cigar-shaped on sagittal images, and wedge-shaped on axial images 2

Differential Diagnosis Based on Imaging Features

Multiple Sclerosis

• MS lesions typically develop in both hemispheres but can be asymmetric in early stages 2
• MS lesions tend to affect specific white matter regions, including infratentorial areas (especially pons and cerebellum) and spinal cord (preferentially cervical segment) 2
• Infratentorial MS lesions commonly occur near the surface, or when more centrally, usually have an ovoid/round shape 2

Other Conditions to Consider

• Cavernous malformations of the brainstem can present with similar symptoms 5
• Neurobrucellosis can cause lesions in the brainstem, spinal cord, and nerve roots 6
• Thalamic lesions can cause gait instability and ataxia, sometimes with hemisensory symptoms 3

Imaging Recommendations

MRI Brain and Spine

• MRI is the preferred imaging modality for evaluating ataxia unrelated to trauma 2
• Brain MRI should include T2-weighted, T2-FLAIR, and T1-weighted sequences to evaluate for infratentorial lesions 2
• Spinal cord MRI, particularly of the cervical region, is essential to evaluate for lesions that may cause upper limb symptoms 2
• Use of intravenous contrast is generally helpful in distinguishing active lesions 2

Advanced Imaging Techniques

• Diffusion tensor imaging (DTI) may detect intramedullary lesions that are not apparent on conventional sequences in early stages 2
• Double inversion recovery (DIR) and phase-sensitive inversion recovery (PSIR) sequences can improve detection of cortical and juxtacortical lesions 2

Clinical Pearls and Pitfalls

• Ataxia with hemiparesis can result from a cerebral infarct involving the thalamus, pons, corona radiata, or internal capsule 2
• Lesions in the spinal cord can cause cerebellar signs such as dysmetria, even though they are not in the cerebellum itself 4
• When evaluating infratentorial lesions, it's important to distinguish MS lesions from other conditions like anti-MOG-IgG disease and progressive multifocal leukoencephalopathy 2
• Careful attention to lesion morphology is essential - MS lesions often have an ovoid/round shape, while linear plate-like hyperintensities may indicate other conditions 2