Scrotal imaging.

Pathological lesions within the scrotum are relatively rare in imaging except for ultrasonography. The diseases presented in the paper are usually found in men at the age of 15-45, i.e. men of reproductive age, and therefore they are worth attention. Scrotal ultrasound in infertile individuals should be conducted on a routine basis owing to the fact that pathological scrotal lesions are frequently detected in this population. Malignant testicular cancers are the most common neoplasms in men at the age of 20-40. Ultrasound imaging is the method of choice characterized by the sensitivity of nearly 100% in the differentiation between intratesticular and extratesticular lesions. In the case of doubtful lesions that are not classified for intra-operative verification, nuclear magnetic resonance is applied. Computed tomography, however, is performed to monitor the progression of a neoplastic disease, in pelvic trauma with scrotal injury as well as in rare cases of scrotal hernias involving the ureters or a fragment of the urinary bladder.

Introduction

The scrotum is the bulging of the abdominal wall in the form of a sack of skin and muscle. It is localized between the penis and anus, and divided into two compartments by a thin septum. Each contains a testicle, epididymis and spermatic cords. The structure of the scrotum enables to maintain a temperature lower than in the rest of the body by approximately 2°C thus facilitating sperm cell production. Testicular diseases and pathological conditions of other structures located in the scrotum can cause infertility, i.e. impair their basic function. Apart from infertility, some pathological processes, such as cancer or acute and chronic inflammation, can have systemic effects. The location of the scrotum is conductive to various injuries, but direct testicular injury is uncommon.

Imaging examinations are used to assess the morphology of the scrotal structures and certain function parameters, such as arterial vascularity, the condition of venous outflow with venous reflux, blood flow in the testicular parenchyma or patency of the deferent ducts.

The primary imaging modality is ultrasonography. The indications for scrotal ultrasound include: a suspicion of cancerous lesions, hydrocele, epididymo-orchitis, testicular asymmetry, anorchism, testicular torsion, scrotal injury, development disorders, infertility, hematospermia, scrotal or inguinal hernia as well as inguinal, retroperitoneal or mediastinal adenopathy. Moreover, the suspicion of varicocele as well as the assessment of their advancement and evaluation of treatment efficacy are also important indications. Of the indications mentioned above, the one concerning infertility is becoming increasingly important. Apart from conventional B-mode ultrasonography, color Doppler assessment has been used as a standard element of the examination for some time. The assessment of blood flow, abnormal testicular structure and pathological lesions in the scrotum deliver important diagnostic information enabling the differentiation between various pathological processes(.

Scrotal and pelvic MRI is also becoming increasingly important since it delivers significant supplementary information about the morphology of the structures, vascularity and the size of intercellular diffusion(. The examination helps differentiate the nature of fluid in the scrotum. It is conducted in accordance with a standard protocol for multiphase MRI in the coronal and transverse planes with the immobilization of the penis and scrotum.

Computed tomography of the scrotum is performed rarely, for example in scrotal herniation involving the ureters( or fragments of the urinary bladder(, as well as in post-traumatic changes of the pelvic floor and scrotum, particularly when US or MRI cannot be conducted.

Nuclear medicine techniques are also used rather rarely and only in single situations, e.g. to detect the presence of pathological shunting between the peritoneum and the scrotum in conditions with peritoneal dialysis(.

Male infertility

Approximately 15% of couples cannot have children. Male infertility can be diagnosed if pregnancy does not occur after a year of having unprotected intercourse, and appropriate medical therapy can be implemented(. In approximately 50% of such couples, impaired sperm quality is diagnosed. The causes of this condition can include: congenital or acquired urogenital disorders, cancer, inflammatory conditions, increased temperature in the scrotum (e.g. due to varicocele), endocrine disorders, genetic defects and immune factors. The cause of male infertility remains unidentified in 1/3 of patients. In this case, the condition is referred to as idiopathic infertility. Scrotal US in infertile men is (or should be) conducted on a routine basis. The goal is to detect abnormalities that could result in infertility. In this population, pathological lesions in the scrotum are a very common phenomenon. Such lesions include testicular tumors (which are even 100 times more common than in healthy men)(.

