Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

Prior hypospadias repair and urethral reconstruction using bladder mucosa, appears to predispose to urethral nephrogenic adenoma formation either at the anastomosis or the graft. Their gross appearance mimicks a carcinoma.

Nonurethral

A corpus cavernosum hemangioma is rare. Some of these have an atypical appearance, are inhomogeneous and even MRI does not distinguish between benign and malignant disease.

A squamous cell carcinoma is the most common penile tumor. Phimosis or human papilloma virus infection are often present. Nodal metastases are common at initial presentation. Tumor stage, lymph node metastasis, and tumor differentiation are independent prognostic factors for survival. Computed tomography often detects inguinal adenopathy at initial presentation, but it should be kept in mind that inflammatory causes for adenopathy are common. Magnetic resonance T2-weighted images are more useful than T1 images in evaluating penile cancers.

Metastases to the penis are uncommon. Among other tumors, prostatic carcinoma has metastasized to the penis. Magnetic resonance imaging is helpful in establishing the extent of invasion.

Cowper’s Glands

Paired Cowper’s glands and ducts are located along the ventral surface of the bulbous urethra. Not uncommonly these ducts fill during an urethrogram or, rarely, on IV urography after voiding. Normal ducts are readily differentiated from fistulas and contrast extravasation.

Duct obstruction results in a retention cyst, which, if large enough, produces a soft tissue impression along the ventral surface during voiding cystourethrography. An occasional one enlarges sufficiently to obstruct the urethra. These glands are also occasionally involved by neoplasms, infection, or stones.

Priapism

Priapism is a sustained erection caused by an abnormal process. It can be partial. In adults, most are idiopathic, with an occasional one a

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direct result of trauma or a posttraumatic arteriovenous fistula. Rarely, priapism is associated with drug therapy, thromboemboli, sickle cell disease, malignant infiltration of surrounding structures, an adjacent abscess, or a neurologic condition. In pediatrics, aside from trauma, priapism is most often secondary to sickle cell disease or a hematologic malignancy.

Priapism is classifications into low-flow (venous) and high-flow (arterial) states. The low-flow or ischemic type occurs with perineal trauma–induced venous thrombosis, hematoma, or edema of adjacent tissue. The resultant vascular stasis within the corpora leads to a delay in penile venous drainage. Highflow priapism is due to persistent blood inflow, such as with a cavernosal artery laceration (arteriocavernosal fistula).

Doppler US aids in distinguishing the two types of priapism. Arteriosinusoidal fistulas result in pulsatile, high-flow corpora cavernosa signals. Perineal duplex Doppler US achieves almost 100% sensitivity in detecting high-flow arterial priapism, but false positives do occur and limit the specificity.

In low-flow priapism, pudendal arteriography opacifies the dorsal and bulbar arteries, but not cavernosal arteries because of decreased inflow and stasis.

In selected individuals both CT and US are useful in excluding an underlying neoplasm or abscess as the etiology for the priapism.

High-flow priapism, generally related to trauma, can be treated with selective bulbocavernosal artery embolization.

Peyronie’s Disease

Peyronie’s disease consists of excessive fibrosis and plaques in the sheath covering the corpora cavernosa. It is probably caused by a vasculitis or inflammation. Calcified plaques develop eventually, and if sufficiently extensive, they are visible with conventional radiography. Soft tissue radiography using a mammography technique detects calcifications but does not detect plaques without calcification. Calcifications are also detected with US and CT.

Palpation and US are the examinations of choice in detecting plaques. Plaques vary in size from less than 1cm to several cm in length and from 2 to 4mm in thickness. Ultrasonography reveals more extensive plaques than does clini-

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cal evaluation. Ultrasonography detects tunica albuginea thickening. Some investigators consider inflammation to be present if hypoechoic foci are identified around a central hyperechoic region.

Doppler US after intracavernosal papaverine injection in these patients reveals decreased peak systolic flow velocity and increased end diastolic flow velocity. Contrast enhanced color and power Doppler US identifies vascularity around plaques in about one-third of patients with established Peyronie’s disease. Doppler US shows that penile cavernosal-spongiosal communications near plaques remain patent with low resistance flow, providing a pathway for blood leakage (63); these findings are difficult to place in proper perspective.

