Uterine fibroids are the most common gynecologic tumors in women of reproductive age (Table 12.3). In autopsy series, fibroids were found in up to 77 % of women with the incidence increasing with age, most markedly after age 40. This is because their development and growth is hormone dependent (Cramer and Patel 1990; Flake et al. 2003). Uterine fibroids are round to oval lesions consisting of smooth muscle cells, collagen, extracellular matrix, fat, and fibrin. Women usually have multiple fibroids. Fibroids are found within the endometrial cavity, in the uterine wall, or extending beyond the uterus. Diffuse presence of fibroids within the myometrium is referred to as myomatous uterus. MRI is considered the most suitable imaging modality for detecting and characterizing uterine fibroids. On T2-weighted images, fibroids are usually conspicuous as smooth and sharply demarcated homogeneous masses of low signal intensity compared with the surrounding myometrium (Fig. 12.2). On T1-weighted pulse sequences, they have the same signal intensity as the myometrium. Intralesional calcifications appear dark and are quite common. Degeneration of fibroids is also common and is associated with the presence of intralesional hemorrhage (high T1 signal intensity, variable T2 signal intensity), cystic portions (high T2 signal intensity), or mucinous degeneration (very high T2 signal intensity) (Fig. 12.3). Fibroids can exhibit homogeneous contrast enhancement (Murase et al. 1999). Uterine fibroids must be distinguished from adenomyosis (a form of endometriosis formerly known as internal endometriosis). Adenomyosis is the presence of ectopic endometrial glands in the myometrium. It is usually diffuse but may also be focal. Diffuse adenomyosis is suggested by widening of the junctional zone (>12 mm) and is best evaluated on T2-weighted images. The junctional zone has low T2 signal intensity, delineating it from the endometrium (high signal intensity) and the myometrium (intermediate signal intensity). Areas of adenomyosis are characterized by low T2 signal intensity interspersed with bright foci. Focal forms of adenomyosis appear as poorly marginated areas of low signal intensity that are less well defined than fibroids (Murase et al. 1999). Other differential diagnoses are focal myometrial contraction (which can be ruled out by serial imaging) and leiomyosarcoma.

Endometrial cancer is diagnosed in 11,700 women in Germany each year. The annual incidence is 20–30 new diagnoses per 100,000 women and is on the rise. It is the fourth most common cancer in women, accounting for 5.7 % of all cancers in women, and the most common cancer of the female reproductive organs. Most uterine cancers arise in the endometrium with over 90 % being adenocarcinomas. The mean age at presentation is 68 years (Table 12.4) (Robert-Koch-Institut und die Gesellschaft der Epidemiologischen Krebsregister in Deutschland e.V. 2008). MRI has limitations in detecting early endometrial cancer (especially when imaging protocols without contrast medium administration are used). Depending on the stage of endometrial cancer, the appearance on MR images may range from minimal changes to massive enlargement of the uterus. On T1-weighted images, endometrial cancer is isointense or hypointense relative to the endometrium or myometrium. On T2-weighted images, the cancer is isointense or hypointense to endometrium and usually slightly hyperintense relative to myometrium. The higher cellularity of endometrial carcinomas results in high signal intensity on diffusion-weighted images with lower ADC values. Following administration of contrast medium, endometrial cancer enhances earlier than normal endometrium and is hypointense to the myometrium (Namimoto et al. 2009; Sala et al. 2007). Several entities have to be considered in the differential diagnosis: endometrial hyperplasia or polyps (difficult to differentiate; DWI is helpful), fibroids, adenomyosis, and uterine sarcoma (2–6 % of malignant uterine tumors, typically larger and more heterogeneous).

