Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

struction. A urethral stricture is a potential postreconstruction complication.

Penis

The most common conditions resulting in priapism due to trauma are an intracavernosal arteriovenous fistula, a pseudoaneurysm, or asymmetric cavernosal arterial blood flow. These fistulas can be detected by selective angiography, and subsequent embolization can be therapeutic. The embolic materials used are autologous blood clots, N-butyl-cyanoacrylate, and others.

With suspected penile fracture some surgeons operate without any diagnostic imaging being performed, with imaging requested primarily for equivocal clinical findings. In this setting, however, traumatic rupture of the corpus cavernosum is not uncommon and some investigators believe that preoperative cavernosography should be performed and therapy modified accordingly. A corpus cavernosum tear is identified as contrast extravasation during cavernosography. Most corpora cavernosa ruptures are proximal, the vast majority being unilateral; associated complete urethral rupture is rare.

Mostly anecdotal reports suggest that MRI is superior to US in identifying corpus cavernosum rupture; the role of MR will undoubtedly expand. MRI detects corpus cavernosum rupture as a discontinuity in the hypointense tunica albuginea (10); associated subcutaneous haematoma were identified both on T1and T2weighted images, but corpus cavernosum haematomas were better seen on contrast enhanced T1-weighted images.

Follow-up MRI after surgical repair reveals a hyperintense signal at the tunical suture site on precontrast T1-weighted images, enhancing with contrast (10); the tear site gradually recovered its hypointensity on spin echo sequences.

Scrotum and Testes

A painful, ecchymotic scrotum is common after scrotal trauma. Preoperative US is useful in suspected testicular rupture. Still, both falsepositive and false-negative findings occur. For instance, fracture of the tunica albuginea can

ADVANCED IMAGING OF THE ABDOMEN

be missed with US. Ultrasonography cannot provide an accurate diagnosis of rupture. On the other hand, if US is abnormal, even if the findings are nonspecific, testicular rupture should be suspected. Ultrasonography reveals testicular rupture as regions of heterogeneous echogenicity and loss of normal contour. Only occasional fracture planes are identified by US.

An intratesticular pseudoaneurysm developed after blunt trauma (11).

Traumatic dislocation of the testis is rare and most are inguinal in location. Associated spermatic cord injury is also often present. Imaging is helpful in guiding surgical correction.

Among mountain bikers (with less than half being symptomatic), 94% had abnormal scrotal US, consisting of scrotal calculi (81%), epididymal cysts (46%), epididymal calcifications (40%), testicular calcifications (32%), hydroceles (28%), varicoceles (11%), and testicular microlithiasis (1%) (12).

Prostate and Adjacent

Structures

Hyperplasia/Hypertrophy

Clinical

Benign prostatic hyperplasia (BPH), also called benign hypertrophy, adenomatous hypertrophy, or simply adenoma, increases with age. Some physicians use this term to describe a symptom complex rather than use it as an anatomic entity. The term lower urinary tract symptoms is used by some for this broad clinical entity.

The prevalence varies among racial and ethnic groups; it is considerably less common among Japanese men than among Caucasians. Estrogen has a role in its development. Serum beta-carotene and smoking appear to be risk factors for BPH. Familial BPH does exist.

Most benign hyperplasia occurs in the transition zone and only occasionally in the periurethral glandular zone. Some enlarged glands contain cysts, calcifications, or even regions of hemorrhage. Little correlation is apparent between prostatic calcifications and the extent of hyperplasia. Likewise, endorectal US measurements of prostate size or transition zone volume do not relate to the degree of bladder outlet obstruction. Also, the volume of residual

MALE REPRODUCTIVE ORGANS

urine correlates poorly with prostate size and flow rate. Prostatic capsule rigidity may play a role in benign hyperplasia. Prostatic innervation also appears to be a factor, because a- adrenergic receptor blocking agents lower resistance to flow in those with an enlarged prostate. On the other hand, in a setting of benign hyperplasia ischemia does not appear to be a factor in bladder outlet obstruction.

Occasionally a prostatic biopsy suggests a low-grade adenocarcinoma, which actually represents hyperplasia of verumontanum mucosal glands.

At times voiding cystourethrography shows a smooth posterior impression at the bladder neck. If this impression is only several millimeters in length, it probably should be considered within the normal range. When enlarged, it is called median lobe hyperplasia and is produced by periurethral gland hyperplasia. Such hyperplasia occurs in men with spinal cord injury and in those who have undergone numerous catheterizations.

