At the middle of the inner borders of the kidneys are situated the hiluses into which enter veins, arteries, ureters, nerves, and lymphatics, united by connective tissue and forming a sort of pedicle.
The normal weight of each kidney is to be expressed by a rough average as from four and a quarter avoirdupois ounces, or one hundred and twenty grammes, on the one hand, to seven ounces, or two hundred grammes, on the other; but since a deficiency in the size of one is not unfrequently compensated by an increase in the other, it would be safer to give the weight of the pair as from two hundred and forty to four hundred grammes, the lesser number representing those organs which are not only small but anæmic, and the larger those which are either distinctly hypertrophied or much congested: many diseased kidneys will also be found within these limits.
The size of the kidney is in a general way proportioned to the size of the body: the proportion is stated as 1 to about 240. A disproportionate change in the size of both kidneys without any change in structure is a true hypertrophy, and may be met with in persons whose habits as regards the ingestion of fluids (especially such as are freely secreted by the kidneys—for instance, beer or other forms of dilute alcohol) tend toward excess, or where a disease like diabetes throws a large amount of diuretic material into the circulation.
The deep position of the kidneys makes them usually inaccessible to physical exploration to any practical extent. In stout persons they are so entirely covered by their own immediate envelope of fat, by the adipose tissue of the mesentery, and by the thick abdominal walls as to be completely indistinguishable. In thinner persons deep palpation with both hands may enable us to say that there is a diminished resistance to pressure, as in the case of movable kidney, or that there is or is not any decided enlargement. Slighter changes in size cannot be accurately determined, although Bartels1 states that he was once enabled to detect a considerable enlargement in a case of parenchymatous nephritis by double palpation. In moderately thin persons the lower end of the kidney can be more or less distinctly felt.
1 Ziemssen, vol. xv.
A position upon the hands and knees (not the gynecological semi-prone position), allowing the whole abdomen to gravitate directly away from the backbone, is said to afford, by the varying concavity of the lumbar region on the two sides, information as to the absence of either kidney from its usual place. When the kidney, however, is displaced, and when it comes decidedly forward from increase in its own size or from the pressure of a tumor behind it, it may very often become extremely accessible.
Percussion gives even less information than palpation, since the dulness of the lumbar muscles extends laterally beyond that of the kidneys, and is of itself so complete as to offer no change from the addition or subtraction of the resistance of the underlying organ.2
2 It is probable that Simon's method of thrusting the hand into the rectum and large intestine might be made available by a person with a small hand and arm for diagnosis in doubtful cases where the value of the information to be obtained would be sufficient to compensate for the risk of serious injury.
The removal of the kidneys may be accomplished through the rectum—and has been effected many times by myself and assistants—in cases where a complete autopsy is refused. The manoeuvre is not very difficult through a large and especially a female pelvis, but under other circumstances may be somewhat fatiguing. Considerable post-mortem information in regard to other organs may be obtained in the same way.
The most marked anomaly in the shape of the kidneys when both are present, and the only one which possesses a clinical interest, is that known as the horseshoe kidney, being a more or less complete fusion of the organs of each side in front of the vertebral column and the great vessels. This fusion is usually at the lower end, but may be in the middle or at the upper end. Sometimes there is a portion lying directly in front of the vertebral column so large and thick as to appear almost like a middle lobe or a third kidney. In a few rare instances this portion has formed a pulsating enlargement mistaken for an aortic aneurism or other abdominal tumor. In others compression of the great vessels has given rise to phlebitis, or the abnormal position of the ureters has obstructed the passage of the urine, with the results, as regards the secondary affection of the kidneys, to be described below. These instances are, however, among the curiosities of medicine, and no rule for their diagnosis can be laid down. A horseshoe kidney is usually discovered only after death, and with no special frequency in cases of renal disease.