A hydrocele is a congenital or acquired collection of serous fluid in the space of the tunica vaginalis testis (Table 12.8). Detection of acquired hydroceles is relevant in the screening situation (Akin et al. 2004). They tend to occur in middle-aged or older men on one or both sides. A definitive pathomechanism has not been established (Woodward et al. 2003). A thin layer of fluid around the testis is normal and has been demonstrated in 86 % of men in an ultrasound study (Leung et al. 1984). Acquired hydroceles are usually idiopathic in origin and predominantly affect men after age 40. Less commonly, acquired hydroceles are associated with tumors, inflammation, or infection. Hydrocele is bilateral in 7–10 % of cases (Leung et al. 1984). It is depicted with very high contrast on fat-saturated T2-weighted images; usually there is no compression of the underlying testis (Fig. 12.11). In the differential diagnosis, hematocele and pyocele must be ruled out (Woodward et al. 2003).

Aberrations in number are easily identified and are usually known to a man. Polyorchidism is very rare, with about 100 cases reported in the literature worldwide. The most common form is the presence of three testicles within the scrotum. However, supernumerary testicles may also be located inguinally or intra-abdominally. It is still under debate whether surgical exploration or a conservative approach with serial imaging is the best management option in these cases (Sheah et al. 2004; Yeniyol et al. 2004; Chung and Yao 2002). On MR images, an accessory testicle has the same signal intensity as orthotopic intrascrotal testicles. A testicular tumor must be ruled out in the differential diagnosis.

The absence of one or both testicles from the scrotum is nearly always due to surgical removal, because of testicular cancer or testicular torsion, for instance. Nevertheless, a careful search for a cryptorchid testis should always be done in such cases.

A normal adult testis is 3–5 cm long, 2–4 cm wide, and about 3 cm in anteroposterior extension with marked interindividual variation in dimensions (Kim et al. 2007). An exact size threshold for diagnosing testicular atrophy does not exist. This is why both testicles are measured and atrophy is assumed when there is a significant difference (>50 %) in one or more dimensions between the two testicles (Fig. 12.12). When bilateral testicular atrophy is present, the size of both testicles is well below the normal range. Often, there is concomitant atrophy of the epididymis and vascular structures. Testicular atrophy may be due to cryptorchidism, postinflammatory changes, or trauma.

Significant enlargement of one testicle should prompt further diagnostic workup to rule out a testicular tumor.

Cryptorchidism is the failure of one or both testes to descend into the scrotum (Table 12.9). An undescended testis may be found anywhere along its normal pathway of descent (abdominal, inguinal). Incomplete or absent testicular descent is the most common congenital anomaly in boys (2–8 %). The unilateral form is four times more common than bilateral cryptorchidism. Congenital cryptorchidism usually disappears within the first year of life (due to endogenous testosterone production), resulting in a prevalence of 1–2 % at the age of 3–12 months (Virtanen et al. 2007). An infant diagnosed with cryptorchidism should undergo orchidopexy. An undescended testicle compromises fertility and has a five times higher risk of testicular cancer (Dieckmann and Pichlmeier 2004). A retractile testis is an intermediate form with the testis tending to retract from its normal position in the scrotum.

When MRI fails to demonstrate one or both testicles in the scrotum, this should prompt an evaluation for cryptorchidism. A coronal T2-weighted pulse sequence with fat saturation is well suited for this purpose, as it increases the contrast between the high-signal-intensity testicle and surrounding tissue (Fig. 12.13). An atrophic undescended testis may be more difficult to detect. A careful search along the course of the spermatic cord may help the radiologist in identifying a missing testis (Nguyen et al. 1999).

A varicocele is the dilatation of the veins of the pampiniform plexus, which may be secondary or idiopathic. A secondary varicocele results from compromised venous drainage, e.g., when a tumor is present. The more common idiopathic form has been attributed to incompetent testicular vein valves. Varicoceles are found in about 15 % of all men and in 40 % of infertile men (Table 12.10). A varicocele is considered to be present if pampiniform plexus veins are dilated to diameters of 2–3 mm (Kim and Lipshultz 1996). The markedly dilatated and tortuous veins are clearly depicted on coronal T2-weighted images with fat saturation (Fig. 12.14). The veins have intermediate signal intensity on T1-weighted images and are markedly hyperintense on T2-weighted images with the signal intensity generally being determined by the flow rate. The varicose veins enhance after contrast medium administration.