Occasionally an inguinal cystocele mimics clinical findings of prostatic enlargement but without actual evidence of bladder outlet obstruction. Also, not all prostatic enlargement is secondary to hyperplasia or neoplasm; in some parts of the world bladder schistosomiasis is a cause of prostatic enlargement.

Imaging

Does intravenous (IV) urography have a continued role in men with prostatism? In a large minority of patients with prostatism, IV urography reveals excretory system dilation, calculi, an unexpected congenital anomaly, or other abnormality. Voiding cystourethrography adds little to the diagnosis, except perhaps in younger men in a search for alternate diagnoses for urethral obstruction. Prostate size cannot be evaluated with this examination.

Computed tomography reveals prostatic hypertrophy as a smooth homogeneous, but CT is not indicated for simple benign prostatism. Computed tomography attenuation values are similar for benign disease and a malignancy.

Bladder wall thickening is common with bladder outlet obstruction. To obtain reproducible US results, bladder wall thickness should be measured after bladder filling with a standardized amount of fluid—about 150mL.

Not all bladder wall thickening is due to bladder outlet obstruction.

The sonographic appearance varies from a fine to a rough pattern or a combination, and hypoechoic to hyperechoic. Echogenicity in any one patient is due to a mix of complex hyperplastic glands and a cystic atrophic component. Nodules are detected in some glands. Any calcifications present appear hyperechoic. At times the central and peripheral gland portions appear to be separated.

Prostatic size estimates are of less importance in BPH than with a suspected cancer. In addition, a “gold standard” is more difficult to establish than with a radical prostatectomy for cancer. Studies suggest that endorectal US and MRI measurements of prostatic hyperplasia are similar, although endorectal US may underestimate prostatic weight. Gross prostate size estimates, however, are useful; transurethral resection is more difficult with a very large gland.

Magnetic resonance imaging reveals BPH to be hypointense on T1and heterogeneous and mildly hyperintense on T2-weighted images (Fig. 13.3).

Figure 13.3. Benign prostatic hypertrophy, bladder outlet obstruction, and thick bladder wall (arrows), detected on T2weighted magnetic resonance (MR) image. (Source: Burgener FA, Meyers SP, Tan RK, Zaunbauer W. Differential Diagnosis in Magnetic Resonance Imaging. Stuttgart: Thieme, 2002, with permission.)

Therapy

Resection

Currently surgical resection is the gold standard in treating BPH, most often using a transurethral approach. Post-resection MRI reveals degenerative changes near the prostate surface and shrinkage of the prostatic capsule. A dilated prostatic urethra is readily identified.

A complication of a radical retropubic prostatectomy is an inguinal hernia. Most of these hernias are indirect. Fistulas are uncommon; with surgery being close to the symphysis pubis, an occasional fistula leads to osteitis pubis.

Bladder hypertrophy due to obstruction by BPH is to a large extent reversible after surgical relief, except in those with irreversible degenerative changes.

Nonsurgical

The natural progression of BPH suggests that in many men an initial decision to prescribe no therapy is a viable option; symptoms in most men do not progress. In some, a-adrenergic- blocker therapy and 5a-reductase inhibitor therapy are helpful.

Although a number of nonsurgical techniques, such as laser therapy, microwave thermotherapy, and others have been tried, thermal ablation is currently the only viable alternative to surgery, achieving similar results. Balloon dilation has been disappointing.

Laser Therapy

Laser ablation thermotherapy leads to coagulation necrosis, with eventual reepithelialization. In theory, laser coagulation shrinks the prostate by inducing prostatic necrosis without injury to the urethra or surrounding tissues. Currently, results from US-guided laser-induced transurethral thermal therapy appear inferior to those obtained with transurethral resection. One disadvantage of laser therapy is that no tissue is obtained and it takes longer to attain symptomatic improvement compared to transurethral resection. Prostatic volume initially is not reduced, and postprocedure urinary retention is common. Laser therapy, however, is still a new technique, and further advances are to be expected.

ADVANCED IMAGING OF THE ABDOMEN

Few complications are encountered and symptoms eventually improve in most. Rarely, the loss of ejaculation, epididymitis, or an abscess develops. Urethral stricture is a late complication.

Magnetic resonance imaging detects prostate changes during and after laser-induced thermotherapy. Repetitive T2-weighted fast spin echo (FSE) MRI during coagulative laser thermotherapy revealed persistent hypointense regions, presumably representing coagulation necrosis. These regions increase in size during therapy. The prostate remains enlarged shortly after treatment, and contains poorly defined hypointense regions surrounding the urethra; with time, the prostate gland returns to its preoperative size.

