Snell's Clinical Neuroanatomy


Answers and Explanations to Clinical Problem Solving

2. Two physicians are talking in the street when one turns to the other and says, “Look at that man over there. Look at the way he is walking. He is not swing ing his right arm at all; it is just hanging down by his side. I wonder if he has a cerebellar lesion.” Does a person with a unilateral cerebellar hemisphere tumor tend to hold the arm limply at the side when he walks? 3. A 37-year-old male visits his physician because he has noticed clumsiness of his right arm. The symptoms started 6 months previously and are getting worse. He also notices that his right hand has a tremor when he attempts to insert a key in a lock. When he walks, he notices that now and again he tends to reel over to the right, “as if he had too much alcohol.” On physi cal examination, the face is tilted slightly to the left, and the right shoulder is held lower than the left. Passive movements of the arms and legs reveal hypo tonia and looseness on the right side. When asked to walk heel to toe along a straight line on the floor, he sways over to the right side. When he was asked to touch his nose with his right index finger, the right hand displays tremor, and the finger tends to over shoot the target. Speech is normal, and nystagmus is not present. Using your knowledge of neuroanatomy, explain each sign and symptom. Is the lesion of the cerebellum likely to be in the midline or to one side? 1. This patient had the symptoms and signs of Friedreich ataxia, an inherited degenerative disease of the cerebellum and posterior and lateral parts of the spinal cord. Degeneration of the cerebellum was revealed by the altered gait, clumsy movements of the right arm, tendency to fall to the right, intention tremor of the right arm and leg, hypotonicity of the right arm and right leg, and nystagmus of both eyes. Involvement of the fasciculus gracilis was evi denced by loss of vibratory sense, loss of two-point discrimination, and loss of muscle joint sense of the lower limbs. Corticospinal tract degeneration resulted in weak ness of the legs and the presence of the Babinski plantar response. The exaggerated knee jerk reflexes were due to the involvement of the upper motor neu rons other than the corticospinal tract. Loss of the ankle jerk reflexes was due to the interruption of the reflex arcs at spinal levels S1–S2 by the degenerative process. The clubfoot and scoliosis can be attributed to altered tone of the muscles of the leg and trunk over a period of many years. 2. Yes. A person who has a unilateral lesion involving one cerebellar hemisphere demonstrates absence of coordination between different groups of muscles on the same side of the body. This disturbance affects not only agonists and antagonists in a single joint movement but also all associated muscle activity.

4. A 4½-year-old male is taken to a neurologist because his mother is concerned about his attacks of vomit ing on waking in the morning and his tendency to be unsteady on standing up. The mother also notices that the child walks with an unsteady gait and often falls backward. On physical examination, the child tends to stand with the legs well apart—that is, broad based. The head is larger than normal for his age, and the suture lines of the skull can be easily felt. A retinal examination with an ophthalmoscope shows severe papilledema in both eyes. The muscles of the upper and lower limbs show some degree of hypotonia. Nystagmus is not present, and the child showed no tendency to fall to one side or the other when asked to walk. Using your knowledge of neuroanatomy, explain the symptoms and signs. Is the lesion in the cerebellum likely to be in the midline or to one side? 5. During a ward round, a third-year student is asked to explain the phenomenon of nystagmus. How would you have answered that question? Why do patients with cerebellar disease exhibit nystagmus? 6. What is the essential difference between the symp toms and signs of acute and chronic lesions of the cerebellum? Explain these differences. 3. This man, at operation, was found to have an astro cytoma of the right cerebellar hemisphere, which explains the unilateral symptoms and signs. The lesion was on the right side, and the clumsiness, tremor, muscle incoordination, and hypotonia occurred on the right side of the body. The pro gressive worsening of the clinical condition could be explained by the progressive cerebellar destruc tion as the tumor rapidly expanded. The flaccidity of the muscles of the right arm and leg was due to hypotonia, that is, a removal of the influence of the cerebellum on the simple stretch reflex involving the muscle spindles and tendon organs. The clum siness, tremor, and overshooting on the finger-nose test were caused by the lack of cerebellar influence on the process of coordination between different groups of muscles. The falling to the right side, tilt ing of the head, and drooping of the right shoulder were due to loss of muscle tone and fatigue. 4. The diagnosis was medulloblastoma of the brain in the region of the roof of the fourth ventricle, with involvement of the vermis of the cerebellum. The child died 9 months later after extensive deep x-ray therapy. The sudden onset of vomiting, the increased size of the head beyond normal limits, the sutural separation, and the severe bilateral papilledema could all be accounted for by the For example, a person walking normally swings their arms at both sides; with cerebellar disease, this activity would be lost on the side of the lesion.

Answers and Explanations to Clinical Problem Solving

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