In this unit we will explore the pathology of the lower urinary tract (bladder and urethra) and male reproductive system (testis and prostate).

The urinary bladder is a muscular bag lined by a transitional epithelium. It can distend considerably and serves as a reservoir for urine before it leaves the body. Major disases of the urinary bladder include acute and chronic cystitis and cancer (transitional cell carcinoma).

The testes are suspended outside the body in the scrotum. They have two major functions: i) production of spermatozoa (spermatogenesis) and ii) secretion of hormones (most notably testosterone). The prostate gland is located directly below the bladder. It is shaped like a doughnut, with the urethra passing through the small hole in the center.

Together the testes, prostate, and penis serve to deliver sperm to the female reproductive tract during sexual intercourse. Major diseases affecting the male reproductive system are classified as congenital, inflammatory, and neoplastic.

Here are the Key Points:

1. Exstrophy of the bladder is a congenital anomaly characterized by the absence of a portion of the lower abdominal wall and the anterior wall of the bladder.

2. Cystitis refers to inflammation of the urinary bladder. Factors related to bladder infection include the age and sex of the patient, presence of bladder stones, bladder outlet obstruction, diabetes mellitus, immunodeficiency, catheterization, and radiation or chemotherapy. The risk of cystitis in females is increased because of a short urethra (especially during pregnancy). Bladder outlet obstruction associated with prostatic hyperplasia predisposes men to cystitis.

3. Obstruction to the flow of urine from the bladder results in bladder dilatation, muscular hypertrophy, and trabeculation of the mucosal surface.

4. Neoplastic lesions arising from the bladder mucosa include benign papillomatous lesions, as well as invasive transitional cell carcinomas. An increased risk of bladder cancer is seen among workers in the leather, rubber, paint, and organic chemical industries. Smoking is also associated with an increased risk of bladder carcinoma.

5. The classic cause of urethritis is infection with Neisseria gonorrhoeae. However, today urethritis results more commonly from infection with Chlamydia species, E. coli, or Mycoplasma. In males, urethritis typically complicates prostatitis, whereas in females it follows cystitis.

6. Cryptorchidism refers to the failure of a testis to descend within the scrotum. At term, 4% of male newborns are cryptorchid. In the large majority of these infants, the testis descends within the first year of life. Long-term complications of untreated cryptorchidism include infertility and testicular cancer.

7. Orchitis refers to acute or chronic inflammation of the testis, often secondary to urinary tract infection. Syphilis and mumps can both produce orchitis.

8. Neoplastic transformation of a male germ cell gives rise to seminoma (an undifferentiated tumor) or embryonal carcinoma (a tumor of totipotential cells). In turn, embryonal carcinomas may undergo somatic differentiation to become a teratoma.

9. Seminomas account for half of all germ cell tumors. Most patients are between the ages of 25 and 55 years. Teratomas are germ cell tumors characterized by tissues from all three embryonic germ layers: ectoderm, endoderm, and mesoderm.

10. Yolk sac tumors are the most common germ cell tumors of infants. Choriocarcinoma is a highly malignant testicular tumor that represents extraembryonic differentiation to components of the placenta, namely syncytiotrophoblast and cytotrophoblast.

11. Infection of the prostate (prostatitis) usually follows a lower urinary tract infection with reflux of infected urine into the prostate.

12. Nodular hyperplasia of the prostate is a common disorder characterized clinically by enlargement of the gland with obstruction to the flow of urine through the bladder outlet. Nodular hyperplasia is characterized pathologically by the proliferation of both glands and stroma.

13. Clinical symptoms of nodular hyperplasia of the prostate result from compression of the prostatic urethra and obstruction to the bladder outlet. A history of decreased vigor of the urinary stream and increasing urinary frequency is typical. Rectal examination reveals a firm, enlarged and nodular prostate.

14. Prostate cancer is a disease of elderly men. Most cases are incidental findings at autopsy or are discovered in surgical specimens of nodular hyperplasia. Prostatic adenocarcinomas are commonly multicentric. They are typically located in the peripheral zones of the prostate gland.

The following images illustrate Key Morphological Concepts:

1. This is an example of ACUTE HEMORRHAGIC CYSTITIS. This patient had an indwelling catheter that caused an ascending bacterial infection.

2. This is an example of CHRONIC CYSTITIS caused by repeated infections of residual urine. Retention of residual urine in the bladder of this patient was caused by an enlarged prostate gland with bladder outlet obstruction.

3. This is an example of NODULAR HYPERPLASIA of the prostate. The enlarged prostate compressed the urethra and caused bladder outlet obstruction. Effects of chronic bladder obstruction include dilatation, muscle hypertrophy, and trabeculation of the mucosal surface. This patient most likely complained of dysuria, frequency, and urgency.

4. This is another example of NODULAR HYPERPLASIA of the prostate. The normal weight of the prostate is 20g, whereas the weight of this hyperplastic prostate is nearly 300g. Growth of prostatic tissue is stimulated by dihydrotestosterone.

5. This is an example of BLADDER CANCER. This woman (note uterus and ovary) presented with painless hematuria. The most common histologic type of bladder cancer is transitional cell carcinoma.

6. This is an example of SEMINOMA arising in a seminiferous tubule of the testis. The tumor is yellow, lobulated, and well circumscribed. Seminoma is the most common germ cell tumor in men between the ages of 25 and 55.

7. This is an example of EMBRYONAL CARCINOMA arising in a seminiferous tubule of the testis. The tumor appears variegated and shows evidence of hemorrhage. Mouse and human embryonal carcinomas have been successfully cultured in vitro, providing a useful model system for studying mechanisms of development and differentiation.

8. This is an example of MATURE CYSTIC TERATOMA. This germ cell tumor contains differentiated tissues derived from all three embryonic germ layers. The most important predictor of the biologic behavior of testicular teratoma is the age of the patient. In adult men, teratomas are commonly malignant and metastasize. By contrast, teratomas in infants and children are invariably benign.