Central coagulation necrosis is seen as a hypointense region surrounded by a hyperintense rim. The prostate increases in size, presumably due to edema; edema is evident in the surrounding tissues and the presacral space thickens. Subtracting postprocedure laserinduced lesion volume (obtained via MR planimetry) from preprocedure volume predicts prostatic volumes at late follow-up (13), although transitional zone volume was underestimated and peripheral zone volume was overestimated.

Microwave Ablation

Transurethral microwave thermotherapy is a potential outpatient procedure requiring little or no anesthesia. A temperature ≥60°C results in coagulation and tissue necrosis. Tissue vaporization ensues if the temperature is >100°C. Use of higher energy levels improves results but at the expense of increased morbidity.

Symptomatic improvement is achieved in about half of men treated with microwave thermotherapy. Imaging findings are inconstant. Magnetic resonance imaging detects prostatic urethral widening. Necrosis is an inconstant finding. Findings on voiding cystourethrography and retrograde urethrography before and after transurethral microwave therapy do not correlate with subjective improvement. The transition zone volume, obtained from pretreatment endorectal US, appears to relate to long-term microwave thermotherapy efficacy.

MALE REPRODUCTIVE ORGANS

Other Therapy

Self-expanding endourethral stents have been used to treat bladder outlet obstruction due to prostatic hyperplasia; still, urethral stents have had limited success, with some stents dislodge or become encrusted.

Preliminary results using an electrosurgical generator for transurethral prostatic electrovaporization are encouraging. Postoperative urine incontinence is a potential complication.

High-intensity focused ultrasound therapy is still experimental.

Infection/Inflammation

Prostatitis

Prostatitis can be either acute or chronic. At times a specific pathogen is detected; if not, the clinical symptoms are often ascribed to prostatodynia, a previously poorly defined condition. In this work prostatodynia is used to designate pelvic venous congestion and is discussed later (see Vascular Abnormalities).

Granulomatous prostatitis is a histologic diagnosis. Common causes are prior prostatic surgery and prostatic needle biopsy. Occasionally prostatic granulomas develop in a setting of prior bacillus Calmette-Guérin therapy.

Ultrasonography reveals a complex pattern in prostatitis. At times prostatic nodules are present. In a normal gland Doppler US using a coronal plane reveals capsular and parenchymal arteries radiating symmetrically. These arteries become more prominent in acute prostatitis.

Ejaculatory duct calcifications develop in chronic prostatitis.

Early prostatic cancer and prostatitis are difficult to differentiate with current imaging. Of interest is that in some patients with prostatitis MR spectroscopy detects an elevated choline peak and reduced or no citrate, findings mimicking those of cancer (14).

prostate can be involved, and an abscess may or may not communicate with the urethra. Some prostatic abscesses result in bladder outlet obstruction.

A prostatic abscess is detected either by CT or endorectal US. Typically US reveals hypoechoic or anechoic regions with internal echoes, suggesting fluid-filled structures containing septations. Some mimic loculated cystic prostatic tumor.

Once diagnosed, a prostatic abscess can be drained using endorectal US guidance, and a perineal or transurethral drainage approach can be used.

Tuberculosis

Tuberculosis either is primarily genital in origin and involves the seminal vesicles, prostate, and adjacent structures, or these structures are involved by extension from the kidneys. An occasional tuberculous prostatitis is associated with intravesical carcinoma therapy with bacillus Calmette-Guérin.

Tuberculosis results in prostatic inflammation, enlargement, necrosis, or abscess. Cystography reveals prostatic enlargement simply as bladder base elevation. Urethrography identifies any urethral stricture or fistula to adjacent structures. Endorectal US reveals prostatic enlargement with multiple hypoechoic foci within the gland, usually anteriorly in the transition zone, representing necrotizing granulomas. Eventually these granulomas calcify.

In some men seminal vesicle and vas deferens calcifications are the only imaging abnormality. Vas deferens calcifications are either intramural or intraluminal in location, and the appearance mimics findings seen with diabetes mellitus.

Computed tomography reveals inflammation of the surrounding structures, including perivesical fat stranding.

Abscess

Predisposing factors for periprostatic or prostatic abscesses are diabetes mellitus, urethral catheterization or manipulation, and an immunocompromised status. Most abscesses are infected, with only an occasional sterile abscess encountered. Any portion of the

Other infections

The seminal vesicles dilate and calcify secondary to schistosomal involvement. At times the ejaculatory ducts also dilate. Schistosomiasis induces prostatic retention cyst formation and eventual prostatic enlargement and calcifications.