The genitourinary system

Male genital organs

Anatomy

The normal prostate is formed like a pyramid with the widest part, the base, which lies adjacent to the bladder, measuring approximately 4.5 cm in diameter. The apex lies adjacent to the membranous urethra (Fig.16). The prostate is approximately 3.5 cm in length and weighs approximately 20 gram in healthy young men. At both ultrasonography and MRI one can distinguish between the central gland, which consists of the histological central and transition zones, and a peripheral zone. This distinction is of great importance, since hypertrophy mainly originates in the transition zone, which is the area around urethra above the verumontanum, whereas malignant tumors are most frequently found the peripheral zone. Prostatitis can originate in any part of the prostate.

The normal testis measures approximately 4-5 x 3 x 2.5 cm and has at both ultrasonography and MRI an homogenous structure. An inhomogeneous structure indicates occurrence of disease.

The penis consists of three cavernous bodies, a corpus spongiosum which surrounds the urethra, and paired corpora cavernosa which lie dorsal to the urethra (Fig. 16). The penis receives its blood supply from the internal pudendal branch of the internal iliac artery.

Pathology

Diseases in the prostate occur frequently. For the most part, however, the spectrum of diseases is limited to infection, hyperplasia and cancer. Today prostate cancer is the most frequent cancer among males in North America and parts of Europe.

Figure 94. Urethral obstruction due to BPH demonstrated at urethrography. Note the narrowed elongated prostatic urethra.

Prostatitis and abscess
Prostatitis is a clinical diagnosis; imaging is irrelevant. If an abscess is suspected a transrectal ultrasonogram should be done. At ultrasonography a relatively echo-poor area - often surrounded by an echogenic rim - is seen. Needle aspiration and drainage can be carried out concurrently. Prostatic abscesses can also be image d by MRI and CT. At MRI a signal intense area is seen on T2-weighted images. At CT a low attenuating area is seen; after contrast "rim" enhancement may be seen.

Benign prostate hyperplasia
Benign prostate hyperplasia (BPH) does not in itself require any imaging examination. It is often found at examinations performed for other reasons. On plain abdominal radiographs bladder stones and/or a full bladder may be seen and after injection of contrast medium an elevated bladder with a smooth floor may be found; sometimes there is dilatation of the upper urinary tract. In case of median-Iobe (Albarrans) BPH a filling de feet in the bladder is seen. These changes are non-specific and may also be seen in prostate cancer. The size of the prostate can not be determined at urography. The volume of BPH can be determined at MRI,

Figure 95. Prostate cancer. a: Hypoechoic process on transrectal ultrasonography. b: Ultrasonography is an excellent method for biospy guidance.

CT and transrectal ultrasonography, however. At the latter examination discrete centrally localized nodules with varying echogenicity are found in BPH. On T1-weighted MRI a heterogeneous prostate with discrete nodules or a homogenous gland are found; T2-weighted MRI shows centrally localized nodules with varying signal intensity and a bright peripheral zone. At CT a homogenous enlarged gland with smooth demarcation is found. The elongated prostatic urethra can be appreciated at urethrography (Fig. 94).

Prostate cancer
Diagnostic imaging in prostate cancer includes primary diagnosis and staging, but not screening. For the first purpose transrectal ultrasonography is suitable as the primary examination, since it may demonstrate a hypoechoic area in the peripheral zone. However, hypoechoic processes may also represent benign nodules and invasive rectal cancer. Therefore, a biopsy must be taken from any suspicious hypoechoic area (Fig. 95). In case of a normal transrectal ultrasonography prostate cancer

	Figure 96. Low-signal prostate cancer (arrow) in the left side of the peripheral zone. T2-weighted image obtained with whole body coil.
	Figure 97. Prostate cancer in the right side. The cancer breaks through the fibrous capsule so it is a stage C cancer (arrow). T2-weighted image obtained with an endorectal coil.

can not be excluded. If the clinical suspicion of prostate cancer is high, e.g. elevated PSA, the next step should be random biopsies or MRI. On T2-weighted images signal poor areas may be seen in the otherwise signal rich peripheral zone (Fig. 96). However, similar signal changes may also be se en in BPH and prostatitis; the diagnostic problem is greatest if the disease is present in the signal poorer central zone. The advantage of MRI is its ability to scan in multiple planes. With an endorectal coil it is possible to demonstrate invasion of the fibrous capsule and hereby discriminate between stage B and C (Fig. 97). Correct staging is of major importance for the choice of treatment: e.g. radical prostatectomy (stage B) and radiation/chemotherapy (stage C). Regarding peripheral soft tissue metastases the capabilities of MRI are similar to those of CT. Bone metastases should primarily be diagnosed at bone scintigraphy followed by confirming conventional X-rays or CT of the region with increased accumulation of radioactivity. MRI can be helpful in equivocal cases, but sometimes bone biopsy must be done (Fig. 98).