Whether MRI detects more plaques than does US is debatable. Some plaques show postcontrast enhancement, suggesting active inflammation, and MR appears superior in monitoring the progression of the inflammation.

Peyronie’s disease has been treated with local injection of interferon-alfa-2b into plaques. Noncalcified plaques respond best. Extracorporeal shock-wave lithotripsy (ESWL) has been used to treat symptomatic plaques believed to be of recent origin. The preliminary results appear encouraging (64).

Impotence

Vascular causes of impotence are most common, followed by diabetes mellitus and others. Vasculogenic impotence is usually divided into insufficient arterial inflow (arteriogenic) and excessive venous leakage (venogenic).

Arteriogenic

Internal iliac arteriography has been considered the gold standard in detecting arteriogenic impotence, and although numerous studies over the years have established its usefulness, it is little used today. An erection developing after intracavernosal injection of papaverine is presumed to be evidence that the arterial and venous pathways are intact. Following papaverine injection, diabetic individuals have a significantly lower cavernosal artery peak blood flow velocity than do nondiabetics.

Color Doppler US evaluates arteriogenic impotence by measuring peak systolic velocity and systolic rise time of deep arteries supplying the corpora cavernosa. Following papaverine injection, a systolic rise time of 110msec or greater appears to be a good discriminant for arterial disease. A peak systolic velocity in the cavernosal arteries of greater than 25 to 30cm/ sec is a normal response to papaverine or prostaglandin B1 injection. These values should be accepted with caution because they are lower if penile arterial communications exist. Marked differences in velocity between the two cavernosal arteries suggest unilateral disease. Reversal of systolic flow implies proximal penile artery obstruction.

Extensive vascular connections exist between the penile dorsal artery and cavernous arteries, but the dorsal artery function in impotence is not clear. Normally dorsal artery color Doppler US reveals an increase both in systolic and diastolic velocities after intracavernous papaverine injection. Flow is decreased or even absent in the dorsal artery in men with arteriogenic impotence.

Venogenic

The gold standard in diagnosing venogenic impotence is pharmacologically aided cavernosometry and cavernosography. Role of color Doppler US after cavernosal papaverine injection in diagnosing venous dysfunction is not clear; published sensitivities have ranged from 50% to 100% in detecting venous dysfunction.

The cavernous artery resistance index (RI) is obtained from Doppler US data by:

RI = (peak systolic velocity - end diastolic velocity)/peak systolic velocity

After intracavernous injection of prostaglandin, Doppler US in men with suspected venogenic impotence found RI values in those with corporal leakages to be significantly lower than in those with previously normal cavernosometry and cavernosography, although some overlap exists (65); men with an RI >0.9 were not venogenic impotent and those with an RI <0.75 had corporal leakages, while in those with an RI between 0.75 and 0.9, cavernosometry and cavernosography were necessary for diagnosis.

Thrombophlebitis

Anecdotal reports of thrombophlebitis of the penile superficial dorsal vein have been reported. Etiologies include trauma associated with sexual intercourse, penile strangulation, penile injection, infection, neoplasms, and prior surgery.

Scrotum and Spermatic Cord

Acute Scrotum

Acute onset of scrotal swelling and pain should be approached as an emergency. The most common etiologies are testicular torsion, testicular appendage torsion, acute epididymitis, acute epididymo-orchitis, and trauma. Less common are vasculitis, hematoma, and a strangulated hernia. Both a perforated appendicitis and laparoscopic appendectomy can result in an abscess, even in the scrotum. Some of these conditions mimic testicular torsion on scrotal US. Testicular torsion is most common in infants under 1 year, while in older individuals testicular appendage torsion predominates. Epididymoorchitis increases in frequency with age. A differential diagnosis based on age should be used with caution, however, because considerable overlap exists.

Especially in pediatric patients, Doppler US is often the study of choice to differentiate conditions associated with decreased blood flow, such as torsion, from inflammatory disorders where blood flow is often increased. Scrotal scintigraphy is also sensitive in differentiating ischemic conditions from inflammation, realizing that a choice of imaging modality is often based on relative availability and local expertise.

