Pathology of the Neurons

The reactions of neurons to disease manifest in alterations in the size, shape, and staining properties of the

FIGURE 2.2

Neuronal alterations. A. Vacuolated swollen motor neuron in medulla. B. Chronic atrophy of pyramidal neuron: The perikaryon is shrunken, the dendrites are corkscrew-like, and the nucleus is densely basophilic. C. Axonal or retrograde changes in hypo-glossal neuron caused by tumorous infiltration of the nerve roots. The swollen perikaryon is rounded, the dendrites are retracted, the Nissl bodies are partially dissolved, and remaining ones are clustered around the peripherally displaced nucleus (hematoxy-lin-eosin [HE] stain). D. Ischemic Purkinje cells in the cerebellar cortex showing eosinophilic shrunken perikaryons and homogenous basophilic nuclei (HE). E. Spinal motor storage neuron in Tay-Sachs disease; the cytoplasm is markedly distended and the nucleus displaced to the periphery (LFB-CV).

perikaryon and nucleus, and in reduction or loss of the Nissl bodies and dendrites. Some alterations are nonspecific, whereas others characterize particular diseases (Figs. 2.2 and 2.3; Table 2.2).

Acute Changes

Swelling, vacuolation of the perikaryon, dissolution of the Nissl bodies (chromatolysis), and shrinkage of the nucleus appear in a variety of acute infectious, toxic, vascular, and metabolic diseases.

Chronic Changes

Atrophic neurons with shrunken cell bodies, corkscrewlike dendrites, and shrunken and intensely basophilic nuclei are common in degenerative diseases.

Lipofuscin accumulation consists of small golden brown pigments that are deposited in the perikaryon of the neurons during normal aging.

Specific Neuronal Changes

Axonal or Retrograde Neuronal Changes Axonal changes develop in response to a transection of their axon. The cytoplasm swells and becomes rounded with retracted dendrites. The Nissl bodies partially dissolve and some of the remaining Nissl bodies surround the eccentrically displaced nucleus.

Hypoxic-Ischemic Changes (Red Neurons) The shrunken perikaryon, partially or totally devoid of Nissl bodies, stains brightly red with eosin, and the pyknotic triangular- shaped nucleus stains uniformly blue with hematoxylin.

Ferrugination of the Neurons

Ferrugination in chronic ischemic-hypoxic lesions results from the deposition (incrustation) of basophilic calcium and iron granules on the dendrites and cytoplasm of dead neurons.

Neuron Achromasia

FIGURE 2.3

Neuronal inclusions. A. Neurofibrillary tangles in Alzheimer's disease (Gallyas silver stain), showing (B) positive immunostain-ing for tau protein, (C) Pick bodies in pyramidal neurons of hippocampus (Bodian silver stain), (D) Lewy body in substantia nigra in Parkinson's disease (HE), and (E) Hirano body in pyramidal neuron of hippocampus (HE).

FIGURE 2.3

Neuronal inclusions. A. Neurofibrillary tangles in Alzheimer's disease (Gallyas silver stain), showing (B) positive immunostain-ing for tau protein, (C) Pick bodies in pyramidal neurons of hippocampus (Bodian silver stain), (D) Lewy body in substantia nigra in Parkinson's disease (HE), and (E) Hirano body in pyramidal neuron of hippocampus (HE).

TABLE 2.2.

Pathology of Neurons

Acute swelling, chromatolysis Chronic atrophy Axonal/retrograde reaction Hypoxic-ischemic changes Ferrugination

Distension in storage diseases Ballooned achromasia Granulovacuolar degeneration Inclusion bodies Degenerative Viral

Neoplastic transformation

Distended Storage Neurons

Distended storage neurons in neurometabolic diseases are markedly swollen and pear-shaped, with the nucleus and the Nissl bodies displaced toward the apical den-drite. Histochemical stains reveal the composition of the substances stored within the perikaryon.

Ballooned Achromatic Neurons

Ballooned neurons seen in corticobasal dementia display enlarged palely stained perikaryon, a lack of Nissl bodies, and argyrophilic fibrillary structures.

Granulo-Vacuolar Degeneration

This degenerative change manifests small basophilic granules within vacuoles in the pyramidal neurons of the hippocampus. It is found both in Alzheimer's disease and normal aging.

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