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FOCAL CENTRAL NERVOUS SYSTEM LESIONS

Magnetic resonance imaging (MRI) usually confirms the location of the lesion (anatomical diagnosis) and often substantiates the tentative pathological diagnosis. The most frequent focal pathological processes in the central nervous system are vascular accidents, tumors, malformations, and infections. Vascular accidents include infarcts and hemorrhages, porencephalic cysts, and schizoencephaly. Tumors include neoplasms and aneurysms. Malformations include encephalocele and myelomeningocele. Infections include congenital or acquired, viral or bacterial processes.

CENTRAL NERVOUS SYSTEM INFARCTS

Central nervous system infarcts may occur in the brain, brainstem, cerebellum, or spinal cord. They may involve the arterial or the venous systems. Infarcts may be ischemic or hemorrhagic. Arterial infarcts are produced by hypoperfusion, embolic or thrombotic phenomena, or by vasospasm. Venous infarcts are usually thrombotic in nature.
A CNS infarct should be suspected in a neonates with predisposing conditions (prematurity, hypercoagulation states, polycythemia, dehydration, hypotension, extracorporeal circulation, or in neonates whose mother had hypertension or used cocaine during pregnancy) and suggestive clinical findings
such as clinical paroxysmal events, apnea, coma, facial weakness, or decreased limb movements (monoparesis, hemiparesis, paraparesis, upper extremity diplegia, and quadriparesis).
When a CNS infarct is suspected, B-mode ultrasonogrpahy, MRI, MRA, or CT with and without contrast of the appropriate region should be performed as soon as possible after the onset of the clinical manifestations (Figure 244.1).

A
B
C

Figure 244.1. [A] MRI of the brain demonstrating a large infarct in the distribution of the left middle cerebral artery; [B] B-mode ultrasonography demonstrating a thrombus at the origin of the internal carotid artery; [C] MRA of the brain demonstrating a narrow internal carotid artery and absence of the middle cerebral artery.

Nevertheless, a normal MRI or CT within the first 24 hours after the onset of clinical manifestations does not eliminate the possibility of an ischemic infarct because ischemic central nervous system parenchymal changes may not be detected by these studies during this period. Diffusion-weighted imaging may reveal ischemic CNS parenchymal changes earlier than other MRI modalities.Hemorrhagic infarcts are usually detected within the first 24 hours after the onset of symptoms by any of the above mentioned modalities. Computed tomography shows blood better than MRI in the first 24 hours after an event. Magnetic resonance arteriogram may demonstrate the flow abnormality earlier than MRI or CT in ischemic infarcts. B-mode ultrasonography should be used to diagnose arterial infarcts if transportation to the MRI area is not possible. B-mode ultrasonography is very useful in premature neonates with periventricular leukomalacia. The studies of choice to diagnose arterial infarcts are MRI and MRA of the appropriate area.
The next step after the diagnosis of a CNS infarct is diagnosed is to find the cause. The cause of the infarct should be sought in all patients except premature neonates with periventricular infarcts. The search for the cause of the infarct should start with a review of the history of the present illness and the family history, followed by a carefully performed physical examination searching for clues that might suggest the cause of the infarct. If a clue is present, the tests should be guided by it. If there are no clues, an extensive evaluation is necessary. The evaluation includes: complete blood cell count with differential and platelets, prothrombin time (PT), partial thromboplastin time (PTT), fibrinolytic proteins, antithrombin III, erythrocyte sedimentation rate, antiphospholipid antibodies, amino and organic acids in serum and urine, proteins S and C, urine analysis, urine for drug screening, and ultrasonographic evaluation of the heart and carotid arteries. Evaluation of the placenta may be helpful in patients with arterial infarcts. Lumbar puncture should be performed if the possibility of a CNS infectious process is suspected. Magnetic resonance angiogram of the brain and neck should be performed to visualize the vascular tree in all patients with cerebral infarct.
Arterial and venous CNS ischemic or hemorrhagic infarcts do not have specific treatment. If the primary disorder is found, treatment is indicated. Supportive treatment consists of maintaining systemic blood pressure, oxygenation, and glycemia within normal limits.

 

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area of left cerebral artery right middle cerebral artery anterior cerebral artery thrombus internal carotid artery common carotid artery left middle cerebral artery infarct Barkovich., 1995 Click on figure for animated labels.  Pause pointer on different areas of the figure for labels. Figure must be centered. Krishnamoorthy, 2000 Alffonso, In Press middle cerebral artery infarct thalamus lenticular nucleus caudate nucleus thrombus narrow internal carotid artery external carotid artery common carotid artery middle cerebral artery