Dynamic contrast-enhanced subtraction MRI evaluates testicular perfusion and relies more on functional rather than anatomic criteria. Dynamic MRI has better spatial resolution than scintigraphy. It aids in differentiating testicular from extratesticular disorders. One limitation is the need for sedation for younger boys.

Testicular Torsion

Testicular torsion (or spermatic cord torsion) occurs at all ages of childhood, but with two

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peaks: one in newborns where presumably it represents continued evolution of an intrauterine condition, and another during puberty and adolescence. It is uncommon after the age of 35 years.

Newborn

Spermatic cord torsion occurs both prenatally and postnatally. In the newborn, torsion manifests as a testicular tumor. Occasionally a neonate is found with bilateral testicular torsion.

Gray-scale US shows an enlarged testis. A hydrocele is present in some. Color Doppler US is useful in detecting testicular torsion, although the small testicular size in newborns makes evaluation difficult; intratesticular blood flow is lacking on the affected side and normal on the contralateral side.

Delayed therapy or tight torsion consisting of several turns is associated with a poor prognosis. Yet a case can be made for conserving even a necrotic testes found at surgery; some partially necrotic testes retain normal long-term function.

Children and Adults

Clinical

Testicular torsion occurs primarily in postpuberty boys and young men. Torsion of the testicular appendage should be suspected in younger boys. Simultaneous bilateral testicular torsion has been reported. The incidence of torsion increases after orchiopexy for an undescended testis.

Torsion is treated as an emergency. Torsion obstructs venous blood flow and leads to congestion, swelling, hemorrhage, and eventual ischemia. The time frame for ischemia to develop varies depending on the degree of torsion and the resultant vascular obstruction. A delay of 6 to 12 hours increases testicular loss rate considerably. Without therapy, torsion eventually progresses to testicular atrophy.

Nausea and vomiting are common in boys with testicular torsion, findings uncommon in those with testicular appendage torsion or those with epididymoorchitis. Some surgeons consider that older boys with acute scrotal pain less

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than 12 hours in duration, especially if associated with nausea or vomiting, have testicular torsion, imaging is not necessary and exploration is performed. Although currently diagnostic imaging prior to surgical correction is often performed, an occasional publication still maintains (66):

. . . physical examination is sufficient to manage patients with torsion of the spermatic cord.

In view of more recent sonographic refinements, some institutions have modified their previous policy of surgical intervention for all those with an acute scrotum; one approach is to operate when a surgeon has a high degree of suspicion for torsion and perform emergency Doppler US in the rest; those having a normal or increased testicular blood flow are presumed not to have testicular torsion and are treated medically. Such an approach assumes ready availability, on an emergency basis, of experienced sonographic personnel and equipment.

Intermittent testicular torsion results in recurrent testicular pain that remits either spontaneously or after self-manipulation. Imaging is often noncontributory in this condition. In one such 12-year-old, color Doppler detected bilateral flow but pulsed Doppler revealed asymmetric high-impedance flow with an increased resistive index on the involved side (67).

Imaging

With testicular torsion, gray-scale US shows testicular enlargement, varying testicular echogenicity, and often a hydrocele. At times US also detects any related complications requiring surgical intervention. When performed for testicular torsion, a US finding of an inhomogeneous or hypoechoic testis suggests a nonviable testis, and a normal homogeneous, isoechoic appearance suggests a viable testis. Nevertheless, these findings are often not clearly identified; overlap exists, and gray-scale US alone often cannot be relied on during the immediate decision-making time frame.

The primary role of color Doppler US is to differentiate acute testicular torsion from other acute conditions such as acute epididymitis, sequelae of trauma, or a neoplasm. Ideally, normal blood flow and a cord compression test should exclude torsion in most individuals.

Figure 13.5. Testicular torsion. Transverse Doppler image of both testes shows completely absent flow to left testis. (Courtesy of Deborah Rubens MD, University of Rochester.)