Varicocele

The most common pathology detected in the scrotum of infertile individuals is varicocele (15–40%)(. In 85% of cases, they involve the left spermatic cord, and the remaining 15% are found on the right side usually with coexisting varicocele on the left. Isolated right-side varicocele is rare. Urologists use a grading system proposed by Dubin and Amelar in 1970(. Grade 1 refers to varicocele that is palpable during the Valsalva maneuver. Grade 2 is associated with varicocele palpable without the Valsalva maneuver, but the scrotum is not visibly deformed. In grade 3, varicocele is palpable without the Valsalva maneuver and the scrotum is deformed in a characteristic way. A clinical examination consisting in visual inspection of the scrotum and palpation of the spermatic cords is of limited efficacy. That is why an ultrasound examination with the color Doppler assessment is currently the recommended option( (Fig. 1 A ,B). The diagnostic criterion of varicocele is the venous diameter above 2 mm and an increase in the diameter in the patient's upright position or during the Valsalva maneuver, as well as the presence of reflux in the pampiniform venous plexus. The accuracy of Doppler ultrasound enables 5 grades of advancement to be distinguished. In grades 1, 2 and 3, there is no scrotal deformation or testicular hypotrophy and the grading depends on the level of reflux (grade 1 – in the groin, 2 – in the proximal part of the pampiniform plexus, and 3 – in the distal vessels in the inferior part of the scrotum). In grade 4, one can observe spontaneous retrograde flow that intensifies during the Valsalva maneuver, scrotal deformation and possible testicular hypotrophy. In grade 5, reflux in the dilated pampiniform plexus is observed at rest and may not increase during the Valsalva maneuver; testicular hypotrophy is observed. Iosa et al.( proposed varicocele classification based only on a US image and the analysis of venous reflux in Doppler imaging. Grade 1 is characterized by venous reflux lasting more than 1 second only during the Valsalva maneuver. Grade 2 refers to spontaneous, discontinuous reflux that is not increased by the Valsalva maneuver whereas in grade 3, it increases markedly. Grade 4A is diagnosed when continuous venous reflux is not increased by the Valsalva maneuver, and grade 4B refers to massive venous reflux that increases by the Valsalva maneuver. This grading system is easy to implement if the complete examination is conducted (i.e. in the supine and upright positions) and when the patient has been instructed about the Valsalva maneuver. Some centers use a quantitative method for evaluating hemodynamic parameters in the pampiniform venous plexus for academic purposes using angioscintigraphy(.

Fig. 1 A

Varicocele

Fig. 1 B

Varicocele. Reflux during the Valsalva maneuver

Testicular volume

Testicular hypotrophy is a relatively common cause of male infertility and can result from various processes (Fig. 2). Normally, the volume of the testicles ranges between 8 and 18 ml in the adult population. This concerns the measurements taken with ultrasonography or a different imaging modality(. It is calculated using the following formula: π/6 × length × width × thickness. One should remember to apply the slightest possible pressure with a US transducer while taking the measurements. A hypotrophic testicle is frequently flaccid, very flexible and prone to deformation upon compression. The Prader orchidometer, which is used in clinical examinations, overestimates the measurements by approximately 100%. The testicular volume of up to 6 ml is equivalent to hypotrophy. The testicular volume does not have to be associated with echotexture disorders. Hypotrophy is equivalent to a reduction in the amount of the parenchyma, which in 98% is made of the seminiferous tubules, developing gametes and interstitial cells of Leydig that produce testosterone and other androgens. The most common cause of hypotrophy is prolonged increased temperature due to varicocele. Undiagnosed cryptorchidism or the history of testicular torsion can also lead to testicular hypotrophy. The former is mainly found in children. Based on the assessment of the size, vascularity and flexibility of the parenchyma, the degree of testicular degradation can be estimated. Testicular vascularity in patients with the history of cryptorchidism is lower(. Bilateral hypotrophy is usually found in Klinefelter syndrome in men with a 47, XXY karyotype. The history of orchitis (mumps) and injuries can result in their decreased volume. All of these factors lead to decreased sperm quality.

