1. Considering the patient’s history and physical examination, how precisely can the neurologic lesion be localized in this case?
Not very precisely (see below and see slide #1)
2. Indicate the structures involved by the pathologic process to produce this patient’s right upper limb weakness. If precise localization is not possible, list as many levels or structures as you can that might produce the same clinical picture.
Left corticospinal tract, involving fibers to the right upper limb only, from its origin in the precentral gyrus (plus premotor area and supplementary motor area possibly) down to the pyramidal decussation in the lower medulla; or right lateral corticospinal tract in the cervical spinal cord above the C5 level.
3. Indicate the structures involved by the pathologic process to produce this patient’s right upper limb findings on cerebellar examination. If precise localization is not possible, list as many levels or structures as you can that might produce the same clinical picture.
Right cerebellar hemisphere, right superior cerebellar peduncle (SCP) below (or left SCP above) the inferior midbrain, left VL nucleus of the thalamus, left thalamocortical radiations, left precentral gyrus or premotor area, left frontopontine tracts, left pontine nuclei in the basilar part of the pons
4. Discuss the “localization of the lesion” in this case.
It is difficult to localize the lesion in this case and in this syndrome. Basically, this syndrome can be caused by a fairly discrete lesion at any location where the corticospinal fibers and the neocerebellar (cortico-ponto-cerebellar) pathways lie in close approximation. The usual lesions (in a case such as this) would be in the left base of the pons, left cerebral peduncle involving the pyramidal tract in the crus cerebri and the superior cerebellar peduncle (SCP) after its decussation, and the left posterior limb of the internal capsule involving the pyramidal tract and the thalamocortical radiations and/or the frontopontine fibers.
5. The findings in this case represent a partial example of a classic neurologic syndrome. What is the name of that syndrome, and what is its usual cause?
Ataxic hemiparesis (ataxic monoparesis, in this case).
Lacunar infarct (variable locations, as above)
6. In general, what type of pathologic process do you think is involved in this case?
Vascular – Lacunar infarct is most common. Here the lesion was a small infarct involving the “upper limb region” of the left precentral gyrus, which interrupted both the origin of the corticospinal fibers of the pyramidal tract and the frontopontine tract of the neocerebellar (cortico-ponto-cerebellar) pathways (review the “motor homunculus” on the primary motor cortex [area 4]).
7. What diagnostic procedure(s) would you undertake at this point?
References:
1. Fisher CM, Cole M. J Neurol Neurosurg Psychiatry 1965;28:48-55.
2. Koppel BS, Weinberger G. Eur Neurol 1987;26:211-215.
3. Nabatame H, Fukuyama H, Akiguchi I, et al. Ann Neurol 1987;21:204-207.
4. Helweg-Larsen S, Larsson H, Henriksen O, Sorensen PS. Neurology 1988;38:1322-1324
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