Torsion results in no perfusion and thus no Doppler signal on the affected side (Fig. 13.5). A potential pitfall in a Doppler US diagnosis of testicular torsion includes the occasional spontaneous testicular detorsion; Doppler US reveals normal or even increased testicular blood flow with detorsion. In some studies, Doppler US reaches a sensitivity and specificity of >90% in detecting testicular torsion, although in one study Doppler US identified no blood flow in the symptomatic testis in 61% of individuals with proven testicular torsion, but in the other 39% Doppler US was unreliable (intratesticular perfusion was present or no signal was obtained in either testis) (68); in all individuals with testicular torsion, however, high-resolution US detected a spiral twist of the spermatic cord at the external inguinal canal. A twisted spermatic cord in the scrotum is identified as a round or oval extratesticular mass connecting superiorly with a normal inguinal cord.

Nevertheless, imaging and diagnostic problems remain. One should keep in mind that Doppler US also detects the lack of perfusion in some normal prepubertal testes. At times Doppler US identifies blood flow in a setting of partial necrosis. Operator experience, use of appropriate Doppler US equipment, and knowledge of study limitations play a role.

An MRI of testicular torsion shows a twisting spermatic cord, described as a whirlpool

appearance. The twist has a hypointense signal. Currently, however, MRI is limited in evaluating torsion, often due to logistic problems.

Considerable literature exists for radionuclide scrotal imaging with Tc-99m- pertechnetate for suspected testicular torsion, although this examination has been supplanted by Doppler US in some institutions. Among individuals presenting with acute scrotal pain, published scintigraphy specificities and sensitivities approach 100% in detecting testicular torsion. A photopenic region in the hemiscrotum is compatible with testicular torsion, although cysts such as hydroceles and spermatoceles are also photopenic, and care is necessary to distinguish these entities. An inguinal testis needs to be excluded. Also, early torsion may not show asymmetry.

Color Doppler US and scintigraphy achieved similar statistical significance in detecting testicular torsion in boys with acute scrotal symptoms and clinically equivocal clinical presentations, except that scintigraphic specificity was greater (69); scintigraphy appears to prevent unnecessary surgery in some of those with equivocal findings on Doppler US. Which modality to employ often evolves into relative imaging availability for this acute condition.

Testicular Appendage Torsion

A distinction of testicular torsion and torsion of the testicular appendages is of clinical importance because the latter does not require emergency surgery.

Ultrasonography of appendix testis torsion shows an enlarged, homogeneous appendix testis medial or posterior to the head of the epididymis; some US scans reveal varying echogenicity. A hydrocele may be identified. Scrotal wall thickening and an enlarged epididymis head can develop. Color Doppler US reveals normal or increased flow, a finding that usually excludes testicular torsion.

A scintigraphy finding of a normal radionuclide angiogram and a localized focus of increased tracer activity suggest testicular appendage torsion, but keep in mind that increased tracer uptake is not present during the first several hours after onset of symptoms and radionuclide scrotal imaging may be falsely negative for testicular appendage torsion during this time.

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Infection/Inflammation

Epididymitis

Acute

Acute epididymitis is the most common cause of acute scrotal pain and swelling in teenagers and young men. It is usually due to retrograde spread of infection from either the bladder or prostate, and it tends to be unilateral. Most acute scrotal infections originate in the epididymis rather than the testis and result in isolated epididymal involvement (epididymitis). Less common is both epididymal and testicular involvement (epididymo-orchitis). Especially in infants and children, associated congenital anomalies are common and they should undergo full urologic evaluation.

Amiodarone, an antiarrhythmic agent, induces a sterile epididymitis; it is treated by lowering the drug dosage. Hemorrhagic epididymitis occurs in Henoch-Schönlein purpura. Acute unilateral epididymitis with an abscess developed in a patient after bacillus CalmetteGuérin therapy for superficial bladder cancer (70).

Acute testicular segmental infarction is a complication of epididymitis (Fig. 13.6). In addition to findings of epididymitis, gray-scale US reveals a testicular infarct as a discrete hypoechoic testicular tumor that has little or no flow detected with color Doppler US. An occa-

Figure 13.6. Magnetic resonance imaging of segmental testicular infarction (arrow). [Courtesy of Gabriel Fernández, M.D.,Vigo (Pontevedra), Spain.]