RESUMO
A 52-year-old man developed sudden occipital headache followed by vomiting and vertigo. On admission, he displayed right Horner syndrome with ipsilateral reduced facial sensation to pain and temperature that crossed in the body, affecting the left limbs. In addition, he had right hemiparesis. Diffusion weighted magnetic resonance images showed a high intensity lesion localized in the lower and right lateral medulla oblongata. Magnetic resonance angiography showed severe luminal stenosis in the right vertebral artery and T2-weighted sampling perfection with application optimized contrasts using different flip angle evolution (SPACE) showed arterial wall expansion. T1-weighted SPACE showed subacute intramural hematoma at that point, suggesting arterial dissection. First described in 1946, Opalski syndrome is considered a variant of Wallenberg syndrome with ipsilateral hemiparesis. This motor impairment is considered as a result of extension of the ischemia from the lateral medulla to the upper cervical cord involving corticospinal fibers caudal to pyramidal decussation. This case adds information regarding the anatomy of the pyramidal decussation.