Fig. 2

Testicular hypoplasia following a surgery to treat cryptorchidism (v = 1 ml)

Azoospermia

Azoospermia frequently results from mechanical factors in the structures that lead sperm cells to the ejaculatory duct. The determination whether the patency of the vas deferens is normal is practically impossible using imaging examinations. The incidence of azoospermia among infertile men is relatively high and ranges from 10–15%. It is most commonly caused by epididymal obstruction (30–67% men with azoospermia), sometimes resulting from vasectomy(. The obstructed epididymis is frequently palpable. Pezzella et al. demonstrated that the size of the epididymal head is correlated with the presence of obstruction(. The diameter of the caput epididymis above 10.85 mm is indicative of obstruction with over 92% of likelihood (Fig 3). These studies suggest that a simple measurement of the epididymal head can be a significant information about the cause of azoospermia. Epididymal obstruction and consequent infertility are also frequent signs of cystic fibrosis in men( (Fig. 4).

Fig. 3

Enlarged epididymis with inflammatory pseudotumor

Fig. 4

Enlarged epididymis in cystic fibrosis. Aspermia

Testicular microlithiasis

Testicular microlithiasis is the presence of diffuse slight calcifications – hyperechoic points in ultrasound, but without an acoustic shadow. They can occur within the entire testicle or only in its fragment (a focus of microlithiasis). As an isolated sign, they are of no pathognomonic significance but when they coexist with other lesions, they can be treated as cancer risk factors( (Fig. 5). According to the latest ESUR recommendations, isolated microlithiasis is not an indication for monitoring.

Fig. 5

Testicular tumor (Teratoma maturum) with coexisting microlithiasis

Inflammation

Orchitis or epididymitis are caused by a bacterial infection. Scrotal edema (usually unilateral), pain and tenderness are observed. Most patients are aged 25–45( constituting a group of 40 per 10,000 patients annually (the fifth most common cause of reporting to the doctor). The most common pathogen is Neisseria gonorrhoeae, Chlamydia and Mycoplasma. Escherichia coli can be the causative agent in men over the age of 50. The scrotum is involved via the ascending mechanism in the presence of a bladder outlet obstruction in the urogenital tract (BPH). Boys with isolated orchitis (without epididymitis) in the course of mumps are a separated group. In every sixth patient, acute inflammation develops into a chronic condition that can lead to urinary obstruction (Fig. 6). In the EAU guidelines concerning the diagnosis and treatment of uncomplicated epididymo-orchitis, the authors do not mention any indications for a radiological examination(. However, since the age group of such patients is the same as those at the greatest risk of testicular cancer, the coincidence of these two conditions must be considered. Typical treatment lasts 2–3 weeks, and a scrotal US examination is indicated after this period, particularly if testicular enlargement persists (Fig. 7). Imaging examinations are more important in patients with chronic inflammatory conditions that can lead to epididymal and deferential obstruction. However, radiological images do not deliver significant information of pathognomonic significance either. Only persisting enlargement of the epididymal head (above 11 mm) and coexisting azoospermia indicate that epididymal obstruction is highly likely( (Fig. 3 and 6).

Fig. 6

Enlarged body of the epididymis causing obstruction

Fig. 7

Disordered parenchymal architecture following orchitis

Injuries, testicular torsion

Despite the vulnerable position of the testicles and scrotum, which are not shielded by muscles and bones, testicular and scrotal injuries are relatively uncommon. Usually, such injuries are observed in men at the age of 15–40, being a result of traffic accidents (cycling or motorcycling).