Figure 98. "Super" bone scan demonstrating symmetrical increased uptake of the radiopharmaceutical with diffusely metastatic disease due to prostatic cancer. It is significant that the kidneys are not seen due to extensive skeletal deposition of the radionuclide.

Scrotal enlargement
Despite the fact that the scrotal contents including the testes can easily be examined manually it may be difficult to determine the character and cause of scrotal enlargement. The most important diagnoses are epididymitis, orchitis, abscess, hydrocele, spermatocele, varicocele (Fig. 99), testicular tumor, torsion and testicular rupture. Ultrasonography with a 7 MHz probe is valuable in most cases, since it can distinguish between solid and cystic lesions and determine whether the lesion is intra- and extra testicular. In case of epididymitis an enlarged epididymis, which is more echo rich than the normal epidydimis, containing small cystic areas is found. In case of orchitis the testis is uniformly enlarged with either an unchanged or slightly diminished echopattern. The ultrasonographic signs of a scrotal abscess are similar to those of abscesses in other organs. Testicular cancer breaks the homogenous echopattern of the normal testis; more or less well demarcated areas are found in the diseased testes (Fig. 100). There is no relation between the echopattern including demarcation and the various cancers, although presence of amourphous calcification should raise the possibility of teratoma. Approximately one-half of the testicular cancers are seminomas; the remaining cancers are embryonal cell carcinoma, teratoma, and teratosarcoma and choriocarcinoma. In older men lymphoma is the most common tumor. In case of diffuse infiltrating cancer the ultrasonographic findings are non-specific, but diffusely enlarged, hypoechoic (and painless)

	Figure 99. Hydrocele (arrow), spematocele (arrowhead) and varicocele (open arrows) at scrotal ultrasonography.
	Figure 100. Testis cancer. Ultrasonography demonstrating echo poor tumor in the right testis. Normal left testis.

testes are suspect of infiltrating cancer. T2-weighted MRI is advantages for the diagnosis of testicular tumors. A low signal intensity focus is the usual finding (Fig. 101). In contrast to ultrasonography MRI can sometimes differentiate between seminoma, non-seminoma and leukemic infiltration. Testicular cancer usually spreads by the lymphatic system, which together with the venous blood passes directly toward the renal hilum on the left and the aorto-caval interspace on the right. CT and MRI are equally good for the diagnosis of metastatic nodes.

At both ultrasonography and MRI cystic areas are found in case of occurrence of the various fluid collections: hydrocele, spermatocele and varicocele.

Figure 101. Testis cancer. Signalpoor process in the left testis, whereas the right testis has a high homogenous signal on this T2-weighted image

Testicular trauma
An echo-poor area may be found by ultrasonography in a patient having been subjected to a testicular trauma. This finding may to due testicular bleeding and a hematoma in the surrounding tissues. MRI may be able to demonstrate the rupture of the tunica albuginea.

Testicular torsion
Doppler ultrasonography is the most appropriate examination to perform when testicular torsion is suspected. Demonstration of blood flow in the mediastinum testis nearly always rules out testicular torsion, since the torsion most frequently takes place in the spermate cord just proximal to this level. Alternatively MRI or scintigraphy may be performed; the latter will show photon deficient area at the site of the torsed testes.

Impotence
In impotence of organic origin Doppler ultrasonography may be useful for obtaining information about the arterial blood flow to the penis. If an abnormally low blood flow is found, selective arteriography of the internal pudendal arteries before and after papaverine are indicated to

Figure 102. Normal female genitals. Sagittal T2-weighted image demonstrating a normal cervix with a central high signal intensive stripe (the canal) surrounded by low signal intensity due to fibrous tissue. The uterine body has also a zonal structure with a high signal centrally (endometrium), a thick outer myometrial zone with an intermediate signal intensity, and a narrow inner zone with low signal intensity.

demonstrate stenosis or occlusion as a cause of impotence. If cavernosometry is indicative of insufficient venous occlusion during erection, cavernosography may useful for determining the site of massive venous leaks. Cavernosography can also be used for demonstration of traumatic penile rupture.

Intervention

Imaging guided intervention is limited to biopsy of the prostate - mainly guided by ultrasonography (Fig. 95), dilatation/embolization of penile arteries/veins in patients with impotence or priaprism and embolization of varicoceles.

 

Henrik S. Thomsen and Howard M. Pollack