Collaterals

COLLATERALS, connections between systems of two different arteries or veins. Under normal conditions, small vessels-collaterals almost always exist, connecting areas supplied by different vessels. These collaterals acquire special significance in conditions of complete or partial obstruction of any arterial or venous trunk, since only through the resulting collateral circulation is it possible to maintain circulation in the corresponding part of the body. Collateral circulation occurs through pre-existing anastomoses of vessels in the same areas or through newly formed distant and often very complex bypass routes. In such cases, the primary collateral pathway is understood to be the system of vessels that immediately and directly participates in restoring the disrupted blood supply; subsequently, the collateral pathways that have taken over the restoration of circulation undergo a series of characteristic changes, such as: increase in vessel caliber (capillaries can give rise to arteries), thickening of walls, often considerable tortuosity of these vessels, especially veins (see Medusa head). As a result, so-called final collateral pathways are formed. A clear demonstration of collateral circulation is given by Magath and Mann {Magath, Mann) in liver extirpation. In the "inverted Eck fistula," i.e., after ligation of the inferior vena cava after suturing it to the portal vein, all blood from the lower extremities must pass through the liver. Due to the great resistance of liver capillaries, collateral circulation gradually formed through the developing system of v. azygos, after which the liver could be removed without disturbance to circulation. In clinical practice, cases of collateral circulation after thrombosis of v. iliacae or v. cavae inf. are described (of course, if the latter obstruction did not occur suddenly). Collateral circulation in these cases is carried out through vv. epigastricae, mammaria int. and intercostales, through which blood enters v. azygos and v. cava superior. Arterial collateral circulation forms just as easily in case of artery obstruction. Experiments have shown that as early as six days after ligation of art. femoralis, proliferation of small arteries begins in the area subjected to anemia (Nothnagel). Regarding the mechanism of collateral circulation, unity of views has not been achieved. Apparently, the matter by no means reduces to increased pressure in the central (from the site of ligation or obstruction) segment of the artery. Only vessels going to the area undergoing anemia proliferate, and by no means those vessels in which increased pressure prevails due to ligation of the main trunk. According to Baylies, increased pressure causes a reaction of vessel constriction, not dilation. The role of a nervous factor must be acknowledged, which many authors connect with the irritating effect of metabolic products in the area of anemia. This view has been defended for 30 years by Bier (Bier), who considers that capillaries in the area of anemia "suck blood toward themselves." This is evidenced by the reaction of physiological hyperemia after removing a tourniquet from a limb.

K. Kovradi. Collateral (Latin collateralis), a term used in pathology to denote phenomena and processes arising at the periphery of one or another pathological process and genetically connected with it. Thus, one speaks of collateral hyperemia or edema at the periphery of the main inflammatory focus, of collateral (non-specific) inflammation around some specific process, e.g., in tuberculous pneumonias. The volume of such collateral (syn. perifocal) processes can even be greater than the volume of the main process; their outcome differs from the latter by relative benignity, since previously existing relations are usually restored in their place. Collaterals, collateral (lateral, accessory), terms used in neuropathology in various senses to denote both anatomical formations and various pathological processes. In the anatomy of the nervous system, collaterals are called lateral branches extending from the main nerve trunk throughout its entire course (as opposed to terminal branches). Collaterals are observed on peripheral nerves-cranial, spinal, and vegetative-and in the central nervous system on all processes of the nerve cell (axonal, protoplasmic). Collaterals emerge from myelinated fibers at the level of Ranvier's nodes, and on unmyelinated fibers they can emerge everywhere. Collaterals in the peripheral system serve for anastomoses (see) with other nerves and for innervation of organs through which the main trunk passes (muscles, bones, tendons, vessels, etc.). Numerous anastomoses with neighboring nerves ensure the so-called collateral innervation of the corresponding tissue, thanks to which complete anesthesia does not occur when a nerve is severed, since the corresponding part of the cortex will receive a sensory impulse. This phenomenon is explained by the fact that when one nerve is severed, irritation is perceived by the peripheral part of a neighboring nerve and through anastomoses passes to the upper parts of the same nerve. In the central nervous system, collaterals serve to achieve synergistic activity of its different parts: different areas of the cerebral cortex with each other and with underlying formations-the brainstem, subcortical nodes, the trunk part of the brain, the spinal cord. Reflex collaterals close the reflex arc; thus, some branches of the posterior roots of the spinal cord end around cells of the anterior horns, conducting impulses from the sensory neuron to the motor neuron. The term "collateral" is used in diseases of the cerebral hemispheres to denote symptoms (collateral or accessory symptoms) that depend not on the localization of the process in one or another area, but on changes in blood or lymph circulation in the immediate vicinity of the focus; these symptoms are unstable and disappear as circulation is restored. Collateral hemiplegia-hemiplegia on the side opposite the focus-is observed in rare cases, mostly in tumors; a tumor of one hemisphere compresses or displaces the pyramidal pathways of the opposite hemisphere, thereby causing collateral or homolateral hemiplegia (observed in tumors of the cerebellopontine angle). Collateral synkinesias, or associated movements, are added to involuntary movements (see Synkinesias). E. Kononova.