|
|
Cerebellum 1. VASCULAR LESIONS - OCCLUSION OF THE SUPERIOR CEREBELLAR ARTERY A Sample Case: A 50 year old man had headache and vomiting. As he walked he staggered; his gait was broad-based and he drifted to the left. His mental status was normal but the cranial nerve exam showed a nystagmus to the left on attempted horizontal gaze to the left. All volitional eye movements were normal but the left pupil was smaller than the right though both responded normally to light. The left palpebral fissure was narrower than the right. Sensation on the face was normal as was the corneal reflex. The muscles of the lower face and the muscles of mastication were weaker on the right. He had intention tremor of the left arm and leg. Two-point discrimination on the body was normal but pain and temperature sensation was reduced from the right arm and legs. Explanation - The sudden onset of symptoms such as staggering gait suggests a vascular lesion. Though there is headache and vomiting, the patient's mental status suggests that the cerebral hemispheres are unaffected. The nystagmus upon gaze to the left suggests a lesion of the vestibular system or a left cerebellar involvement. The patient's left eyelid drooped and the pupil was constricted as in a Horner's syndrome where the descending autonomics (sympathetic innervation) are compromised. Weakness of the lower facial muscles and muscles of mastication on the right indicates impairment of the upper motor neurons on the left to the motor nuclei of the 5th and 7th cranial nerves. This helps localize the level of this lesion to above the mid-pons. The strength and deep tendon reflexes of both arms and legs were noted to be generally normal yet there was weakness of the left arm as indicated by pronator drift. The unsteady gait and ataxia on the left are signs of left cerebellar hemisphere disease or the superior cerebellar peduncle from the left. Diminished sensation on the right side of the body indicates involvement of the spinothalamic tracts on the left, located in the reticular formation near descending autonomic fibers. The signs of cerebellar ataxia might indicate of involvement of several vessels supplying the cerebellum. The superior cerebellar artery wraps around the cerebral peduncle of the midbrain arching backwards to the superior surface of the cerebellum. In its passage to the cerebellum it crosses over the superior cerebellar peduncle, which it supplies along with the lateral tegmentum of the upper pons, the site of the lesion, wherein lie the spinothalamic tracts, the descending autonomics and, presumably, the upper motor neurons to the facial and trigeminal motor nuclei .
|