Medulla
Lesions

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1) VASCULAR LESIONS - MEDIAL MEDULLARY SYNDROME (INFERIOR ALTERNATING HEMIPLEGIA)

A Sample Case: A 63 year old woman suddenly fell to the floor and was unable to rise. She found that her left arm and leg were paralyzed and her speech was "thick".

Neurologic examination some months later showed that she had a spastic paralysis of her left limbs with increased tone and exaggerated deep tendon reflexes. Motor examination of the face was normal, however upon protrusion, the tongue pointed toward her right side; the right side of her tongue was atrophic.

The sensory exam indicated that pain and temperature was bilaterally normal from the body and face but there was loss of proprioception from the left lower extremity. Examination of other cranial nerves was normal.

Explanation -

Spastic paralysis of the left arm and leg indicates injury to the corticospinal tract somewhere along its length. The additional tongue signs places the corticospinal lesion above the cord, in the medulla, on the right side. The tongue usually points to the side of a lesion of the nucleus or fibers of CN XII. Atrophy of its muscles confirms a lower motor neuron lesion of the fibers of CN XII on the right side.

Loss of proprioception from the left lower extremity is consistent with injury to the ventral-most fibers of the medial lemniscus on the right side. Absence of other sensory findings limit the area of involvement to the distribution of the penetrating branches of the vertebral or anterior spinal artery, which include the pyramids, exiting fibers of CN XII, and the medial lemniscus.