5

COMA

Coma in neonates is due to dysfunction of the arousing system. The arousing system has two components: the ascending reticular activating system (ARAS) and the cortex. The ARAS consists of a network of neurons that form a single midline column in the midbrain and upper half of the pons. This column divides into two smaller columns in the diencephalon (Figure 61.1). The ARAS receives information from multiple areas of the spinal cord, brainstem, and brain. The ARAS projects to the cerebral cortex. The cerebral cortex is located at the rim of the brain.

Figure 61.1.— The arousing system. A: brain; B: brainstem; C: pons; D: medulla; 1: cerebral cortex; 2: ascending reticular activating system efferent projection (curved arrows); 3: diencephalom; 4: ascending reticular activating system; 5: ascending reticular activating system afferent projection (straight arrows).

Coma may be produced by involvement of the ARAS, its projection, or the cerebral cortex. Coma due to ARAS involvement may occur with a small midline lesion in the central core of the midbrain or the upper half of the pons where the ARAS forms a single midline structure. Coma due to involvement of the smaller ARAS columns in the diencephalon, the ARAS projection fibers, or the cerebral cortex occur with extensive and diffuse bilateral diencephalic and brain hemispheric lesions.