The complications of such injuries include: contusion, torsion, hydrocele (Fig. 8), scrotal hematoma, testicular hematoma (Fig. 9), ruptured tunica albuginea, testicular rupture, testicular fragmentation, dislocation and abscess (Fig. 10).

Fig. 8

Bilateral hydrocele

Fig. 9

Posttraumatic testicular hematoma (30 × 39 mm)

Fig. 10

Testicular abscess

Based on the mechanism, the following types of trauma are distinguished: blunt, penetrating and avulsion. Blunt injuries include traffic injuries, those resulting from battery or from practicing certain sports. Penetrating trauma mainly includes gun shots and stabs. Avulsion injuries, in turn, are usually associated with work-related accidents.

Blunt injuries account for 80–85% of cases. Most of such injuries require conservative treatment only. However, a single paper reports that the ruptured tunica albuginea was observed in 46% of patients with a blunt injury(.

Penetrating trauma is diagnosed in approximately 15–20% of patients. By contrast with blunt trauma patients, this group requires surgical interventions more frequently. The ruptured tunica albuginea, testicular rupture, enlarging hematoma and testicular dislocation are indications for a surgery. In the case of fragmentation, testicular amputation is the method of choice.

Avulsion injuries are rare. They usually result from accidents involving industrial or agricultural machinery(.

Iatrogenic injuries are yet another, separate group of very rare injuries. In single reports, authors present epididymal trauma( and azoospermia due to hydrocelectomy(.

The imaging method of choice is ultrasonography with the color Doppler mode(. It is a non-invasive and readily available examination. It enables the assessment of not only the structures inside the scrotal sack, but also of blood flow. Ultrasound imaging is characterized by a high sensitivity in diagnosing scrotal trauma(. In ambiguous, doubtful cases, such as inflammation and trauma, multiple testicular hematomas or a tumor, magnetic resonance is the method of choice(. Computed tomography is used in cases of testicular dislocation and concomitant injury to the pelvic structures(. A post-traumatic hematoma with no tunica rupture is treated conservatively when it is stable, small and does not cause severe pain or surgically when it is sizable, increases and causes strong pain(. The aim of the intervention is preserving the testicle, alleviating pain and shortening the duration of the procedure. Epididymal hematomas are even rarer(. Dale et al. have reported a case of a post-traumatic hematoma of the left epididymis. It was treated conservatively (analgesics and ice) with good effects. The diagnosis was made on the basis of ultrasound findings with the color Doppler help. An avascular, heterogeneous mass in the left epididymis was visualized in a patient who had sustained a blunt scrotal injury. If some time has passed from trauma and the abnormal structure in the testicle is the only pathology with no other clinical signs, it must be differentiated with a tumor. A typical MRI image of extravasated blood correlated with recent injury enables the identification of extravasation with a high probability(. Moreover, the evolution of the focus with time can be an additional piece of differentiating information.

Testicular torsion is an acute condition that can cause testicular necrosis. In a clinical examination, it is differentiated from acute inflammation by inducing Prehn's sign. The lifting of the affected scrotum intensifies pain in torsion (a negative sign) and relieves it in acute inflammation (a positive sign). The most common cause of so-called acute scrotum is testicular torsion (80–90%). It is diagnosed in boys aged 12–18 and too frequently leads to the loss of a testicle. A US Doppler examination is the method of choice in the differential diagnosis of testicular torsion. However, it must be remembered that its sensitivity is not 100% but 85–90%. This means that in 10–15% of patients with testicular torsion, it is possible to detect flow in testicular vessels although it is frequently only an artefact(. Vasdev et al. report on the possibility to apply angioscintigraphy and scrotal MRI to confirm torsion. However, they mention the limitations concerning the access to and duration of both procedures in an emergency department. In this case, they propose an exploratory surgery as the management of choice. Sharp et al. go even further by considering any imaging in patients with suspected testicular torsion non-indicated and recommending an immediate surgical intervention instead(. They believe that imaging can be useful when the clinical picture is dubious. Currently, the possibility of the assessment of vascularization in testicular torsion and calculating quantitative values of the vascularization index, i.e. the ratio of the number of vessels to a given volume, is being paid more and more attention(. In normal conditions, it is approximately 10%, and it is higher in processes with accompanying hypervascularization. This fact can be used to monitor the efficacy of treatment.

