The most frequent variety of prostatic enlargement is that in which, with or without enlargement of the lateral lobes, posterior median hypertrophy exists forming the so-called middle lobe. This form of hypertrophy is also the most important because of the fact that a comparatively slight overgrowth in this situation produces an amount of mechanical obstruction and irritation of the vesical neck which is greatly disproportionate to the degree of the enlargement. The form of median hypertrophy varies considerably. In some cases a distinct fibro-adenomatous overgrowth of pedunculated form is met with. This, as already suggested, is likely to have a valve like action producing intermittence of the stream of urine during micturition, with perhaps more or less spasmodic action of the part about the neck of the bladder which is strongly suggestive of vesical calculus. Cases presenting this form of hypertrophy are, other things being equal, quite amenable to surgical interference, inas much as the necessary operation is very simple, and if it be performed at an early period before the kidneys are extensively diseased, the result is likely to be excellent. Whether pedunculated or not, the overgrowth in posterior median hypertrophy projects backward and upward, producing serious mechanical disturbances at the neck of the bladder.
Some theorizing has been clone upon the causes of the transforma tion of posterior median overgrowths into polypoicl tumors. It has been asserted that the mechanical squeezing to which the part is sub jected during frequent, painful, and more or less spasmodic efforts at micturition is responsible for the jutting out and eventual peduncula tion of the growth. It seems reasonable to suppose that in certain instances such an explanation is logical, especially where the point of departure of hypertrophy is thoioughly circumscribed in the posterior median portion of the organ.
The term median lobe is an unfortunate one, as it is apt to lead to the supposition that a third or middle lobe exists in the normal pros tate, when, as a matter of fact, the projecting growth is invariably a pathological formation, being due primarily in all probability to a peculiar circumscribed hyperplasia of that portion of the organ con stituting the posterior portion of the floor of the prostatic urethra. This portion of the organ is quite important in its relations to the sexual function, and it is possible that the frequent limitation of prostatic hypertrophy to this region is a point in evidence of the causal relation of aberrations of sexual physiology to the disease. In a general way, whatever the form of hypertrophy may be, it pro duces its most serious effects by mechanically obstructing the outflow of urine. Marked secondary changes in the floor of the bladder are chiefly dependent upon this mechanical obstruction. The pouching of the vesical walls in the vicinity of the trigone, known as the bas fond or lower bottom, depends for its formation chiefly upon the intravesi cal pressure incidental to mechanical obstruction of the vesical neck.
As classified by Thompson, there are four varieties of hypertrophy according to the relative degree of involvement of the several struc tures of which the prostate is composed, viz. : (1) Simple increase in the development of all the component tissues of the organ in about equal ratio. (2) Excess of development of the stromatous and fibrous
structures—i.e., pale muscular fibre, connective tissue and elastic tis sue—over the glandular portion. (3) Excess of development in the glandular portion—i.e., basement membrane, follicles, excretory ducts, and epithethun—over the stromatous. (4) Rearrangement of the structures, stromatous and glandular, in the form of a tumor—cir cumscribed or localized development. Of these varieties the second or stromatous variety is the most frequent. It is stated by Thompson that of 70 specimens of hypertrophied prostate in the Museum of the Royal College of Surgeons, in 17 there were isolated tumors which were clearly discernible. These tumors he divides into (1) those embedded in the substance of the organ, but the structure of which is isolated from that surrounding them, and (2) outgrowths or tumors which are continuous in structure with the portion of the prostate from which they spring, but which manifest a tendency to become partially isolated by assuming a more or less polypoid form and maintaining attachment to the parent body through the medium of a peclicle only.
Some cases of isolated tumor approximate very closely in their structure, myo-fibroma. Indeed, Rokitansky formerly considered these tumors to be simple fibrous formations similar to fibroids oc curring in other portions of the body. Upon careful examination they are usually—according to some authorities, always—found to be of a structure quite similar to that of the remainder of the organ, i.e., of a fibro-adenomatous character with but little muscular tissue. They may, however, be completely isolated by a true fibrous capsule from which they may be readily shelled out. It is not un usual to find circumscribed posterior median growths which are cov ered apparently only by vesical mucous membrane, and which are readily shelled out with the finger after incision of the overlying tissues. In a recent operation, the author removed a growth of this kind with the index finger with very little force and without any pre liminary cutting whatever. These growths resemble adenoma rather than fibro-myoma.
Bar at the Vesical Neck.—There occurs in some cases, as a conse quence of hypertrophy of the prostate, what was called by Guthrie " bar at the neck of the bladder." The classical form may occur in dependently of prostatic hypertrophy, from enlargement of the mus cular fibres which run across the trigonum vesicm just behind the prostate. As a consequence of this enlargement the bundle of mus cular fibres projects from the floor of the bladder so as to produce decided obstruction to the flow of urine. Prostatic hypertrophy proper produces bar at the neck of the bladder in two ways. In the first instance, the hypertrophy of the prostatic tissue is circum scribed, runs transversely across the floor of the prostatic sinus, and does not form a definite tumor. The other method of formation is by the projection of two portions (lobes) of the hypertrophied pros tate, in such a manner that the mucous membrane is stretched across the neck of the bladder between them. In some cases the bar is seemingly due to a general atheroma of the bladder and is associated with columnar formation of hyperplastic tissue in the course of the ureters. The author has seen one specimen of bar in a subject thirty two years of age.