A spermatic cord tumor must be ruled out in the differential diagnosis (Mattrey 1991; Cramer et al. 1991).

Spermatic cord tumors are very rare. Lipomas account for half of all masses of the spermatic cord and, as elsewhere in the body, have characteristic MRI features (Beccia et al. 1976). Other benign spermatic cord tumors include leiomyoma, dermoid cysts, and lymphangioma. Once a lipoma has been ruled out on the basis of its MRI appearance, the likelihood of a malignant tumor increases to over 50 % (Beccia et al. 1976). The most common malignant tumors are sarcomas (rhabdo- and leiomyosarcoma, liposarcoma).

Prostate cancer is the most common cancer in men, accounting for 25 % of all male malignancies (Table 12.11). In Germany, 58,000 men are diagnosed with prostate cancer each year. It is the third most common cause of death from cancer. The mean age at diagnosis is 69 years. However, it is assumed that over 50 % of all prostate cancers diagnosed with the PSA test would not have become apparent through symptoms during a man’s lifetime (Robert-Koch-Institut und die Gesellschaft der Epidemiologischen Krebsregister in Deutschland e.V. 2008). Ninety-five percent of all prostate cancers are adenocarcinomas.

The zonal anatomy of the prostate is helpful for interpreting and reporting MRI findings.

Four zones are distinguished:

The normal prostate gland has homogeneous intermediate signal intensity on T1-weighted images, which do not depict the zonal anatomy and provide poor soft-tissue contrast for identification of pathology. T2-weighted images are more useful, allowing differentiation of the zonal anatomy. The peripheral zone has high signal intensity and is surrounded by a black line, which corresponds to the prostate capsule. The central and transitional zones are of inhomogeneous low signal intensity due to the high proportion of stroma. Prostate cancer usually has low T2 signal intensity (and may be multifocal), which is why it is easier to detect in the hyperintense peripheral zone than in the remaining prostate (Fuchsjager et al. 2008; Turkbey et al. 2009). DWI may show restricted diffusion with an increased signal intensity and low ADC values (Issa 2002). Common accessory findings include infiltration of the bladder base, invasion of surrounding fatty tissue, locoregional lymph node metastases, and (osteoblastic) bone metastases.

The differential diagnosis includes benign prostatic hyperplasia (typically developing in the transitional zone), hemorrhage, prostatitis, and bladder cancer extending into the prostate (Fuchsjager et al. 2008; Chang et al. 2008). It is likely that, with the protocol used for a whole-body screening examination, many prostate cancers are overlooked (thick slices, surface coils).

Benign prostatic hyperplasia (BPH) is nonmalignant enlargement of the prostate gland resulting from a nodular increase in volume of the transitional zone due to cellular hyperplasia. The prevalence increases with age (Table 12.12). An autopsy study showed a prevalence of 40 % at age 50 and of 70 % at age 60 with 90 % of men in the ninth decade of life having signs of BPH (Berry et al. 1984). The predominant symptoms are due to obstruction and irritation. One method of diagnosing BPH is measurement of prostate volume. However, changes in prostate volume over time are subject to wide interindividual variation. While hyperplasia is common, a considerable proportion of aging men have a stable or decreasing prostate size (Loeb et al. 2009). The only feature seen on T1-weighted images is enlargement, while T2-weighted pulse sequences also show that the enlarged transitional zone is very heterogeneous and of low signal intensity. Often, the enlarged gland will elevate the bladder base. In advanced BPH, MRI depicts signs of urinary obstruction with a large bladder volume or evidence of a trabeculated bladder. Ultimately, however, BPH cannot be confidently differentiated from prostate cancer in the screening situation (Fig. 12.15) (Fuchsjager et al. 2008).