A variety of structural lesions can cause parkinsonism. Siderowf et al. (93) argue that the first described case of PSP in a patient with progressive opthalmoparesis and postural instability, and structural lesion with a tumor in the right cerebral peduncle is not idiopathic PSP. Brainstem astrocytoma was reported to be the cause of unilateral parkinsonian symptoms; the symptoms resolved after resection of the tumor (94). A frontal meningioma can sometimes present with rest tremor without other signs of parkinsonism (95). Dopa-responsive parkinsonism has been reported resulting from a right temporal lobe hemorrhage (96). Intrinsic brainstem tumors can cause parkinsonism. Posterior fossa tumors present with pyramidal tract signs, cerebellar signs, and hydrocephalus in addition to parkinsonism. The parkinsonian symptoms predominantly are seen contralateral to the lesion. In some cases ipsilateral symptoms have also been reported. The parkinsonism associated with mass lesions of the infratentorial compartment is usually on the contralateral side with other cranial nerve lesions or sensory symptoms depending on the location of the lesion. MRI of the brain is usually diagnostic. Pathophysiologic mechanisms include mechanical compression or distortion of the rostral midbrain and substantia nigra, infiltration and destruction of substantia nigra, impairment of the nigrostriatal pathways, and a combination of these mechanisms (97).
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