Neoplasms

Testicular cancer accounts for 1.6% of all malignant neoplasms diagnosed in men. Within the past 30 years, the incidence rate has been observed to increase considerably(. In 2010, approximately 1,100 cases of malignant testicular cancer (incidence rate 5.1/100,000/year) and 123 deaths (mortality rate 0.5/100,000/year) were recorded in Poland( (Fig. 5 and 11). Malignant testicular cancers are the most common neoplasms of men at the age of 20–40 (70% of cancers) with the peak incidence between the age of 30 and 34(. Seminoma is usually diagnosed in men aged 25–45 whereas non-seminomas develop in patients at the age of 15–35. The incidence of seminoma is slightly higher(.

Fig. 11

Seminoma testis (16 × 13 mm)

The main risk factors include: the Caucasian race(, cryptorchidism( (if the testicle descended to the scrotum in the later stages of life or the descent was treatmentinduced, the increased risk of developing testicular cancer persists), cancer in the contralateral testicle(, testicular cancer in the family( and infertility(.

The basic signs of a neoplasm include the presence of a nodule or a change in testicular consistency. Approximately 1/3 of patients experience pain or a feeling of heaviness in the scrotum or in the small pelvis.

The modality of choice in imaging is ultrasound with the color Doppler assessment(. The sensitivity in the differentiation between intra- and extratesticular lesions in 98–100%(. Most extratesticular lesions are benign and intratesticular ones tend to be malignant. A normal testicle is homogeneous with granular echotexture. The epididymis is isoechoic or slightly hyperechoic compared with the testicle. Most tumors are hypoechoic compared with the surrounding tissue. The echogenicity of tumors can also be heterogeneous with hyperechoic areas; they can contain calcifications or be solid-cystic(.

Metastases to the lymph nodes usually involve the retroperitoneal region. Those from the right testicle involve the lymph nodes below the right renal hilum laterally, ventrally and medially in relation to the vena cava. Metastases from the left testicle, however, involve the group of nodes above the inferior mesenteric artery laterally and ventrally in relation to the aorta.

In the case of ambiguous lesions, nuclear magnetic resonance is used(, particularly to differentiate extratesticular lesions(. Solid lesions are characterized by a low signal in T2-weighted contrast-enhanced images compared with the high signal of the surrounding tissue. Moreover, multiparameteric ultrasound involving the assessment of the vascularization index and elasticity of the focus is becoming more common(. The loss of tissue elasticity, i.e. their increased stiffness, which is assessed in elastography, can deliver valuable information to the differential diagnosis. It suggests the proliferative nature of the focus. Computed tomography is not used for the assessment of scrotal lesions, but it is the basic tool for tumor staging.

Tumor staging consists in the operative and histological verification, imaging (CT of the chest, abdomen and small pelvis) and tumor marker assessment (AFP, beta-hCG and LDH) before and after tumor removal. If bone or brain metastases are suspected, imaging is extended to include adequate modalities(.

Below, the radiological follow-up according to the National Comprehensive Cancer Network is presented.

Surveillance for seminoma

Patients with stage I seminoma: in the first year, abdominal and pelvic CT should be conducted at 3, 6 and 12 months. In the second and third year, abdominal and pelvic CT should be conducted at 6 and 12 months. In the fourth and fifth year, abdominal and pelvic CT should be performed every 12–24 months.

Patients with stage I seminoma after chemo- or radiotherapy: in the first 3 years, abdominal and pelvic CT should be conducted annually.

Patients with clinical stage IIA and non-bulky stage IIB seminomas: in the first year, abdominal and pelvic CT should be conducted after a month, and subsequently every 6 and 12 months; low-dose CT (LDCT) of the chest should be performed every 6 months. In the second year, abdominal and pelvic CT should be conducted once a year, and chest LDCT – every 6 months. In the third year, abdominal and pelvic CT should be conducted once a year. In the fourth and fifth year, abdominal and pelvic CT should be conducted as clinically indicated.

In patients with bulky clinical stage IIB and stage III seminomas with a PET-negative residual mass >3 cm after chemotherapy, abdominal and pelvic CT should be performed every 6 months for the first year, then annually for 5 years. Chest CT should be conducted as clinically indicated. Chest LDCT is a routine follow-up once a year.

In patients with bulky stage IIB and stage III seminoma with no residual mass or a residual mass <3 cm, the following schedule is recommended: chest LDCT every 2 months and a complete chest CT if there have been lesions in the subphrenic region. Subsequently, chest LDCT should be conducted every year for 3 years.

In all patients, scrotal ultrasound can be conducted as an additional examination.

Surveillance for nonseminoma

Patients with stage IA nonseminoma: in the first year, abdominal and pelvic CT should be conducted every 4–6 months, and chest LDCT – at 4 and 12 months. In the second year, abdominal and pelvic CT should be conducted every 6–12 months, and chest LDCT – once a year. In the third year, abdominal and pelvic CT and chest LDCT should be conducted once a year. In the fourth and fifth year, chest LDCT should be conducted annually.

Patients with stage IB: in the first year, abdominal and pelvic CT should be conducted every 4 months, and chest LDCT – every 2 months. In the second year, abdominal and pelvic CT should be conducted every 4–6 months, and chest LDCT – every 3 months. In the third year, abdominal and pelvic CT should be conducted every 6 months, and chest LDCT – every 4–6 months. In the fourth year, abdominal and pelvic CT should be conducted once a year, and chest LDCT – every 6 months. From the fifth year, chest LDCT should be conducted annually.

Patients with stage IB treated with chemotherapy: in the first year, abdominal and pelvic CT should be conducted once a year, and chest LDCT – every 6–12 months. In the second year, abdominal and pelvic CT and chest LDCT should be conducted once a year.

Patients with stage II and III nonseminoma with a complete response to chemotherapy: in the first year, abdominal and pelvic CT and chest LDCT should be conducted every 6 months. In the second year, abdominal and pelvic CT should be conducted once a year, and chest LDCT – every 6 months. In the third and fourth year, chest LDCT should be conducted once a year.

Patients with stage IIA–B after retroperitoneal lymph node dissection (RPLND) and chemotherapy: in the first year, abdominal and pelvic CT should be conducted after RPLND, and chest LDCT should be performed every 6 months. In the second, third, fourth and fifth year, abdominal and pelvic CT should be conducted as clinically indicated and chest LDCT should be performed annually.

Patients with stage IIA–B after RPLND but not treated with chemotherapy: in the first year, abdominal and pelvic CT should be conducted every 3–4 months and chest LDCT – every 2–4 months. In the second year, chest LDCT should be conducted every 3–6 months. In the third and fourth year, abdominal and pelvic CT should be conducted as clinically indicated and chest LDCT should be performed annually.

What should a radiologist know?

Malignant testicular cancers are the most common neoplasms in men at the age of 20–40.

Ultrasound imaging helps distinguish the intratesticular lesions, which are usually malignant, from extratesticular ones, which are usually benign.

Most tumors are of hypoechoic structure compared with the surrounding tissue.

In tumor staging, all radiological methods are used, depending on the purpose and the investigated region.

In doubtful cases, nuclear magnetic resonance is the method of choice.

Computed tomography is the method of choice in treatment monitoring.